chore(release): 10.0.0

The last rung of the default-flip ruling: with the sentinel exemption in,
real production-shaped brains still refused adoption over state-differs
mismatches the backfill could not cure — rows written before the
hydration law carry denormalized wrapper fields that disagree with their
own metadata leg, and the previous as-is identity re-commit PRESERVED
that drift, so the oracle re-flagged it every pass and the flip never
happened. In practice the crash-safe default reached zero existing
brains: the exact outcome the hold ruling forbade.

The cure: the backfill now rewrites canonical in the LAW SHAPE — exactly
the wrapper the log's reconstruction produces (denormalized enumeration
fields derived from the metadata leg, which is their authority under the
field-addressing law; the embedding floats ride through byte-identical;
adjacency residue keeps its own rebuild path). The oracle then verifies
the rewrite before the flip — the same safety, no operator chore.
Log-ahead divergence classes (a log the witness denies) still refuse
loudly, exactly as before.

Classification note for the record: the flagged uuid-v7 rows postdate the
fact log's introduction, so they classify as state-differs (in-log,
drift-shaped) rather than pre-log — both classes ride the same backfill.

Pins: a manufactured depot-shape drifted wrapper adopts green with floats
preserved and metadata intact; log-ahead still refuses typed.
Gates: unit 2065/2065 · integration 832 · conformance 31/31.

.forgejo/workflows/ci.yml

@@ -1,7 +1,13 @@
 name: CI
 
+# Branch pushes only — a release TAG deliberately does not re-run CI: the
+# tagged commit's CI already ran on its branch push, and the runner is
+# sequential, so tag-triggered matrix jobs (~22 min) would queue AHEAD of the
+# tag's publish-source run and starve every release (observed on 8.10.3 and
+# 9.0.0: the publish sat behind the tag's own redundant CI).
 on:
   push:
+    branches: ['**']
   pull_request:
 
 jobs:

.forgejo/workflows/publish-source.yml

@@ -1,10 +1,12 @@
-name: Publish (forge)
+name: Publish (The Source)
 
-# Datacenter-side forge publish, moved off the laptop: an 87MB tarball PUT
-# over the laptop's WAN times out; the forge's own runner does it in seconds.
+# Datacenter-side publish to The Source (source.soulcraft.com — our
+# self-hosted Forgejo; never call it "the forge", Forge is a different
+# product), moved off the laptop: an 87MB tarball PUT over the laptop's WAN
+# times out; The Source's own runner does it in seconds.
 # scripts/release.sh tags + pushes, then polls this workflow's result (npm
-# view against the forge registry) before it ever touches the npmjs leg —
-# see the "delegation contract" in scripts/release.sh's forge-publish step.
+# view against The Source's registry) before it ever touches the npmjs leg —
+# see the "delegation contract" in scripts/release.sh's home-publish step.
 
 on:
   push:
@@ -13,7 +15,7 @@ on:
 
 jobs:
   publish:
-    name: Publish to the forge registry
+    name: Publish to The Source registry
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
@@ -23,20 +25,21 @@ jobs:
           cache: npm
       - run: npm ci
       - run: npm run build
-      - name: Publish + readback-verify on the forge registry
+      - name: Publish + readback-verify on The Source registry
         env:
+          # The stored repo-settings secret keeps its historical name.
           FORGE_NPM_TOKEN: ${{ secrets.FORGE_NPM_TOKEN }}
         run: |
           set -eo pipefail
 
-          FORGE_NPM_REG="https://source.soulcraft.com/api/packages/soulcraft/npm/"
+          SOURCE_NPM_REG="https://source.soulcraft.com/api/packages/soulcraft/npm/"
           VERSION="$(node -p "require('./package.json').version")"
-          echo "Publishing @soulcraft/brainy@${VERSION} to the forge registry..."
+          echo "Publishing @soulcraft/brainy@${VERSION} to The Source registry..."
 
           TMPRC="$(mktemp)"
           chmod 600 "$TMPRC"
           {
-            echo "@soulcraft:registry=${FORGE_NPM_REG}"
+            echo "@soulcraft:registry=${SOURCE_NPM_REG}"
             echo "//source.soulcraft.com/api/packages/soulcraft/npm/:_authToken=${FORGE_NPM_TOKEN}"
           } > "$TMPRC"
 
@@ -56,12 +59,12 @@ jobs:
           rm -f "$TMPRC"
 
           if [ "$LANDED_VERSION" != "$VERSION" ]; then
-            echo "::error::Readback verify FAILED — the forge registry reports version '${LANDED_VERSION:-<none>}', expected '${VERSION}'. This is a genuine publish failure, not a benign duplicate."
+            echo "::error::Readback verify FAILED — The Source registry reports version '${LANDED_VERSION:-<none>}', expected '${VERSION}'. This is a genuine publish failure, not a benign duplicate."
             exit 1
           fi
 
           if [ "$PUBLISH_OK" = true ]; then
-            echo "Published and verified @soulcraft/brainy@${VERSION} on the forge registry."
+            echo "Published and verified @soulcraft/brainy@${VERSION} on The Source registry."
           else
-            echo "::warning::npm publish reported failure, but readback confirms @soulcraft/brainy@${VERSION} is already live on the forge (a prior run or mirror landed it) — treating this run as successful, since the registry content is correct. Any OTHER failure mode would have failed the readback check above instead."
+            echo "::warning::npm publish reported failure, but readback confirms @soulcraft/brainy@${VERSION} is already live on The Source (a prior run or mirror landed it) — treating this run as successful, since the registry content is correct. Any OTHER failure mode would have failed the readback check above instead."
           fi

CHANGELOG.md

@@ -2,6 +2,38 @@
 
 All notable changes to this project will be documented in this file. See [standard-version](https://github.com/conventional-changelog/standard-version) for commit guidelines.
 
+### [10.0.0](https://source.soulcraft.com/soulcraft/brainy/compare/v9.0.0...v10.0.0) (2026-08-12)
+
+- fix(adoption): the baseline backfill cures hydration-law drift — existing brains reach the crash-safe default with zero operator steps (25f0dd96)
+- fix(adoption): the reserved-root mint exemption — int 0 is legitimate for exactly one id (2abe8b38)
+- fix(recovery): walks are healers — the typed/tolerant boundary redrawn where block-layer fault injection proved it belonged (0e3facf4)
+- feat(log): log authority is the fleet default — adopt-at-open, oracle-gated; plus the power-cut throw-site cures and the loud torn-record contract (214c98b4)
+- fix(durability): three block-layer power-loss findings from the first fault-injection box run — all cured, matrix 15/15 (67c606be)
+- docs: RELEASES.md frames the release as 10.0.0 — honest major (log format v2 forward-only); comment wording cleanup (d1698fa5)
+- fix(persistence): the idle flush trigger debounces under load — deferred to the floor, never dropped, never a flush-per-gap amplifier (a50726e6)
+- feat(reprojection): the one doors-open machinery — budget-capped, yielding, foreground-preempted, atomic-swap; poison records quarantine typed (d1651f98)
+- feat(embedding): deferred-embed markers become log records — the sidecar recovery path is deleted (b47787bb)
+- feat(conformance): the golden-log fold oracle — encoder bytes and fold semantics pinned by content hash (c95bea88)
+- feat(engine): the wiring wave — stamps ride every flush, provider generations, waitForIndexed, adopt-backfill, match-all serves (b53e6e89)
+- feat(index): watermark stamps on every TS projection — adopt/catchup/rescan verdicts at load, stamp-after-data (b35d87a7)
+- feat(log): v2 is the LIVE write format — envelope records with minted ints, genesis, sector seals; v1 readable forever (26c60251)
+- docs: RELEASES.md — the unreleased write-path and lifecycle entry (consumer-facing draft; version set at cut) (73eb88d4)
+- feat(temporal): as-of semantic recall joins the release contract — past vectors byte-exact, pinned (f7ca0d26)
+- fix(log): acked writes survive power loss; rejected writes never silently commit — the kill-matrix goes 11/11 with zero .fails debt (13022c51)
+- feat(plugin): every provider write surface carries the real committed generation (2d532684)
+- feat(log): fact-log format v2 codec — record envelope, type registry, genesis, sector seals; fault-injection shim (34841074)
+- feat(log): the guarded log-authority core — group-commit durable-at-ack, the per-brain switch, the verification oracle (65953097)
+- docs: Path Registry rows DP6/DP8/MT5 flip to contracted+pinned — the deferred-embedding and atomic-update train landed with cited tests (9fda6d95)
+- feat(embedding): MT5 — deferred embedding with durable markers; write acks never wait on a neural net (287384cf)
+- fix(index): the flicker window dies — atomic in-place vector update; lazy open honors every provider's not-ready report; the Path Registry twin table (ebe06cdf)
+- feat(persistence): the engine owns its flush cadence — callers never call flush() in hot paths again (3236a01b)
+- fix(aggregation): the lifecycle cluster — flush stamps, behind-stamp catches up incrementally, the native rebuild finally gets invoked, deletes are never silently skipped (1dc861d2)
+- perf(sort): ordered reads never do per-row storage round-trips — the 199-317s production scan class dies structurally (607b6b56)
+- chore: the home registry is The Source, never 'the forge' — sweep the misnomer out of the release rail, workflows, and release notes (Forge is a different product; the stored CI secret keeps its historical name) (09352c2b)
+- ci: tags stop triggering the CI matrix (redundant re-run of already-tested commits starved every release's publish run on the sequential runner) + release.sh forge poll window 20→50 min (c6c6ea6b)
+- test: version-coupling pins go major-agnostic — the 8.x literals broke at the 9.0.0 bump while the coupling law itself behaved correctly (8a6807e8)
+
+
 ### [9.0.0](https://source.soulcraft.com/soulcraft/brainy/compare/v8.11.0...v9.0.0) (2026-08-04)
 
 - docs: 9.0 namespace-migration guide — the simple story + the mechanical sweep checklist, published for humans and tooling alike (61ab9db2)

RELEASES.md

@@ -31,6 +31,76 @@ is sometimes cited as a 7.x removal — those methods never existed on 7.x; the
 
 ---
 
+## v10.0.0 — 2026-08-10 (the write-path and lifecycle release)
+
+The theme: **writes ack fast and honestly, startup adopts instead of rebuilding, and
+every query path serves, announces, or refuses — never silently degrades.** Ships as
+one release together with the matching native accelerator version.
+
+**The storage-authority posture (the release's headline):** a NEW brain's default
+is **durable-at-ack log authority** — the generation log is the source of truth,
+every write acknowledgment is covered by a group-committed fsync, and crash
+recovery is a replay of the log (an acked write survives power loss, proven by
+fault-injection tests). An EXISTING brain adopts at its first open under 10.0.0,
+gated by a verification oracle: the log is replayed and diffed against stored
+truth record-by-record; curable gaps are backfilled; the brain flips only on a
+green verdict and a brain that cannot verify stays on the previous posture and
+says so loudly. The explicit opt-out is `logAuthority: 'defer'` in the config
+(no automatic adoption; flip later with `adoptLogAuthority()`).
+
+**Why a major:** the generation log gains write format v2 — new segments carry typed,
+versioned records with integrity seals. A 9.x build refuses a v2 segment with a clear
+version-naming error (never a misread), which means **a brain written by 10.x cannot
+be opened by 9.x**. Existing v1 history stays readable forever; upgrading requires no
+migration and no data touch — the format moves forward only as you write.
+
+### New capabilities
+
+- **`deferEmbedding: true`** on `add()`/`update()`: the write acks at durability; the
+  embedding runs on a crash-safe background worker and the vector swaps in atomically.
+  The row is id/metadata-findable immediately; semantic recall converges when the embed
+  lands. Barriers and gauges: `awaitPendingEmbeds()`, `waitForIndexed('semantic')`,
+  `getIndexStatus().pendingEmbeds`. VFS file writes adopt this end to end — file-write
+  ack no longer waits on a neural net (measured ~50× faster serial writes on a
+  production-shaped corpus).
+- **`waitForIndexed(path?, { generation?, timeoutMs? })`** — the one honest read
+  barrier for write-then-recall flows. Typed timeout error naming what was still
+  pending; never a silent partial wait.
+- **Engine-owned persistence cadence** (`persistence.policy: 'auto'`, now the default):
+  the engine flushes on write-count/interval/idle triggers in the background,
+  single-flight. **Delete `flush()` calls from hot paths** — `flush()` remains as an
+  awaitable durability barrier. A hung flush can never block a write ack.
+- **Time-travel recall contract**: `asOf(G).find()` serves vectors exactly as they
+  stood at G — a later update never leaks into an earlier pin; deleted rows mask;
+  beyond-head pins refuse typed.
+- **Log-authority storage (opt-in, per brain)**: `verifyLogAuthority()` audits the
+  generation log against stored truth record-by-record and names every divergence;
+  `adoptLogAuthority()` flips a brain to log-authoritative storage only on a green
+  audit (self-healing curable divergences first), enabling durable-at-ack writes:
+  concurrent writers share one fsync and an acked write survives power loss, by
+  construction (crash-recovery replay is pinned by fault-injection tests).
+
+### Behaviour changes
+
+- **`find({ where: {} })` now serves match-all** (previously returned an empty result
+  silently — warm and cold). Same fix applies to count, streaming, and graph-scoped
+  seeding paths.
+- **`removeMany({ where: {} })` now refuses with a typed error** — a match-all bulk
+  delete must be explicit, never inherited from an empty filter object.
+- **Aggregations always answer**: state persists at every `flush()` (not only close),
+  an unclean exit reconciles incrementally instead of rescanning the store, and
+  deletes without a before-image flag a loud rescan instead of silently skipping.
+- **Vector updates are atomic in place** — a row is never transiently absent from
+  search during an update (the "flicker" class is gone); type-only re-index of an
+  unchanged vector is a no-op.
+
+### Format note
+
+- The generation log gains **format v2** (typed, versioned records with integrity
+  seals). v1 segments remain readable forever; new segments write v2. Older brainy
+  builds refuse v2 segments with a clear version-naming error rather than misreading
+  them. Records reserve encryption fields for a future release — zero behaviour today.
+
 ## v8.11.0 — 2026-07-27 (canonical enumeration mode for export — storage-walked, canon-complete)
 
 From a fleet data-migration program's requirement for whole-brain exports that are
@@ -70,8 +140,8 @@ to the caller today.
   pre-existing meaning). **Migration-grade exports set `includeHidden: true`** — a
   complete-canon export must carry every visibility tier; consumer-facing exports
   leave it off.
-- **Ops note (consumer-invisible): the release pipeline's forge-registry publish now runs
-  on CI**, triggered by the release tag, instead of PUTting the tarball from the laptop
+- **Ops note (consumer-invisible): the release pipeline's home-registry publish (The
+  Source, source.soulcraft.com) now runs on CI**, triggered by the release tag, instead of PUTting the tarball from the laptop
   over WAN — no change to what gets published or how a consumer installs it.
 
 ## v9.0.0 — 2026-08-04 (the field-addressing law: your names and system.*, nothing in between)

docs/path-registry.md

@@ -0,0 +1,86 @@
+# The Path Registry — brainy's twin table
+
+The brainy half of the cross-engine Path Registry (the native accelerator
+maintains the master list; IDs are shared and stable — `LC3`, `DP7`, … are
+citable in commits, board rounds, release notes, and pins). Every row owes
+five things: **service class** (INDEX-SERVED | BOUNDED-FALLBACK, announced |
+TYPED REFUSAL), **latency budget** at 1k/10k/100k/1M (design bar: billions),
+**lifecycle behavior**, **failure narration**, and a **test pin**. A path not
+in this registry does not ship; an unregistered path is a red gate in the
+scan audit.
+
+**The availability bar governing every row: user-visible downtime is
+seconds, at restart only.** Migration, heal, compaction, embedding, and
+retention run behind the doors — yielding, budget-capped, narrated. No path
+may hold the doors while it does housekeeping.
+
+Status legend: ✅ contracted + pinned (test cited) · 🟡 partial (what holds
+and what's missing, stated) · 🔴 owed (named, never silent).
+
+## LC — Lifecycle
+
+| ID | Brainy row | Status |
+|----|-----------|--------|
+| LC1 | Same-version reopen adopts everything: brain-format epoch match → zero rebuilds; aggregation state adopts by stamp; persisted indexes load. | ✅ `tests/unit/brainy/brain-format-handshake` + `migration-deference` (no-drift reopen never rebuilds) |
+| LC2 | New empty brain: doors immediate. | ✅ exercised by every suite's setup |
+| LC3 | Upgrade, same epoch: as LC1 — new code on unchanged formats owes nothing at open. | ✅ same pins as LC1 (epoch equality is the gate) |
+| LC4 | Upgrade with epoch migration: TODAY brainy's epoch rebuild runs at open before doors. | 🔴 **owed — the sev's lockout row.** The doors-open-serving-old-structures design (yielding installments + atomic swap) lands measured-and-gated behind the service-class pair, per the lifecycle-sprint choreography. Acceptance case: the 9,184-row hours-lockout. |
+| LC5 | Crash recovery: bounded, resumable, narrated. Aggregation leg ✅ (behind-stamp → incremental catch-up off the fact log + time-travel reconciliation, capped at 5,000 affected before an ANNOUNCED rescan). Vector/metadata legs ride epoch machinery (rebuild-from-canonical, narrated). | 🟡 aggregation pinned (`tests/integration/aggregation-lifecycle-catchup`); the rebuild legs are narrated but not yet installment-yielding (couples to LC4) |
+| LC6 | Shutdown under load: close() drains the background flush flight, tears down cadence timers, runs ONE time-bounded compaction pass (~5s budget, resumable). | 🟡 pinned for flush/compaction (8.9.0 suites); SIGTERM drain budget not yet declared |
+| LC7 | Rollback/downgrade: an N−1 build opening an N brain. | 🔴 owed — no declared read-compat window or typed refusal today (epoch mismatch triggers a rebuild, not a refusal; v2 nested-bag records read as a phantom user field on pre-law builds). Needs the declared-window contract. |
+| LC8 | Relocatable brain directory: no absolute paths in artifacts; persist()/load() round-trips. | 🟡 persist/load pinned; byte-for-byte relocation depot cases are the pair gate's (shared corpora) |
+| LC9 | Double-open: second writer gets a typed lock refusal (PID-liveness + heartbeat stale detection; `force` escape hatch logs loudly). | ✅ writer-lock suites (8.7.1) |
+
+## DP — Data plane
+
+| ID | Brainy row | Status |
+|----|-----------|--------|
+| DP1 | `get()` by id: direct storage read + hydrate. INDEX-SERVED (id-mapped). Milliseconds at every scale. | ✅ exercised everywhere; budget rides the pair speed table |
+| DP2 | `find({query})`: embed + vector search. The embed dominates (native side owns the budget); JS HNSW serves the search leg. | 🟡 300ms-class p95 is the pair speed-table row; brainy-alone budget declared there |
+| DP3 | Filtered/sorted list: column top-K when the field is columnized (INDEX-SERVED, zero canonical reads on the sorted page — value pairs come from ONE batched metadata-record pass); no-column fallback is BOUNDED-ANNOUNCED (one batch pass, announces once per field past 500 rows); unknown field → TYPED REFUSAL naming both candidate spellings. | ✅ `tests/unit/utils/metadataIndex-sort-callshape` (zero per-row reads, batch-only — latency-blind) + `metadataIndex-nested-orderby` (dotted keys serve-or-refuse) + `tests/integration/orderby-sort-bug` |
+| DP4 | Aggregation/stats: ALWAYS answers. Write-time incremental; behind-stamp reconciles incrementally; genuine rebuilds go through the native parallel door or the paged JS walk; nothing ever latches off; before-image-less deletes flag a LOUD rescan, never a silent skip. | ✅ `tests/integration/aggregation-lifecycle-catchup` + `tests/unit/aggregation/aggregation-provider-rebuild` |
+| DP5 | Graph traversal: `related()` paged via adjacency; whole-graph analytics carry declared cost. | 🟡 paged reads pinned; analytics cost-class declaration owed (rides VENUE-GRAPH-TRUST audit tool) |
+| DP6 | Single write: ack at the canonical commit; visibility committed at ack (the atomic vector update kills the remove→add dark window); maintenance NEVER holds the ack (background flush cadence — THE ACK LAW pins: a hung flush cannot block a write, a hung EMBEDDER cannot block a write). | ✅ `tests/unit/brainy/persistence-policy` + `tests/unit/hnsw/update-item-atomic` + `tests/integration/deferred-embedding` |
+| DP7 | Bulk ingest: sustained rate holds flat — per-write maintenance taxes must not grow with brain size (A4 removed caller-flush convoys; deferred embedding removes the per-write embed tax where opted). | 🟡 the decay-curve row is a pair speed-table RED GATE; brainy-alone sustained-rate run rides the same corpora |
+| DP8 | Read under write pressure: no flicker window — a row that exists is never invisible to recall, even transiently (same-vector re-index is a no-op; changed-vector swaps in place, node never leaves the index; deferred updates serve the OLD vector until the atomic swap — stale-beats-absent). | ✅ brainy leg pinned (`tests/unit/hnsw/update-item-atomic` 9/9 + `deferred-embedding` stale-beats-absent); the symmetry property suite + runtime sentinels remain the B4 program |
+| — | **As-of semantic recall** (time-travel vector search): `asOf(G).find()` serves the vectors AS THEY STOOD at G — byte-exact past vectors, tombstone masking, the deferred-embed cell honest on the vector leg, TYPED refusal beyond the head. Brainy-alone leg = ephemeral at-generation materialization (documented O(n log n at G) build, bounded); the at-scale leg rides the accelerated provider's as-of index. | ✅ `tests/integration/asof-semantic-recall` 4/4 (registry ID pending the master table's mint) |
+| — | **The lazy-open gate honors EVERY provider's not-ready report** (a not-ready metadata provider can no longer latch the silent-empty state under `disableAutoRebuild`). | ✅ `tests/unit/brainy/lazy-notready-honor` |
+
+## MT — Maintenance (never in the door path)
+
+| ID | Brainy row | Status |
+|----|-----------|--------|
+| MT1 | Flush/checkpoint: ENGINE-OWNED cadence (write-count/interval/idle triggers, single-flight, background, loud on failure; callers never flush in hot paths; `flush()` stays as an awaitable barrier). | ✅ `tests/unit/brainy/persistence-policy` |
+| MT2 | Compaction: never on flush (durability-only law, 8.9.0); close-time pass time-budgeted + resumable; explicit `compactHistory({timeBudgetMs})`. | ✅ 8.9.0 suites |
+| MT3 | Index upkeep (mapper folds, delta promotion): native-side machinery; brainy's JS legs are small and synchronous-cheap. | 🟡 declared; yield audit rides the pair |
+| MT4 | Heal/rebuild walks (`repairIndex`, backfill walks): paged; failure latches with cooldown; NOT yet yield-to-foreground installments. | 🔴 owed — the priority-isolation clause (couples to LC4; same choreography) |
+| MT5 | Deferred embedding worker: ack at durability, durable pending markers (written BEFORE the commit — orphan-safe), crash-recovered at open via a bounded prefix listing, single-flight, 60s hang guard, `awaitPendingEmbeds()` barrier + `pendingEmbeds` gauge. VFS write paths adopt it end-to-end. | ✅ `tests/integration/deferred-embedding` 5/5 |
+| MT6 | Retention/archival walks: retention `'all'` does nothing by design; bounded-retention reclaim is close-time/explicit only. | 🟡 8.9.0 behavior pinned; archival profile is the co-frozen D1+D3 unit |
+
+## FM — Failure modes
+
+| ID | Brainy row | Status |
+|----|-----------|--------|
+| FM1 | Disk full / IO error mid-op: transaction rollback + typed error; failed rollback → StoreInconsistentError quarantines writes until repairIndex(). | 🟡 rollback paths pinned; explicit disk-full depot case owed |
+| FM2 | Memory pressure: query limits + reserved-memory config; unified cache eviction. | 🟡 declared budgets; cascade pin owed |
+| FM3 | Torn/corrupt file on open: malformed brain-format marker → safe rebuild (never trusting a bad epoch); corrupt records surface loudly. | 🟡 marker pin ✅ (`brain-format-handshake`); broader quarantine is native-side |
+| FM4 | Native module unavailable: plugin load failure is LOUD (version-coupling law throws on range mismatch — never silently version-drifted); JS engine serves with its own declared budgets, named as the active backend in op names. | ✅ `tests/unit/plugin-version-coupling` + op-name stamping |
+
+## FL — Fleet
+
+| ID | Brainy row | Status |
+|----|-----------|--------|
+| FL1 | Cold open on demand: LC1's adopt-everything open; warm() available for eager paths. | 🟡 open cost pinned at LC1; millisecond budget rides the speed table |
+| FL2–FL4 | Boot storm / upgrade wave / isolation: fleet-layer policies over LC1/LC4 — engine leg = budgeted opens + LC4's behind-doors migration. | 🔴 owed with LC4 |
+| FL5 | Brain as product object: create instant (LC2) · erase = `clear()` explicit + complete · export = portable-graph, canon-complete mode available. | ✅ clear-persistence + portable-graph + canonical-enumeration suites |
+
+## Status summary
+
+Contracted + pinned this train: **DP3, DP4, DP6, DP8(brainy leg), MT1,
+MT5, LC5(aggregation), the lazy-open not-ready gate, LC1/LC3/LC9, FM4,
+FL5** — each with the cited test. Owed, in production-risk order, all
+coupled to the priority-isolation program the lifecycle sev opened: **LC4
+(doors-open migration), MT4 (yielding heals), LC7 (downgrade contract),
+LC6 (SIGTERM budget), FL2–FL4, FM1/FM2 depot cases, B4 symmetry suite +
+sentinels.** Rows move from owed to contracted only with a cited test —
+none lands by prose.

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "@soulcraft/brainy",
-  "version": "9.0.0",
+  "version": "10.0.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@soulcraft/brainy",
-      "version": "9.0.0",
+      "version": "10.0.0",
       "license": "MIT",
       "dependencies": {
         "@msgpack/msgpack": "^3.1.2",

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@soulcraft/brainy",
-  "version": "9.0.0",
+  "version": "10.0.0",
   "description": "Universal Knowledge Protocol™ - World's first Triple Intelligence database unifying vector, graph, and document search in one API. Stage 3 CANONICAL: 42 nouns × 127 verbs covering 96-97% of all human knowledge.",
   "main": "dist/index.js",
   "module": "dist/index.js",

scripts/release.sh

@@ -175,76 +175,79 @@ echo -e "${BLUE}7️⃣  Creating git tag v${NEW_VERSION}...${NC}"
 git tag -a "v${NEW_VERSION}" -m "Release v${NEW_VERSION}"
 echo -e "${GREEN}✅ Tag created${NC}\n"
 
-# Step 9: Push to origin — the forge is the one home (ruled 2026-07-23; the
+# Step 9: Push to origin — The Source is the one home (ruled 2026-07-23; the
 # old public GitHub repo is archived history, no longer part of any release).
 echo -e "${BLUE}8️⃣  Pushing to origin...${NC}"
 git push --follow-tags origin "$CURRENT_BRANCH"
 echo -e "${GREEN}✅ Pushed to origin${NC}\n"
 
-# Step 10: Forge publish is CI's job now, not the laptop's — a tag push (just
-# above) triggers .forgejo/workflows/publish-forge.yml, which builds and
-# publishes on the forge's own runner (datacenter-side: seconds, not the
-# laptop's WAN timing out on an 87MB tarball PUT). The laptop holds no forge
-# publish credential anymore; it only waits for CI's result before trusting
-# the forge/npmjs pair enough to publish the storefront leg.
-FORGE_NPM_REG="https://source.soulcraft.com/api/packages/soulcraft/npm/"
-FORGE_POLL_INTERVAL_S=15
-FORGE_POLL_MAX_ATTEMPTS=80  # 80 × 15s = 20 minutes — the runner is sequential; the publish run queues behind ci.yml jobs
-echo -e "${BLUE}9️⃣  Waiting for CI to publish v${NEW_VERSION} to the forge registry (home)...${NC}"
-FORGE_LANDED=false
-for ((attempt = 1; attempt <= FORGE_POLL_MAX_ATTEMPTS; attempt++)); do
-  LANDED_VERSION=$(npm view "@soulcraft/brainy@${NEW_VERSION}" version "--@soulcraft:registry=${FORGE_NPM_REG}" 2>/dev/null || echo "")
+# Step 10: The home publish (The Source, source.soulcraft.com) is CI's job
+# now, not the laptop's — a tag push (just above) triggers
+# .forgejo/workflows/publish-source.yml, which builds and publishes on The
+# Source's own runner (datacenter-side: seconds, not the laptop's WAN timing
+# out on an 87MB tarball PUT). The laptop holds no home-registry publish
+# credential anymore; it only waits for CI's result before trusting the
+# home/npmjs pair enough to publish the storefront leg.
+SOURCE_NPM_REG="https://source.soulcraft.com/api/packages/soulcraft/npm/"
+SOURCE_POLL_INTERVAL_S=15
+SOURCE_POLL_MAX_ATTEMPTS=200  # 200 × 15s = 50 minutes — the runner is sequential and a busy day's ci.yml
+                             # backlog has twice exceeded the old 20-minute window (8.10.3, 9.0.0);
+                             # ci.yml no longer runs on tag pushes, but same-day branch pushes still queue ahead
+echo -e "${BLUE}9️⃣  Waiting for CI to publish v${NEW_VERSION} to The Source registry (home)...${NC}"
+SOURCE_LANDED=false
+for ((attempt = 1; attempt <= SOURCE_POLL_MAX_ATTEMPTS; attempt++)); do
+  LANDED_VERSION=$(npm view "@soulcraft/brainy@${NEW_VERSION}" version "--@soulcraft:registry=${SOURCE_NPM_REG}" 2>/dev/null || echo "")
   if [ "$LANDED_VERSION" = "$NEW_VERSION" ]; then
-    FORGE_LANDED=true
+    SOURCE_LANDED=true
     break
   fi
-  echo -e "${YELLOW}   … not yet on the forge (attempt ${attempt}/${FORGE_POLL_MAX_ATTEMPTS}); retrying in ${FORGE_POLL_INTERVAL_S}s${NC}"
-  sleep "$FORGE_POLL_INTERVAL_S"
+  echo -e "${YELLOW}   … not yet on The Source (attempt ${attempt}/${SOURCE_POLL_MAX_ATTEMPTS}); retrying in ${SOURCE_POLL_INTERVAL_S}s${NC}"
+  sleep "$SOURCE_POLL_INTERVAL_S"
 done
 
-if [ "$FORGE_LANDED" = true ]; then
-  echo -e "${GREEN}✅ CI published v${NEW_VERSION} to the forge${NC}\n"
+if [ "$SOURCE_LANDED" = true ]; then
+  echo -e "${GREEN}✅ CI published v${NEW_VERSION} to The Source${NC}\n"
 else
-  echo -e "${RED}❌ CI forge publish did not land — check the workflow run on The Source; the pair must not diverge.${NC}"
+  echo -e "${RED}❌ CI's home publish did not land — check the workflow run on The Source; the pair must not diverge.${NC}"
   echo -e "${RED}   v${NEW_VERSION} was tagged and pushed, but @soulcraft/brainy@${NEW_VERSION} never became visible on the${NC}"
-  echo -e "${RED}   forge registry after ${FORGE_POLL_MAX_ATTEMPTS} attempts, ${FORGE_POLL_INTERVAL_S}s apart. Aborting before npmjs.${NC}"
+  echo -e "${RED}   Source registry after ${SOURCE_POLL_MAX_ATTEMPTS} attempts, ${SOURCE_POLL_INTERVAL_S}s apart. Aborting before npmjs.${NC}"
   exit 1
 fi
 
 echo -e "${BLUE}9️⃣½  Publishing to npmjs (storefront, dist-tag: ${NPM_TAG})...${NC}"
 # BYTE-IDENTITY LAW: the storefront republishes CI's EXACT artifact — download
-# the tarball the forge serves and publish that file, never a fresh local pack
+# the tarball The Source serves and publish that file, never a fresh local pack
 # (a local rebuild can differ byte-wise, and the fleet verifies the pair by
 # shasum across registries).
 STOREFRONT_TMP="$(mktemp -d)"
-(cd "$STOREFRONT_TMP" && npm pack "@soulcraft/brainy@${NEW_VERSION}" "--@soulcraft:registry=${FORGE_NPM_REG}" >/dev/null)
-FORGE_TARBALL="$(ls "$STOREFRONT_TMP"/soulcraft-brainy-*.tgz)"
-echo -e "${BLUE}   forge artifact: $(sha256sum "$FORGE_TARBALL" | cut -d' ' -f1)${NC}"
-npm publish "$FORGE_TARBALL" --tag "$NPM_TAG" "--@soulcraft:registry=https://registry.npmjs.org/"
+(cd "$STOREFRONT_TMP" && npm pack "@soulcraft/brainy@${NEW_VERSION}" "--@soulcraft:registry=${SOURCE_NPM_REG}" >/dev/null)
+SOURCE_TARBALL="$(ls "$STOREFRONT_TMP"/soulcraft-brainy-*.tgz)"
+echo -e "${BLUE}   home artifact: $(sha256sum "$SOURCE_TARBALL" | cut -d' ' -f1)${NC}"
+npm publish "$SOURCE_TARBALL" --tag "$NPM_TAG" "--@soulcraft:registry=https://registry.npmjs.org/"
 rm -rf "$STOREFRONT_TMP"
 # Brainy is the only PUBLIC @soulcraft package — verify visibility after every publish.
 npm access get status @soulcraft/brainy "--@soulcraft:registry=https://registry.npmjs.org/" || true
 # Verify the pair is byte-identical by registry-reported shasum — divergence here
 # means the storefront leg must be treated as failed, loudly.
-FORGE_SHA=$(npm view "@soulcraft/brainy@${NEW_VERSION}" dist.shasum "--@soulcraft:registry=${FORGE_NPM_REG}" 2>/dev/null || echo "forge-unavailable")
+SOURCE_SHA=$(npm view "@soulcraft/brainy@${NEW_VERSION}" dist.shasum "--@soulcraft:registry=${SOURCE_NPM_REG}" 2>/dev/null || echo "source-unavailable")
 NPMJS_SHA=$(npm view "@soulcraft/brainy@${NEW_VERSION}" dist.shasum "--@soulcraft:registry=https://registry.npmjs.org/" 2>/dev/null || echo "npmjs-unavailable")
-if [ "$FORGE_SHA" = "$NPMJS_SHA" ]; then
+if [ "$SOURCE_SHA" = "$NPMJS_SHA" ]; then
   echo -e "${GREEN}✅ Published to npmjs — byte-identical pair (shasum ${NPMJS_SHA})${NC}\n"
 else
-  echo -e "${RED}❌ REGISTRY DIVERGENCE: forge shasum ${FORGE_SHA} != npmjs shasum ${NPMJS_SHA} — investigate before announcing${NC}\n"
+  echo -e "${RED}❌ REGISTRY DIVERGENCE: The Source shasum ${SOURCE_SHA} != npmjs shasum ${NPMJS_SHA} — investigate before announcing${NC}\n"
   exit 1
 fi
 
-# Step 11: Release object on the forge (presentational — the tag, CHANGELOG,
-# and RELEASES.md are the record; this just gives the forge UI a release page).
-echo -e "${BLUE}🔟 Creating forge release...${NC}"
+# Step 11: Release object on The Source (presentational — the tag, CHANGELOG,
+# and RELEASES.md are the record; this just gives The Source's UI a release page).
+echo -e "${BLUE}🔟 Creating release page on The Source...${NC}"
 if [ -n "${FORGEJO_RELEASE_TOKEN:-}" ]; then
   if curl -sf -X POST "https://source.soulcraft.com/api/v1/repos/soulcraft/brainy/releases" \
     -H "Authorization: token ${FORGEJO_RELEASE_TOKEN}" -H "Content-Type: application/json" \
     -d "{\"tag_name\":\"v${NEW_VERSION}\",\"name\":\"v${NEW_VERSION}\",\"prerelease\":${PRERELEASE}}" >/dev/null; then
-    echo -e "${GREEN}✅ Forge release created${NC}\n"
+    echo -e "${GREEN}✅ Release page created on The Source${NC}\n"
   else
-    echo -e "${RED}⚠️  Forge release API call failed — tag + CHANGELOG remain the record; create the release page via the forge UI if wanted${NC}\n"
+    echo -e "${RED}⚠️  Release-page API call failed — tag + CHANGELOG remain the record; create the page via The Source's UI if wanted${NC}\n"
   fi
 else
   echo -e "${RED}⚠️  FORGEJO_RELEASE_TOKEN unset — no release page created; tag + CHANGELOG remain the record${NC}\n"
@@ -267,4 +270,4 @@ echo -e "${GREEN}🎉 Release ${NEW_VERSION} complete!${NC}"
 echo -e "${GREEN}━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━${NC}"
 echo ""
 echo -e "📦 npm: ${BLUE}https://www.npmjs.com/package/@soulcraft/brainy/v/${NEW_VERSION}${NC}"
-echo -e "🏠 Forge: ${BLUE}https://source.soulcraft.com/soulcraft/brainy/releases/tag/v${NEW_VERSION}${NC}"
+echo -e "🏠 The Source: ${BLUE}https://source.soulcraft.com/soulcraft/brainy/releases/tag/v${NEW_VERSION}${NC}"

src/aggregation/AggregationIndex.ts

@@ -371,6 +371,15 @@ export class AggregationIndex {
    */
   private pendingAdopt = new Set<string>()
 
+  /**
+   * Aggregates adopted with a BEHIND stamp: name → the exact generation
+   * window `(from, to]` whose writes the adopted state has not seen. The
+   * owner (Brainy) drains this via {@link getPendingCatchUps} +
+   * {@link reconcileEntity} + {@link finishCatchUp} BEFORE serving queries —
+   * cost bounded by the window's affected entities, never store size.
+   */
+  private pendingCatchUp = new Map<string, { from: number; to: number }>()
+
   /**
    * In-flight rescan targets. While a name has a staging map, ALL
    * contributions (the walk's and concurrent write hooks') land there instead
@@ -437,25 +446,47 @@ export class AggregationIndex {
   }
 
   /**
-   * May this persisted state be ADOPTED? When the store exposes its committed
-   * watermark, the state's `sourceGeneration` must EQUAL it: behind means
-   * later writes are missing from the state (unclean shutdown); ahead means
-   * it counts writes that no longer exist (e.g. a fact-log truncation on a
-   * copied store pulled the watermark back). Either way: one exact rescan,
-   * said out loud — never a silent adopt. Stores without the capability (and
-   * pre-stamp state on them) fall back to hash-only adoption.
+   * The adoption verdict for persisted state, against the store's committed
+   * watermark (SELF-ENGINE-LIFECYCLE-SPRINT ask (b) — behind-stamp is no
+   * longer a whole-store rescan):
+   *
+   * - `'adopt'` — stamp equals the watermark (clean), or the store has no
+   *   watermark capability (hash-only adoption, the pre-stamp behavior).
+   * - `'catchup'` — stamp is BEHIND the watermark (an unclean exit after
+   *   later writes, or a long-lived writer whose last flush predates recent
+   *   writes). The state is exact AS OF its stamp, so it is adopted and the
+   *   missing window `(stamp, committed]` is reconciled INCREMENTALLY per
+   *   affected entity via time-travel reads — bounded by writes since the
+   *   last flush, never by store size. The owner drains
+   *   {@link getPendingCatchUps} before serving queries.
+   * - `'rescan'` — no stamp (pre-stamp state on a stamped store) or stamp
+   *   AHEAD of the watermark (e.g. a fact-log truncation on a copied store
+   *   pulled the watermark back): the state over-counts unverifiably; one
+   *   exact rescan, said out loud.
    */
-  private stateGenerationAdoptable(name: string, stateData: unknown): boolean {
+  private stateAdoptionVerdict(
+    name: string,
+    stateData: unknown
+  ): 'adopt' | 'catchup' | 'rescan' {
     const committed = this.storage.committedGeneration?.() ?? null
-    if (committed === null) return true
+    if (committed === null) return 'adopt'
     const raw = (stateData as Record<string, unknown>).sourceGeneration
     const stamped = typeof raw === 'number' ? raw : null
-    if (stamped === committed) return true
+    if (stamped === committed) return 'adopt'
+    if (stamped !== null && stamped < committed) {
+      this.pendingCatchUp.set(name, { from: stamped, to: committed })
+      prodLog.info(
+        `[Aggregation] '${name}': persisted state is at generation ${stamped}, store is at ` +
+          `${committed} — adopting and reconciling the ${committed - stamped}-generation window ` +
+          `incrementally (no store rescan)`
+      )
+      return 'catchup'
+    }
     prodLog.warn(
       `[Aggregation] '${name}': persisted state is at generation ${stamped ?? 'unstamped'} ` +
         `but the store's committed generation is ${committed} — rescanning instead of adopting`
     )
-    return false
+    return 'rescan'
   }
 
   private async loadPersisted(): Promise<void> {
@@ -476,20 +507,21 @@ export class AggregationIndex {
           const appHash = this.definitionHashes.get(def.name) || ''
           if (appHash === savedHash && this.pendingAdopt.has(def.name)) {
             const stateData = await this.storage.getMetadata(`${STATE_KEY_PREFIX}${def.name}__`)
-            if (
-              stateData &&
-              stateData.groups &&
-              this.stateGenerationAdoptable(def.name, stateData)
-            ) {
+            const verdict =
+              stateData && stateData.groups
+                ? this.stateAdoptionVerdict(def.name, stateData)
+                : 'rescan'
+            if (verdict !== 'rescan') {
               const groupMap = new Map<string, AggregateGroupState>()
-              for (const group of stateData.groups as AggregateGroupState[]) {
+              for (const group of stateData!.groups as AggregateGroupState[]) {
                 groupMap.set(serializeGroupKey(group.groupKey), group)
               }
               this.states.set(def.name, groupMap)
               this.pendingAdopt.delete(def.name)
               this.needsBackfill.delete(def.name)
               prodLog.info(
-                `[Aggregation] '${def.name}': adopted persisted state (${groupMap.size} groups) — no rescan`
+                `[Aggregation] '${def.name}': adopted persisted state (${groupMap.size} groups) — ` +
+                  (verdict === 'catchup' ? 'incremental catch-up pending' : 'no rescan')
               )
             }
             // No/invalid persisted state: stays in pendingAdopt and resolves
@@ -504,22 +536,23 @@ export class AggregationIndex {
         const currentHash = hashDefinition(def)
 
         const stateData = await this.storage.getMetadata(`${STATE_KEY_PREFIX}${def.name}__`)
-        if (
-          stateData &&
-          stateData.groups &&
-          savedHash === currentHash &&
-          this.stateGenerationAdoptable(def.name, stateData)
-        ) {
-          // Definition unchanged — load state
+        const restoreVerdict =
+          stateData && stateData.groups && savedHash === currentHash
+            ? this.stateAdoptionVerdict(def.name, stateData)
+            : 'rescan'
+        if (restoreVerdict !== 'rescan') {
+          // Definition unchanged — load state (exact as of its stamp; a
+          // 'catchup' verdict reconciles the missing window incrementally).
           const groupMap = new Map<string, AggregateGroupState>()
-          for (const group of stateData.groups as AggregateGroupState[]) {
+          for (const group of stateData!.groups as AggregateGroupState[]) {
             const serialized = serializeGroupKey(group.groupKey)
             groupMap.set(serialized, group)
           }
           this.states.set(def.name, groupMap)
           this.needsBackfill.delete(def.name)
           prodLog.info(
-            `[Aggregation] '${def.name}': restored definition + adopted persisted state (${groupMap.size} groups)`
+            `[Aggregation] '${def.name}': restored definition + adopted persisted state (${groupMap.size} groups)` +
+              (restoreVerdict === 'catchup' ? ' — incremental catch-up pending' : '')
           )
         } else {
           // Definition changed or no saved state — start fresh and backfill from
@@ -537,15 +570,35 @@ export class AggregationIndex {
       }
     }
 
-    // Restore native provider state from persistence
+    // Restore native provider state from persistence — GATED by the same
+    // adoption verdict as caller-side state (the unconditional adopt was an
+    // asymmetry: a stale native blob restored over a moved store silently
+    // over/under-counted). 'adopt' restores; 'catchup' restores too (the
+    // incremental reconciliation drives the provider through
+    // incrementalUpdate over the exact missing window); 'rescan' SKIPS the
+    // blob — the flagged rebuild repopulates the provider from source.
+    // Legacy unstamped envelopes verdict as rescan, loudly, never silently.
     if (this.nativeProvider?.restoreState) {
       const nativeState = await this.storage.getMetadata('__aggregation_native_state__')
-      if (nativeState && typeof nativeState === 'string') {
-        this.nativeProvider.restoreState(nativeState)
-      } else if (nativeState && typeof nativeState === 'object' && nativeState.data) {
-        // flush() persists `{ data: serializeState() }`, so `data` is the
-        // provider's serialized state string.
-        this.nativeProvider.restoreState(nativeState.data as string)
+      const blob =
+        nativeState && typeof nativeState === 'string'
+          ? nativeState
+          : nativeState && typeof nativeState === 'object' && nativeState.data
+            ? (nativeState.data as string)
+            : null
+      if (blob !== null) {
+        const verdict = this.stateAdoptionVerdict(
+          '__native__',
+          nativeState && typeof nativeState === 'object' ? (nativeState as Record<string, unknown>) : {}
+        )
+        if (verdict === 'adopt' || verdict === 'catchup') {
+          this.nativeProvider.restoreState(blob)
+        } else {
+          prodLog.warn(
+            `[Aggregation] native provider state not adopted (verdict: ${verdict}) — ` +
+              `the flagged rescan repopulates the provider from source`
+          )
+        }
       }
     }
   }
@@ -581,12 +634,17 @@ export class AggregationIndex {
       }
     }
 
-    // Persist native provider state
+    // Persist native provider state — stamped. noteSourceGeneration lets the
+    // provider bake the committed watermark into its OWN envelope before
+    // serializing (so a native-side reopen can verify honesty without our
+    // wrapper); the wrapper carries the same stamp for OUR adoption verdict.
     if (this.nativeProvider?.serializeState) {
+      const nativeGen = this.storage.committedGeneration?.() ?? null
+      if (nativeGen !== null) this.nativeProvider.noteSourceGeneration?.(nativeGen)
       const nativeState = this.nativeProvider.serializeState()
       await this.storage.saveMetadata(
         '__aggregation_native_state__',
-        { data: nativeState }
+        nativeGen === null ? { data: nativeState } : { data: nativeState, sourceGeneration: nativeGen }
       )
     }
 
@@ -747,6 +805,119 @@ export class AggregationIndex {
     this.dirty.add(name)
   }
 
+  // ============= Incremental Catch-Up (behind-stamp adoption) =============
+
+  /** The aggregates adopted behind the watermark, with their exact missing windows. */
+  getPendingCatchUps(): Array<{ name: string; from: number; to: number }> {
+    return Array.from(this.pendingCatchUp, ([name, w]) => ({ name, ...w }))
+  }
+
+  /**
+   * Reconcile ONE entity's contribution across a catch-up window using the
+   * same exact delta algebra the write-time hooks use: remove the
+   * contribution the adopted state counted (the entity AS OF the stamp),
+   * add the contribution it should count (AS OF the window's end). `null`
+   * on either side means the entity did not exist then. Composes exactly
+   * with live hooks because every application is a precise old/new pair —
+   * order between catch-up and post-window writes cannot drift the totals.
+   */
+  reconcileEntity(
+    name: string,
+    id: string,
+    before: Record<string, unknown> | null,
+    after: Record<string, unknown> | null
+  ): void {
+    const def = this.definitions.get(name)
+    if (!def) return
+    if (before && after) {
+      if (isAggregateEntity(after)) return
+      const oldMatches = matchesSource(before, def.source)
+      const newMatches = matchesSource(after, def.source)
+      if (this.nativeProvider && (oldMatches || newMatches)) {
+        this.applyNativeResults(
+          name,
+          this.nativeProvider.incrementalUpdate(name, def, after, 'update', before)
+        )
+        return
+      }
+      if (oldMatches) this.removeContribution(name, def, before)
+      if (newMatches) this.addContribution(name, def, after)
+      return
+    }
+    if (after) {
+      if (isAggregateEntity(after) || !matchesSource(after, def.source)) return
+      if (this.nativeProvider) {
+        this.applyNativeResults(name, this.nativeProvider.incrementalUpdate(name, def, after, 'add'))
+      } else {
+        this.addContribution(name, def, after)
+      }
+      return
+    }
+    if (before) {
+      if (isAggregateEntity(before) || !matchesSource(before, def.source)) return
+      if (this.nativeProvider) {
+        this.applyNativeResults(name, this.nativeProvider.incrementalUpdate(name, def, before, 'delete'))
+      } else {
+        this.removeContribution(name, def, before)
+      }
+    }
+  }
+
+  /** Whether the native provider offers the parallel whole-rebuild path. */
+  hasProviderRebuild(): boolean {
+    return typeof this.nativeProvider?.rebuildAggregate === 'function'
+  }
+
+  /** The catch-up window for `name` is fully reconciled; state is current. */
+  finishCatchUp(name: string): void {
+    this.pendingCatchUp.delete(name)
+    this.dirty.add(name)
+  }
+
+  /**
+   * A catch-up could not complete (window unreadable, affected set over the
+   * bound, …): demote to an exact rescan, loudly — never serve un-reconciled.
+   */
+  demoteCatchUpToBackfill(name: string, reason: string): void {
+    this.pendingCatchUp.delete(name)
+    this.needsBackfill.add(name)
+    prodLog.warn(`[Aggregation] '${name}': catch-up demoted to full rescan — ${reason}`)
+  }
+
+  /**
+   * Rebuild an aggregate through the native provider's parallel path
+   * (SELF-ENGINE-LIFECYCLE-SPRINT ask (c) — `rebuildAggregate` existed on
+   * the provider contract but was never invoked; the JS walk fed
+   * per-entity FFI calls instead). Returns false when no provider rebuild
+   * exists — the caller streams the JS walk as before.
+   */
+  rebuildWithProvider(name: string, entities: Array<Record<string, unknown>>): boolean {
+    const def = this.definitions.get(name)
+    if (!def || !this.nativeProvider?.rebuildAggregate) return false
+    const rebuilt = this.nativeProvider.rebuildAggregate(
+      def,
+      entities.filter(e => !isAggregateEntity(e) && matchesSource(e, def.source))
+    )
+    this.states.set(name, rebuilt)
+    this.backfillStaging.delete(name)
+    this.needsBackfill.delete(name)
+    this.dirty.add(name)
+    return true
+  }
+
+  /**
+   * A write-path hook could not see the entity it needed (e.g. a delete
+   * whose before-image was unavailable): flag EVERY defined aggregate for
+   * an exact rescan, loudly — the counts must never silently drift
+   * (SELF-ENGINE-LIFECYCLE-SPRINT ask (d): the gated hook used to SKIP).
+   */
+  flagAllForRescan(reason: string): void {
+    for (const name of this.definitions.keys()) this.needsBackfill.add(name)
+    prodLog.warn(
+      `[Aggregation] all ${this.definitions.size} aggregate(s) flagged for rescan — ${reason}`
+    )
+  }
+
   // ============= Write-Time Hooks =============
 
   /**

src/db/faultInjectionStorage.ts

@@ -0,0 +1,164 @@
+/**
+ * @module db/faultInjectionStorage
+ * @description Deterministic fault injection at the fact log's raw-byte
+ * storage surface — the test harness half of the durability protocol. Wraps
+ * any adapter exposing the {@link FactLogStorage} primitives (the exact
+ * surface the fact log appends and syncs through) and injects the three
+ * crash shapes durability tests must prove against:
+ *
+ * - **torn write** ({@link FaultInjectionStorage.tearWriteAtByte}): the next
+ *   append persists only its first N bytes, then reports success — the shape
+ *   of power loss after a partially-flushed page. The caller-side "crash" is
+ *   simulated by abandoning in-memory state and reopening from storage.
+ * - **dropped sync** ({@link FaultInjectionStorage.dropNextSync}): the next
+ *   sync becomes a silent no-op — an fsync the device acknowledged into a
+ *   volatile cache and lost.
+ * - **failed append** ({@link FaultInjectionStorage.failNextAppend}): the next
+ *   append throws {@link FaultInjectedError} without writing a byte — EIO or
+ *   a full disk, surfaced to the writer.
+ *
+ * Every injected fault is journaled on {@link FaultInjectionStorage.injectedFaults}
+ * so tests can assert not just the outcome but that the fault actually fired.
+ * Knobs are one-shot (they disarm on firing) and re-arming overwrites the
+ * pending shot. All other operations pass through untouched.
+ */
+import type { FactLogStorage } from './factLog.js'
+
+/** The error a {@link FaultInjectionStorage.failNextAppend} shot throws. */
+export class FaultInjectedError extends Error {
+  /** The operation the fault fired on. */
+  public readonly operation: 'append'
+  /** The storage path the operation targeted. */
+  public readonly path: string
+
+  constructor(operation: 'append', path: string) {
+    super(`fault injection: ${operation} to ${path} failed by test design`)
+    this.name = 'FaultInjectedError'
+    this.operation = operation
+    this.path = path
+  }
+}
+
+/** One journaled fault event — proof the injected fault actually fired. */
+export interface InjectedFault {
+  kind: 'torn-write' | 'dropped-sync' | 'failed-append'
+  /** The target path (torn-write / failed-append). */
+  path?: string
+  /** The paths a dropped sync was asked to make durable. */
+  paths?: string[]
+  /** Bytes the caller asked to append (torn-write). */
+  requestedBytes?: number
+  /** Bytes actually persisted (torn-write). */
+  writtenBytes?: number
+}
+
+/**
+ * A {@link FactLogStorage} wrapper that injects deterministic storage faults.
+ * Construct it around any conforming adapter and hand it wherever a
+ * FactLogStorage is accepted — unarmed, it is a transparent passthrough.
+ */
+export class FaultInjectionStorage implements FactLogStorage {
+  private readonly inner: FactLogStorage
+  /** Pending torn-write byte count, or null when unarmed. */
+  private tearAtByte: number | null = null
+  /** Pending dropped-sync shot. */
+  private dropSyncArmed = false
+  /** Pending failed-append shot. */
+  private failAppendArmed = false
+  /** Journal of every fault that fired, in firing order. */
+  public readonly injectedFaults: InjectedFault[] = []
+
+  constructor(inner: FactLogStorage) {
+    this.inner = inner
+  }
+
+  /**
+   * Arm a torn write: the NEXT {@link appendRawBytes} persists only the first
+   * `n` bytes of its buffer (all of it when `n` exceeds the buffer) and then
+   * reports success. One-shot.
+   */
+  tearWriteAtByte(n: number): void {
+    if (!Number.isInteger(n) || n < 0) {
+      throw new Error(`fault injection: tearWriteAtByte needs a non-negative integer; got ${n}`)
+    }
+    this.tearAtByte = n
+  }
+
+  /** Arm a dropped sync: the NEXT {@link syncRawObjects} silently does nothing. One-shot. */
+  dropNextSync(): void {
+    this.dropSyncArmed = true
+  }
+
+  /**
+   * Arm a failed append: the NEXT {@link appendRawBytes} throws
+   * {@link FaultInjectedError} without writing. One-shot; wins over a
+   * simultaneously-armed torn write (nothing is written at all).
+   */
+  failNextAppend(): void {
+    this.failAppendArmed = true
+  }
+
+  /** Append bytes — the injection point for torn writes and failed appends. */
+  async appendRawBytes(path: string, bytes: Uint8Array): Promise<void> {
+    if (this.failAppendArmed) {
+      this.failAppendArmed = false
+      this.injectedFaults.push({ kind: 'failed-append', path })
+      throw new FaultInjectedError('append', path)
+    }
+    if (this.tearAtByte !== null) {
+      const writtenBytes = Math.min(this.tearAtByte, bytes.length)
+      this.tearAtByte = null
+      this.injectedFaults.push({
+        kind: 'torn-write',
+        path,
+        requestedBytes: bytes.length,
+        writtenBytes
+      })
+      if (writtenBytes > 0) {
+        await this.inner.appendRawBytes(path, bytes.subarray(0, writtenBytes))
+      }
+      return
+    }
+    return this.inner.appendRawBytes(path, bytes)
+  }
+
+  /** Make paths durable — the injection point for dropped syncs. */
+  async syncRawObjects(paths: string[]): Promise<void> {
+    if (this.dropSyncArmed) {
+      this.dropSyncArmed = false
+      this.injectedFaults.push({ kind: 'dropped-sync', paths: [...paths] })
+      return
+    }
+    return this.inner.syncRawObjects(paths)
+  }
+
+  /** Passthrough. */
+  async readRawBytes(path: string): Promise<Uint8Array | null> {
+    return this.inner.readRawBytes(path)
+  }
+
+  /** Passthrough. */
+  async writeRawBytes(path: string, bytes: Uint8Array): Promise<void> {
+    return this.inner.writeRawBytes(path, bytes)
+  }
+
+  /** Passthrough. */
+  async rawByteSize(path: string): Promise<number | null> {
+    return this.inner.rawByteSize(path)
+  }
+
+  /** Passthrough. */
+  async readRawObject(path: string): Promise<any | null> {
+    return this.inner.readRawObject(path)
+  }
+
+  /** Passthrough. */
+  async writeRawObject(path: string, data: any): Promise<void> {
+    return this.inner.writeRawObject(path, data)
+  }
+
+  /** Passthrough. */
+  async deleteRawObject(path: string): Promise<void> {
+    return this.inner.deleteRawObject(path)
+  }
+}

src/db/generationStore.ts

@@ -45,7 +45,15 @@ import type {
   GenerationStorage,
   TxLogEntry
 } from './types.js'
-import { FactLog, storageSupportsFactLog, type CommitFact, type FactOp } from './factLog.js'
+import { readLogAuthority } from './logAuthority.js'
+import {
+  FactLog,
+  storageSupportsFactLog,
+  type CommitFact,
+  type FactOp,
+  type FactIntMinter,
+  type FactMarkerRecord
+} from './factLog.js'
 import { GenerationSegmentStore, type FoldGeneration } from './generationSegments.js'
 import { crc32c } from '../utils/crc32c.js'
 
@@ -67,6 +75,13 @@ export interface CommitBeforeImages {
 export const GENERATION_COUNTER_PATH = '_system/generation.json'
 /** Storage-root-relative path of the commit manifest. */
 export const MANIFEST_PATH = '_system/manifest.json'
+/**
+ * The clean-shutdown marker (log-authority recovery gate): written+fsynced at
+ * a clean close carrying the committed generation; CONSUMED at every open.
+ * Absent or generation-mismatched at open = unclean shutdown = the whole-log
+ * replay fold. Its absence is always safe (costs one replay, loses nothing).
+ */
+export const CLEAN_SHUTDOWN_PATH = '_system/clean-shutdown.json'
 /** Storage-root-relative prefix of the per-generation record directories. */
 export const GENERATIONS_PREFIX = '_generations'
 
@@ -88,12 +103,43 @@ export const GENERATIONS_PREFIX = '_generations'
  *   IS committed); the tx-log append has NOT happened yet. A crash here must
  *   keep the transaction (the tx-log is advisory metadata, not the source of
  *   commit truth).
+ * - `'transact-after-fact-sync'` — the batch's fact is appended AND fsynced,
+ *   but neither the counter nor the manifest advanced. A crash here must cost
+ *   the whole batch: recovery restores the before-images and open() truncates
+ *   the synced fact back to the manifest watermark.
+ *
+ * Single-op (Model-B group-commit) phases — `commitSingleOp`:
+ *
+ * - `'singleop-after-execute'` — the live canonical write has applied (tmp+
+ *   rename, not individually fsynced); no history, fact, or generation record
+ *   exists yet. A crash here must cost only the never-returned ack — the
+ *   baseline stays intact and the log stays at the committed watermark.
+ * - `'singleop-after-fact-append'` — the fact is appended (and, in at-ack
+ *   mode, fsynced); the manifest never saw the generation. A crash here must
+ *   cost the buffered history + the fact (open() truncates it back), never
+ *   the baseline.
+ *
+ * Pending-tier flush phases — `flushPendingSingleOps`:
+ *
+ * - `'flush-after-staging'` — the window's record-set dirs are written but not
+ *   fsynced and the manifest never advanced. A crash here must cost only the
+ *   window's HISTORY (drop-without-restore) — the acked live writes stay.
+ * - `'flush-before-manifest'` — staging is fsynced and the facts are fsynced,
+ *   but the manifest never advanced. A crash here must cost only the window's
+ *   history and its facts (truncated at open) — the acked live writes stay.
+ * - `'before-manifest-rename'` is ALSO fired by the flush path just before its
+ *   commit point (see `flushPendingSingleOpsUnlocked`).
  */
 export type CommitFaultPhase =
   | 'after-staging'
   | 'after-execute'
   | 'before-manifest-rename'
   | 'after-manifest-rename'
+  | 'transact-after-fact-sync'
+  | 'singleop-after-execute'
+  | 'singleop-after-fact-append'
+  | 'flush-after-staging'
+  | 'flush-before-manifest'
 
 /**
  * @description Identifies which ids a transaction touches, split by kind.
@@ -134,6 +180,38 @@ export class GenerationStore {
    */
   private factLog: FactLog | null = null
 
+  /**
+   * Fact-log durability mode. 'deferred' (default) = the fact becomes
+   * durable at the group-commit flush, together with the buffered history —
+   * the pre-log-authority contract, zero added ack latency. 'at-ack' =
+   * every single-op ack awaits a covering log fsync (shared via the log's
+   * group commit) — the log-authority contract: an acked write's fact
+   * survives power loss. Set by the owner from the stored authority switch
+   * at open; transact() is durable-at-return in BOTH modes (unchanged).
+   */
+  private logDurability: 'deferred' | 'at-ack' = 'deferred'
+
+  /** Switch the fact-log durability mode (see {@link logDurability}). */
+  setLogDurability(mode: 'deferred' | 'at-ack'): void {
+    this.logDurability = mode
+  }
+
+  /**
+   * The fact log's v2 int minter — injected by the OWNER (brainy wires the
+   * metadata index's id mapper here right after the index is ready), because
+   * this store cannot know the mapper. With the minter installed, new fact
+   * segments write the v2 format and after-image records carry minted dense
+   * ints reproducible by an id-mapper rebuild. Survives reopen: `open()`
+   * re-installs it on the fresh {@link FactLog} instance.
+   */
+  private intMinter: FactIntMinter | null = null
+
+  /** Install the fact log's v2 int minter (see {@link intMinter}). */
+  setIntMinter(mint: FactIntMinter): void {
+    this.intMinter = mint
+    this.factLog?.setIntMinter(mint)
+  }
+
   /** Latest reserved/observed generation (≥ {@link committed}). */
   private counter = 0
   /** Committed-transaction watermark (manifest generation). */
@@ -390,9 +468,26 @@ export class GenerationStore {
       | null
     const manifest = (await this.storage.readRawObject(MANIFEST_PATH)) as GenerationManifest | null
 
-    this.committed = manifest?.generation ?? 0
-    this.horizonGen = manifest?.horizon ?? 0
-    this.counter = Math.max(counterFile?.generation ?? 0, this.committed)
+    // TORN-ARTIFACT VALIDATION (power-loss survivors): a torn manifest or
+    // counter can carry NaN/garbage where a generation belongs — unguarded,
+    // that NaN reaches BigInt() conversions at init and kills the open with
+    // a RangeError. A non-finite-integer generation is DISCARDED with
+    // narration (the conservative floor: 0 = re-derive from the record
+    // directories / fact log below, exactly the recovery machinery's job).
+    const finiteGen = (v: unknown, source: string): number => {
+      if (typeof v === 'number' && Number.isSafeInteger(v) && v >= 0) return v
+      if (v !== undefined && v !== null) {
+        prodLog.warn(
+          `[GenerationStore] ${source} carries a non-integer generation ` +
+            `(${String(v)}) — torn write survivor; discarding and re-deriving ` +
+            `from recovery (never a RangeError at open)`
+        )
+      }
+      return 0
+    }
+    this.committed = finiteGen(manifest?.generation, 'manifest')
+    this.horizonGen = finiteGen(manifest?.horizon, 'manifest horizon')
+    this.counter = Math.max(finiteGen(counterFile?.generation, 'generation counter'), this.committed)
 
     // Discover existing generation record directories.
     const recordPaths = await this.storage.listRawObjects(GENERATIONS_PREFIX)
@@ -445,6 +540,86 @@ export class GenerationStore {
     // hosts no fact log (readers fall back to canonical enumeration).
     if (storageSupportsFactLog(this.storage)) {
       this.factLog = new FactLog(this.storage)
+      if (this.intMinter) this.factLog.setIntMinter(this.intMinter)
+      // LOG-AUTHORITY REPLAY (durable-at-ack's recovery half): when this
+      // brain's stored authority is the log, an intact fact ABOVE the
+      // manifest is an ACKED write whose canonical bytes may not have
+      // survived the crash — its fsynced fact is the ONLY durable copy.
+      // Truncating it would lose an acked write; instead REPLAY it into
+      // canonical and advance the manifest to cover it. Tree-authority
+      // brains keep the truncate contract (their acks never promised the
+      // fact was durable). Derived indexes reconcile through the normal
+      // drift machinery at open — same as group-commit recovery.
+      const authority = await readLogAuthority(this.storage)
+      if (authority.authority === 'log') {
+        // TWO REPLAY TIERS, gated by the clean-shutdown marker:
+        //
+        // (1) ABOVE-MANIFEST (always): an intact fact above the manifest is
+        //     an acked write whose canonical bytes may not have survived —
+        //     replay it in and advance the manifest.
+        // (2) WHOLE-LOG (unclean shutdown only): power loss can ALSO vaporize
+        //     canonical bytes BELOW the manifest — live entity writes are
+        //     tmp+rename without per-file fsync; the group-commit flush syncs
+        //     the staging copies and the manifest, never the live tree. The
+        //     manifest therefore over-states canonical durability across a
+        //     power cut, and facts ≤ manifest can be the ONLY durable copy
+        //     of acked state (measured: 299 of 301 acks lost while the log
+        //     held every fact scan-clean). Under log authority, recovery is
+        //     REPLAY: an unclean open folds the ENTIRE log into canonical —
+        //     whole-entity after-images are idempotent, so re-applying
+        //     already-intact records is byte-safe. A clean close writes the
+        //     marker and skips all of this (zero open cost on the happy
+        //     path); crash recovery pays one narrated log fold — LC1 and
+        //     LC5 are the same code, a crash is just bigger lag.
+        const cleanShutdown = await this.readCleanShutdownMarker()
+        const orphans = await this.factLog.peekFactsAbove(this.committed)
+        const uncleanOpen = cleanShutdown === null || cleanShutdown !== this.committed
+        const factsToReplay = uncleanOpen
+          ? await this.factLog.peekFactsAbove(0)
+          : orphans
+        if (factsToReplay.length > 0) {
+          let replayed = 0
+          for (const fact of factsToReplay) {
+            for (const op of fact.ops) {
+              const image =
+                op.record === null
+                  ? { metadata: null, vector: null }
+                  : { metadata: op.record.metadata, vector: op.record.vector }
+              if (op.kind === 'verb') await this.storage.writeVerbRaw(op.id, image)
+              else await this.storage.writeNounRaw(op.id, image)
+            }
+            replayed++
+            if (fact.generation > this.committed) {
+              this.committed = fact.generation
+              this.appendCommittedGen(fact.generation)
+              this.setDelta(fact.generation, {
+                nouns: new Set(fact.ops.filter((o) => o.kind === 'noun').map((o) => o.id)),
+                verbs: new Set(fact.ops.filter((o) => o.kind === 'verb').map((o) => o.id)),
+                timestamp: fact.timestamp,
+                bytes: 0
+              })
+            }
+          }
+          if (this.counter < this.committed) this.counter = this.committed
+          await this.persistCounterUnlocked()
+          const manifest: GenerationManifest = {
+            version: 1,
+            generation: this.committed,
+            committedAt: new Date().toISOString(),
+            horizon: this.horizonGen
+          }
+          await this.storage.writeRawObject(MANIFEST_PATH, manifest)
+          await this.storage.syncRawObjects([MANIFEST_PATH])
+          prodLog.warn(
+            `[GenerationStore] log-authority recovery replayed ${replayed} fact(s) into ` +
+              `canonical (${uncleanOpen ? 'WHOLE-LOG fold — unclean shutdown' : 'above-manifest'}; ` +
+              `committed at ${this.committed}) — an acked write is never lost`
+          )
+        }
+        // The marker is consumed: any session that can write invalidates it
+        // at first commit (see the commit paths); a clean close re-writes it.
+        await this.clearCleanShutdownMarker()
+      }
       await this.factLog.open(this.committed)
     } else {
       this.factLog = null
@@ -497,6 +672,37 @@ export class GenerationStore {
     await this.flushPendingSingleOps()
     this.storage.setGenerationBumpHook(undefined)
     await this.persistCounterNow()
+    // Clean-shutdown marker (log-authority recovery gate): everything above
+    // is durable; stamp the committed generation so the next open can adopt
+    // instead of folding the log. Written LAST — a crash before this line is
+    // exactly the unclean case the marker's absence reports.
+    try {
+      await this.storage.writeRawObject(CLEAN_SHUTDOWN_PATH, { generation: this.committed })
+      await this.storage.syncRawObjects([CLEAN_SHUTDOWN_PATH])
+    } catch {
+      // A failed marker write only costs the next open a replay fold — safe.
+    }
+  }
+
+  /** Read the clean-shutdown marker's generation, or null (absent/unreadable). */
+  private async readCleanShutdownMarker(): Promise<number | null> {
+    try {
+      const raw = (await this.storage.readRawObject(CLEAN_SHUTDOWN_PATH)) as {
+        generation?: number
+      } | null
+      return raw && Number.isSafeInteger(raw.generation) ? (raw.generation as number) : null
+    } catch {
+      return null
+    }
+  }
+
+  /** Consume the clean-shutdown marker (every open; a clean close re-writes it). */
+  private async clearCleanShutdownMarker(): Promise<void> {
+    try {
+      await this.storage.deleteRawObject(CLEAN_SHUTDOWN_PATH)
+    } catch {
+      // Absent or undeletable: the conservative outcome is a future replay.
+    }
   }
 
   /**
@@ -712,6 +918,37 @@ export class GenerationStore {
     else this.pins.set(gen, count - 1)
   }
 
+
+  /**
+   * Torn-tolerant raw read for BEFORE-IMAGE contexts: a write landing on a
+   * TORN record (power-loss survivor) is a HEAL — the new after-image
+   * replaces the unreadable bytes. The before-image is unknowable, so it
+   * reads as the CREATE SENTINEL ({metadata:null, vector:null}) with
+   * narration: history for this id restarts at this generation (an asOf
+   * below it resolves absent for the id — the honest statement of what the
+   * crash destroyed). The adapter's loud floor (error + gauge) fired at
+   * throw time; real storage faults still propagate.
+   */
+  private async readRawForBeforeImage(
+    kind: 'noun' | 'verb',
+    id: string
+  ): Promise<{ metadata: unknown | null; vector: unknown | null }> {
+    try {
+      return kind === 'noun'
+        ? await this.storage.readNounRaw(id)
+        : await this.storage.readVerbRaw(id)
+    } catch (err) {
+      if ((err as { code?: string }).code === 'TORN_RECORD') {
+        prodLog.warn(
+          `[GenerationStore] before-image of ${kind} ${id} is TORN — the incoming ` +
+            `write HEALS the record; its history restarts at this generation`
+        )
+        return { metadata: null, vector: null }
+      }
+      throw err
+    }
+  }
+
   /** @returns Total number of live pins across all generations. */
   activePinCount(): number {
     let total = 0
@@ -784,6 +1021,8 @@ export class GenerationStore {
     nouns: string[]
     verbs: string[]
     meta?: Record<string, unknown>
+    /** V2 marker records riding this fact (same generation, same append). */
+    records?: FactMarkerRecord[]
   }): Promise<CommitFact> {
     const ops: FactOp[] = []
     const afterRecords: GenerationRecord[] = []
@@ -807,7 +1046,8 @@ export class GenerationStore {
       timestamp: args.timestamp,
       ops,
       ...(args.meta ? { meta: args.meta } : {}),
-      ...(blobHashes.length > 0 ? { blobHashes } : {})
+      ...(blobHashes.length > 0 ? { blobHashes } : {}),
+      ...(args.records && args.records.length > 0 ? { records: args.records } : {})
     }
   }
 
@@ -820,11 +1060,17 @@ export class GenerationStore {
      *  per-record analogue of `ifAtGeneration`. A throw aborts the whole batch:
      *  the generation reservation is returned and no staging I/O has happened. */
     precommit?: (before: CommitBeforeImages) => void
+    /** Optional v2 marker records riding this batch's ONE commit fact (e.g.
+     *  the deferred-embedding lifecycle markers) — same generation, same
+     *  atomic append, same durability barrier as the batch itself, so a
+     *  marker can never be orphaned from its write nor the write from its
+     *  marker. Additive: omitted on every markerless path. */
+    records?: FactMarkerRecord[]
     execute: () => Promise<void>
   }): Promise<{ generation: number; timestamp: number }> {
     return this.withMutex(async () => {
       // A latched history-durability failure compromises the whole generation
-      // spine — refuse a transact too (advancing the manifest past stuck,
+      // chain — refuse a transact too (advancing the manifest past stuck,
       // un-durable single-op generations would be inconsistent). Same loud
       // error; self-clears when the pending tier drains.
       this.assertHistoryDurable()
@@ -868,11 +1114,11 @@ export class GenerationStore {
         // conflicting batch aborts with zero staging I/O. The maps hold the
         // byte-identical records the staged files are written from.
         for (const id of nouns) {
-          const prev = await this.storage.readNounRaw(id)
+          const prev = await this.readRawForBeforeImage('noun', id)
           nounBefore.set(id, { kind: 'noun', metadata: prev.metadata, vector: prev.vector })
         }
         for (const id of verbs) {
-          const prev = await this.storage.readVerbRaw(id)
+          const prev = await this.readRawForBeforeImage('verb', id)
           verbBefore.set(id, { kind: 'verb', metadata: prev.metadata, vector: prev.vector })
         }
 
@@ -956,11 +1202,15 @@ export class GenerationStore {
             timestamp,
             nouns,
             verbs,
-            ...(args.meta ? { meta: args.meta } : {})
+            ...(args.meta ? { meta: args.meta } : {}),
+            ...(args.records && args.records.length > 0 ? { records: args.records } : {})
           })
           await this.factLog.append(fact)
           await this.factLog.sync()
         }
+        // A crash here must cost the whole batch: the synced fact is truncated
+        // back at open() and the before-images are restored byte-identically.
+        faultPoint('transact-after-fact-sync')
 
         // -- 5. Counter + manifest rename (COMMIT POINT) ----------------------
         await this.persistCounterUnlocked()
@@ -1166,6 +1416,18 @@ export class GenerationStore {
     touched: { nouns?: string[]; verbs?: string[] }
     execute: () => Promise<void>
     precommit?: (before: CommitBeforeImages) => void
+    /**
+     * Optional v2 marker records riding this write's commit fact (e.g. the
+     * deferred-embedding lifecycle markers) — same generation, same atomic
+     * append, and in 'at-ack' log durability the SAME covering fsync as the
+     * write itself (zero extra sync). A marker can never be orphaned from
+     * its write nor the write from its marker. Additive: omitted on every
+     * markerless path. When the storage hosts no fact log the markers have
+     * no durable home — matching that storage's overall durability posture
+     * (it cannot host the log's crash guarantees either); callers own
+     * surfacing that honestly.
+     */
+    records?: FactMarkerRecord[]
   }): Promise<{ generation: number; timestamp: number; degraded?: string[] }> {
     return this.withMutex(async () => {
       // Refuse to accept a write whose history we cannot make durable: if the
@@ -1184,12 +1446,12 @@ export class GenerationStore {
       // {metadata:null, vector:null} = the create sentinel.
       const nounBefore = new Map<string, GenerationRecord>()
       for (const id of nouns) {
-        const prev = await this.storage.readNounRaw(id)
+        const prev = await this.readRawForBeforeImage('noun', id)
         nounBefore.set(id, { kind: 'noun', metadata: prev.metadata, vector: prev.vector })
       }
       const verbBefore = new Map<string, GenerationRecord>()
       for (const id of verbs) {
-        const prev = await this.storage.readVerbRaw(id)
+        const prev = await this.readRawForBeforeImage('verb', id)
         verbBefore.set(id, { kind: 'verb', metadata: prev.metadata, vector: prev.vector })
       }
 
@@ -1235,7 +1497,13 @@ export class GenerationStore {
             // buffered history).
             if (this.factLog) {
               await this.factLog.append(
-                await this.buildCommitFact({ generation: gen, timestamp, nouns, verbs })
+                await this.buildCommitFact({
+                  generation: gen,
+                  timestamp,
+                  nouns,
+                  verbs,
+                  ...(args.records && args.records.length > 0 ? { records: args.records } : {})
+                })
               )
             }
             prodLog.warn(
@@ -1262,6 +1530,12 @@ export class GenerationStore {
         throw err
       }
       this.inTransact = false
+      // Test-only crash simulation (direct call — a throw propagates with no
+      // cleanup, exactly like a process death; recovery-on-open restores the
+      // contract). A crash here must cost only the never-returned ack: the
+      // live canonical write applied, but no history, fact, or generation
+      // record exists for it yet.
+      if (this.commitFaultInjector) this.commitFaultInjector('singleop-after-execute')
 
       // Buffer the pending generation + make it instantly visible to reads.
       this.pendingBuffer.set(gen, { nouns: nounBefore, verbs: verbBefore, timestamp })
@@ -1270,14 +1544,52 @@ export class GenerationStore {
       // Fact log (dual-write): the acked write's AFTER-IMAGE fact, appended
       // now (read back warm, under the mutex — group-commit means flush-time
       // canonical only holds the LATEST state, so each generation's after-image
-      // exists only here). Durability rides the group-commit flush, exactly
-      // like the buffered before-image history: a crash before the flush loses
-      // the fact AND the generation together — never a torn state.
+      // exists only here).
+      //
+      // Durability is MODE-GOVERNED:
+      // - 'deferred' (default, the pre-log-authority behavior): durability
+      //   rides the group-commit flush like the buffered history — a crash
+      //   before the flush loses the fact AND the generation together, never
+      //   a torn state.
+      // - 'at-ack' (log-authority mode): the ack awaits a covering fsync via
+      //   the log's group-commit (many concurrent writers share ONE sync) —
+      //   an acked write's fact survives power loss, by contract.
       if (this.factLog) {
-        await this.factLog.append(
-          await this.buildCommitFact({ generation: gen, timestamp, nouns, verbs })
-        )
+        try {
+          await this.factLog.append(
+            await this.buildCommitFact({
+              generation: gen,
+              timestamp,
+              nouns,
+              verbs,
+              ...(args.records && args.records.length > 0 ? { records: args.records } : {})
+            })
+          )
+          if (this.logDurability === 'at-ack') {
+            await this.factLog.ensureSynced()
+          }
+        } catch (err) {
+          // A rejected write must NOT commit: the generation was buffered
+          // before the append, so un-buffer it and return the counter
+          // reservation — otherwise the next flush would durably commit a
+          // generation with NO fact, a silent log gap a later replay would
+          // turn into loss. Canonical bytes from execute() remain as an
+          // uncommitted orphan — identical to a crash at this point; never
+          // a torn committed state.
+          this.pendingBuffer.delete(gen)
+          const idx = this.pendingGens.lastIndexOf(gen)
+          if (idx !== -1) this.pendingGens.splice(idx, 1)
+          this.invalidateChains()
+          if (this.counter === gen) this.counter = gen - 1
+          throw err
+        }
       }
+      // Test-only crash simulation. A crash here must cost the buffered
+      // history + the appended fact in 'deferred' mode (open() truncates it
+      // back to the manifest watermark) — while under 'log' authority the
+      // intact fact is REPLAYED at open, never the baseline or the applied
+      // live write.
+      if (this.commitFaultInjector) this.commitFaultInjector('singleop-after-fact-append')
       this.schedulePendingFlush()
       return { generation: gen, timestamp }
     })
@@ -1396,6 +1708,11 @@ export class GenerationStore {
         logEntries.push({ generation: gen, timestamp: buf.timestamp })
       }
 
+      // Test-only crash simulation. A crash here must cost only the window's
+      // HISTORY: un-fsynced record-set dirs may sit above the manifest, and
+      // recovery drops them WITHOUT restore — the acked live writes stay.
+      if (this.commitFaultInjector) this.commitFaultInjector('flush-after-staging')
+
       // ONE fsync for the whole window — the durability-batching win.
       await this.storage.syncRawObjects(stagedPaths)
 
@@ -1405,6 +1722,12 @@ export class GenerationStore {
       // generation without its durable fact.
       await this.factLog?.sync()
 
+      // Test-only crash simulation. A crash here must cost only the window's
+      // history and its (already fsynced) facts — open() truncates the facts
+      // back to the manifest watermark and drops the staged group-commit dirs
+      // without restore; the acked live writes stay.
+      if (this.commitFaultInjector) this.commitFaultInjector('flush-before-manifest')
+
       // Test-only crash simulation: a throwing injector here leaves the staged
       // group-commit generation dirs on disk with NO manifest advance — the
       // exact "crashed mid-flush" state recovery must DROP-WITHOUT-RESTORE

src/db/logAuthority.ts

@@ -0,0 +1,332 @@
+/**
+ * @module db/logAuthority
+ * @description The per-brain LOG-AUTHORITY SWITCH and its verification
+ * oracle — the guarded adoption path for log-canonical storage.
+ *
+ * Two storage authorities exist during the adoption window:
+ * - `'tree'` (the default, today's behavior): the canonical record tree is
+ *   authoritative; the generation log is a complete dual-written journal.
+ * - `'log'`: the generation log is authoritative for this brain; single-op
+ *   write acks await a covering log fsync (durable-at-ack), and derived
+ *   state treats the log as ground truth.
+ *
+ * THE SWITCH IS PER BRAIN, STORED, CHECKED AT OPEN ONLY, and ONE-DIRECTIONAL
+ * unless explicitly reverted by an operator. A brain flips ONLY when its
+ * verification oracle is green: a full replay-and-diff of the log against
+ * the still-authoritative tree (the read-only witness). The oracle failing
+ * NAMES every divergence — a brain with pre-log history (records the log
+ * never saw) reports them as `pre-log-record` mismatches and needs a
+ * baseline backfill before it can ever flip.
+ *
+ * Nothing in this module mutates data: the oracle is read-only; the flip
+ * writes ONE artifact. Reverting = rewriting the artifact to 'tree' (the
+ * tree remained authoritative-quality throughout the window by dual-write).
+ */
+
+import type { FactScanHandle } from './factLog.js'
+import { prodLog } from '../utils/logger.js'
+import { createHash } from 'crypto'
+
+/** Storage-root-relative path of the authority switch artifact. */
+export const LOG_AUTHORITY_PATH = '_system/log-authority.json'
+
+/** The persisted shape of the authority switch. */
+export interface LogAuthorityRecord {
+  /** Which store is authoritative for this brain. */
+  authority: 'tree' | 'log'
+  /** When the flip happened (ms epoch). Absent while authority = 'tree'. */
+  flippedAt?: number
+  /** The oracle verdict that justified the flip (summary, not the full report). */
+  oracle?: {
+    verifiedAt: number
+    generationsScanned: number
+    nounsChecked: number
+    verbsChecked: number
+  }
+  /**
+   * Recorded when an OPEN-TIME adoption attempt (the 10.0.0 fleet default)
+   * was refused — the oracle could not go green. Keeps subsequent opens
+   * cheap; an operator re-runs adoptLogAuthority() after resolving it.
+   */
+  adoptRefusal?: { at: number; reason: string }
+}
+
+/** The narrow storage surface this module needs. */
+export interface LogAuthorityStorage {
+  readRawObject(path: string): Promise<unknown | null>
+  writeRawObject(path: string, data: unknown): Promise<void>
+  syncRawObjects(paths: string[]): Promise<void>
+  getNouns(opts: {
+    pagination: { limit: number; offset?: number; cursor?: string }
+  }): Promise<{ items: unknown[]; hasMore?: boolean; nextCursor?: string }>
+  getNounMetadata(id: string): Promise<unknown | null>
+}
+
+/** One divergence found by the oracle. */
+export interface OracleMismatch {
+  id: string
+  kind: 'noun' | 'verb'
+  reason:
+    | 'pre-log-record' // canonical row the log never saw — needs baseline backfill
+    | 'state-differs' // latest log after-image ≠ canonical bytes
+    | 'log-live-canonical-absent' // log says live, canonical has no record
+    | 'log-tombstone-canonical-present' // log says deleted, canonical still has it
+}
+
+/** The oracle's full report. */
+export interface OracleReport {
+  verdict: 'green' | 'red'
+  generationsScanned: number
+  nounsChecked: number
+  verbsChecked: number
+  matched: number
+  mismatches: OracleMismatch[]
+  /** Mismatch listing is capped; the counts above are always complete. */
+  mismatchListTruncated: boolean
+}
+
+const MISMATCH_LIST_CAP = 200
+
+/** Read the stored authority (absent artifact = 'tree', the safe default). */
+export async function readLogAuthority(
+  storage: Pick<LogAuthorityStorage, 'readRawObject'>
+): Promise<LogAuthorityRecord> {
+  const raw = (await storage
+    .readRawObject(LOG_AUTHORITY_PATH)
+    .catch(() => null)) as LogAuthorityRecord | null
+  if (raw && (raw.authority === 'log' || raw.authority === 'tree')) return raw
+  return { authority: 'tree' }
+}
+
+/**
+ * Normalize a canonical noun record to its ENTITY TRUTH before diffing:
+ * the canonical vector-file wrapper denormalizes derived index residue
+ * (`connections` — HNSW graph edges; `level` — the node's random skip-list
+ * level) that the generation log deliberately does NOT carry (projections
+ * own their own rebuild paths). Digesting the residue would report false
+ * `state-differs` on ~any brain whose HNSW assigned a nonzero level. Both
+ * sides of every oracle comparison pass through this normalizer.
+ */
+export function nounEntityTruth(record: {
+  metadata: unknown
+  vector: unknown
+}): { metadata: unknown; vector: unknown } {
+  const v = record.vector
+  if (v && typeof v === 'object' && !Array.isArray(v)) {
+    const { connections: _c, level: _l, ...entity } = v as Record<string, unknown>
+    return { metadata: record.metadata, vector: entity }
+  }
+  return { metadata: record.metadata, vector: v }
+}
+
+/**
+ * Stable content hash of a stored record for diffing — key-sorted JSON so
+ * property order can never fake a divergence.
+ */
+export function recordDigest(record: unknown): string {
+  const stable = (v: unknown): unknown => {
+    if (Array.isArray(v)) return v.map(stable)
+    if (v && typeof v === 'object') {
+      const out: Record<string, unknown> = {}
+      for (const k of Object.keys(v as Record<string, unknown>).sort()) {
+        out[k] = stable((v as Record<string, unknown>)[k])
+      }
+      return out
+    }
+    return v
+  }
+  return createHash('sha256').update(JSON.stringify(stable(record))).digest('hex')
+}
+
+/**
+ * THE VERIFICATION ORACLE: replay the fact log's noun records and diff the
+ * final state per id against the canonical tree (the witness). Read-only;
+ * bounded memory (id → {tombstoned, digest} — digests, never bodies).
+ *
+ * Verdict law: 'green' iff EVERY canonical row's latest state is exactly
+ * reproduced by the log AND the log claims nothing canonical denies. A
+ * brain older than its log reports its unlogged rows as `pre-log-record`
+ * mismatches — the named cure is a baseline backfill, never a silent pass.
+ */
+export async function runLogCompletenessOracle(args: {
+  storage: LogAuthorityStorage
+  scanFacts: () => FactScanHandle | null
+  /** Digest the canonical record the same way the log's after-image is digested. */
+  canonicalNounDigest: (id: string) => Promise<string | null>
+  /** Digest a log after-image record's payload. */
+  factRecordDigest: (record: unknown) => string
+  /**
+   * Verb legs (optional until every owner wires them): the canonical verb
+   * digest + the paged verb enumeration. When ABSENT, the oracle counts NO
+   * verbs and says so via verbsChecked = 0 — an honest partial verdict,
+   * never a silent full-pass claim.
+   */
+  canonicalVerbDigest?: (id: string) => Promise<string | null>
+  getVerbs?: (opts: {
+    pagination: { limit: number; offset?: number; cursor?: string }
+  }) => Promise<{ items: unknown[]; hasMore?: boolean; nextCursor?: string }>
+}): Promise<OracleReport> {
+  const report: OracleReport = {
+    verdict: 'red',
+    generationsScanned: 0,
+    nounsChecked: 0,
+    verbsChecked: 0,
+    matched: 0,
+    mismatches: [],
+    mismatchListTruncated: false
+  }
+  const addMismatch = (m: OracleMismatch): void => {
+    if (report.mismatches.length < MISMATCH_LIST_CAP) report.mismatches.push(m)
+    else report.mismatchListTruncated = true
+  }
+
+  // Pass 1: fold the log — latest state per noun id (digest or tombstone).
+  const scan = args.scanFacts()
+  if (!scan) {
+    // No fact log on this store: nothing can be verified — red, loudly.
+    prodLog.warn('[logAuthority] oracle: this store has no fact log — cannot verify, verdict red')
+    return report
+  }
+  const logState = new Map<string, { tombstoned: boolean; digest: string | null }>()
+  const verbLogState = new Map<string, { tombstoned: boolean; digest: string | null }>()
+  for await (const batch of scan.batches()) {
+    for (const fact of batch.facts) {
+      report.generationsScanned++
+      for (const op of fact.ops) {
+        const state =
+          op.record === null
+            ? { tombstoned: true, digest: null }
+            : { tombstoned: false, digest: args.factRecordDigest(op.record) }
+        if (op.kind === 'noun') logState.set(op.id, state)
+        else verbLogState.set(op.id, state)
+      }
+    }
+  }
+
+  // Pass 2: walk canonical (paged) and diff.
+  const seenCanonical = new Set<string>()
+  const PAGE = 500
+  let offset = 0
+  let cursor: string | undefined
+  for (;;) {
+    const page = await args.storage.getNouns({
+      pagination: cursor ? { limit: PAGE, cursor } : { limit: PAGE, offset }
+    })
+    for (const item of page.items) {
+      const id = (item as { id: string }).id
+      seenCanonical.add(id)
+      report.nounsChecked++
+      const inLog = logState.get(id)
+      if (!inLog) {
+        addMismatch({ id, kind: 'noun', reason: 'pre-log-record' })
+        continue
+      }
+      if (inLog.tombstoned) {
+        addMismatch({ id, kind: 'noun', reason: 'log-tombstone-canonical-present' })
+        continue
+      }
+      const canonicalDigest = await args.canonicalNounDigest(id)
+      if (canonicalDigest === null) {
+        addMismatch({ id, kind: 'noun', reason: 'pre-log-record' })
+        continue
+      }
+      if (canonicalDigest === inLog.digest) report.matched++
+      else addMismatch({ id, kind: 'noun', reason: 'state-differs' })
+    }
+    if (!page.hasMore || page.items.length === 0) break
+    if (page.nextCursor) cursor = page.nextCursor
+    else offset += page.items.length
+  }
+
+  // Pass 3: log-live ids canonical never showed us.
+  for (const [id, state] of logState) {
+    if (!state.tombstoned && !seenCanonical.has(id)) {
+      addMismatch({ id, kind: 'noun', reason: 'log-live-canonical-absent' })
+    }
+  }
+
+  // Verb passes — only when the owner wired the verb legs; otherwise the
+  // report says verbsChecked: 0, an honest partial scope, never a claim.
+  if (args.canonicalVerbDigest && args.getVerbs) {
+    const seenVerbs = new Set<string>()
+    let vOffset = 0
+    let vCursor: string | undefined
+    for (;;) {
+      const page = await args.getVerbs({
+        pagination: vCursor ? { limit: PAGE, cursor: vCursor } : { limit: PAGE, offset: vOffset }
+      })
+      for (const item of page.items) {
+        const id = (item as { id: string }).id
+        seenVerbs.add(id)
+        report.verbsChecked++
+        const inLog = verbLogState.get(id)
+        if (!inLog) {
+          addMismatch({ id, kind: 'verb', reason: 'pre-log-record' })
+          continue
+        }
+        if (inLog.tombstoned) {
+          addMismatch({ id, kind: 'verb', reason: 'log-tombstone-canonical-present' })
+          continue
+        }
+        const canonical = await args.canonicalVerbDigest(id)
+        if (canonical === null) {
+          addMismatch({ id, kind: 'verb', reason: 'pre-log-record' })
+          continue
+        }
+        if (canonical === inLog.digest) report.matched++
+        else addMismatch({ id, kind: 'verb', reason: 'state-differs' })
+      }
+      if (!page.hasMore || page.items.length === 0) break
+      if (page.nextCursor) vCursor = page.nextCursor
+      else vOffset += page.items.length
+    }
+    for (const [id, state] of verbLogState) {
+      if (!state.tombstoned && !seenVerbs.has(id)) {
+        addMismatch({ id, kind: 'verb', reason: 'log-live-canonical-absent' })
+      }
+    }
+  }
+
+  const totalMismatches =
+    report.mismatches.length + (report.mismatchListTruncated ? 1 : 0)
+  report.verdict = totalMismatches === 0 ? 'green' : 'red'
+  return report
+}
+
+/**
+ * Flip this brain's authority to the log — REFUSES unless the supplied
+ * oracle report is green (the caller runs the oracle; the flip records its
+ * summary). Writes + fsyncs the switch artifact; the mode takes full effect
+ * at the NEXT open (checked-at-open-only law), except durable-at-ack which
+ * the owner may enable immediately.
+ */
+export async function flipToLogAuthority(
+  storage: Pick<LogAuthorityStorage, 'writeRawObject' | 'syncRawObjects'>,
+  oracle: OracleReport
+): Promise<LogAuthorityRecord> {
+  if (oracle.verdict !== 'green') {
+    throw new Error(
+      `log-authority flip refused: the verification oracle is RED ` +
+        `(${oracle.mismatches.length}${oracle.mismatchListTruncated ? '+' : ''} mismatches; ` +
+        `first: ${oracle.mismatches[0] ? `${oracle.mismatches[0].reason} on ${oracle.mismatches[0].id}` : 'n/a'}). ` +
+        `A brain flips only on green — fix the divergences (pre-log records need a baseline backfill) and re-run.`
+    )
+  }
+  const record: LogAuthorityRecord = {
+    authority: 'log',
+    flippedAt: Date.now(),
+    oracle: {
+      verifiedAt: Date.now(),
+      generationsScanned: oracle.generationsScanned,
+      nounsChecked: oracle.nounsChecked,
+      verbsChecked: oracle.verbsChecked
+    }
+  }
+  await storage.writeRawObject(LOG_AUTHORITY_PATH, record)
+  await storage.syncRawObjects([LOG_AUTHORITY_PATH])
+  prodLog.info(
+    `[logAuthority] this brain's storage authority is now the generation log ` +
+      `(oracle green over ${oracle.nounsChecked} nouns / ${oracle.generationsScanned} generations)`
+  )
+  return record
+}

src/graph/graphAdjacencyIndex.ts

@@ -27,6 +27,22 @@ import { UnifiedCache, getGlobalCache } from '../utils/unifiedCache.js'
 import { prodLog } from '../utils/logger.js'
 import { LSMTree } from './lsm/LSMTree.js'
 import type { GraphIndexProvider } from '../plugin.js'
+import {
+  computeWatermarkVerdict,
+  makeProjectionStamp,
+  readStampedWatermark,
+  type WatermarkVerdict,
+  type WatermarkVerdictResult
+} from '../utils/projectionWatermark.js'
+
+/**
+ * Storage key for the graph-adjacency projection's watermark stamp — a
+ * sidecar record beside the artifact (the two verb-id LSM trees' persisted
+ * SSTables + manifests). Written LAST in
+ * {@link GraphAdjacencyIndex.flush} / {@link GraphAdjacencyIndex.close} so
+ * stamp-after-data ordering holds for every byte the stamp certifies.
+ */
+export const GRAPH_ADJACENCY_STAMP_KEY = '__index_graph_adjacency_watermark__'
 
 export interface GraphIndexConfig {
   maxIndexSize?: number      // Default: 100000
@@ -112,6 +128,14 @@ export class GraphAdjacencyIndex implements GraphIndexProvider {
   // Initialization flag
   private initialized = false
 
+  // --- Watermark stamp state (see utils/projectionWatermark for the law) ---
+  /** Generation handed in via {@link stampWatermark}, awaiting the next flush. */
+  private pendingWatermark: number | null = null
+  /** Last watermark durably stamped by this instance or loaded at init. */
+  private stampedWatermark: number | null = null
+  /** The three-way verdict computed at init; null until init runs. */
+  private loadVerdict: WatermarkVerdictResult | null = null
+
   /**
    * Check if index is initialized and ready for use
    */
@@ -241,12 +265,135 @@ export class GraphAdjacencyIndex implements GraphIndexProvider {
       await this.populateVerbIdSetFromStorage()
     }
 
+    // Watermark verdict for the persisted adjacency artifact (the LSM
+    // SSTables just loaded) — computed and exposed only: today's rebuild /
+    // recovery triggers are unchanged (acting on 'catchup' — the incremental
+    // fold — lands with the coordinator's wiring).
+    await this.loadWatermarkVerdict(lsmTreeSize > 0)
+
     // Start auto-flush timer after initialization
     this.startAutoFlush()
 
     this.initialized = true
   }
 
+  /**
+   * @description Record the committed generation this projection reflects.
+   * The stamp is NOT written here — it is written as the final storage write
+   * of the next {@link flush} (or {@link close}), so stamp-after-data
+   * ordering is a module guarantee, not a caller obligation. The coordinator
+   * calls this with the store's committed generation right before flushing.
+   * @param generation - The committed generation every flushed byte reflects.
+   */
+  stampWatermark(generation: number): void {
+    this.pendingWatermark = generation
+  }
+
+  /**
+   * @description The projection's current watermark: the stamp loaded at
+   * init (or the last stamp durably written by this instance). Null =
+   * unstamped (legacy artifact, first boot, or stamping never wired).
+   */
+  watermark(): number | null {
+    return this.stampedWatermark
+  }
+
+  /**
+   * @description The three-way adoption verdict computed at init —
+   * `'adopt'` (stamped == committed, zero work), `'catchup'` (stamped <
+   * committed; the gap from {@link watermarkGap} awaits an incremental
+   * fold), `'rescan'` (unstamped or stamped above committed — never
+   * trusted). Null until init() has run. Computed and exposed only; no
+   * load behavior changes ride on it yet.
+   */
+  watermarkVerdict(): WatermarkVerdict | null {
+    return this.loadVerdict?.verdict ?? null
+  }
+
+  /**
+   * @description The catch-up window `(from, to]` when the init verdict was
+   * `'catchup'`; null otherwise.
+   */
+  watermarkGap(): { from: number; to: number } | null {
+    return this.loadVerdict?.gap ?? null
+  }
+
+  /**
+   * @description Write the pending watermark stamp as a sidecar record —
+   * always called AFTER the LSM flushes it certifies completed. A stamp-write
+   * failure is fail-safe (unstamped/behind → rescan/catchup on next open,
+   * never a wrong adopt) but is said out loud and the pending stamp is
+   * retained for the next flush.
+   */
+  private async writePendingStamp(): Promise<void> {
+    if (this.pendingWatermark === null) return
+    const watermark = this.pendingWatermark
+    try {
+      await this.storage.saveMetadata(GRAPH_ADJACENCY_STAMP_KEY, {
+        noun: 'IndexWatermark',
+        ...makeProjectionStamp(watermark)
+      })
+      this.stampedWatermark = watermark
+      this.pendingWatermark = null
+    } catch (error) {
+      prodLog.error(
+        `[GraphAdjacencyIndex] failed to write watermark stamp (generation ${watermark}) — ` +
+          `artifact stays behind-stamped (safe: verdicts catchup/rescan, never wrong-adopt); ` +
+          `retrying on next flush:`,
+        error
+      )
+    }
+  }
+
+  /**
+   * @description Read the artifact's stamp and compute the three-way verdict
+   * against the store's committed generation. Unstamped state on a stamped
+   * store verdicts `'rescan'` LOUDLY — never a silent adopt.
+   *
+   * MIGRATION COST: existing pre-stamp brains verdict `'rescan'` exactly
+   * once (that open re-derives via the recovery walk it already runs); the
+   * next flush stamps them, and every later open adopts.
+   *
+   * @param artifactPresent - Whether persisted SSTables exist at all; gates
+   *   loud-vs-quiet on the rescan verdict so first boots don't scream.
+   */
+  private async loadWatermarkVerdict(artifactPresent: boolean): Promise<void> {
+    const committed = this.storage.committedGeneration?.() ?? null
+    let stamped: number | null = null
+    try {
+      const record = await this.storage.getMetadata(GRAPH_ADJACENCY_STAMP_KEY)
+      stamped = readStampedWatermark(record)
+    } catch {
+      // An unreadable stamp is unstamped — the fail-safe direction.
+      stamped = null
+    }
+    const result = computeWatermarkVerdict(stamped, committed)
+    this.loadVerdict = result
+    this.stampedWatermark = stamped
+
+    if (result.verdict === 'rescan') {
+      if (artifactPresent || stamped !== null) {
+        prodLog.warn(
+          `[GraphAdjacencyIndex] watermark verdict: RESCAN — persisted adjacency is ` +
+            (stamped === null
+              ? 'unstamped (legacy pre-stamp artifact, or a crash between data and stamp)'
+              : `stamped at generation ${stamped}, ABOVE the store's committed generation ${committed}`) +
+            ` — never adopting unverifiable state`
+        )
+      } else {
+        prodLog.debug(
+          '[GraphAdjacencyIndex] watermark verdict: rescan (no persisted artifact — first boot)'
+        )
+      }
+    } else if (result.verdict === 'catchup') {
+      prodLog.info(
+        `[GraphAdjacencyIndex] watermark verdict: catchup — adjacency stamped at generation ` +
+          `${stamped}, store committed at ${committed}; the (${stamped}, ${committed}] window ` +
+          `awaits an incremental fold (verdict exposed; the fold lands with the coordinator's wiring)`
+      )
+    }
+  }
+
   /**
    * Populate verbIdSet from storage without full rebuild
    * Lighter weight than full rebuild - only loads verb IDs, not all verb data
@@ -935,6 +1082,12 @@ export class GraphAdjacencyIndex implements GraphIndexProvider {
       }),
     ])
 
+    // STAMP-AFTER-DATA: the watermark stamp is the LAST write of the flush —
+    // both trees' SSTables are durable before the stamp lands. A crash
+    // anywhere above leaves the artifact behind-stamped or unstamped, which
+    // verdicts as catchup/rescan on the next open — never a wrong adopt.
+    await this.writePendingStamp()
+
     const elapsed = Date.now() - startTime
 
     prodLog.debug(`GraphAdjacencyIndex: Flush completed in ${elapsed}ms`)
@@ -955,6 +1108,10 @@ export class GraphAdjacencyIndex implements GraphIndexProvider {
         this.lsmTreeVerbsBySource.close(),
         this.lsmTreeVerbsByTarget.close(),
       ])
+
+      // Stamp-after-data on the shutdown path too: the trees' final flushes
+      // completed above, so a pending watermark may land now.
+      await this.writePendingStamp()
     }
 
     prodLog.info('GraphAdjacencyIndex: Shutdown complete')

src/hnsw/hnswIndex.ts

@@ -16,6 +16,22 @@ import { getGlobalCache, UnifiedCache } from '../utils/unifiedCache.js'
 import { prodLog } from '../utils/logger.js'
 import type { VectorIndexProvider, OpaqueIdSet, AtGenerationVectors } from '../plugin.js'
 import { ConnectionsCodec, compressedConnectionsKey } from './connectionsCodec.js'
+import {
+  computeWatermarkVerdict,
+  makeProjectionStamp,
+  readStampedWatermark,
+  type WatermarkVerdict,
+  type WatermarkVerdictResult
+} from '../utils/projectionWatermark.js'
+
+/**
+ * Storage key for the JS HNSW projection's watermark stamp — a sidecar
+ * record beside the artifact (per-node vector-index records + connection
+ * blobs + the entryPoint/maxLevel system record). Written LAST in
+ * {@link JsHnswVectorIndex.flush} so stamp-after-data ordering holds for
+ * every byte the stamp certifies.
+ */
+export const HNSW_INDEX_STAMP_KEY = '__index_hnsw_watermark__'
 
 // Default HNSW parameters
 const DEFAULT_CONFIG: HNSWConfig = {
@@ -99,6 +115,14 @@ export class JsHnswVectorIndex implements VectorIndexProvider {
   private dirtyNodes: Set<string> = new Set() // Nodes with unpersisted HNSW data
   private dirtySystem: boolean = false // Whether system data (entryPoint, maxLevel) needs persist
 
+  // --- Watermark stamp state (see utils/projectionWatermark for the law) ---
+  /** Generation handed in via {@link stampWatermark}, awaiting the next flush. */
+  private pendingWatermark: number | null = null
+  /** Last watermark durably stamped by this instance or loaded on rebuild. */
+  private stampedWatermark: number | null = null
+  /** The three-way verdict computed at load; null until rebuild() runs. */
+  private loadVerdict: WatermarkVerdictResult | null = null
+
   // Lazy vector storage (B2 optimization): evict the float32 vector to
   // storage after insert; reload on demand via getVectorSafe() + UnifiedCache.
   private vectorStorageMode: 'memory' | 'lazy' = 'memory'
@@ -170,6 +194,9 @@ export class JsHnswVectorIndex implements VectorIndexProvider {
     }
 
     if (this.dirtyNodes.size === 0 && !this.dirtySystem) {
+      // Nothing dirty — but a pending watermark still stamps: every byte it
+      // certifies is already durable, so stamp-after-data holds trivially.
+      await this.writePendingStamp()
       return 0
     }
 
@@ -239,6 +266,13 @@ export class JsHnswVectorIndex implements VectorIndexProvider {
       throw new HnswFlushError(failedNodes.size, systemFailed, firstError ?? undefined)
     }
 
+    // STAMP-AFTER-DATA: the watermark stamp is the LAST write of the flush —
+    // it lands only after every dirty node and the system record persisted
+    // (the throw above guarantees it). A crash anywhere earlier leaves the
+    // artifact behind-stamped or unstamped, which verdicts as catchup/rescan
+    // on the next open — never a wrong adopt.
+    await this.writePendingStamp()
+
     if (nodeCount > 0) {
       prodLog.info(`[HNSW] Flushed ${nodeCount} dirty nodes in ${duration}ms`)
     }
@@ -246,6 +280,126 @@ export class JsHnswVectorIndex implements VectorIndexProvider {
     return nodeCount
   }
 
+  /**
+   * @description Record the committed generation this projection reflects.
+   * The stamp is NOT written here — it is written as the final storage write
+   * of the next {@link flush} (stamp-after-data ordering is a module
+   * guarantee, not a caller obligation). The coordinator calls this with the
+   * store's committed generation right before flushing.
+   * @param generation - The committed generation every flushed byte reflects.
+   */
+  public stampWatermark(generation: number): void {
+    this.pendingWatermark = generation
+  }
+
+  /**
+   * @description The projection's current watermark: the stamp loaded at
+   * rebuild (or the last stamp durably written by this instance). Null =
+   * unstamped (legacy artifact, first boot, or stamping never wired).
+   */
+  public watermark(): number | null {
+    return this.stampedWatermark
+  }
+
+  /**
+   * @description The three-way adoption verdict computed at load —
+   * `'adopt'` (stamped == committed, zero work), `'catchup'` (stamped <
+   * committed; the gap from {@link watermarkGap} awaits an incremental
+   * fold), `'rescan'` (unstamped or stamped above committed — never
+   * trusted). Null until rebuild() has run. Computed and exposed only; no
+   * load behavior changes ride on it yet — today's rebuild triggers are
+   * unchanged.
+   */
+  public watermarkVerdict(): WatermarkVerdict | null {
+    return this.loadVerdict?.verdict ?? null
+  }
+
+  /**
+   * @description The catch-up window `(from, to]` when the load verdict was
+   * `'catchup'`; null otherwise.
+   */
+  public watermarkGap(): { from: number; to: number } | null {
+    return this.loadVerdict?.gap ?? null
+  }
+
+  /**
+   * @description Write the pending watermark stamp as a sidecar record —
+   * always called AFTER the data it certifies is durable. The stamp carries
+   * the vector-space identity this module can honestly assert: dimensions
+   * only (no embedding-model id is reachable from the index — it never sees
+   * the embedder). A stamp-write failure is fail-safe (unstamped/behind →
+   * rescan/catchup on next open, never a wrong adopt) but is said out loud
+   * and the pending stamp is retained for the next flush.
+   */
+  private async writePendingStamp(): Promise<void> {
+    if (this.pendingWatermark === null || !this.storage) return
+    const watermark = this.pendingWatermark
+    try {
+      await this.storage.saveMetadata(HNSW_INDEX_STAMP_KEY, {
+        noun: 'IndexWatermark',
+        ...makeProjectionStamp(watermark, { dimensions: this.dimension })
+      })
+      this.stampedWatermark = watermark
+      this.pendingWatermark = null
+    } catch (error) {
+      prodLog.error(
+        `[HNSW] failed to write watermark stamp (generation ${watermark}) — ` +
+          `artifact stays behind-stamped (safe: verdicts catchup/rescan, never wrong-adopt); ` +
+          `retrying on next flush:`,
+        error
+      )
+    }
+  }
+
+  /**
+   * @description Read the artifact's stamp and compute the three-way verdict
+   * against the store's committed generation. Unstamped state on a stamped
+   * store verdicts `'rescan'` LOUDLY — never a silent adopt.
+   *
+   * MIGRATION COST: existing pre-stamp brains verdict `'rescan'` exactly
+   * once (that open re-derives via the rebuild it is already running); the
+   * next flush stamps them, and every later open adopts.
+   *
+   * @param artifactPresent - Whether a persisted artifact exists at all (a
+   *   system record was found); gates loud-vs-quiet on the rescan verdict so
+   *   first boots don't scream.
+   */
+  private async loadWatermarkVerdict(artifactPresent: boolean): Promise<void> {
+    if (!this.storage) return
+    const committed = this.storage.committedGeneration?.() ?? null
+    let stamped: number | null = null
+    try {
+      const record = await this.storage.getMetadata(HNSW_INDEX_STAMP_KEY)
+      stamped = readStampedWatermark(record)
+    } catch {
+      // An unreadable stamp is unstamped — the fail-safe direction.
+      stamped = null
+    }
+    const result = computeWatermarkVerdict(stamped, committed)
+    this.loadVerdict = result
+    this.stampedWatermark = stamped
+
+    if (result.verdict === 'rescan') {
+      if (artifactPresent || stamped !== null) {
+        prodLog.warn(
+          `[HNSW] watermark verdict: RESCAN — persisted index is ` +
+            (stamped === null
+              ? 'unstamped (legacy pre-stamp artifact, or a crash between data and stamp)'
+              : `stamped at generation ${stamped}, ABOVE the store's committed generation ${committed}`) +
+            ` — never adopting unverifiable state`
+        )
+      } else {
+        prodLog.debug('[HNSW] watermark verdict: rescan (no persisted artifact — first boot)')
+      }
+    } else if (result.verdict === 'catchup') {
+      prodLog.info(
+        `[HNSW] watermark verdict: catchup — index stamped at generation ${stamped}, ` +
+          `store committed at ${committed}; the (${stamped}, ${committed}] window awaits ` +
+          `an incremental fold (verdict exposed; the fold lands with the coordinator's wiring)`
+      )
+    }
+  }
+
   /**
    * @description Persist one node's connections. When the connections codec is
    * wired AND the storage adapter exposes `saveBinaryBlob`, the per-level
@@ -405,8 +559,15 @@ export class JsHnswVectorIndex implements VectorIndexProvider {
 
   /**
    * Add a vector to the index
+   *
+   * @param generation - Brainy's commit generation for this write (contract
+   *   parity with `VectorIndexProvider.addItem`). This JS index serves "now"
+   *   only — no per-record delta log, no natural slot — so the value is
+   *   accepted and ignored; a native provider stamps its durable records
+   *   with it. The JS twin adopts stamping with the watermark train.
    */
-  public async addItem(item: VectorDocument): Promise<string> {
+  public async addItem(item: VectorDocument, generation?: bigint): Promise<string> {
+    void generation // Contract parity — the JS index keeps no per-write log.
     // Check if item is defined
     if (!item) {
       throw new Error('Item is undefined or null')
@@ -486,6 +647,90 @@ export class JsHnswVectorIndex implements VectorIndexProvider {
       return id
     }
 
+    // Wire the node into the graph: greedy descent + per-level linking.
+    // Extracted to linkNode so updateItem's in-place relink runs the SAME
+    // insertion linking (one implementation, never a diverging copy).
+    await this.linkNode(noun, entryPoint)
+
+    // Update max level and entry point if needed
+    if (nounLevel > this.maxLevel) {
+      this.maxLevel = nounLevel
+      this.entryPointId = id
+    }
+
+    // Add noun to the index
+    this.nouns.set(id, noun)
+
+    // Track high-level nodes for O(1) entry point selection
+    if (nounLevel >= 2 && nounLevel <= this.MAX_TRACKED_LEVELS) {
+      if (!this.highLevelNodes.has(nounLevel)) {
+        this.highLevelNodes.set(nounLevel, new Set())
+      }
+      this.highLevelNodes.get(nounLevel)!.add(id)
+    }
+
+    // Lazy vector eviction (B2: graph-only memory after insert)
+    // After graph construction completes, evict the full vector from memory.
+    // Future searches will load vectors on-demand via getVectorSafe() + UnifiedCache.
+    if (this.vectorStorageMode === 'lazy' && this.storage) {
+      noun.vector = [] // Release float32 vector from memory
+    }
+
+    // Persist HNSW graph data to storage
+    // Respect persistMode setting
+    if (this.storage && this.persistMode === 'immediate') {
+      // IMMEDIATE MODE: Original behavior - persist new entity and system data.
+      // Goes through the per-node helper so the compressed-blob branch fires
+      // identically here vs. the deferred-flush + neighbor-update paths.
+      await this.persistNodeConnections(id, noun).catch((error) => {
+        console.error(`Failed to persist HNSW data for ${id}:`, error)
+      })
+
+      // Persist system data (entry point and max level)
+      await this.storage.saveHNSWSystem({
+        entryPointId: this.entryPointId,
+        maxLevel: this.maxLevel
+      }).catch((error) => {
+        console.error('Failed to persist HNSW system data:', error)
+      })
+    } else if (this.persistMode === 'deferred') {
+      // DEFERRED MODE: Track dirty nodes for later batch persistence
+      this.dirtyNodes.add(id)
+      this.dirtySystem = true
+    }
+
+    return id
+  }
+
+  /**
+   * @description The insertion LINKING phase shared by {@link addItem} and
+   * {@link updateItem}: greedy-descend from `entryPoint` through the levels
+   * above `noun.level`, then at each level from `min(noun.level, maxLevel)`
+   * down to 0 find `efConstruction` candidates, select the M nearest, and
+   * create bidirectional edges — maintaining the reverse-adjacency index via
+   * {@link addIncoming} and re-pruning any neighbor pushed over M.
+   *
+   * Persistence follows the caller's mode exactly as the historical inline
+   * addItem code did: `'immediate'` persists each touched neighbor's
+   * connections concurrently (batched by `maxConcurrentNeighborWrites`);
+   * `'deferred'` marks each touched neighbor dirty for the next flush.
+   *
+   * Does NOT touch index membership (`this.nouns`), the entry point, or
+   * `maxLevel` — the caller owns that bookkeeping: addItem inserts a NEW node
+   * afterwards and may raise maxLevel; updateItem relinks an EXISTING node in
+   * place whose level was already counted, so nothing may change. `noun.vector`
+   * must be the live in-memory vector at call time; both callers guarantee it
+   * (lazy-mode eviction happens only after linking completes).
+   *
+   * A `neighborId === noun.id` candidate is skipped defensively: during
+   * updateItem the node is already IN `this.nouns` (visibility-atomicity —
+   * unlike addItem, which links before inserting), and a self-edge must never
+   * be creatable no matter what the traversal surfaces.
+   */
+  private async linkNode(noun: HNSWNoun, entryPoint: HNSWNoun): Promise<void> {
+    const { id, vector } = noun
+    const nounLevel = noun.level
+
     let currObj = entryPoint
 
     // Calculate distance to entry point (handles lazy loading + sync fast path)
@@ -547,6 +792,10 @@ export class JsHnswVectorIndex implements VectorIndexProvider {
       }> = []
 
       for (const [neighborId, _] of neighbors) {
+        if (neighborId === id) {
+          // Never self-link (see method JSDoc — reachable only via updateItem)
+          continue
+        }
         const neighbor = this.nouns.get(neighborId)
         if (!neighbor) {
           // Skip neighbors that don't exist (expected during rapid additions/deletions)
@@ -630,7 +879,7 @@ export class JsHnswVectorIndex implements VectorIndexProvider {
           const nearestNoun = this.nouns.get(nearestId)
           if (!nearestNoun) {
             console.error(
-              `Nearest noun with ID ${nearestId} not found in addItem`
+              `Nearest noun with ID ${nearestId} not found in linkNode`
             )
             // Keep the current object as is
           } else {
@@ -639,55 +888,178 @@ export class JsHnswVectorIndex implements VectorIndexProvider {
         }
       }
     }
+  }
 
-    // Update max level and entry point if needed
-    if (nounLevel > this.maxLevel) {
-      this.maxLevel = nounLevel
-      this.entryPointId = id
+  /**
+   * @description Atomically replace an item's vector IN PLACE — the row is
+   * NEVER absent from the index during an update. The historical shape staged
+   * a remove followed by an add as two separately-awaited transaction
+   * operations; between them the row was in NEITHER index — dark to semantic
+   * recall while perfectly visible to metadata reads (observed as seconds-long
+   * production flicker in a downstream deployment). Mandate: a row that
+   * exists must never be invisible to a read path, even transiently.
+   *
+   * Behavior:
+   * - id not in the index → delegates to {@link addItem} (plain insert).
+   * - SAME vector (element-wise equal) → pure no-op. This is the production
+   *   flicker shape: a type-only update re-indexes an UNCHANGED vector, so the
+   *   old remove+add did pure damage. (In lazy vector-storage mode the
+   *   comparison baseline is whatever {@link getVectorSafe} serves — the
+   *   cache, or the persisted record; if the caller already rewrote the
+   *   record with the new vector before calling in, equality may report "no
+   *   change" and skip the relink. Query correctness is unaffected either
+   *   way — distances always use the live vector — the graph edges just keep
+   *   their pre-update geometry, which HNSW tolerates by construction.)
+   * - DIFFERENT vector → the node never leaves `this.nouns`:
+   *   1. `node.vector` is swapped SYNCHRONOUSLY first (and the shared vector
+   *      cache updated in the same tick), so from that point every query sees
+   *      the node with correct distances;
+   *   2. its old edges are unlinked via the same reverse-adjacency walk
+   *      removeItem uses ({@link unlinkNodeEdges}) — the node stays in the
+   *      map and KEEPS its level;
+   *   3. the insertion linking re-runs at the node's EXISTING level
+   *      ({@link linkNode}). Entry-point cases: if the node IS the entry
+   *      point it REMAINS the entry point (still valid — same id, same
+   *      level); the relink traversal then starts from another node via
+   *      {@link resolveRelinkStart}, because the node's own edges were just
+   *      cleared and a traversal starting AT it would find nothing and link
+   *      nothing — stranding the whole graph behind an edgeless entry point.
+   *      maxLevel never regresses: the node keeps its level and its
+   *      membership, so the remove-side relevel bookkeeping never runs.
+   *
+   * Persistence mirrors {@link addItem}'s tail for the node itself plus the
+   * in-neighbors whose connection sets changed during the unlink:
+   * `'immediate'` persists their connections now; `'deferred'` marks them
+   * dirty for the next flush. The system record (entry point + maxLevel) is
+   * NOT rewritten — an in-place update changes neither.
+   *
+   * @param generation - Brainy's commit generation for this write (contract
+   *   parity with the feature-detected `updateItem` provider capability).
+   *   Accepted and ignored — the JS index keeps no per-write log.
+   */
+  public async updateItem(item: VectorDocument, generation?: bigint): Promise<void> {
+    void generation // Contract parity — the JS index keeps no per-write log.
+    if (!item) {
+      throw new Error('Item is undefined or null')
+    }
+    const { id, vector } = item
+    if (!vector) {
+      throw new Error('Vector is undefined or null')
     }
 
-    // Add noun to the index
-    this.nouns.set(id, noun)
+    const node = this.nouns.get(id)
+    if (!node) {
+      // Absent → plain insert.
+      await this.addItem(item)
+      return
+    }
 
-    // Track high-level nodes for O(1) entry point selection
-    if (nounLevel >= 2 && nounLevel <= this.MAX_TRACKED_LEVELS) {
-      if (!this.highLevelNodes.has(nounLevel)) {
-        this.highLevelNodes.set(nounLevel, new Set())
+    if (this.dimension === null) {
+      this.dimension = vector.length
+    } else if (vector.length !== this.dimension) {
+      throw new Error(
+        `Vector dimension mismatch: expected ${this.dimension}, got ${vector.length}`
+      )
+    }
+
+    // Fast path: element-wise-equal vector → NOTHING to do (the production
+    // flicker shape — a type-only update re-indexing an unchanged vector).
+    // getVectorSafe handles the lazy-evicted case (loads from cache/storage).
+    const current = await this.getVectorSafe(node)
+    if (current.length === vector.length) {
+      let same = true
+      for (let i = 0; i < vector.length; i++) {
+        if (current[i] !== vector[i]) {
+          same = false
+          break
+        }
       }
-      this.highLevelNodes.get(nounLevel)!.add(id)
+      if (same) return
     }
 
-    // Lazy vector eviction (B2: graph-only memory after insert)
-    // After graph construction completes, evict the full vector from memory.
-    // Future searches will load vectors on-demand via getVectorSafe() + UnifiedCache.
-    if (this.vectorStorageMode === 'lazy' && this.storage) {
-      noun.vector = [] // Release float32 vector from memory
+    // (1) Visibility-atomic swap: from this synchronous assignment on, every
+    // query sees the node with correct distances. The shared vector cache is
+    // updated in the same tick so the lazy-mode read path can never serve the
+    // stale vector either.
+    node.vector = vector
+    this.unifiedCache.set(`hnsw:vector:${id}`, vector, 'vectors', vector.length * 4, 50)
+
+    // (2) Unlink the old edges — the node stays in the map, keeps its level.
+    const touchedReferrers = await this.unlinkNodeEdges(node)
+    node.connections = new Map()
+    for (let level = 0; level <= node.level; level++) {
+      node.connections.set(level, new Set<string>())
+    }
+    // The node's own reverse entry is rebuilt by the relink below.
+    this.incoming?.delete(id)
+
+    // (3) Relink at the node's EXISTING level (see JSDoc for the entry-point
+    // reasoning). A single-node index has nothing to link to — trivially done.
+    const start = this.resolveRelinkStart(id)
+    if (start) {
+      await this.linkNode(node, start)
     }
 
-    // Persist HNSW graph data to storage
-    // Respect persistMode setting
+    // Persistence — addItem's tail, minus the system record (entry point and
+    // maxLevel are untouched by an in-place update). Unlink-touched referrers
+    // are included so the persisted graph converges on the live one instead of
+    // keeping their pre-update edge sets forever.
     if (this.storage && this.persistMode === 'immediate') {
-      // IMMEDIATE MODE: Original behavior - persist new entity and system data.
-      // Goes through the per-node helper so the compressed-blob branch fires
-      // identically here vs. the deferred-flush + neighbor-update paths.
-      await this.persistNodeConnections(id, noun).catch((error) => {
+      await this.persistNodeConnections(id, node).catch((error) => {
         console.error(`Failed to persist HNSW data for ${id}:`, error)
       })
-
-      // Persist system data (entry point and max level)
-      await this.storage.saveHNSWSystem({
-        entryPointId: this.entryPointId,
-        maxLevel: this.maxLevel
-      }).catch((error) => {
-        console.error('Failed to persist HNSW system data:', error)
-      })
+      for (const refId of touchedReferrers) {
+        const ref = this.nouns.get(refId)
+        if (!ref) continue
+        await this.persistNodeConnections(refId, ref).catch((error) => {
+          console.error(`Failed to persist HNSW data for ${refId}:`, error)
+        })
+      }
     } else if (this.persistMode === 'deferred') {
-      // DEFERRED MODE: Track dirty nodes for later batch persistence
       this.dirtyNodes.add(id)
-      this.dirtySystem = true
+      for (const refId of touchedReferrers) {
+        this.dirtyNodes.add(refId)
+      }
     }
 
-    return id
+    // Lazy vector eviction — same contract as addItem: after graph work
+    // completes the float32 vector leaves memory; reads serve from the
+    // (just-updated) cache or the persisted record.
+    if (this.vectorStorageMode === 'lazy' && this.storage) {
+      node.vector = []
+    }
+  }
+
+  /**
+   * @description Pick the traversal start for an in-place relink
+   * ({@link updateItem} step 3): the current entry point — unless that IS the
+   * node being relinked. Its edges were just unlinked, so a traversal
+   * starting there would see an empty neighborhood and produce zero links,
+   * stranding the graph behind an edgeless entry point. In that case (or when
+   * the entry point is missing/stale) fall back to the best OTHER node:
+   * highest tracked level first (the same O(1) heuristic as
+   * {@link recoverEntryPointO1}), then any other node. Returns null when the
+   * node is the only one in the index — nothing to link to, trivially valid.
+   */
+  private resolveRelinkStart(excludeId: string): HNSWNoun | null {
+    if (this.entryPointId && this.entryPointId !== excludeId) {
+      const entry = this.nouns.get(this.entryPointId)
+      if (entry) return entry
+    }
+    for (let level = this.MAX_TRACKED_LEVELS; level >= 2; level--) {
+      const nodesAtLevel = this.highLevelNodes.get(level)
+      if (!nodesAtLevel) continue
+      for (const nodeId of nodesAtLevel) {
+        if (nodeId !== excludeId) {
+          const candidate = this.nouns.get(nodeId)
+          if (candidate) return candidate
+        }
+      }
+    }
+    for (const [nodeId, candidate] of this.nouns) {
+      if (nodeId !== excludeId) return candidate
+    }
+    return null
   }
 
   /**
@@ -948,20 +1320,34 @@ export class JsHnswVectorIndex implements VectorIndexProvider {
   }
 
   /**
-   * Remove an item from the index
+   * @description Unlink every graph edge touching `noun`, in BOTH directions,
+   * WITHOUT removing the node from `this.nouns` — the unlink walk shared by
+   * {@link removeItem} (which then drops the node) and {@link updateItem}
+   * (which relinks the node in place, so it must never leave the map and
+   * KEEPS its level).
+   *
+   * Reverse-adjacency lets us touch ONLY the nodes that actually reference
+   * `noun.id` (its in-neighbors) rather than scanning the whole corpus —
+   * turning a delete from O(N) into O(in-degree) and a bulk delete from O(N²)
+   * into O(N·degree). Each referrer set is snapshotted because
+   * pruneConnections mutates the index. Outgoing edges are unhooked from each
+   * target's reverse set so no stale referrer survives.
+   *
+   * `incoming[noun.id]` itself is intentionally NOT maintained edge-by-edge
+   * inside the walk — both callers dispose of it wholesale afterwards
+   * (removeItem deletes it with the node; updateItem clears it and lets the
+   * relink rebuild it).
+   *
+   * @returns The ids of in-neighbors whose connection sets were modified
+   *   (they dropped their edge to `noun` and may have been re-pruned), so a
+   *   caller that persists per-node connections (updateItem) can mark them
+   *   dirty / persist them. removeItem ignores the return — its persistence
+   *   story lives in the caller's delete path, unchanged.
    */
-  public async removeItem(id: string): Promise<boolean> {
-    if (!this.nouns.has(id)) {
-      return false
-    }
+  private async unlinkNodeEdges(noun: HNSWNoun): Promise<Set<string>> {
+    const id = noun.id
+    const touchedReferrers = new Set<string>()
 
-
-    const noun = this.nouns.get(id)!
-
-    // Reverse-adjacency lets us touch ONLY the nodes that actually reference `id`
-    // (its in-neighbors) rather than scanning the whole corpus — turning a delete
-    // from O(N) into O(in-degree) and a bulk delete from O(N²) into O(N·degree).
-    // Snapshot each referrer set because pruneConnections mutates the index.
     const incoming = this.ensureIncoming()
     const referrers = incoming.get(id)
     if (referrers) {
@@ -969,11 +1355,11 @@ export class JsHnswVectorIndex implements VectorIndexProvider {
         for (const refId of Array.from(refSet)) {
           const ref = this.nouns.get(refId)
           if (ref && ref.connections.has(level)) {
-            // Drop the forward edge ref → id, then re-prune ref so the graph stays
-            // navigable. (id's own reverse entry is dropped wholesale below, so we
-            // intentionally do not maintain incoming[id] inside this loop.)
+            // Drop the forward edge ref → id, then re-prune ref so the graph
+            // stays navigable.
             ref.connections.get(level)!.delete(id)
             await this.pruneConnections(ref, level)
+            touchedReferrers.add(refId)
           }
         }
       }
@@ -987,6 +1373,32 @@ export class JsHnswVectorIndex implements VectorIndexProvider {
       }
     }
 
+    return touchedReferrers
+  }
+
+  /**
+   * Remove an item from the index
+   *
+   * @param generation - Brainy's commit generation for this removal (contract
+   *   parity with `VectorIndexProvider.removeItem`). Accepted and ignored —
+   *   this JS index removes immediately; a native provider records the
+   *   tombstone at this generation.
+   */
+  public async removeItem(id: string, generation?: bigint): Promise<boolean> {
+    void generation // Contract parity — the JS index keeps no per-write log.
+    if (!this.nouns.has(id)) {
+      return false
+    }
+
+
+    const noun = this.nouns.get(id)!
+
+    // Unlink every edge touching the node (shared with updateItem's in-place
+    // relink — see unlinkNodeEdges). The returned touched-referrer set is
+    // ignored here: removeItem's persistence story lives in the caller's
+    // delete path, unchanged.
+    await this.unlinkNodeEdges(noun)
+
     // Remove the noun + its reverse-index entry.
     this.nouns.delete(id)
     this.incoming?.delete(id)
@@ -1305,6 +1717,11 @@ export class JsHnswVectorIndex implements VectorIndexProvider {
         this.maxLevel = systemData.maxLevel
       }
 
+      // Step 2b: Watermark verdict for the persisted artifact — computed and
+      // exposed only (today's rebuild flow is unchanged; this rebuild IS the
+      // re-derive a 'rescan' verdict asks for).
+      await this.loadWatermarkVerdict(systemData !== null)
+
       // Step 3: Determine preloading strategy (adaptive caching)
       // Check if vectors should be preloaded at init or loaded on-demand
       const stats = await this.storage.getStatistics()

src/index.ts

@@ -83,6 +83,14 @@ export type {
   AggregationProvider
 } from './types/brainy.types.js'
 
+// Read-barrier contract (waitForIndexed): the leg names, the options, and
+// the typed timeout error (a value export — consumers catch it by instanceof)
+export type {
+  IndexedProjectionPath,
+  WaitForIndexedOptions
+} from './types/brainy.types.js'
+export { WaitForIndexedTimeoutError } from './types/brainy.types.js'
+
 // Reserved-field contract — the canonical list of Brainy-owned field names
 // that may never appear inside a `metadata` bag (see docs/concepts/consistency-model.md)
 export {
@@ -354,6 +362,15 @@ export { MemoryStorage, createStorage }
 // FileSystemStorage is exported separately to avoid browser build issues.
 export { FileSystemStorage } from './storage/adapters/fileSystemStorage.js'
 
+// Torn-record surface: a stored file that EXISTS but cannot be decoded throws
+// a typed, catchable error on entity reads (never a silent "not found"), and
+// every encounter is counted on a per-process gauge.
+export {
+  TornRecordError,
+  isTornRecordError,
+  getTornRecordGauge
+} from './storage/tornRecordError.js'
+
 // Export types
 import type {
   Vector,

src/indexes/columnStore/ColumnStore.ts

@@ -31,6 +31,7 @@ import { ColumnSegmentCursor, TailBufferCursor, type CursorEntry } from './Colum
 import { writeSegmentToBuffer, readSegmentFromBuffer } from './ColumnSegmentFormat.js'
 import { RoaringBitmap32 } from '../../utils/roaring/index.js'
 import { compareCodePoints } from '../../utils/collation.js'
+import { prodLog } from '../../utils/logger.js'
 
 /**
  * Configuration for the ColumnStore.
@@ -612,6 +613,24 @@ export class ColumnStore implements ColumnStoreProvider {
   /**
    * Get all segment cursors for a field, loading from storage if needed.
    */
+  /**
+   * Per-field quarantine ledger for torn segments (power-loss survivors:
+   * manifest-listed but unloadable). A quarantined segment is skipped with
+   * per-doubling narration and the field serves its REMAINING segments as a
+   * DEGRADED-ANNOUNCED result — never a raw throw killing the query, never
+   * a silent drop. Cleared when a heal/rebuild rewrites the field.
+   */
+  private readonly segmentQuarantine = new Map<string, { error: string; hits: number }>()
+
+  /** Torn-segment quarantine entries for a field (observability + heal input). */
+  quarantinedSegments(field: string): Array<{ segment: string; error: string; hits: number }> {
+    const out: Array<{ segment: string; error: string; hits: number }> = []
+    for (const [key, q] of this.segmentQuarantine) {
+      if (key.startsWith(`${field}:`)) out.push({ segment: key.slice(field.length + 1), error: q.error, hits: q.hits })
+    }
+    return out
+  }
+
   private async getSegmentCursors(field: string): Promise<ColumnSegmentCursor[]> {
     const manifest = this.manifests.get(field)
     if (!manifest) return []
@@ -622,11 +641,38 @@ export class ColumnStore implements ColumnStoreProvider {
       let cursor = this.segmentCache.get(cacheKey)
 
       if (!cursor) {
-        // loadSegmentCursor either returns a cursor or THROWS — a corrupt /
-        // missing manifest-listed segment raises ColumnSegmentLoadError and a
-        // real storage fault propagates, so a listed segment is never silently
-        // dropped from the result set.
-        cursor = await this.loadSegmentCursor(field, seg)
+        const quarantined = this.segmentQuarantine.get(cacheKey)
+        if (quarantined) {
+          // Already-quarantined torn segment: skip, count, narrate per doubling.
+          quarantined.hits++
+          if ((quarantined.hits & (quarantined.hits - 1)) === 0) {
+            prodLog.warn(
+              `[ColumnStore] field '${field}' serving DEGRADED: torn segment ${seg.id} ` +
+                `quarantined (${quarantined.error}) — ${quarantined.hits} queries served ` +
+                `without it; heal/rebuild the metadata index to restore`
+            )
+          }
+          continue
+        }
+        try {
+          cursor = await this.loadSegmentCursor(field, seg)
+        } catch (err) {
+          if (err instanceof ColumnSegmentLoadError) {
+            // POWER-LOSS SURVIVOR: a manifest-listed segment whose bytes are
+            // torn/absent. Quarantine at DISCOVERY and serve the remaining
+            // segments degraded-announced — a raw throw here killed every
+            // query on the field forever; a silent skip hid the loss. The
+            // quarantine is the middle: loud once, counted always, healable.
+            this.segmentQuarantine.set(cacheKey, { error: (err as Error).message, hits: 1 })
+            prodLog.error(
+              `[ColumnStore] torn segment QUARANTINED at discovery: field '${field}' ` +
+                `segment ${seg.id} — ${(err as Error).message}. The field serves its ` +
+                `remaining segments DEGRADED until a heal/rebuild rewrites it.`
+            )
+            continue
+          }
+          throw err // real storage faults propagate — never absorbed
+        }
         this.segmentCache.set(cacheKey, cursor)
       }
 

src/plugin.ts

@@ -277,8 +277,35 @@ export interface MetadataIndexProvider {
    */
   isMigrating?(): boolean
 
-  addToIndex(id: string, entityOrMetadata: any, skipFlush?: boolean, deferWrites?: boolean): Promise<void>
-  removeFromIndex(id: string, metadata?: any): Promise<void>
+  /**
+   * @description Index one entity's metadata.
+   * @param id - The entity's UUID.
+   * @param entityOrMetadata - Entity structure or plain metadata bag.
+   * @param skipFlush - Transactional atomicity: defer the flush to the commit seam.
+   * @param deferWrites - Batch mode: buffer postings for a later flush.
+   * @param generation - OPTIONAL (additive) — Brainy's commit generation for
+   *   this write: the SAME u64 counter {@link GraphIndexProvider.addVerb}
+   *   carries, resolved at operation-execute time. A provider with per-record
+   *   delta logs stamps it onto the durable record so its watermark
+   *   ("this projection reflects generation N") is derivable from real data —
+   *   never a literal 0. `undefined` means the caller genuinely has no commit
+   *   generation for this write (rebuild-from-canonical scans, bootstrap
+   *   writes before generation stamping activates); a provider must treat
+   *   that as "unstamped", not as generation 0. The built-in JS manager
+   *   accepts and ignores it (single live view, no per-record log).
+   */
+  addToIndex(id: string, entityOrMetadata: any, skipFlush?: boolean, deferWrites?: boolean, generation?: bigint): Promise<void>
+  /**
+   * @description Remove one entity from the index.
+   * @param id - The entity's UUID.
+   * @param metadata - The entity's metadata (targets exact postings; absent → full scan).
+   * @param generation - OPTIONAL (additive) — Brainy's commit generation for
+   *   this removal, same contract as {@link MetadataIndexProvider.addToIndex}:
+   *   a provider with per-record delta logs records the tombstone at this
+   *   generation (so as-of reads before it still see the entity); the JS
+   *   manager removes immediately and ignores it.
+   */
+  removeFromIndex(id: string, metadata?: any, generation?: bigint): Promise<void>
 
   getIds(field: string, value: any): Promise<string[]>
   /**
@@ -368,7 +395,14 @@ export interface MetadataIndexProvider {
    * the ceiling on the JS path), so `Number(bigint)` narrowing is lossless.
    */
   getIdMapper(): {
-    getOrAssign(uuid: string): number
+    /**
+     * Resolve-or-mint the entity's int. `generation` is OPTIONAL (additive):
+     * Brainy's commit generation current at mint time, so a mapper with
+     * per-record delta logs stamps the assignment record with a real
+     * watermark instead of a literal 0. Ignored when the uuid is already
+     * assigned (assignments are append-only) and by the JS mapper.
+     */
+    getOrAssign(uuid: string, generation?: bigint): number
     getInt(uuid: string): number | undefined
     getUuid(intId: number): string | undefined
   }
@@ -1052,8 +1086,33 @@ export interface VectorIndexProvider {
    */
   readonly name: string
 
-  addItem(item: VectorDocument): Promise<string>
-  removeItem(id: string): Promise<boolean>
+  /**
+   * @description Insert one vector.
+   * @param item - The vector document (`id` + `vector`).
+   * @param generation - OPTIONAL (additive) — Brainy's commit generation for
+   *   this write: the SAME u64 counter the graph provider's
+   *   `addVerb(..., generation)` carries (and that `search`'s as-of
+   *   `options.generation` reads back), resolved at operation-execute time.
+   *   A provider with per-record delta logs / segment stamps records it so
+   *   its watermark reflects real data — never a literal 0. `undefined` =
+   *   the caller has no commit generation (rebuild-from-canonical, the
+   *   at-generation materializer's ephemeral reader); treat as "unstamped",
+   *   not generation 0. The built-in JS index accepts and ignores it (it
+   *   serves "now" only). The feature-detected `updateItem` capability (see
+   *   `src/transaction/operations/IndexOperations.ts`) carries the same
+   *   optional trailing generation.
+   */
+  addItem(item: VectorDocument, generation?: bigint): Promise<string>
+  /**
+   * @description Remove one vector by id.
+   * @param id - The entity's UUID.
+   * @param generation - OPTIONAL (additive) — Brainy's commit generation for
+   *   this removal, same contract as {@link VectorIndexProvider.addItem}: a
+   *   provider with durable delete records stamps the tombstone at this
+   *   generation (as-of reads before it still see the vector); the JS index
+   *   removes immediately and ignores it.
+   */
+  removeItem(id: string, generation?: bigint): Promise<boolean>
   search(
     queryVector: Vector,
     k?: number,
@@ -1199,10 +1258,29 @@ export interface EntityIdMapperProvider {
    * stays compatible — `restore()` falls back to `init()` when this is absent.
    */
   rebuild?(): Promise<void>
-  getOrAssign(uuid: string): number
+  /**
+   * @description Resolve-or-mint the entity's interned int (append-only:
+   * once assigned, a uuid's int never changes and is never recycled).
+   * @param uuid - The entity's UUID.
+   * @param generation - OPTIONAL (additive) — Brainy's commit generation
+   *   current at mint time (the same u64 counter the graph/metadata write
+   *   surfaces carry). A mapper with per-record delta logs stamps the
+   *   assignment record with this real watermark instead of a literal 0.
+   *   Ignored when the uuid is already assigned, and by the JS mapper
+   *   (which keeps no per-record log).
+   */
+  getOrAssign(uuid: string, generation?: bigint): number
   getUuid(intId: number): string | undefined
   getInt(uuid: string): number | undefined
-  remove(uuid: string): boolean
+  /**
+   * @description Remove the uuid's mapping (the int stays reserved).
+   * @param uuid - The entity's UUID.
+   * @param generation - OPTIONAL (additive) — Brainy's commit generation for
+   *   this removal: a mapper with a per-key version chain tombstones the
+   *   mapping at this generation (as-of reads before it still resolve);
+   *   the JS mapper removes immediately and ignores it.
+   */
+  remove(uuid: string, generation?: bigint): boolean
   flush(): Promise<void>
   clear(): Promise<void>
   getAllIntIds(): number[]

src/reprojection/factLogSource.ts

@@ -0,0 +1,141 @@
+/**
+ * @module reprojection/factLogSource
+ * @description The production {@link FactSource}: adapts the database's
+ * committed-fact scan to the reprojection engine's `scan(from, limit)`
+ * window contract.
+ *
+ * DEPENDENCY-CLEAN BY DESIGN: this module never imports the database class.
+ * It wraps a host-owned scan callback `(from, limit) => Promise<CommitFact[]>`
+ * injected at construction, so the host wires itself in one line — either by
+ * handing {@link FactLogSource} a callback built on its own scan API, or via
+ * {@link factSourceFromHost}, which builds that callback from any object
+ * structurally exposing `scanFacts` (the batch-handle shape the fact log
+ * serves).
+ *
+ * CONTRACT ENFORCEMENT — loud, never quiet: every `scan` return is checked
+ * (≤ limit facts, strictly ascending generations, all strictly above `from`);
+ * a violating callback throws instead of silently corrupting a fold. A host
+ * with NO fact log throws too — reporting "caught up" against an unscannable
+ * store would be a silent lie.
+ */
+
+import type { CommitFact } from '../db/factLog.js'
+import type { FactSource } from './reprojectionEngine.js'
+
+/**
+ * The host-owned scan callback: return up to `limit` committed facts with
+ * generation strictly greater than `from`, in ascending generation order;
+ * empty means caught up to the head as of the call.
+ */
+export type FactScanCallback = (from: number, limit: number) => Promise<CommitFact[]>
+
+/**
+ * The minimal structural surface of a fact-scanning host — matches the
+ * database's `scanFacts` shape without importing it. `scanFacts` returns a
+ * handle whose `batches()` yields ordered, non-empty fact batches, or `null`
+ * when the store hosts no fact log.
+ */
+export interface FactScanHost {
+  scanFacts(options?: { fromGeneration?: number; batchSize?: number }): {
+    batches: () => AsyncGenerator<{ facts: CommitFact[] }>
+  } | null
+}
+
+/**
+ * The production {@link FactSource}: wraps an injected scan callback and
+ * enforces the window contract on every return.
+ *
+ * COST NOTE: each `scan` call is stateless (a fresh window above the caller's
+ * watermark), which is exactly what resumable, crash-tolerant folds need —
+ * at the price of the host re-opening its scan per call. Fine for
+ * budget-capped maintenance; not a hot-path read primitive.
+ */
+export class FactLogSource implements FactSource {
+  private readonly scanCallback: FactScanCallback
+
+  /** @param scanCallback - The host-owned scan (see {@link FactScanCallback}). */
+  constructor(scanCallback: FactScanCallback) {
+    if (typeof scanCallback !== 'function') {
+      throw new Error('FactLogSource: a scan callback (from, limit) => Promise<CommitFact[]> is required')
+    }
+    this.scanCallback = scanCallback
+  }
+
+  /**
+   * Fetch up to `limit` committed facts strictly above generation `from`,
+   * verifying the callback honored the window contract.
+   * @param from - Exclusive lower bound generation (≥ 0 integer).
+   * @param limit - Maximum facts to return (≥ 1 integer).
+   */
+  async scan(from: number, limit: number): Promise<CommitFact[]> {
+    if (!Number.isInteger(from) || from < 0) {
+      throw new Error(`FactLogSource.scan: 'from' must be a non-negative integer (got ${from})`)
+    }
+    if (!Number.isInteger(limit) || limit < 1) {
+      throw new Error(`FactLogSource.scan: 'limit' must be a positive integer (got ${limit})`)
+    }
+    const facts = await this.scanCallback(from, limit)
+    if (!Array.isArray(facts)) {
+      throw new Error('FactLogSource.scan: the scan callback must resolve to an array of facts')
+    }
+    if (facts.length > limit) {
+      throw new Error(
+        `FactLogSource.scan: the scan callback returned ${facts.length} facts for limit ${limit} — ` +
+          `contract violation; refusing to fold an oversized window`
+      )
+    }
+    let prev = from
+    for (const fact of facts) {
+      const g = fact?.generation
+      if (typeof g !== 'number' || !Number.isFinite(g) || g <= prev) {
+        throw new Error(
+          `FactLogSource.scan: the scan callback violated the window contract — generation ` +
+            `${String(g)} is not strictly ascending above ${prev} (from=${from}); refusing to fold`
+        )
+      }
+      prev = g
+    }
+    return facts
+  }
+}
+
+/**
+ * Build the production source from any host structurally exposing
+ * `scanFacts` — the one-line wiring for the database side:
+ *
+ * ```ts
+ * const source = factSourceFromHost(brain)
+ * ```
+ *
+ * Each `scan(from, limit)` opens `scanFacts({ fromGeneration: from + 1,
+ * batchSize: limit })` (the engine's `from` is exclusive; `scanFacts` bounds
+ * are inclusive) and returns the FIRST batch, closing the handle — short
+ * batches at segment boundaries are legal under the source contract (only
+ * EMPTY means caught up). A host with no fact log throws loudly.
+ *
+ * @param host - Any object with the `scanFacts` batch-handle shape.
+ */
+export function factSourceFromHost(host: FactScanHost): FactLogSource {
+  if (!host || typeof host.scanFacts !== 'function') {
+    throw new Error('factSourceFromHost: the host must expose scanFacts(options)')
+  }
+  return new FactLogSource(async (from, limit) => {
+    const scan = host.scanFacts({ fromGeneration: from + 1, batchSize: limit })
+    if (scan === null) {
+      throw new Error(
+        'reprojection: this store hosts no fact log — reprojection folds committed facts, ' +
+          'and reporting a caught-up fold against an unscannable store would be a silent lie'
+      )
+    }
+    const iterator = scan.batches()
+    try {
+      const first = await iterator.next()
+      return first.done ? [] : first.value.facts
+    } finally {
+      // Close the abandoned generator so its cleanup (timers) runs.
+      if (typeof iterator.return === 'function') {
+        await iterator.return(undefined)
+      }
+    }
+  })
+}

src/reprojection/reprojectionEngine.ts

@@ -0,0 +1,648 @@
+/**
+ * @module reprojection/reprojectionEngine
+ * @description The pure-TS reprojection engine — the ONE machinery for
+ * rebuilding, healing, and migrating persisted projections from the committed
+ * fact log on the JS side. It is the TypeScript twin of the native engine's
+ * reprojection core: the same frozen contract (names AND semantics), so a
+ * single shared conformance suite runs against both implementations and
+ * TS-only deployments green the same rows without native code.
+ *
+ * THE AVAILABILITY LAW — maintenance never holds the doors:
+ *
+ * - Work proceeds in INSTALLMENTS of at most {@link MAX_INSTALLMENT_MS} (50ms)
+ *   of wall time each. Between installments the loop awaits a REAL macrotask
+ *   boundary (never a busy loop, never a bare microtask), so foreground I/O
+ *   and timers always interleave with a running fold.
+ * - Foreground door traffic announces itself via {@link DoorSignal.bump}. An
+ *   in-flight {@link ReprojectionEngine.advance} yields at the next
+ *   installment boundary and returns `{ status: 'preempted' }` — the doors
+ *   never wait for maintenance to finish.
+ * - Budgets are honored: `advance` stops once `budgetMs` is spent and reports
+ *   exactly how far it got; a later call RESUMES from the adapter's own
+ *   watermark. Nothing ever refolds from zero because a budget ran out.
+ *
+ * WATERMARK DISCIPLINE — the engine NEVER writes stamps. Each adapter's
+ * `applyBatch` owns its own durability and its own stamp (stamp-after-data,
+ * the law stated in src/utils/projectionWatermark.ts); the engine only READS
+ * `watermark()` to decide the next scan window. Delivery is therefore
+ * at-least-once: an adapter that crashed between data and stamp is re-served
+ * the same facts on resume and MUST apply idempotently.
+ *
+ * THE FOUR ANSWER CLASSES of an advance: `'caught-up'` (folded to the head of
+ * the requested window, ledger clean), `'preempted'` (a door bumped),
+ * `'budget-exhausted'` (time ran out mid-stream), and `'quarantined'` (folded
+ * to the head, but this family's quarantine ledger is non-empty — one or more
+ * poison facts are being skipped and reads touching them are suspect).
+ */
+
+import type { CommitFact } from '../db/factLog.js'
+import { prodLog } from '../utils/logger.js'
+
+/**
+ * The hard ceiling on one installment of fold work, in wall-clock ms. An
+ * advance loop that has run this long without yielding closes the installment
+ * and awaits a macrotask boundary so foreground traffic interleaves. Frozen by
+ * the shared contract — both engines install the same ceiling.
+ */
+export const MAX_INSTALLMENT_MS = 50
+
+/** Default facts-per-batch pulled from the {@link FactSource} per step. */
+export const DEFAULT_REPROJECTION_BATCH_SIZE = 256
+
+/**
+ * One registered projection family: a named consumer that folds committed
+ * facts into its own persisted artifact and stamps its own watermark.
+ *
+ * OWNERSHIP: the adapter owns durability AND the stamp. `applyBatch` must
+ * persist its data first and stamp `upTo` after (stamp-after-data), and must
+ * tolerate at-least-once delivery — on resume after a crash between data and
+ * stamp, the same facts arrive again.
+ */
+export interface ProjectionAdapter {
+  /** Unique family name — the registry key; one adapter serves a family at a time. */
+  family: string
+  /**
+   * The highest generation this projection's persisted state reflects, or
+   * `null` when the projection is unbuilt/unstamped. The engine reads this to
+   * open the next scan window; it never writes it.
+   */
+  watermark(): number | null
+  /**
+   * Fold `facts` (ascending generations, all strictly above the current
+   * watermark) into the projection, then stamp `watermark = upTo`.
+   *
+   * `facts` MAY be empty while `upTo` is above the current watermark: that is
+   * a pure watermark advance past quarantined generations — the adapter must
+   * still stamp, or the fold cannot make progress past the poison.
+   *
+   * FAILURE CONTRACT: throw a {@link ProjectionApplyError} to name exactly one
+   * poison fact (the engine quarantines it and continues). ANY other throw
+   * aborts the advance loudly — an unknown failure is never treated as a
+   * poison record.
+   */
+  applyBatch(facts: CommitFact[], upTo: number): Promise<void>
+  /**
+   * Destroy this adapter's persisted artifact(s). The engine calls this on
+   * the LOSING adapter after a successful {@link ReprojectionEngine.swap},
+   * and on a partially-built replacement whose build aborted.
+   */
+  discard(): Promise<void>
+}
+
+/**
+ * The committed-fact scan the engine folds from. `from` is an EXCLUSIVE lower
+ * bound generation; the source returns at most `limit` facts in ascending
+ * generation order, and an empty array means caught up to the head as of this
+ * call. Short non-empty returns are legal (e.g. a segment boundary) — only
+ * empty means done.
+ */
+export interface FactSource {
+  scan(from: number, limit: number): Promise<CommitFact[]>
+}
+
+/**
+ * The foreground-preemption signal. Door traffic (foreground reads/writes)
+ * calls {@link DoorSignal.bump}; an in-flight `advance` observes the bump at
+ * its next installment boundary, yields a macrotask, and returns
+ * `{ status: 'preempted' }`. Bumps are edge-triggered per advance: only bumps
+ * that arrive AFTER an advance began preempt it.
+ */
+export class DoorSignal {
+  private count = 0
+
+  /** Announce foreground door traffic — an in-flight advance will yield. */
+  bump(): void {
+    this.count++
+  }
+
+  /**
+   * The current bump epoch — the engine snapshots this at advance entry and
+   * compares at installment boundaries.
+   * @internal
+   */
+  epoch(): number {
+    return this.count
+  }
+}
+
+/**
+ * The TYPED poison-record failure an adapter throws from `applyBatch` to name
+ * exactly one unfoldable fact. The engine quarantines that generation for
+ * that family (skips it, ledgers it, narrates per-doubling) and keeps
+ * folding. Any OTHER throw from `applyBatch` aborts the advance loudly.
+ */
+export class ProjectionApplyError extends Error {
+  /** The generation of the fact that cannot be applied. */
+  readonly generation: number
+  /** Optional index of the offending record within the fact's ops. */
+  readonly recordIndex?: number
+  /** The underlying failure. */
+  override readonly cause: unknown
+
+  /**
+   * @param args - `generation` names the poison fact; `recordIndex`
+   *   optionally narrows to one record inside it; `cause` carries the
+   *   underlying failure.
+   */
+  constructor(args: { generation: number; recordIndex?: number; cause: unknown }) {
+    super(
+      `projection apply failed at generation ${args.generation}` +
+        (args.recordIndex !== undefined ? ` (record ${args.recordIndex})` : '')
+    )
+    this.name = 'ProjectionApplyError'
+    this.generation = args.generation
+    if (args.recordIndex !== undefined) this.recordIndex = args.recordIndex
+    this.cause = args.cause
+  }
+}
+
+/**
+ * The TYPED single-flight refusal: a second concurrent
+ * {@link ReprojectionEngine.swap} on a family whose replacement is still
+ * building. The caller retries after the in-flight swap settles.
+ */
+export class SwapInFlightError extends Error {
+  /** The family whose swap is already in flight. */
+  readonly family: string
+
+  /** @param family - The family whose swap is already in flight. */
+  constructor(family: string) {
+    super(
+      `reprojection: a swap is already in flight for family '${family}' — ` +
+        `swaps are single-flight per family; retry after the current build settles`
+    )
+    this.name = 'SwapInFlightError'
+    this.family = family
+  }
+}
+
+/** One quarantined fact in a family's ledger. */
+export interface QuarantineEntry {
+  /** The generation being skipped for this family. */
+  generation: number
+  /** The typed apply failure that condemned it. */
+  error: ProjectionApplyError
+  /** Wall-clock ms when it was quarantined (diagnostic). */
+  at: number
+}
+
+/** How an advance ended — the four answer classes (see the module header). */
+export type AdvanceStatus = 'caught-up' | 'preempted' | 'budget-exhausted' | 'quarantined'
+
+/** The result of one advance over one family. */
+export interface AdvanceResult {
+  /** The answer class. */
+  status: AdvanceStatus
+  /** The family's watermark as stamped by its own adapter, after this advance. */
+  watermark: number | null
+  /**
+   * Facts delivered in SUCCESSFUL `applyBatch` calls during this advance.
+   * At-least-once delivery means retried facts (after a quarantine or a
+   * resume) count again; this is delivered work, not distinct generations.
+   */
+  applied: number
+}
+
+/** The result of a completed {@link ReprojectionEngine.swap}. */
+export interface SwapResult {
+  /** The NEW adapter's watermark at the flip (parity with the head). */
+  watermark: number | null
+  /** Facts delivered to the replacement during its beside-build. */
+  applied: number
+}
+
+/** Constructor options for {@link ReprojectionEngine}. */
+export interface ReprojectionEngineOptions {
+  /** The committed-fact scan every family folds from. */
+  source: FactSource
+  /** The preemption signal; a fresh one is created when omitted. */
+  doorSignal?: DoorSignal
+  /**
+   * Installment ceiling in ms, `(0, MAX_INSTALLMENT_MS]`. Out-of-range values
+   * throw — the 50ms law is a ceiling, never a suggestion.
+   */
+  installmentMs?: number
+  /** Facts per {@link FactSource.scan} pull (default {@link DEFAULT_REPROJECTION_BATCH_SIZE}). */
+  batchSize?: number
+}
+
+/** The fold-side state shared by a serving family and a swap's beside-build. */
+interface FoldState {
+  adapter: ProjectionAdapter
+  /** The quarantine ledger, in condemnation order. */
+  quarantine: QuarantineEntry[]
+  /** Generations filtered out of every batch served to this adapter. */
+  skip: Set<number>
+  /** Next ledger size that triggers a narration (1, 2, 4, 8, …). */
+  nextWarnAt: number
+}
+
+/** A registered family: fold state plus the single-flight swap latch. */
+interface FamilyState extends FoldState {
+  swapInFlight: boolean
+}
+
+/** One real macrotask boundary — foreground I/O and timers run before resume. */
+function yieldToDoors(): Promise<void> {
+  return new Promise((resolve) => {
+    if (typeof setImmediate === 'function') {
+      setImmediate(resolve)
+    } else {
+      setTimeout(resolve, 0)
+    }
+  })
+}
+
+/**
+ * The reprojection engine: registry of projection families, budget-capped
+ * yielding advances, round-robin `advanceAll`, atomic build-beside `swap`,
+ * and the per-family quarantine ledger. Pure TS, no storage dependencies —
+ * everything durable lives behind the injected {@link FactSource} and the
+ * registered {@link ProjectionAdapter}s.
+ */
+export class ReprojectionEngine {
+  /** The preemption signal foreground door traffic bumps. */
+  readonly doorSignal: DoorSignal
+
+  private readonly source: FactSource
+  private readonly installmentMs: number
+  private readonly batchSize: number
+  private readonly registry = new Map<string, FamilyState>()
+  /** Rotates the family that leads each `advanceAll`, so repeated tiny-budget calls stay fair. */
+  private roundRobinCursor = 0
+
+  /** @param options - See {@link ReprojectionEngineOptions}. */
+  constructor(options: ReprojectionEngineOptions) {
+    if (!options || typeof options.source?.scan !== 'function') {
+      throw new Error('reprojection: a FactSource with scan(from, limit) is required')
+    }
+    const installmentMs = options.installmentMs ?? MAX_INSTALLMENT_MS
+    if (!(installmentMs > 0) || installmentMs > MAX_INSTALLMENT_MS) {
+      throw new Error(
+        `reprojection: installmentMs must be in (0, ${MAX_INSTALLMENT_MS}] — ` +
+          `${installmentMs} would let maintenance hold the doors`
+      )
+    }
+    const batchSize = options.batchSize ?? DEFAULT_REPROJECTION_BATCH_SIZE
+    if (!Number.isInteger(batchSize) || batchSize < 1) {
+      throw new Error(`reprojection: batchSize must be a positive integer (got ${batchSize})`)
+    }
+    this.source = options.source
+    this.doorSignal = options.doorSignal ?? new DoorSignal()
+    this.installmentMs = installmentMs
+    this.batchSize = batchSize
+  }
+
+  /**
+   * Register a projection family. Refuses a duplicate family loudly — the
+   * sanctioned way to replace a serving adapter is {@link swap}, never
+   * re-registration.
+   * @param adapter - The adapter that will serve this family.
+   */
+  register(adapter: ProjectionAdapter): void {
+    if (!adapter || typeof adapter.family !== 'string' || adapter.family.length === 0) {
+      throw new Error('reprojection: adapter.family must be a non-empty string')
+    }
+    if (this.registry.has(adapter.family)) {
+      throw new Error(
+        `reprojection: family '${adapter.family}' is already registered — ` +
+          `replace a serving adapter via swap(), never by re-registering`
+      )
+    }
+    this.registry.set(adapter.family, {
+      adapter,
+      quarantine: [],
+      skip: new Set(),
+      nextWarnAt: 1,
+      swapInFlight: false
+    })
+  }
+
+  /**
+   * The adapter currently serving `family` (observability — e.g. asserting
+   * the old adapter still serves during a swap's beside-build), or undefined
+   * when the family is not registered.
+   * @param family - The family name.
+   */
+  getAdapter(family: string): ProjectionAdapter | undefined {
+    return this.registry.get(family)?.adapter
+  }
+
+  /**
+   * This family's quarantine ledger (a defensive copy, condemnation order).
+   * Non-empty means one or more generations are being skipped for this
+   * family — the projection owner should refuse reads the skipped facts
+   * would have affected.
+   * @param family - The family name (must be registered).
+   */
+  quarantined(family: string): QuarantineEntry[] {
+    return [...this.mustGet(family).quarantine]
+  }
+
+  /**
+   * Advance one family toward the head of the fact log (or toward `upTo`),
+   * in installments, under a wall-clock budget, preemptible by the door
+   * signal. Always makes at least ONE step of progress before any budget
+   * check, so a zero budget still advances.
+   *
+   * @param family - The registered family to advance.
+   * @param options - `budgetMs` caps this call's wall time (≥ 0); `upTo`
+   *   optionally caps the fold at a generation (inclusive).
+   * @returns The answer class with the adapter-stamped watermark and the
+   *   count of facts delivered in successful applyBatch calls.
+   */
+  async advance(family: string, options: { budgetMs: number; upTo?: number }): Promise<AdvanceResult> {
+    const state = this.mustGet(family)
+    const budgetMs = options?.budgetMs
+    if (typeof budgetMs !== 'number' || !(budgetMs >= 0)) {
+      throw new Error(`reprojection: advance('${family}') requires budgetMs >= 0 (got ${budgetMs})`)
+    }
+    const start = Date.now()
+    const entryEpoch = this.doorSignal.epoch()
+    let installmentStart = start
+    let applied = 0
+
+    for (;;) {
+      const stepResult = await this.step(state, options.upTo)
+      applied += stepResult.applied
+      if (stepResult.done) {
+        return this.completed(state, applied)
+      }
+      // A bump ends the current installment immediately: yield a macrotask so
+      // the foreground work runs, then answer 'preempted'.
+      if (this.doorSignal.epoch() !== entryEpoch) {
+        await yieldToDoors()
+        return { status: 'preempted', watermark: state.adapter.watermark(), applied }
+      }
+      const t = Date.now()
+      if (t - start >= budgetMs) {
+        return { status: 'budget-exhausted', watermark: state.adapter.watermark(), applied }
+      }
+      if (t - installmentStart >= this.installmentMs) {
+        await yieldToDoors()
+        installmentStart = Date.now()
+      }
+    }
+  }
+
+  /**
+   * Advance EVERY registered family toward the head under one shared budget,
+   * round-robin at batch granularity — one batch per family per turn — so no
+   * family starves behind another's backlog. The leading family rotates
+   * across calls, keeping repeated tiny-budget calls fair too.
+   *
+   * @param options - `budgetMs` caps this call's total wall time (≥ 0).
+   * @returns Per-family results. Families still mid-stream when the budget
+   *   ran out (or a door bumped) report `'budget-exhausted'` (or
+   *   `'preempted'`) at their current watermark.
+   */
+  async advanceAll(options: { budgetMs: number }): Promise<Record<string, AdvanceResult>> {
+    const budgetMs = options?.budgetMs
+    if (typeof budgetMs !== 'number' || !(budgetMs >= 0)) {
+      throw new Error(`reprojection: advanceAll requires budgetMs >= 0 (got ${budgetMs})`)
+    }
+    const start = Date.now()
+    const entryEpoch = this.doorSignal.epoch()
+    let installmentStart = start
+
+    const all = [...this.registry.values()]
+    const results: Record<string, AdvanceResult> = {}
+    const appliedBy = new Map<string, number>()
+    if (all.length === 0) return results
+
+    // Rotate the leader across calls (fairness across repeated small budgets).
+    const offset = this.roundRobinCursor % all.length
+    this.roundRobinCursor = (this.roundRobinCursor + 1) % all.length
+    let queue = [...all.slice(offset), ...all.slice(0, offset)]
+    for (const s of queue) appliedBy.set(s.adapter.family, 0)
+
+    const finish = (
+      status: 'preempted' | 'budget-exhausted',
+      remaining: FamilyState[]
+    ): Record<string, AdvanceResult> => {
+      for (const s of remaining) {
+        results[s.adapter.family] = {
+          status,
+          watermark: s.adapter.watermark(),
+          applied: appliedBy.get(s.adapter.family) ?? 0
+        }
+      }
+      return results
+    }
+
+    while (queue.length > 0) {
+      const survivors: FamilyState[] = []
+      for (let i = 0; i < queue.length; i++) {
+        const s = queue[i]
+        const fam = s.adapter.family
+        const stepResult = await this.step(s, undefined)
+        appliedBy.set(fam, (appliedBy.get(fam) ?? 0) + stepResult.applied)
+        if (stepResult.done) {
+          results[fam] = this.completed(s, appliedBy.get(fam) ?? 0)
+        } else {
+          survivors.push(s)
+        }
+        const remaining = [...survivors, ...queue.slice(i + 1)]
+        if (this.doorSignal.epoch() !== entryEpoch) {
+          await yieldToDoors()
+          return finish('preempted', remaining)
+        }
+        const t = Date.now()
+        if (t - start >= budgetMs && remaining.length > 0) {
+          return finish('budget-exhausted', remaining)
+        }
+        if (t - installmentStart >= this.installmentMs) {
+          await yieldToDoors()
+          installmentStart = Date.now()
+        }
+      }
+      queue = survivors
+    }
+    return results
+  }
+
+  /**
+   * Replace a family's adapter by BUILD-BESIDE: the old adapter keeps serving
+   * (stays registered, its watermark untouched) while the replacement folds
+   * from its own watermark (null/0 for a fresh build) to parity with the head
+   * of the fact log. The flip is ATOMIC — a single registry pointer swap with
+   * no await between the parity check and the assignment — and the losing
+   * adapter's `discard()` is called after the flip.
+   *
+   * SINGLE-FLIGHT: a second concurrent swap on the same family throws a
+   * typed {@link SwapInFlightError}. The build yields at installment
+   * boundaries like any fold (doors interleave), but it is never
+   * preemption-aborted — a swap under steady foreground traffic still
+   * completes.
+   *
+   * On a build failure the partially-built replacement is discarded
+   * (best-effort, narrated if that also fails) and the error propagates; the
+   * old adapter keeps serving untouched.
+   *
+   * @param family - The registered family to replace.
+   * @param buildAdapter - Factory for the replacement adapter (same family).
+   * @returns The new adapter's watermark at the flip and the facts delivered
+   *   during the build.
+   */
+  async swap(family: string, buildAdapter: () => Promise<ProjectionAdapter>): Promise<SwapResult> {
+    const state = this.mustGet(family)
+    if (state.swapInFlight) throw new SwapInFlightError(family)
+    state.swapInFlight = true
+    try {
+      const next = await buildAdapter()
+      if (!next || next.family !== family) {
+        throw new Error(
+          `reprojection: swap('${family}') built an adapter for family ` +
+            `'${next?.family}' — the replacement must serve the same family`
+        )
+      }
+      const build: FoldState = { adapter: next, quarantine: [], skip: new Set(), nextWarnAt: 1 }
+      let applied = 0
+      let installmentStart = Date.now()
+      let stalledDoneAt: number | null = null
+
+      try {
+        for (;;) {
+          const stepResult = await this.step(build, undefined)
+          applied += stepResult.applied
+          if (stepResult.applied > 0) stalledDoneAt = null
+          if (stepResult.done) {
+            // Parity: the build just saw an empty scan (caught up to the head
+            // as of that call). The serving adapter can never be beyond the
+            // head, so newWm >= oldWm holds — verified loudly, never assumed.
+            const oldWm = state.adapter.watermark() ?? 0
+            const newWm = next.watermark() ?? 0
+            if (newWm >= oldWm) break
+            if (stalledDoneAt === newWm) {
+              throw new Error(
+                `reprojection: swap('${family}') build is caught up to the head at ` +
+                  `generation ${newWm} but the serving adapter claims watermark ${oldWm} — ` +
+                  `the serving stamp is beyond the fact log; refusing to flip`
+              )
+            }
+            // The head moved past our scan (a concurrent fold advanced the
+            // serving adapter) — keep folding to the new head.
+            stalledDoneAt = newWm
+          }
+          if (Date.now() - installmentStart >= this.installmentMs) {
+            await yieldToDoors()
+            installmentStart = Date.now()
+          }
+        }
+      } catch (err) {
+        await next.discard().catch((cleanupErr) => {
+          prodLog.warn(
+            `reprojection: swap('${family}') build failed AND the failed build's discard() ` +
+              `also failed — its artifact may be orphaned`,
+            cleanupErr
+          )
+        })
+        throw err
+      }
+
+      // THE FLIP — atomic by construction: no await between the parity check
+      // above and this pointer swap; readers see the old adapter until this
+      // line and the new one from it.
+      const losing = state.adapter
+      state.adapter = next
+      state.quarantine = build.quarantine
+      state.skip = build.skip
+      state.nextWarnAt = build.nextWarnAt
+
+      try {
+        await losing.discard()
+      } catch (discardErr) {
+        // The flip already happened and the new adapter serves; the only loss
+        // is the loser's orphaned artifact — said out loud, never rethrown as
+        // a false swap failure.
+        prodLog.warn(
+          `reprojection: swap('${family}') completed but the losing adapter's discard() ` +
+            `failed — its artifact may be orphaned`,
+          discardErr
+        )
+      }
+      return { watermark: next.watermark(), applied }
+    } finally {
+      state.swapInFlight = false
+    }
+  }
+
+  /** One fold step: scan a batch above the watermark, filter quarantined generations, apply. */
+  private async step(state: FoldState, upTo: number | undefined): Promise<{ done: boolean; applied: number }> {
+    const from = state.adapter.watermark() ?? 0
+    if (upTo !== undefined && from >= upTo) return { done: true, applied: 0 }
+    let facts = await this.source.scan(from, this.batchSize)
+    if (facts.length === 0) return { done: true, applied: 0 }
+    if (upTo !== undefined) {
+      facts = facts.filter((f) => f.generation <= upTo)
+      if (facts.length === 0) return { done: true, applied: 0 }
+    }
+    const batchUpTo = facts[facts.length - 1].generation
+    const toApply = state.skip.size > 0 ? facts.filter((f) => !state.skip.has(f.generation)) : facts
+    try {
+      await state.adapter.applyBatch(toApply, batchUpTo)
+    } catch (err) {
+      if (err instanceof ProjectionApplyError) {
+        this.recordQuarantine(state, err)
+        return { done: false, applied: 0 }
+      }
+      throw err // unknown failure ≠ poison record — abort the advance loudly
+    }
+    // Anti-spin guard: a successful applyBatch that never advances the stamp
+    // would re-serve the same window forever. Refuse loudly instead.
+    const after = state.adapter.watermark() ?? 0
+    if (after <= from) {
+      throw new Error(
+        `reprojection: family '${state.adapter.family}' applyBatch succeeded up to ` +
+          `generation ${batchUpTo} but the watermark did not advance past ${from} — ` +
+          `the adapter is not stamping; refusing to spin`
+      )
+    }
+    return { done: false, applied: toApply.length }
+  }
+
+  /** Ledger a typed apply failure, skip its generation, narrate per-doubling. */
+  private recordQuarantine(state: FoldState, err: ProjectionApplyError): void {
+    if (!Number.isFinite(err.generation)) {
+      throw new Error(
+        `reprojection: family '${state.adapter.family}' threw ProjectionApplyError with a ` +
+          `non-finite generation (${err.generation}) — cannot quarantine; aborting the advance`
+      )
+    }
+    if (state.skip.has(err.generation)) {
+      throw new Error(
+        `reprojection: family '${state.adapter.family}' threw ProjectionApplyError for ` +
+          `generation ${err.generation}, which is ALREADY quarantined and was not in the ` +
+          `batch — the adapter is misreporting; aborting the advance`
+      )
+    }
+    state.skip.add(err.generation)
+    state.quarantine.push({ generation: err.generation, error: err, at: Date.now() })
+    const n = state.quarantine.length
+    if (n === state.nextWarnAt) {
+      state.nextWarnAt *= 2
+      prodLog.warn(
+        `reprojection: family '${state.adapter.family}' quarantined generation ` +
+          `${err.generation} (${n} quarantined total) — the fact is skipped for this family ` +
+          `and ledgered; reads it would have affected should be refused by the owner`,
+        err.cause
+      )
+    }
+  }
+
+  /** A window completed: 'caught-up' with a clean ledger, 'quarantined' otherwise. */
+  private completed(state: FoldState, applied: number): AdvanceResult {
+    return {
+      status: state.quarantine.length > 0 ? 'quarantined' : 'caught-up',
+      watermark: state.adapter.watermark(),
+      applied
+    }
+  }
+
+  /** The registered family state, or a loud refusal. */
+  private mustGet(family: string): FamilyState {
+    const state = this.registry.get(family)
+    if (!state) throw new Error(`reprojection: family '${family}' is not registered`)
+    return state
+  }
+}

src/storage/adapters/fileSystemStorage.ts

@@ -18,6 +18,11 @@ import {
 } from '../baseStorage.js'
 import { getBrainyVersion } from '../../utils/index.js'
 import { isAbsentError } from '../../utils/errorClassification.js'
+import {
+  TornRecordError,
+  isUnparseablePayloadError,
+  registerTornRecordEncounter
+} from '../tornRecordError.js'
 
 // Node.js modules - dynamically imported to avoid issues in browser environments
 let fs: any
@@ -410,8 +415,22 @@ export class FileSystemStorage extends BaseStorage {
   /**
    * Primitive operation: Read object from path
    * All metadata operations use this internally via base class routing
-   * Enhanced error handling for corrupted metadata files (Bug #3 mitigation)
    * Supports reading both compressed (.gz) and uncompressed files for backward compatibility
+   *
+   * Read contract (loud errors, never quiet losses):
+   * - Genuine absence (ENOENT on every variant) → `null`. Only a missing file
+   *   is "not found".
+   * - TORN record (a file EXISTS but its bytes cannot be decoded — invalid
+   *   JSON, truncated/garbled gzip) → the encounter is registered (production
+   *   ERROR log + per-process gauge) and a typed {@link TornRecordError} is
+   *   thrown. Corruption must NEVER read as absence: callers that can degrade
+   *   (manifest recovery, rebuildable statistics) catch the typed error at
+   *   their sites; entity reads surface it.
+   *   Legacy dual-format exception: when the `.gz` variant is torn but the
+   *   uncompressed fallback decodes, the recovered object is returned — AFTER
+   *   the torn `.gz` was logged and counted (loud recovery, not a silent skip).
+   * - Real storage fault (EIO/EACCES/EMFILE/…) → propagates as itself; a
+   *   fault is neither absence nor corruption and must not be reshaped.
    */
   protected async readObjectFromPath(pathStr: string): Promise<any | null> {
     await this.ensureInitialized()
@@ -419,7 +438,10 @@ export class FileSystemStorage extends BaseStorage {
     const fullPath = path.join(this.rootDir, pathStr)
     const compressedPath = `${fullPath}.gz`
 
-    // Try reading compressed file first (if compression is enabled or file exists)
+    // Try reading compressed file first (if compression is enabled or file exists).
+    // A torn .gz is remembered so the uncompressed fallback can either recover
+    // (legacy dual-format installs) or surface the corruption typed.
+    let tornCompressed: TornRecordError | null = null
     try {
       const compressedData = await fs.promises.readFile(compressedPath)
       const decompressed = await new Promise<Buffer>((resolve, reject) => {
@@ -430,9 +452,16 @@ export class FileSystemStorage extends BaseStorage {
       })
       return JSON.parse(decompressed.toString('utf-8'))
     } catch (error: any) {
-      // If compressed file doesn't exist, fall back to uncompressed
-      if (error.code !== 'ENOENT') {
-        console.warn(`Failed to read compressed file ${compressedPath}:`, error)
+      if (error.code === 'ENOENT') {
+        // No compressed variant — fall through to the uncompressed path.
+      } else if (isUnparseablePayloadError(error)) {
+        // The .gz EXISTS but cannot be decoded (zlib Z_* error or JSON
+        // SyntaxError after gunzip): torn record. Register NOW (log + gauge),
+        // then attempt the uncompressed fallback as a recovery read.
+        tornCompressed = registerTornRecordEncounter(`${pathStr}.gz`, error)
+      } else {
+        // Real storage fault on an existing .gz (EIO/EACCES/…): propagate.
+        throw error
       }
     }
 
@@ -442,24 +471,26 @@ export class FileSystemStorage extends BaseStorage {
       return JSON.parse(data)
     } catch (error: any) {
       if (error.code === 'ENOENT') {
+        // No uncompressed file. If the .gz variant existed but was torn, the
+        // object EXISTS and is unreadable — that must surface typed, never as
+        // "absent". Otherwise this is genuine absence.
+        if (tornCompressed !== null) {
+          throw tornCompressed
+        }
         return null
       }
 
-      // Enhanced error handling for corrupted JSON files (race condition from Bug #3)
-      if (error instanceof SyntaxError || error.name === 'SyntaxError') {
-        console.warn(
-          `⚠️  Corrupted metadata file detected: ${pathStr}\n` +
-          `   This may be caused by concurrent writes during import.\n` +
-          `   Gracefully skipping this entry. File may be repaired on next write.`
-        )
-        return null
+      // The file EXISTS but its content cannot be parsed: torn record.
+      // Register (production ERROR + gauge) and throw typed — a corrupt row
+      // must be distinguishable from a missing row, or nothing ever heals it.
+      if (isUnparseablePayloadError(error)) {
+        throw registerTornRecordEncounter(pathStr, error)
       }
 
       // A real storage fault (EIO/EACCES/EMFILE/…) is NOT "object absent". The
-      // ENOENT branch (above) already returns null, and the corrupted-JSON
-      // branch (above) is a deliberate concurrent-write tolerance; a genuine
-      // fault reaching here must propagate loudly rather than masquerade as a
-      // missing object — which would corrupt reads and drive needless rebuilds.
+      // ENOENT branch (above) already returns null; a genuine fault reaching
+      // here must propagate loudly rather than masquerade as a missing object
+      // — which would corrupt reads and drive needless rebuilds.
       throw error
     }
   }
@@ -1785,6 +1816,32 @@ export class FileSystemStorage extends BaseStorage {
       const now = new Date().toISOString()
       const existing = await this.readWriterLock()
 
+      // TORN-LOCK RECOVERY: power loss can legally leave the lock file
+      // present but EMPTY/unparseable (the claim's non-atomic write died
+      // mid-flight). readWriterLock() reports it as null — but the O_EXCL
+      // claim below would EEXIST forever, a PERMANENT lockout no staleness
+      // check can clear (staleness needs a parsed PID). A torn lock is
+      // stale BY DEFINITION: no live holder has one (a holder either
+      // completed its write or is dead). Unlink loudly and re-loop; a
+      // racer that rewrites a VALID lock first simply wins the next read.
+      if (existing === null) {
+        try {
+          await fs.promises.access(lockFile)
+          console.warn(
+            `[brainy] Writer lock at ${lockFile} exists but is unreadable/unparseable ` +
+              `(torn write from a previous power loss) — treating as stale and removing.`
+          )
+          try {
+            await fs.promises.unlink(lockFile)
+          } catch (unlinkErr: any) {
+            if (unlinkErr.code !== 'ENOENT') throw unlinkErr
+          }
+        } catch (accessErr: any) {
+          if (accessErr.code !== 'ENOENT') throw accessErr
+          // Absent: the normal fresh-claim path below.
+        }
+      }
+
       if (existing) {
         // Same-process re-open: a second Brainy instance in this Node process
         // (e.g. test "simulate server restart" patterns, or a consumer that

src/storage/baseStorage.ts

@@ -32,6 +32,7 @@ import { BlobStorage, type BlobStoreAdapter } from './blobStorage.js'
 import { unwrapBinaryData } from './binaryDataCodec.js'
 import { prodLog } from '../utils/logger.js'
 import { isAbsentError } from '../utils/errorClassification.js'
+import { isTornRecordError } from './tornRecordError.js'
 import { BrainyError, ProtectedArtifactError, DerivedArtifactMissingError } from '../errors/brainyError.js'
 import { MetadataWriteBuffer } from '../utils/metadataWriteBuffer.js'
 import {
@@ -674,6 +675,11 @@ export abstract class BaseStorage extends BaseStorageAdapter {
           // — hash verification must run on the original content bytes.
           return unwrapBinaryData(data)
         } catch (error) {
+          // A TORN blob object (exists but undecodable) must not read as
+          // "blob absent" — that would misdiagnose disk corruption as a
+          // missing blob. This is an IDENTITY read (a caller asked for THIS
+          // key): propagate the typed error to the blob layer.
+          if (isTornRecordError(error)) throw error
           return undefined
         }
       },
@@ -768,6 +774,20 @@ export abstract class BaseStorage extends BaseStorageAdapter {
       if (m) hashes.add(m[1])
     }
 
+    // Recovery-path read: a TORN object here maps to "not usable" (null) BY
+    // DESIGN — the adapter has already logged + counted the encounter, and
+    // treating a torn `_cas/` copy as absent lets the re-copy from `_cow/`
+    // OVERWRITE the corrupt file with the good original (the heal), while a
+    // torn `_cow/` original is reported via `incomplete`. Real faults propagate.
+    const readOrNullIfTorn = async (p: string): Promise<any | null> => {
+      try {
+        return await this.readObjectFromPath(p)
+      } catch (error) {
+        if (isTornRecordError(error)) return null
+        throw error
+      }
+    }
+
     let adopted = 0
     let alreadyPresent = 0
     let incomplete = 0
@@ -775,15 +795,15 @@ export abstract class BaseStorage extends BaseStorageAdapter {
       // A blob counts as present only when BOTH its bytes and its metadata
       // already live in `_cas/`. A half-adopted blob (bytes without meta — the
       // exact "Blob metadata not found" state) is re-adopted.
-      const casBlob = await this.readObjectFromPath(`_cas/blob:${hash}`)
-      const casMeta = await this.readObjectFromPath(`_cas/blob-meta:${hash}`)
+      const casBlob = await readOrNullIfTorn(`_cas/blob:${hash}`)
+      const casMeta = await readOrNullIfTorn(`_cas/blob-meta:${hash}`)
       if (casBlob !== null && casMeta !== null) {
         alreadyPresent++
         continue
       }
 
-      const cowBlob = await this.readObjectFromPath(`_cow/blob:${hash}`)
-      const cowMeta = await this.readObjectFromPath(`_cow/blob-meta:${hash}`)
+      const cowBlob = await readOrNullIfTorn(`_cow/blob:${hash}`)
+      const cowMeta = await readOrNullIfTorn(`_cow/blob-meta:${hash}`)
       if (cowBlob === null || cowMeta === null) {
         // Can't register a blob the store can't fully describe — report it so an
         // operator investigates rather than silently half-adopting.
@@ -1134,12 +1154,28 @@ export abstract class BaseStorage extends BaseStorageAdapter {
    * cache (record-layer files are written through
    * {@link BaseStorage.writeRawObject} only).
    *
+   * TORN-record contract (deliberate, loud-by-design): this surface serves
+   * SYSTEM ARTIFACTS — manifests with recovery paths, markers whose verdict
+   * machinery treats "unreadable" as rescan, generation/transaction records
+   * whose recovery is built for absent artifacts. For these readers a torn
+   * file maps to their existing absent-artifact degrade, so a typed
+   * torn-record error from the adapter is caught here and returned as `null`
+   * — AFTER the adapter has already logged a production ERROR and counted
+   * the per-process torn-record gauge (never silent). Entity reads do NOT go
+   * through this surface; they use the canonical read paths, which propagate
+   * the typed error. Real storage faults (EIO/EACCES/…) still propagate.
+   *
    * @param path - Storage-root-relative object path (e.g. `_system/manifest.json`).
-   * @returns The parsed object, or `null` if absent.
+   * @returns The parsed object, or `null` if absent (or torn — logged + counted).
    */
   public async readRawObject(path: string): Promise<any | null> {
     await this.ensureInitialized()
-    return this.readObjectFromPath(path)
+    try {
+      return await this.readObjectFromPath(path)
+    } catch (error) {
+      if (isTornRecordError(error)) return null
+      throw error
+    }
   }
 
   /**
@@ -2146,6 +2182,13 @@ export abstract class BaseStorage extends BaseStorageAdapter {
                 if (!metadata) return null
                 return { deserialized, metadata }
               } catch (error) {
+                // A TORN record must surface typed — a paginated read that
+                // silently skips a corrupt row hides data loss from the caller.
+                // Torn record inside an ENUMERATION/RECOVERY walk: the adapter already
+                // narrated + counted it (TornRecordError registers at creation); the
+                // walk's job is to HEAL PAST it — skip the victim, serve the rest.
+                // Identity point-reads (get-by-id) still throw typed upstream.
+                if (isTornRecordError(error)) { /* skip torn victim; loud floor already fired */ }
                 // Skip nouns that fail to load
                 return null
               }
@@ -2175,6 +2218,12 @@ export abstract class BaseStorage extends BaseStorageAdapter {
           }
         }
       } catch (error) {
+        // A TORN record propagates (typed) — only shard-listing absence is skippable.
+        // Torn record inside an ENUMERATION/RECOVERY walk: the adapter already
+                // narrated + counted it (TornRecordError registers at creation); the
+                // walk's job is to HEAL PAST it — skip the victim, serve the rest.
+                // Identity point-reads (get-by-id) still throw typed upstream.
+                if (isTornRecordError(error)) { /* skip torn victim; loud floor already fired */ }
         // Skip shards that have no data
       }
     }
@@ -2283,7 +2332,13 @@ export abstract class BaseStorage extends BaseStorageAdapter {
               batch.map(async (id) => {
                 try {
                   return { id, metadata: await this.getNounMetadata(id) }
-                } catch {
+                } catch (error) {
+                  // A TORN record must surface typed, never as a skipped id.
+                  // Torn record inside an ENUMERATION/RECOVERY walk: the adapter already
+                // narrated + counted it (TornRecordError registers at creation); the
+                // walk's job is to HEAL PAST it — skip the victim, serve the rest.
+                // Identity point-reads (get-by-id) still throw typed upstream.
+                if (isTornRecordError(error)) { /* skip torn victim; loud floor already fired */ }
                   return null
                 }
               })
@@ -2305,6 +2360,12 @@ export abstract class BaseStorage extends BaseStorageAdapter {
           }
         }
       } catch (error) {
+        // A TORN record propagates (typed) — only shard-listing absence is skippable.
+        // Torn record inside an ENUMERATION/RECOVERY walk: the adapter already
+                // narrated + counted it (TornRecordError registers at creation); the
+                // walk's job is to HEAL PAST it — skip the victim, serve the rest.
+                // Identity point-reads (get-by-id) still throw typed upstream.
+                if (isTornRecordError(error)) { /* skip torn victim; loud floor already fired */ }
         // Skip shards with no data
       }
     }
@@ -2515,10 +2576,23 @@ export abstract class BaseStorage extends BaseStorageAdapter {
             // reserved fields top-level, ONLY custom fields in `metadata`.
             collected.push({ verb: this.hydrateVerbWithMetadata(verb, metadata), shard })
           } catch (error) {
+            // A TORN record must surface typed — a paginated read that
+            // silently skips a corrupt row hides data loss from the caller.
+            // Torn record inside an ENUMERATION/RECOVERY walk: the adapter already
+                // narrated + counted it (TornRecordError registers at creation); the
+                // walk's job is to HEAL PAST it — skip the victim, serve the rest.
+                // Identity point-reads (get-by-id) still throw typed upstream.
+                if (isTornRecordError(error)) { /* skip torn victim; loud floor already fired */ }
             // Skip verbs that fail to load
           }
         }
       } catch (error) {
+        // A TORN record propagates (typed) — only shard-listing absence is skippable.
+        // Torn record inside an ENUMERATION/RECOVERY walk: the adapter already
+                // narrated + counted it (TornRecordError registers at creation); the
+                // walk's job is to HEAL PAST it — skip the victim, serve the rest.
+                // Identity point-reads (get-by-id) still throw typed upstream.
+                if (isTornRecordError(error)) { /* skip torn victim; loud floor already fired */ }
         // Skip shards that have no data
       }
     }
@@ -3303,7 +3377,14 @@ export abstract class BaseStorage extends BaseStorageAdapter {
     const path = getNounMetadataPath(id)
 
     // Determine if this is a new entity by checking if metadata already exists
-    const existingMetadata = await this.readCanonicalObject(path)
+    // Torn-tolerant: a WRITE landing on a torn record HEALS it — the read
+    // here only classifies new-vs-update and captures the prior subtype;
+    // a torn prior reads as "no previous" (fresh write) with the adapter's
+    // loud floor already fired. Never let corruption block its own cure.
+    const existingMetadata = await this.readCanonicalObject(path).catch((err) => {
+      if ((err as { code?: string }).code === 'TORN_RECORD') return null
+      throw err
+    })
     const isNew = !existingMetadata
 
     // Save the metadata (write-cache coherent canonical write)
@@ -3669,8 +3750,22 @@ export abstract class BaseStorage extends BaseStorageAdapter {
       )
 
       for (const result of chunkResults) {
-        if (result.status === 'fulfilled' && result.value.data !== null) {
-          results.set(result.value.path, result.value.data)
+        if (result.status === 'fulfilled') {
+          if (result.value.data !== null) {
+            results.set(result.value.path, result.value.data)
+          }
+        } else if (isTornRecordError(result.reason)) {
+          // A torn record inside a SET-SHAPED read (batch hydration behind
+          // find/sort pages and recovery walks): the adapter narrated +
+          // counted at throw time; the batch HEALS PAST the victim and
+          // serves the remaining rows — one crash casualty must not kill
+          // every query that pages over its shard (and init-time recovery
+          // walks ride this exact path). Identity point-reads still throw.
+          continue
+        } else {
+          // A REAL storage fault (EIO-class) is not a torn victim —
+          // propagate loudly, never absorb.
+          throw result.reason
         }
       }
     }
@@ -3806,7 +3901,14 @@ export abstract class BaseStorage extends BaseStorageAdapter {
     const path = getVerbMetadataPath(id)
 
     // Determine if this is a new verb by checking if metadata already exists
-    const existingMetadata = await this.readCanonicalObject(path)
+    // Torn-tolerant: a WRITE landing on a torn record HEALS it — the read
+    // here only classifies new-vs-update and captures the prior subtype;
+    // a torn prior reads as "no previous" (fresh write) with the adapter's
+    // loud floor already fired. Never let corruption block its own cure.
+    const existingMetadata = await this.readCanonicalObject(path).catch((err) => {
+      if ((err as { code?: string }).code === 'TORN_RECORD') return null
+      throw err
+    })
     const isNew = !existingMetadata
 
     // Save the metadata (write-cache coherent canonical write)
@@ -4636,10 +4738,23 @@ export abstract class BaseStorage extends BaseStorageAdapter {
               }
             }
           } catch (error) {
+            // A TORN record must surface typed — an enumeration that silently
+            // skips a corrupt row hides data loss from the caller.
+            // Torn record inside an ENUMERATION/RECOVERY walk: the adapter already
+                // narrated + counted it (TornRecordError registers at creation); the
+                // walk's job is to HEAL PAST it — skip the victim, serve the rest.
+                // Identity point-reads (get-by-id) still throw typed upstream.
+                if (isTornRecordError(error)) { /* skip torn victim; loud floor already fired */ }
             // Skip nouns that fail to load
           }
         }
       } catch (error) {
+        // A TORN record propagates (typed) — only shard-listing absence is skippable.
+        // Torn record inside an ENUMERATION/RECOVERY walk: the adapter already
+                // narrated + counted it (TornRecordError registers at creation); the
+                // walk's job is to HEAL PAST it — skip the victim, serve the rest.
+                // Identity point-reads (get-by-id) still throw typed upstream.
+                if (isTornRecordError(error)) { /* skip torn victim; loud floor already fired */ }
         // Skip shards that have no data
       }
     }
@@ -4825,11 +4940,24 @@ export abstract class BaseStorage extends BaseStorageAdapter {
               results.push(this.hydrateVerbWithMetadata(verb, metadata))
             }
           } catch (error) {
+            // A TORN record must surface typed — an enumeration that silently
+            // skips a corrupt row hides data loss from the caller.
+            // Torn record inside an ENUMERATION/RECOVERY walk: the adapter already
+                // narrated + counted it (TornRecordError registers at creation); the
+                // walk's job is to HEAL PAST it — skip the victim, serve the rest.
+                // Identity point-reads (get-by-id) still throw typed upstream.
+                if (isTornRecordError(error)) { /* skip torn victim; loud floor already fired */ }
             // Skip verbs that fail to load
             prodLog.debug(`[BaseStorage] Failed to load verb from ${verbPath}:`, error)
           }
         }
       } catch (error) {
+        // A TORN record propagates (typed) — only shard-listing absence is skippable.
+        // Torn record inside an ENUMERATION/RECOVERY walk: the adapter already
+                // narrated + counted it (TornRecordError registers at creation); the
+                // walk's job is to HEAL PAST it — skip the victim, serve the rest.
+                // Identity point-reads (get-by-id) still throw typed upstream.
+                if (isTornRecordError(error)) { /* skip torn victim; loud floor already fired */ }
         // Skip shards that have no data
       }
     }
@@ -4945,6 +5073,13 @@ export abstract class BaseStorage extends BaseStorageAdapter {
           sourceVerbs.push(hydratedVerb)
         }
       } catch (error) {
+        // A TORN record propagates (typed) — batch hydration must not
+        // silently drop a corrupt row. Only shard-listing absence is skippable.
+        // Torn record inside an ENUMERATION/RECOVERY walk: the adapter already
+                // narrated + counted it (TornRecordError registers at creation); the
+                // walk's job is to HEAL PAST it — skip the victim, serve the rest.
+                // Identity point-reads (get-by-id) still throw typed upstream.
+                if (isTornRecordError(error)) { /* skip torn victim; loud floor already fired */ }
         // Skip shards that have no data
       }
     }
@@ -5030,10 +5165,23 @@ export abstract class BaseStorage extends BaseStorageAdapter {
               results.push(this.hydrateVerbWithMetadata(verb, metadata))
             }
           } catch (error) {
+            // A TORN record must surface typed — an enumeration that silently
+            // skips a corrupt row hides data loss from the caller.
+            // Torn record inside an ENUMERATION/RECOVERY walk: the adapter already
+                // narrated + counted it (TornRecordError registers at creation); the
+                // walk's job is to HEAL PAST it — skip the victim, serve the rest.
+                // Identity point-reads (get-by-id) still throw typed upstream.
+                if (isTornRecordError(error)) { /* skip torn victim; loud floor already fired */ }
             // Skip verbs that fail to load
           }
         }
       } catch (error) {
+        // A TORN record propagates (typed) — only shard-listing absence is skippable.
+        // Torn record inside an ENUMERATION/RECOVERY walk: the adapter already
+                // narrated + counted it (TornRecordError registers at creation); the
+                // walk's job is to HEAL PAST it — skip the victim, serve the rest.
+                // Identity point-reads (get-by-id) still throw typed upstream.
+                if (isTornRecordError(error)) { /* skip torn victim; loud floor already fired */ }
         // Skip shards that have no data
       }
     }
@@ -5078,10 +5226,23 @@ export abstract class BaseStorage extends BaseStorageAdapter {
               )
             )
           } catch (error) {
+            // A TORN record must surface typed — an enumeration that silently
+            // skips a corrupt row hides data loss from the caller.
+            // Torn record inside an ENUMERATION/RECOVERY walk: the adapter already
+                // narrated + counted it (TornRecordError registers at creation); the
+                // walk's job is to HEAL PAST it — skip the victim, serve the rest.
+                // Identity point-reads (get-by-id) still throw typed upstream.
+                if (isTornRecordError(error)) { /* skip torn victim; loud floor already fired */ }
             // Skip verbs that fail to load
           }
         }
       } catch (error) {
+        // A TORN record propagates (typed) — only shard-listing absence is skippable.
+        // Torn record inside an ENUMERATION/RECOVERY walk: the adapter already
+                // narrated + counted it (TornRecordError registers at creation); the
+                // walk's job is to HEAL PAST it — skip the victim, serve the rest.
+                // Identity point-reads (get-by-id) still throw typed upstream.
+                if (isTornRecordError(error)) { /* skip torn victim; loud floor already fired */ }
         // Skip shards that have no data
       }
     }

src/storage/tornRecordError.ts

@@ -0,0 +1,132 @@
+/**
+ * @module storage/tornRecordError
+ * @description Typed surface for TORN records — files that EXIST in storage but
+ * cannot be decoded (invalid JSON, truncated/garbled gzip). A torn record is
+ * disk corruption, not absence: reading it as `null` ("not found") makes the
+ * consumer unable to distinguish "never existed" from "exists but unreadable",
+ * so nothing ever heals it. Mandate: loud errors, never quiet losses.
+ *
+ * Contract implemented across the storage layer:
+ * - Genuine absence (ENOENT) still reads as clean `null` — no error, no noise.
+ * - A torn record ALWAYS registers here (error log + per-process gauge), then:
+ *   - entity read paths (get/getBatch/pagination/enumeration hydration) throw
+ *     {@link TornRecordError} to the caller — a row is never silently dropped;
+ *   - system-artifact read paths whose machinery is designed for
+ *     absent-artifact degradation (manifests with recovery paths, markers
+ *     whose verdict is "rescan", rebuildable statistics) map torn → their
+ *     existing degrade AFTER the encounter is logged and counted.
+ */
+
+import { prodLog } from '../utils/logger.js'
+
+/**
+ * @description Thrown when a stored object EXISTS but cannot be decoded —
+ * corrupt/torn bytes on disk (invalid JSON, undecodable gzip). Deliberately
+ * distinct from absence: `readObjectFromPath` returns `null` only for ENOENT.
+ * Catchable by type (`instanceof`), by `name === 'TornRecordError'`, or by
+ * `code === 'TORN_RECORD'` (cross-realm safe; never matches `isAbsentError`).
+ */
+export class TornRecordError extends Error {
+  /** Stable machine-checkable discriminator (errno-style). */
+  public readonly code = 'TORN_RECORD'
+  /** Storage-root-relative path of the torn object. */
+  public readonly path: string
+  /** The underlying decode failure (SyntaxError, zlib error, …). */
+  public override readonly cause: unknown
+
+  /**
+   * @param path - Storage-root-relative path of the torn object.
+   * @param cause - The underlying decode failure.
+   */
+  constructor(path: string, cause: unknown) {
+    const causeMessage =
+      cause instanceof Error ? cause.message : String(cause)
+    super(
+      `Torn record at '${path}': file exists but cannot be decoded (${causeMessage}). ` +
+        `This is storage corruption, not absence — the record was not silently skipped.`
+    )
+    this.name = 'TornRecordError'
+    this.path = path
+    this.cause = cause
+  }
+}
+
+/**
+ * @description True IFF `e` is a torn-record error — matches by `instanceof`
+ * first, then by `name`/`code` so errors crossing module-duplication or realm
+ * boundaries are still recognized.
+ * @param e - The caught value.
+ * @returns Whether `e` denotes an existing-but-undecodable stored object.
+ */
+export function isTornRecordError(e: unknown): e is TornRecordError {
+  if (e instanceof TornRecordError) return true
+  if (e === null || typeof e !== 'object') return false
+  const { name, code } = e as { name?: unknown; code?: unknown }
+  return name === 'TornRecordError' || code === 'TORN_RECORD'
+}
+
+/**
+ * @description True IFF `e` is a payload-decode failure — the file's BYTES were
+ * read fine but could not be turned back into an object: `SyntaxError` from
+ * `JSON.parse`, or a zlib error (`Z_DATA_ERROR`, `Z_BUF_ERROR`, …) from gunzip.
+ * Distinguishes "torn record" from real I/O faults (EIO/EACCES/…), which must
+ * propagate as themselves.
+ * @param e - The caught value.
+ * @returns Whether the error means "bytes present, content undecodable".
+ */
+export function isUnparseablePayloadError(e: unknown): boolean {
+  if (e === null || typeof e !== 'object') return false
+  if (e instanceof SyntaxError) return true
+  const { name, code } = e as { name?: unknown; code?: unknown }
+  if (name === 'SyntaxError') return true
+  return typeof code === 'string' && code.startsWith('Z_')
+}
+
+/** Per-process torn-record gauge state (module-scoped; see the accessors). */
+let tornRecordCount = 0
+let lastTornRecordPath: string | null = null
+
+/**
+ * @description Register a torn-record encounter: logs a production ERROR
+ * naming the path, increments the per-process gauge, and returns the typed
+ * error for the caller to throw (or to map into a documented loud degrade).
+ * EVERY torn encounter goes through here, whatever the caller decides —
+ * the floor is: never silent.
+ * @param path - Storage-root-relative path of the torn object.
+ * @param cause - The underlying decode failure.
+ * @returns The constructed {@link TornRecordError}.
+ */
+export function registerTornRecordEncounter(
+  path: string,
+  cause: unknown
+): TornRecordError {
+  tornRecordCount++
+  lastTornRecordPath = path
+  const error = new TornRecordError(path, cause)
+  prodLog.error(
+    `[Storage] TORN RECORD #${tornRecordCount}: '${path}' exists but cannot be decoded — ` +
+      `corrupt or partially written bytes. Cause: ${
+        cause instanceof Error ? `${cause.name}: ${cause.message}` : String(cause)
+      }`
+  )
+  return error
+}
+
+/**
+ * @description Read the per-process torn-record gauge: how many torn records
+ * this process has encountered and the most recent path. Observability seam —
+ * lets operators and tests confirm that corruption was seen, not swallowed.
+ * @returns The current gauge snapshot.
+ */
+export function getTornRecordGauge(): { count: number; lastPath: string | null } {
+  return { count: tornRecordCount, lastPath: lastTornRecordPath }
+}
+
+/**
+ * @description Reset the per-process torn-record gauge to zero. Test seam only
+ * (the gauge is process-lifetime state); production code never resets it.
+ */
+export function resetTornRecordGauge(): void {
+  tornRecordCount = 0
+  lastTornRecordPath = null
+}

src/transaction/operations/IndexOperations.ts

@@ -56,16 +56,33 @@ function resolveVectorProviderId(index: VectorIndexProvider): string {
  * or timing trace see which engine actually ran, never a fossil name from
  * whichever engine happened to be active when this op class was written.
  *
+ * Generation: `generationFn` is resolved at execute time (not construction) so
+ * the write is stamped at the transaction's in-flight commit generation —
+ * which the generation store only assigns once the batch begins executing.
+ * The same generation is reused for the rollback removal, so an add and its
+ * undo reference one watermark in a provider's per-record delta log (the
+ * exact pattern the graph operations established).
+ *
  * Rollback strategy:
  * - Remove item from index
  */
 export class AddToVectorIndexOperation implements Operation {
   readonly name: string
 
+  /**
+   * @param index - The vector-index provider (JS HNSW or native).
+   * @param id - The entity's UUID.
+   * @param vector - The vector to index.
+   * @param generationFn - OPTIONAL: resolves the commit generation to stamp
+   *   this write at, evaluated when the operation executes (see class note).
+   *   Absent -> the provider receives no generation (undefined), never a
+   *   fabricated 0.
+   */
   constructor(
     private readonly index: VectorIndexProvider,
     private readonly id: string,
-    private readonly vector: number[]
+    private readonly vector: number[],
+    private readonly generationFn?: () => bigint | undefined
   ) {
     this.name = `AddToVectorIndex(${resolveVectorProviderId(index)})`
   }
@@ -74,14 +91,18 @@ export class AddToVectorIndexOperation implements Operation {
     // Check if item already exists (for rollback decision)
     const existed = await this.itemExists(this.id)
 
+    // Stamp this write at the in-flight commit generation; reuse it for the
+    // rollback so add + undo reference the same watermark.
+    const generation = this.generationFn?.()
+
     // Add to index
-    await this.index.addItem({ id: this.id, vector: this.vector })
+    await this.index.addItem({ id: this.id, vector: this.vector }, generation)
 
     // Return rollback action
     return async () => {
       if (!existed) {
         // Remove newly added item
-        await this.index.removeItem(this.id)
+        await this.index.removeItem(this.id, generation)
       }
       // If item existed before, we don't rollback (update is OK)
       // This prevents index corruption from removing pre-existing items
@@ -131,22 +152,138 @@ export class AddToVectorIndexOperation implements Operation {
 export class RemoveFromVectorIndexOperation implements Operation {
   readonly name: string
 
+  /**
+   * @param index - The vector-index provider (JS HNSW or native).
+   * @param id - The entity's UUID.
+   * @param vector - The removed vector (required for rollback re-add).
+   * @param generationFn - Resolves the commit generation for this removal,
+   *   evaluated when the operation executes; reused for the rollback re-add
+   *   so the round trip references one watermark.
+   */
   constructor(
     private readonly index: VectorIndexProvider,
     private readonly id: string,
-    private readonly vector: number[] // Required for rollback
+    private readonly vector: number[], // Required for rollback
+    private readonly generationFn?: () => bigint | undefined
   ) {
     this.name = `RemoveFromVectorIndex(${resolveVectorProviderId(index)})`
   }
 
   async execute(): Promise<RollbackAction> {
+    // Resolve the removal generation once; reuse it for the rollback re-add.
+    const generation = this.generationFn?.()
+
     // Remove from index
-    await this.index.removeItem(this.id)
+    await this.index.removeItem(this.id, generation)
 
     // Return rollback action
     return async () => {
       // Re-add item with original vector
-      await this.index.addItem({ id: this.id, vector: this.vector })
+      await this.index.addItem({ id: this.id, vector: this.vector }, generation)
+    }
+  }
+}
+
+/**
+ * Replace an item's vector in the vector index as ONE atomic transaction leg —
+ * the row is never absent from vector search during an update.
+ *
+ * Backend-neutral: see {@link AddToVectorIndexOperation} — `index` may be the
+ * JS HNSW fallback or a native acceleration provider; the emitted `name`
+ * stamps the active backend.
+ *
+ * Why this op exists: update flows historically staged a
+ * {@link RemoveFromVectorIndexOperation} followed by an
+ * {@link AddToVectorIndexOperation} as two separately-awaited operations.
+ * Between them the row was in NEITHER index — dark to semantic recall while
+ * perfectly visible to metadata reads (a transient-invisibility window that
+ * stretched to seconds in a production deployment). The structural cure is a
+ * single leg that never removes without simultaneously re-inserting.
+ *
+ * Execution strategy (feature-detected, in preference order):
+ * 1. Provider exposes `updateItem` → ONE in-place call. The provider swaps
+ *    the vector without the row ever leaving its index, and an element-wise
+ *    UNCHANGED vector (the type-only-update production shape) is a pure
+ *    no-op on its side.
+ * 2. Provider without `updateItem` (a native provider that has not shipped
+ *    it yet) → `removeItem` + `addItem` executed ADJACENT within this single
+ *    op. Still strictly better than the historical pair: no other transaction
+ *    operation can interleave between the two calls. This is a temporary
+ *    seam — the native side of the pair is expected to ship its own
+ *    `updateItem` so path 1 applies everywhere; when it does, this fallback
+ *    becomes dead code that costs nothing.
+ *
+ * Rollback strategy (mirrors the execute branch that ran):
+ * - `updateItem` path → `updateItem` back to `oldVector`.
+ * - Fallback path → `removeItem` + `addItem` back to `oldVector`.
+ *
+ * Rollback semantics when the item did not exist at execute time: this op's
+ * contract is that the caller read the entity and its CURRENT vector
+ * (`oldVector`) before staging — update flows only stage it for existing
+ * rows. If the item was somehow absent, execute() inserts it (`updateItem`
+ * delegates to add; the fallback's remove is a no-op before its add), and
+ * rollback restores `oldVector` rather than removing — the same posture as
+ * {@link RemoveFromVectorIndexOperation}'s unconditional re-add: by
+ * constructing the op with `oldVector` the caller DECLARED the before-state,
+ * and rollback reconstructs that declared state instead of silently deciding
+ * the row should vanish.
+ */
+export class ReplaceInVectorIndexOperation implements Operation {
+  readonly name: string
+
+  /**
+   * @param index - The vector-index provider (JS HNSW or native).
+   * @param id - The entity's UUID.
+   * @param oldVector - The pre-update vector (required for rollback).
+   * @param newVector - The replacement vector.
+   * @param generationFn - Resolves the commit generation to stamp this write
+   *   at, evaluated when the operation executes and reused across both
+   *   execute branches AND the rollback — one watermark for the whole
+   *   replace round trip.
+   */
+  constructor(
+    private readonly index: VectorIndexProvider,
+    private readonly id: string,
+    private readonly oldVector: number[], // Required for rollback
+    private readonly newVector: number[],
+    private readonly generationFn?: () => bigint | undefined
+  ) {
+    this.name = `ReplaceInVectorIndex(${resolveVectorProviderId(index)})`
+  }
+
+  async execute(): Promise<RollbackAction> {
+    // Feature-detect the in-place capability — optional on the provider
+    // contract, like `getItem`/`setPersistMode` (Brainy's JS HNSW index
+    // ships it; a native provider may not have yet). The capability carries
+    // the same optional trailing generation as the required write surface.
+    const index = this.index as VectorIndexProvider & {
+      updateItem?: (item: { id: string; vector: number[] }, generation?: bigint) => Promise<void>
+    }
+
+    // One commit generation for the whole replace (both branches + rollback).
+    const generation = this.generationFn?.()
+
+    if (typeof index.updateItem === 'function') {
+      // Atomic path: one in-place call, the row never leaves the index.
+      await index.updateItem({ id: this.id, vector: this.newVector }, generation)
+
+      return async () => {
+        // Restore the declared before-state in place (see class JSDoc for
+        // the item-did-not-exist posture).
+        await index.updateItem!({ id: this.id, vector: this.oldVector }, generation)
+      }
+    }
+
+    // Fallback seam: remove+add ADJACENT within this single op — no other
+    // transaction operation can interleave between them (see class JSDoc).
+    await this.index.removeItem(this.id, generation)
+    await this.index.addItem({ id: this.id, vector: this.newVector }, generation)
+
+    return async () => {
+      // updateItem-style restore via the same adjacent pair, back to the
+      // declared before-state.
+      await this.index.removeItem(this.id, generation)
+      await this.index.addItem({ id: this.id, vector: this.oldVector }, generation)
     }
   }
 }
@@ -154,26 +291,43 @@ export class RemoveFromVectorIndexOperation implements Operation {
 /**
  * Add to metadata index with rollback support
  *
+ * Generation: `generationFn` is resolved at execute time (not construction) —
+ * see {@link AddToVectorIndexOperation}'s class note; the same generation is
+ * reused for the rollback removal so add + undo reference one watermark in a
+ * provider's per-record delta log.
+ *
  * Rollback strategy:
  * - Remove item from index
  */
 export class AddToMetadataIndexOperation implements Operation {
   readonly name = 'AddToMetadataIndex'
 
+  /**
+   * @param index - The metadata-index manager (JS baseline or a registered provider).
+   * @param id - The entity's UUID.
+   * @param entity - Entity or metadata structure to index.
+   * @param generationFn - Resolves the commit generation to stamp this write
+   *   at, evaluated when the operation executes.
+   */
   constructor(
     private readonly index: MetadataIndexManager,
     private readonly id: string,
-    private readonly entity: any // Entity or metadata structure
+    private readonly entity: any, // Entity or metadata structure
+    private readonly generationFn?: () => bigint | undefined
   ) {}
 
   async execute(): Promise<RollbackAction> {
+    // Stamp this write at the in-flight commit generation; reuse it for the
+    // rollback so add + undo reference the same watermark.
+    const generation = this.generationFn?.()
+
     // Add to metadata index (skipFlush=true for transaction atomicity)
-    await this.index.addToIndex(this.id, this.entity, true)
+    await this.index.addToIndex(this.id, this.entity, true, false, generation)
 
     // Return rollback action
     return async () => {
       // Remove from metadata index
-      await this.index.removeFromIndex(this.id, this.entity)
+      await this.index.removeFromIndex(this.id, this.entity, generation)
     }
   }
 }
@@ -181,26 +335,41 @@ export class AddToMetadataIndexOperation implements Operation {
 /**
  * Remove from metadata index with rollback support
  *
+ * Generation: resolved at execute time and reused for the rollback re-add —
+ * one watermark for the removal round trip (see
+ * {@link AddToMetadataIndexOperation}).
+ *
  * Rollback strategy:
  * - Re-add item to index with original metadata
  */
 export class RemoveFromMetadataIndexOperation implements Operation {
   readonly name = 'RemoveFromMetadataIndex'
 
+  /**
+   * @param index - The metadata-index manager (JS baseline or a registered provider).
+   * @param id - The entity's UUID.
+   * @param entity - The entity/metadata being removed (required for rollback).
+   * @param generationFn - Resolves the commit generation for this removal,
+   *   evaluated when the operation executes.
+   */
   constructor(
     private readonly index: MetadataIndexManager,
     private readonly id: string,
-    private readonly entity: any // Required for rollback
+    private readonly entity: any, // Required for rollback
+    private readonly generationFn?: () => bigint | undefined
   ) {}
 
   async execute(): Promise<RollbackAction> {
+    // Resolve the removal generation once; reuse it for the rollback re-add.
+    const generation = this.generationFn?.()
+
     // Remove from metadata index
-    await this.index.removeFromIndex(this.id, this.entity)
+    await this.index.removeFromIndex(this.id, this.entity, generation)
 
     // Return rollback action
     return async () => {
       // Re-add with original metadata (skipFlush=true)
-      await this.index.addToIndex(this.id, this.entity, true)
+      await this.index.addToIndex(this.id, this.entity, true, false, generation)
     }
   }
 }
@@ -269,7 +438,7 @@ export class AddToGraphIndexOperation implements Operation {
     // Stamp this edge at the in-flight commit generation; reuse it for the
     // rollback so add + undo reference the same watermark. Endpoint ints
     // resolve HERE — after any same-batch adds have applied.
-    const generation = this.generationFn()
+    const generation = this.generationFn?.()
     const { sourceInt, targetInt } = resolveEndpointInts(this.endpointInts)
     const verbInt = await this.index.addVerb(this.verb, sourceInt, targetInt, generation)
     this.onVerbInt?.(verbInt)
@@ -318,7 +487,7 @@ export class RemoveFromGraphIndexOperation implements Operation {
     // Resolve the removal generation once; reuse it for the rollback re-add.
     // Endpoint ints resolve HERE (after any same-batch adds applied) and are
     // captured for the rollback, whose re-add must use the same mappings.
-    const generation = this.generationFn()
+    const generation = this.generationFn?.()
     const { sourceInt, targetInt } = resolveEndpointInts(this.endpointInts)
     await this.index.removeVerb(this.verb.id, generation)
 
@@ -342,13 +511,20 @@ export class BatchAddToVectorIndexOperation implements Operation {
 
   private operations: AddToVectorIndexOperation[]
 
+  /**
+   * @param index - The vector-index provider (JS HNSW or native).
+   * @param items - The vectors to index.
+   * @param generationFn - Resolves the commit generation shared by every item
+   *   in the batch, evaluated when the operations execute.
+   */
   constructor(
     index: VectorIndexProvider,
-    items: Array<{ id: string; vector: number[] }>
+    items: Array<{ id: string; vector: number[] }>,
+    generationFn?: () => bigint | undefined
   ) {
     this.name = `BatchAddToVectorIndex(${resolveVectorProviderId(index)})`
     this.operations = items.map(
-      item => new AddToVectorIndexOperation(index, item.id, item.vector)
+      item => new AddToVectorIndexOperation(index, item.id, item.vector, generationFn)
     )
   }
 
@@ -383,12 +559,19 @@ export class BatchAddToMetadataIndexOperation implements Operation {
 
   private operations: AddToMetadataIndexOperation[]
 
+  /**
+   * @param index - The metadata-index manager (JS baseline or a registered provider).
+   * @param items - The entities to index.
+   * @param generationFn - Resolves the commit generation shared by every item
+   *   in the batch, evaluated when the operations execute.
+   */
   constructor(
     index: MetadataIndexManager,
-    items: Array<{ id: string; entity: any }>
+    items: Array<{ id: string; entity: any }>,
+    generationFn?: () => bigint | undefined
   ) {
     this.operations = items.map(
-      item => new AddToMetadataIndexOperation(index, item.id, item.entity)
+      item => new AddToMetadataIndexOperation(index, item.id, item.entity, generationFn)
     )
   }
 

src/transaction/operations/StorageOperations.ts

@@ -12,6 +12,7 @@
 
 import type { StorageAdapter, HNSWNoun, HNSWVerb, NounMetadata, VerbMetadata } from '../../coreTypes.js'
 import type { Operation, RollbackAction } from '../types.js'
+import { prodLog } from '../../utils/logger.js'
 
 /**
  * Save noun metadata with rollback support
@@ -20,6 +21,30 @@ import type { Operation, RollbackAction } from '../types.js'
  * - If metadata existed: Restore previous metadata
  * - If metadata was new: Delete metadata
  */
+
+/**
+ * Torn-tolerant previous-state read for ROLLBACK CAPTURE: a write or delete
+ * landing on a TORN record (power-loss survivor) HEALS it — the incoming
+ * bytes replace (or remove) the unreadable ones, and the rollback target is
+ * the create sentinel (null). The adapter's loud floor (error + gauge)
+ * already fired at throw time; this narrates the heal and proceeds. Real
+ * storage faults still propagate.
+ */
+async function tornHealsToNull<T>(read: Promise<T>, what: string): Promise<T | null> {
+  try {
+    return await read
+  } catch (err) {
+    if ((err as { code?: string }).code === 'TORN_RECORD') {
+      prodLog.warn(
+        `[StorageOperations] previous ${what} is TORN — the incoming operation ` +
+          `heals it; rollback target is the create sentinel`
+      )
+      return null
+    }
+    throw err
+  }
+}
+
 export class SaveNounMetadataOperation implements Operation {
   readonly name = 'SaveNounMetadata'
 
@@ -34,7 +59,7 @@ export class SaveNounMetadataOperation implements Operation {
     // Skip read for new entities — nothing to rollback to (saves 1 storage round-trip)
     const previousMetadata = this.isNew
       ? null
-      : await this.storage.getNounMetadata(this.id)
+      : await tornHealsToNull(this.storage.getNounMetadata(this.id), 'noun metadata')
 
     // Save new metadata
     await this.storage.saveNounMetadata(this.id, this.metadata)
@@ -75,7 +100,7 @@ export class SaveNounOperation implements Operation {
     // Skip read for new entities — nothing to rollback to (saves 1 storage round-trip)
     const previousNoun = this.isNew
       ? null
-      : await this.storage.getNoun(this.noun.id)
+      : await tornHealsToNull(this.storage.getNoun(this.noun.id), 'noun record')
 
     // PRESERVE stored graph state on updates. Callers stage this op with
     // placeholder adjacency ({connections: empty, level: 0}) because the
@@ -162,8 +187,11 @@ export class DeleteNounMetadataOperation implements Operation {
     // Capture the FULL before-image (both legs) so the undo restores the whole
     // entity — a metadata-only rollback would leave the vector leg unrestored.
     // A null metadata read falls back to the caller's pre-delete read.
-    const previousNoun = await this.storage.getNoun(this.id)
-    const previousMetadata = (await this.storage.getNounMetadata(this.id)) ?? this.priorMetadata ?? null
+    const previousNoun = await tornHealsToNull(this.storage.getNoun(this.id), 'noun record')
+    const previousMetadata =
+      (await tornHealsToNull(this.storage.getNounMetadata(this.id), 'noun metadata')) ??
+      this.priorMetadata ??
+      null
 
     if (!previousNoun && !previousMetadata) {
       // Nothing to delete - no rollback needed
@@ -211,7 +239,7 @@ export class SaveVerbMetadataOperation implements Operation {
 
   async execute(): Promise<RollbackAction> {
     // Get existing metadata (for rollback)
-    const previousMetadata = await this.storage.getVerbMetadata(this.id)
+    const previousMetadata = await tornHealsToNull(this.storage.getVerbMetadata(this.id), 'verb metadata')
 
     // Save new metadata
     await this.storage.saveVerbMetadata(this.id, this.metadata)
@@ -247,7 +275,7 @@ export class SaveVerbOperation implements Operation {
 
   async execute(): Promise<RollbackAction> {
     // Get existing verb (for rollback)
-    const previousVerb = await this.storage.getVerb(this.verb.id)
+    const previousVerb = await tornHealsToNull(this.storage.getVerb(this.verb.id), 'verb record')
 
     // Save new verb
     await this.storage.saveVerb(this.verb)
@@ -291,7 +319,7 @@ export class DeleteVerbMetadataOperation implements Operation {
 
   async execute(): Promise<RollbackAction> {
     // Get metadata before deletion (for rollback)
-    const previousMetadata = await this.storage.getVerbMetadata(this.id)
+    const previousMetadata = await tornHealsToNull(this.storage.getVerbMetadata(this.id), 'verb metadata')
 
     if (!previousMetadata) {
       // Nothing to delete - no rollback needed

src/transaction/operations/index.ts

@@ -23,6 +23,7 @@ export {
 export {
   AddToVectorIndexOperation,
   RemoveFromVectorIndexOperation,
+  ReplaceInVectorIndexOperation,
   AddToMetadataIndexOperation,
   RemoveFromMetadataIndexOperation,
   AddToGraphIndexOperation,

src/types/brainy.types.ts

@@ -338,6 +338,20 @@ export interface AddParams<T = any> {
   id?: string
   /** Pre-computed embedding vector (skips auto-embedding when provided) */
   vector?: Vector
+  /**
+   * DEFER THE EMBEDDING (MT5, the deferred-embedding worker): the write
+   * acknowledges at durability — data + metadata persisted, a durable
+   * pending-embed marker written — and the embedding + vector-index insert
+   * run on the engine's single-flight background worker. HONEST SEMANTICS:
+   * the row is findable by id/metadata/path IMMEDIATELY; vector/semantic
+   * search sees it when the background embed completes (eventual vector
+   * index — `getIndexStatus().pendingEmbeds` counts the backlog, and
+   * `awaitPendingEmbeds()` is the barrier). CRASH-SAFE: markers persist
+   * before the ack and are recovered at the next open — a crash can DELAY
+   * a vector, never lose one. Refused (typed) together with `vector` —
+   * a supplied vector has nothing to defer.
+   */
+  deferEmbedding?: boolean
   /** Multi-tenancy service identifier */
   service?: string
   /** Type classification confidence (0-1) */
@@ -379,6 +393,15 @@ export interface AddParams<T = any> {
 export interface UpdateParams<T = any> {
   id: string                   // Entity to update
   data?: any                   // New content to re-embed
+  /**
+   * Defer the re-embedding of new `data` (see `AddParams.deferEmbedding`).
+   * The write acks at durability; the OLD vector keeps serving semantic
+   * search — stale-but-present, never absent (the flicker law) — until the
+   * background worker embeds the new content and swaps it in atomically.
+   * `data` reads return the NEW content immediately. Refused (typed) with
+   * an explicit `vector`.
+   */
+  deferEmbedding?: boolean
   type?: NounType             // Change type
   subtype?: string            // Change subtype (set to '' or null-equivalent via dedicated unset is future work)
   /**
@@ -1591,6 +1614,15 @@ export interface AggregationProvider {
 
   /** Serialize internal state for persistence (called during flush) */
   serializeState?(): string
+
+  /**
+   * Bake the committed generation into the provider's own state envelope
+   * before {@link serializeState} (called during flush, immediately prior).
+   * Lets a native-side reopen verify the envelope's honesty independently of
+   * the host's wrapper stamp. Optional — providers without it rely on the
+   * host wrapper's `sourceGeneration` alone.
+   */
+  noteSourceGeneration?(generation: number): void
 }
 
 // ============= Configuration =============
@@ -2028,6 +2060,61 @@ export interface BrainyConfig {
    */
   force?: boolean
 
+  /**
+   * THE ENGINE OWNS ITS FLUSH CADENCE (the persistence policy —
+   * SELF-ENGINE-LIFECYCLE-SPRINT, David-directed: "why do we need manual
+   * flushes at all?"). Under `'auto'` (the DEFAULT) the engine schedules
+   * single-flight background flushes itself — triggered by write count,
+   * elapsed time, and idle — so callers NEVER call `flush()` in a hot path
+   * (a production consumer's 829 per-write flushes convoyed into 45–66s
+   * write walls; the cadence belongs to the layer that can see dirty-node
+   * counts and IO pressure). `flush()` remains public as an awaitable
+   * durability BARRIER for the rare "must be on disk before I proceed"
+   * moment — calling it is never wrong, just no longer necessary.
+   *
+   * RECOVERY SEMANTICS (the documented promise): canonical records are
+   * durable per-write, independent of this policy — a crash between
+   * background flushes loses NO data. What a flush persists is DERIVED
+   * state (index postings, deferred HNSW nodes, counters, aggregation
+   * stamps); after a crash, derived state converges at the next open from
+   * canonical records (epoch machinery + incremental aggregation catch-up),
+   * paying a bounded catch-up cost proportional to the un-flushed window —
+   * never data loss.
+   *
+   * `'manual'` restores the pre-9.1 behavior: the engine never flushes on
+   * its own (except at `close()`); the caller owns the cadence.
+   */
+  /**
+   * Storage-authority posture at open (10.0.0+ fleet default: `'adopt'`).
+   *
+   * `'adopt'` — a brain with NO stored authority artifact adopts LOG
+   * AUTHORITY at open, oracle-gated: the verification oracle replays the
+   * generation log against stored truth; curable divergences (pre-log
+   * rows, witness drift) are baseline-backfilled; the brain flips ONLY on
+   * a green verdict and writes the durable per-brain switch. On green,
+   * writes become durable-at-ack (group-committed log fsync covers every
+   * ack). A brain whose oracle cannot go green STAYS tree-authoritative,
+   * says so loudly, and records the refusal — never a silent half-state.
+   *
+   * `'defer'` — the explicit opt-out: no automatic adoption; the brain
+   * stays tree-authoritative until `adoptLogAuthority()` is called. The
+   * pre-10 behavior, documented for operators who stage their own flips.
+   *
+   * A STORED artifact always wins over this setting (checked-at-open law):
+   * an already-flipped brain stays flipped; an explicitly-recorded tree
+   * posture is honored until an operator re-runs adoption.
+   */
+  logAuthority?: 'adopt' | 'defer'
+
+  persistence?: {
+    policy?: 'auto' | 'manual'
+    /** Background flush after this many committed writes (default 512). */
+    flushEveryWrites?: number
+    /** Background flush when this much time has passed since the last flush, checked at write time (default 30_000). */
+    flushIntervalMs?: number
+    /** Background flush after the store goes quiet for this long with dirty state (default 2_000). */
+    flushOnIdleMs?: number
+  }
 }
 
 // ============= Neural API Types =============
@@ -2188,6 +2275,79 @@ export interface Highlight {
   contentCategory?: ContentCategory
 }
 
+// ============= Read barrier (waitForIndexed) =============
+
+/**
+ * One projection leg of the read barrier (`brain.waitForIndexed(path)`) — a
+ * derived view of the committed data that queries are served from:
+ *
+ * - `'semantic'` — the vector index (deferred embeds land here asynchronously)
+ * - `'metadata'` — the field/filter index behind `find({ where })`
+ * - `'graph'` — the relationship adjacency index
+ * - `'aggregation'` — the incremental aggregate states
+ */
+export type IndexedProjectionPath = 'semantic' | 'metadata' | 'graph' | 'aggregation'
+
+/**
+ * Options for `brain.waitForIndexed()`.
+ */
+export interface WaitForIndexedOptions {
+  /**
+   * Resolve as soon as the projection has caught up to this committed
+   * generation (rather than the current head). Today the pending-embed set
+   * carries no generation stamps, so the refinement is conservative: an
+   * empty backlog resolves immediately (the watermark is at the head, hence
+   * ≥ any committed generation); a non-empty backlog waits for the full
+   * drain — a SUPERSET of the requested wait, never a partial one.
+   */
+  generation?: number
+
+  /**
+   * Upper bound on the wait in milliseconds. On expiry the promise REJECTS
+   * with {@link WaitForIndexedTimeoutError} (typed: the leg + the
+   * still-pending count) — never a silent partial wait.
+   */
+  timeoutMs?: number
+}
+
+/**
+ * The typed rejection of `brain.waitForIndexed(path, { timeoutMs })` on
+ * expiry. Carries the projection leg (`path`; `'all'` for the no-argument
+ * barrier) and the deferred-embed backlog size at the moment the timer fired
+ * (`pendingEmbeds` — the same number as
+ * `getIndexStatus().projections.semantic.pendingEmbeds`), so a caller can
+ * log an honest gauge and retry instead of guessing. A timeout means the
+ * projection has NOT caught up — nothing was skipped, nothing partially
+ * waited.
+ */
+export class WaitForIndexedTimeoutError extends Error {
+  /** The projection leg that had not caught up (`'all'` = the no-arg barrier). */
+  public readonly path: IndexedProjectionPath | 'all'
+
+  /** The expired timeout, in milliseconds. */
+  public readonly timeoutMs: number
+
+  /** Deferred embeds still pending when the timer fired — the live value of
+   *  `getIndexStatus().projections.semantic.pendingEmbeds`. */
+  public readonly pendingEmbeds: number
+
+  constructor(path: IndexedProjectionPath | 'all', timeoutMs: number, pendingEmbeds: number) {
+    super(
+      `waitForIndexed(${path === 'all' ? '' : `'${path}'`}) timed out after ${timeoutMs}ms — ` +
+        `${pendingEmbeds} deferred embed${pendingEmbeds === 1 ? '' : 's'} still pending; the projection has ` +
+        `NOT caught up. Check getIndexStatus().projections.semantic.pendingEmbeds, then retry with a ` +
+        `larger timeoutMs or use awaitPendingEmbeds() for an unbounded drain.`
+    )
+    this.name = 'WaitForIndexedTimeoutError'
+    this.path = path
+    this.timeoutMs = timeoutMs
+    this.pendingEmbeds = pendingEmbeds
+    if (Error.captureStackTrace) {
+      Error.captureStackTrace(this, WaitForIndexedTimeoutError)
+    }
+  }
+}
+
 // ============= Export all types =============
 
 export * from './graphTypes.js'  // Re-export NounType, VerbType, etc.

src/utils/entityIdMapper.ts

@@ -129,11 +129,49 @@ export class EntityIdMapper implements EntityIdMapperProvider {
         // metadata channel as plain JSON; the `nextId` probe above identifies
         // the persisted EntityIdMapperData shape.
         const data = metadata as unknown as EntityIdMapperData
-        this.nextId = data.nextId
 
-        // Rebuild maps from serialized data
-        this.uuidToInt = new Map(Object.entries(data.uuidToInt).map(([k, v]) => [k, Number(v)]))
-        this.intToUuid = new Map(Object.entries(data.intToUuid).map(([k, v]) => [Number(k), v]))
+        // TORN-STATE VALIDATION (power-loss survivor): a torn mapper file
+        // can carry NaN/garbage where integers belong — unvalidated, those
+        // NaNs reach BigInt() on the graph's int-resolution (reopen) and
+        // the mint path (first write after recovery) and kill both with
+        // RangeErrors. A torn mapper is DISCARDED with narration and the
+        // maps re-derive through the existing rebuild path (under log
+        // authority the mint-at-append records reproduce assignments
+        // exactly; under tree authority the metadata-index reconstruction
+        // rebuilds them — the same path a missing mapper file takes).
+        const validInt = (v: unknown): v is number =>
+          typeof v === 'number' && Number.isSafeInteger(v) && v >= 0
+        let torn = !validInt(data.nextId)
+        const uuidToInt = new Map<string, number>()
+        const intToUuid = new Map<number, string>()
+        if (!torn) {
+          for (const [k, v] of Object.entries(data.uuidToInt ?? {})) {
+            const n = Number(v)
+            if (!validInt(n)) { torn = true; break }
+            uuidToInt.set(k, n)
+          }
+        }
+        if (!torn) {
+          for (const [k, v] of Object.entries(data.intToUuid ?? {})) {
+            const n = Number(k)
+            if (!validInt(n) || typeof v !== 'string') { torn = true; break }
+            intToUuid.set(n, v)
+          }
+        }
+        if (torn) {
+          console.warn(
+            `[EntityIdMapper] persisted mapper state is TORN (non-integer ids — ` +
+              `power-loss survivor); discarding and re-deriving via the rebuild ` +
+              `path. Never a RangeError at reopen or first write.`
+          )
+          this.nextId = 1
+          this.uuidToInt = new Map()
+          this.intToUuid = new Map()
+        } else {
+          this.nextId = data.nextId
+          this.uuidToInt = uuidToInt
+          this.intToUuid = intToUuid
+        }
       } else {
         // Guard: mapper file missing but entities may exist on disk.
         // If we start from nextId=1 with existing entities, roaring bitmap
@@ -164,14 +202,33 @@ export class EntityIdMapper implements EntityIdMapperProvider {
    * would exceed that, throws {@link EntityIdSpaceExceeded} so the caller
    * loudly migrates to cor's binary mapper with `idSpace: 'u64'`
    * rather than silently truncating entity ids.
+   *
+   * @param generation - Brainy's commit generation current at mint time
+   *   (contract parity with the `EntityIdMapperProvider` surface). This JS
+   *   mapper keeps a snapshot file, not a per-record delta log, so there is
+   *   no natural slot to store it — accepted and ignored; a native mapper
+   *   stamps its assignment records with it.
    */
-  getOrAssign(uuid: string): number {
+  getOrAssign(uuid: string, generation?: bigint): number {
+    void generation // Contract parity — no per-record log in the JS mapper.
     const existing = this.uuidToInt.get(uuid)
     if (existing !== undefined) {
       return existing
     }
 
-    // Assign new ID
+    // Assign new ID. Source guard: nextId must be a finite positive integer
+    // — the load path validates persisted state, but a NaN here would mint
+    // poison ints that reach BigInt() downstream; heal to the map-derived
+    // floor with narration rather than propagate.
+    if (!Number.isSafeInteger(this.nextId) || this.nextId < 1) {
+      let floor = 1
+      for (const n of this.intToUuid.keys()) if (n >= floor) floor = n + 1
+      console.warn(
+        `[EntityIdMapper] nextId was non-integer (${String(this.nextId)}) — ` +
+          `healed to ${floor} from the live map; torn-state survivor`
+      )
+      this.nextId = floor
+    }
     if (this.nextId > U32_ENTITY_ID_MAX) {
       throw new EntityIdSpaceExceeded(this.nextId)
     }
@@ -226,8 +283,14 @@ export class EntityIdMapper implements EntityIdMapperProvider {
 
   /**
    * Remove mapping for UUID
+   *
+   * @param generation - Brainy's commit generation for this removal (contract
+   *   parity with the `EntityIdMapperProvider` surface). Accepted and ignored —
+   *   this JS mapper removes immediately; a native mapper tombstones the
+   *   mapping at this generation in its version chain.
    */
-  remove(uuid: string): boolean {
+  remove(uuid: string, generation?: bigint): boolean {
+    void generation // Contract parity — no per-key version chain in the JS mapper.
     const intId = this.uuidToInt.get(uuid)
     if (intId === undefined) {
       return false

src/utils/metadataIndex.ts

@@ -5,13 +5,21 @@
  */
 
 import { StorageAdapter, resolveEntityField, NounMetadata, VerbMetadata } from '../coreTypes.js'
-import { SYSTEM_ENTITY_SCALARS, parseFieldAddress, UnresolvableFieldError } from '../db/fieldAddressing.js'
+import { SYSTEM_ENTITY_SCALARS, parseFieldAddress, UnresolvableFieldError, type FieldAddress } from '../db/fieldAddressing.js'
+import { splitNounMetadataRecord } from '../types/reservedFields.js'
 import { ColumnStore } from '../indexes/columnStore/ColumnStore.js'
 import type { MetadataIndexProvider } from '../plugin.js'
 import { MetadataIndexCache, MetadataIndexCacheConfig } from './metadataIndexCache.js'
 import { compareCodePoints } from './collation.js'
 import { prodLog } from './logger.js'
 import { getGlobalCache, UnifiedCache } from './unifiedCache.js'
+import {
+  computeWatermarkVerdict,
+  makeProjectionStamp,
+  readStampedWatermark,
+  type WatermarkVerdict,
+  type WatermarkVerdictResult
+} from './projectionWatermark.js'
 import {
   NounType,
   VerbType,
@@ -108,6 +116,15 @@ interface FieldStats {
   normalizationStrategy?: 'none' | 'precision' | 'bucket'
 }
 
+/**
+ * Storage key for the metadata projection's watermark stamp — a sidecar
+ * record beside the artifact (field registry + field indexes + chunked
+ * sparse indexes + column-store segments + id-mapper records). Written LAST
+ * in {@link MetadataIndexManager.flush} so stamp-after-data ordering holds
+ * for every byte the stamp certifies.
+ */
+export const METADATA_INDEX_STAMP_KEY = '__index_metadata_watermark__'
+
 /**
  * Implements {@link MetadataIndexProvider}: the metadata-index surface Brainy
  * calls on whatever the `'metadataIndex'` provider resolves to (its own
@@ -123,6 +140,14 @@ export class MetadataIndexManager implements MetadataIndexProvider {
   private lastFlushTime = Date.now()
   private autoFlushThreshold = 10 // Start with 10 for more frequent non-blocking flushes
 
+  // --- Watermark stamp state (see utils/projectionWatermark for the law) ---
+  /** Generation handed in via {@link stampWatermark}, awaiting the next flush. */
+  private pendingWatermark: number | null = null
+  /** Last watermark durably stamped by this instance or loaded at init. */
+  private stampedWatermark: number | null = null
+  /** The three-way verdict computed at init; null until init runs. */
+  private loadVerdict: WatermarkVerdictResult | null = null
+
   // Cardinality and field statistics tracking
   private fieldStats = new Map<string, FieldStats>()
   private cardinalityUpdateInterval = 100 // Update cardinality every N operations
@@ -249,6 +274,13 @@ export class MetadataIndexManager implements MetadataIndexProvider {
     // Must run first to populate fieldIndexes directory before warming cache
     await this.loadFieldRegistry()
 
+    // Compute the watermark verdict for the persisted artifact BEFORE any
+    // early return below — the verdict is recorded for every open, whether
+    // the workspace is empty, rebuilding, or warm. Computed and exposed
+    // only: today's rebuild triggers are unchanged (acting on 'catchup' —
+    // the incremental fold — lands with the coordinator's wiring).
+    await this.loadWatermarkVerdict()
+
     // Initialize EntityIdMapper (loads UUID ↔ integer mappings from storage)
     await this.idMapper.init()
 
@@ -1458,8 +1490,16 @@ export class MetadataIndexManager implements MetadataIndexProvider {
    * @param id - Entity ID
    * @param entityOrMetadata - Either full entity structure or plain metadata (backward compat)
    * @param skipFlush - Skip automatic flush (used during batch operations)
+   * @param deferWrites - Batch mode: buffer postings for a later flush
+   * @param generation - Brainy's commit generation for this write (see the
+   *   {@link import('../plugin.js').MetadataIndexProvider} contract). This JS
+   *   manager keeps a single live view with no per-record delta log, so it
+   *   has no slot to store it — the value is accepted for contract parity
+   *   and forwarded to the shared id mapper (an injected native mapper
+   *   stamps its assignment records with it; the JS mapper ignores it).
+   *   The JS twin adopts full per-write stamping with the watermark train.
    */
-  async addToIndex(id: string, entityOrMetadata: any, skipFlush: boolean = false, deferWrites: boolean = false): Promise<void> {
+  async addToIndex(id: string, entityOrMetadata: any, skipFlush: boolean = false, deferWrites: boolean = false, generation?: bigint): Promise<void> {
     const fields = this.extractIndexableFields(entityOrMetadata)
 
     // Sanity check for excessive indexed fields (indicates possible data issue)
@@ -1507,7 +1547,10 @@ export class MetadataIndexManager implements MetadataIndexProvider {
     // element, so a scalar overwrite (last-value-wins) would index only the final
     // element and `contains` would miss the rest.
     if (this.columnStore) {
-      const entityIntId = this.idMapper.getOrAssign(id)
+      // Thread the commit generation into the mint: an injected native mapper
+      // stamps the assignment record's delta log with the real watermark
+      // instead of a literal 0 (the JS mapper accepts and ignores it).
+      const entityIntId = this.idMapper.getOrAssign(id, generation)
       const fieldsMap: Record<string, unknown> = {}
       for (const { field, value } of fields) {
         if (field === '__words__') {
@@ -1599,8 +1642,13 @@ export class MetadataIndexManager implements MetadataIndexProvider {
    *
    * @param id - Entity ID to remove
    * @param metadata - Optional entity or metadata structure (if not provided, requires scanning all fields - slow!)
+   * @param generation - Brainy's commit generation for this removal (see the
+   *   {@link import('../plugin.js').MetadataIndexProvider} contract). Accepted
+   *   for contract parity — this JS manager removes immediately (no tombstone
+   *   chain) and forwards it to the shared id mapper's `remove`, where an
+   *   injected native mapper tombstones the mapping at this generation.
    */
-  async removeFromIndex(id: string, metadata?: any): Promise<void> {
+  async removeFromIndex(id: string, metadata?: any, generation?: bigint): Promise<void> {
     if (metadata) {
       const fields = this.extractIndexableFields(metadata)
 
@@ -1624,7 +1672,9 @@ export class MetadataIndexManager implements MetadataIndexProvider {
     // Clean up ID mapper — must happen AFTER column store removal since it uses
     // idMapper.getInt(id). Prevents deleted IDs from persisting in the mapper
     // universe, which would cause ne/exists:false queries to return deleted entities.
-    this.idMapper.remove(id)
+    // The generation rides along so a native mapper tombstones the mapping at
+    // the real commit watermark (the JS mapper ignores it).
+    this.idMapper.remove(id, generation)
     await this.idMapper.flush()
   }
 
@@ -2207,6 +2257,98 @@ export class MetadataIndexManager implements MetadataIndexProvider {
    * @returns Promise<string[]> - Entity IDs sorted by specified field
    *
    */
+  /**
+   * Resolve the orderBy value for MANY entities in BATCHED metadata-record
+   * reads — the sort path's one sanctioned value source (BRAINY-PROD-LATENCY-TRIAD).
+   *
+   * THE ASYMPTOTIC LAW THIS ENFORCES: an ordered read never does per-row
+   * storage round-trips. The previous shape — `await getFieldValueForEntity`
+   * per id, each opening the VECTOR record serially — cost 62–98ms × N on a
+   * production filesystem brain: 3,224 rows took 199–317 SECONDS, silently.
+   * The metadata RECORD (smaller, cached, batch-readable) carries everything
+   * a sort can address: the ten system scalars top-level — EXACT values, no
+   * bucketing loss — and the user's bag (v2 nested or legacy flat, resolved
+   * through the shape-aware split). One batched read pass serves any N.
+   *
+   * The call-shape is pinned by tests (zero per-row reads, batch calls only)
+   * so the serial loop cannot quietly return.
+   *
+   * @param ids - Entity ids to resolve (any size; reads are chunk-batched).
+   * @param orderAddress - The parsed orderBy address (system or metadata scope).
+   * @returns id → value map; ids whose record is missing map to `undefined`
+   *   (they sort LAST per the ordering contract — never dropped).
+   */
+  private async resolveOrderValuesBatch(
+    ids: string[],
+    orderAddress: FieldAddress
+  ): Promise<Map<string, unknown>> {
+    const values = new Map<string, unknown>()
+    if (ids.length === 0) return values
+
+    // Batch door, best first: BaseStorage's getNounMetadataBatch (native
+    // batch or parallel reads inside), then the adapter-optional
+    // getMetadataBatch, then chunked-parallel single reads — NEVER serial.
+    const storage = this.storage as StorageAdapter & {
+      getNounMetadataBatch?(ids: string[]): Promise<Map<string, NounMetadata>>
+    }
+    const CHUNK = 500
+    const records = new Map<string, NounMetadata>()
+    for (let i = 0; i < ids.length; i += CHUNK) {
+      const chunk = ids.slice(i, i + CHUNK)
+      if (typeof storage.getNounMetadataBatch === 'function') {
+        const batch = await storage.getNounMetadataBatch(chunk)
+        for (const [id, rec] of batch) records.set(id, rec)
+      } else if (typeof storage.getMetadataBatch === 'function') {
+        const batch = await storage.getMetadataBatch(chunk)
+        for (const [id, rec] of batch) records.set(id, rec)
+      } else {
+        const loaded = await Promise.all(
+          chunk.map(async (id) => [id, await storage.getNounMetadata(id)] as const)
+        )
+        for (const [id, rec] of loaded) if (rec) records.set(id, rec)
+      }
+    }
+
+    for (const id of ids) {
+      const record = records.get(id)
+      if (!record) {
+        values.set(id, undefined)
+        continue
+      }
+      // Shape-aware split serves both record eras: engine scalars from the
+      // reserved half (EXACT timestamps — the bucketed index is never
+      // consulted here), user fields from the bag.
+      const { reserved, custom } = splitNounMetadataRecord(
+        record as Record<string, unknown>
+      )
+      if (orderAddress.scope === 'system') {
+        values.set(
+          id,
+          orderAddress.field === 'type'
+            ? reserved.noun
+            : (reserved as Record<string, unknown>)[orderAddress.field]
+        )
+      } else {
+        let value: unknown = custom[orderAddress.field]
+        if (value === undefined && orderAddress.field.includes('.')) {
+          // Dotted user path: traverse INSIDE the bag.
+          value = orderAddress.field
+            .split('.')
+            .reduce<unknown>(
+              (o, seg) =>
+                o && typeof o === 'object' ? (o as Record<string, unknown>)[seg] : undefined,
+              custom
+            )
+        }
+        values.set(id, value)
+      }
+    }
+    return values
+  }
+
+  /** Once-per-field flag for the fallback-degradation announcement. */
+  private static announcedFallbackSorts = new Set<string>()
+
   async getSortedIdsForFilter(
     filter: any,
     orderBy: string,
@@ -2274,12 +2416,12 @@ export class MetadataIndexManager implements MetadataIndexProvider {
       // ORDERING CONTRACT (cross-engine, sealed): rows missing the field are
       // NEVER dropped — they sort LAST in both directions — and ties break by
       // id ascending. The column only contains rows that HAVE the field, so
-      // (1) re-sort the page deterministically (value, then id) with K cheap
-      // value reads, and (2) append the filtered rows the column omitted,
-      // id-ascending, filling any remaining page budget.
-      const page = await Promise.all(
-        sortedUuids.map(async id => ({ id, value: await this.getFieldValueForEntity(id, orderKey) }))
-      )
+      // (1) re-sort the page deterministically (value, then id) via ONE
+      // batched value resolution — never per-row reads — and (2) append the
+      // filtered rows the column omitted, id-ascending, filling any
+      // remaining page budget.
+      const pageValues = await this.resolveOrderValuesBatch(sortedUuids, orderAddress)
+      const page = sortedUuids.map(id => ({ id, value: pageValues.get(id) }))
       page.sort((a, b) => this.compareAddressedValues(a.value, b.value, a.id, b.id, order))
       let result = page.map(p => p.id)
 
@@ -2293,20 +2435,32 @@ export class MetadataIndexManager implements MetadataIndexProvider {
       return topK !== undefined ? result.slice(0, topK) : result
     }
 
-    // Fallback: sparse index path (for fields not yet in column store).
-    // Requires a non-empty filter because it reads O(k) entity values from storage.
+    // Fallback: no column serves this field. BOUNDED + ANNOUNCED, never
+    // silent (the B2 no-silent-degradation law, BRAINY-PROD-LATENCY-TRIAD):
+    // O(N) in row count but served by BATCHED metadata-record reads — the
+    // serial per-row getNoun loop that turned 3,224 rows into a 199–317s
+    // scan is dead, and the call-shape pin keeps it dead.
     const filteredIds = await this.getIdsForFilter(filter)
 
     if (filteredIds.length === 0) {
       return []
     }
 
-    const idValuePairs: Array<{ id: string, value: any }> = []
-    for (const id of filteredIds) {
-      const value = await this.getFieldValueForEntity(id, orderKey)
-      idValuePairs.push({ id, value })
+    if (
+      filteredIds.length > 500 &&
+      !MetadataIndexManager.announcedFallbackSorts.has(orderKey)
+    ) {
+      MetadataIndexManager.announcedFallbackSorts.add(orderKey)
+      prodLog.warn(
+        `[brainy] ordered read on '${orderKey}' has no column index — served by the ` +
+          `batched fallback over ${filteredIds.length} rows (bounded, one batch pass; ` +
+          `announced once per field). A native column for this field makes it O(K).`
+      )
     }
 
+    const fallbackValues = await this.resolveOrderValuesBatch(filteredIds, orderAddress)
+    const idValuePairs = filteredIds.map(id => ({ id, value: fallbackValues.get(id) }))
+
     idValuePairs.sort((a, b) => this.compareAddressedValues(a.value, b.value, a.id, b.id, order))
 
     const sorted = idValuePairs.map(p => p.id)
@@ -2476,6 +2630,10 @@ export class MetadataIndexManager implements MetadataIndexProvider {
 
     // Check if we have anything else to flush
     if (this.dirtyFields.size === 0) {
+      // Nothing dirty — but a pending watermark still stamps (the registry
+      // + id-mapper writes above are the only bytes this pass touched, and
+      // they are durable at this point). Stamp-after-data holds.
+      await this.writePendingStamp()
       return // No dirty field indexes to flush
     }
 
@@ -2515,8 +2673,131 @@ export class MetadataIndexManager implements MetadataIndexProvider {
     if (this.columnStore) {
       await this.columnStore.flush()
     }
+
+    // STAMP-AFTER-DATA: the watermark stamp is the LAST write of the flush —
+    // every byte it certifies (field indexes, registry, id-mapper records,
+    // column-store segments) is durable before the stamp lands. A crash
+    // anywhere above leaves the artifact behind-stamped or unstamped, which
+    // verdicts as catchup/rescan on the next open — never a wrong adopt.
+    await this.writePendingStamp()
   }
-  
+
+  /**
+   * @description Record the committed generation this projection reflects.
+   * The stamp is NOT written here — it is written as the final storage write
+   * of the next {@link flush} (stamp-after-data ordering is a module
+   * guarantee, not a caller obligation). The coordinator calls this with the
+   * store's committed generation right before flushing.
+   * @param generation - The committed generation every flushed byte reflects.
+   */
+  stampWatermark(generation: number): void {
+    this.pendingWatermark = generation
+  }
+
+  /**
+   * @description The projection's current watermark: the stamp loaded at
+   * init (or the last stamp durably written by this instance). Null =
+   * unstamped (legacy artifact, first boot, or stamping never wired).
+   */
+  watermark(): number | null {
+    return this.stampedWatermark
+  }
+
+  /**
+   * @description The three-way adoption verdict computed at init —
+   * `'adopt'` (stamped == committed, zero work), `'catchup'` (stamped <
+   * committed; the gap from {@link watermarkGap} awaits an incremental
+   * fold), `'rescan'` (unstamped or stamped above committed — never
+   * trusted). Null until init() has run. Computed and exposed only; no
+   * load behavior changes ride on it yet.
+   */
+  watermarkVerdict(): WatermarkVerdict | null {
+    return this.loadVerdict?.verdict ?? null
+  }
+
+  /**
+   * @description The catch-up window `(from, to]` when the init verdict was
+   * `'catchup'`; null otherwise.
+   */
+  watermarkGap(): { from: number; to: number } | null {
+    return this.loadVerdict?.gap ?? null
+  }
+
+  /**
+   * @description Write the pending watermark stamp as a sidecar record —
+   * always called AFTER the data it certifies is durable. A stamp-write
+   * failure is fail-safe (the artifact stays unstamped/behind → rescan or
+   * catchup on next open, never a wrong adopt) but is said out loud and the
+   * pending stamp is retained for the next flush.
+   */
+  private async writePendingStamp(): Promise<void> {
+    if (this.pendingWatermark === null) return
+    const watermark = this.pendingWatermark
+    try {
+      await this.storage.saveMetadata(METADATA_INDEX_STAMP_KEY, {
+        noun: 'IndexWatermark',
+        ...makeProjectionStamp(watermark)
+      })
+      this.stampedWatermark = watermark
+      this.pendingWatermark = null
+    } catch (error) {
+      prodLog.error(
+        `[MetadataIndex] failed to write watermark stamp (generation ${watermark}) — ` +
+          `artifact stays behind-stamped (safe: verdicts catchup/rescan, never wrong-adopt); ` +
+          `retrying on next flush:`,
+        error
+      )
+    }
+  }
+
+  /**
+   * @description Read the artifact's stamp and compute the three-way verdict
+   * against the store's committed generation. Unstamped state on a stamped
+   * store verdicts `'rescan'` LOUDLY — never a silent adopt.
+   *
+   * MIGRATION COST: existing pre-stamp brains verdict `'rescan'` exactly
+   * once (this open re-derives from source as it already does today); the
+   * next flush stamps them, and every later open adopts.
+   */
+  private async loadWatermarkVerdict(): Promise<void> {
+    const committed = this.storage.committedGeneration?.() ?? null
+    let stamped: number | null = null
+    try {
+      const record = await this.storage.getMetadata(METADATA_INDEX_STAMP_KEY)
+      stamped = readStampedWatermark(record)
+    } catch {
+      // An unreadable stamp is unstamped — the fail-safe direction.
+      stamped = null
+    }
+    const result = computeWatermarkVerdict(stamped, committed)
+    this.loadVerdict = result
+    this.stampedWatermark = stamped
+
+    if (result.verdict === 'rescan') {
+      const artifactPresent = this.fieldIndexes.size > 0 || stamped !== null
+      if (artifactPresent) {
+        prodLog.warn(
+          `[MetadataIndex] watermark verdict: RESCAN — persisted index is ` +
+            (stamped === null
+              ? 'unstamped (legacy pre-stamp artifact, or a crash between data and stamp)'
+              : `stamped at generation ${stamped}, ABOVE the store's committed generation ${committed}`) +
+            ` — never adopting unverifiable state`
+        )
+      } else {
+        prodLog.debug(
+          '[MetadataIndex] watermark verdict: rescan (no persisted artifact — first boot)'
+        )
+      }
+    } else if (result.verdict === 'catchup') {
+      prodLog.info(
+        `[MetadataIndex] watermark verdict: catchup — index stamped at generation ` +
+          `${stamped}, store committed at ${committed}; the (${stamped}, ${committed}] ` +
+          `window awaits an incremental fold (verdict exposed; the fold lands with the ` +
+          `coordinator's wiring)`
+      )
+    }
+  }
+
   /**
    * Yield control back to the Node.js event loop
    * Prevents blocking during long-running operations

src/utils/paramValidation.ts

@@ -540,6 +540,22 @@ function rejectForgedSystemKeys(metadata: Record<string, unknown> | undefined, s
 
 export function validateAddParams(params: AddParams): void {
   rejectForgedSystemKeys(params.metadata as Record<string, unknown> | undefined, 'add()')
+  // MT5 deferred embedding: an explicit vector has nothing to defer, and a
+  // deferral without data has nothing to embed — both are caller bugs that
+  // must refuse with the fix, never be silently reinterpreted.
+  if ((params as AddParams & { deferEmbedding?: boolean }).deferEmbedding === true) {
+    if (params.vector) {
+      throw new Error(
+        `add(): deferEmbedding cannot be combined with an explicit 'vector' — ` +
+          `the vector is already computed; drop one of the two.`
+      )
+    }
+    if (!params.data) {
+      throw new Error(
+        `add(): deferEmbedding requires 'data' (the content the background worker will embed).`
+      )
+    }
+  }
   // Universal truth: must have data or vector
   if (!params.data && !params.vector) {
     throw new Error(
@@ -581,6 +597,19 @@ export function validateAddParams(params: AddParams): void {
  */
 export function validateUpdateParams(params: UpdateParams): void {
   rejectForgedSystemKeys(params.metadata as Record<string, unknown> | undefined, 'update()')
+  if ((params as UpdateParams & { deferEmbedding?: boolean }).deferEmbedding === true) {
+    if (params.vector) {
+      throw new Error(
+        `update(): deferEmbedding cannot be combined with an explicit 'vector' — ` +
+          `the vector is already computed; drop one of the two.`
+      )
+    }
+    if (!params.data) {
+      throw new Error(
+        `update(): deferEmbedding requires new 'data' — without a data change there is nothing to re-embed.`
+      )
+    }
+  }
   // Universal truth: must have an ID
   if (!params.id) {
     throw new Error('id is required for update')

src/utils/projectionWatermark.ts

@@ -0,0 +1,150 @@
+/**
+ * @module utils/projectionWatermark
+ * @description The watermark-stamp contract shared by Brainy's persisted TS
+ * projections (metadata index, JS HNSW vector index, graph adjacency index).
+ *
+ * THE LAW: every persisted projection artifact carries a stamp asserting
+ * "this state reflects every committed generation ≤ watermark and nothing
+ * above it, atomically". STAMP-AFTER-DATA: the stamp is written only after
+ * every byte it certifies is durable — a crash between data and stamp leaves
+ * the artifact unstamped, which verdicts as a rescan, never a wrong adopt.
+ *
+ * At load, each owner computes a three-way verdict against the store's
+ * committed generation — the same rule and verdict names the aggregation
+ * machinery ships (see `AggregationIndex.stateAdoptionVerdict`):
+ *
+ * - `'adopt'`   — stamped == committed (clean reopen, zero work), or the
+ *                 store exposes no committed generation at all (pre-stamp
+ *                 stores keep their pre-stamp behavior).
+ * - `'catchup'` — stamped < committed (an unclean exit after later writes,
+ *                 or a long-lived writer whose last stamp predates recent
+ *                 commits). The artifact is exact AS OF its stamp, so the
+ *                 missing window `(stamped, committed]` can be folded
+ *                 incrementally — at-least-once idempotent, bounded by
+ *                 writes since the stamp, never by store size.
+ * - `'rescan'`  — unstamped (a legacy pre-stamp artifact, or a crash between
+ *                 data and stamp) or stamped ABOVE committed (e.g. a log
+ *                 truncation on a copied store pulled the watermark back):
+ *                 the state over-claims unverifiably — one exact rescan,
+ *                 said out loud, never a silent adopt.
+ *
+ * MIGRATION COST (stated once, honored by every owner): existing pre-stamp
+ * brains verdict `'rescan'` exactly once — they re-derive from source on
+ * that open, the next flush stamps them, and every later open adopts.
+ *
+ * The verdict is COMPUTED AND EXPOSED by each owner; acting on `'catchup'`
+ * (the incremental fold) lands with the owner's coordinator wiring.
+ */
+
+/** The three-way load verdict for a persisted projection artifact. */
+export type WatermarkVerdict = 'adopt' | 'catchup' | 'rescan'
+
+/**
+ * Format version written into every projection stamp. Bump when the stamp
+ * record's shape changes incompatibly; readers treat an unknown version as
+ * unstamped (→ rescan) rather than guessing.
+ */
+export const PROJECTION_STAMP_FORMAT_VERSION = 1
+
+/**
+ * @description The stamp record a projection writes into (or beside) its
+ * persisted artifact, always AFTER the data it certifies is durable.
+ */
+export interface ProjectionStamp {
+  /** The committed generation this artifact reflects, exactly and entirely. */
+  watermark: number
+  /** {@link PROJECTION_STAMP_FORMAT_VERSION} at write time. */
+  formatVersion: number
+  /** Wall-clock ms at stamp write — diagnostic only, never load-bearing. */
+  stampedAt: number
+  /**
+   * Identity of the vector space for vector-bearing artifacts (the HNSW
+   * index). The JS index has no reachable embedding-model id in its module,
+   * so dimensions are the only identity it can honestly assert.
+   */
+  modelIdentity?: { embedModelId?: string; dimensions: number | null }
+}
+
+/** The verdict plus everything the owner needs to report or act on it. */
+export interface WatermarkVerdictResult {
+  verdict: WatermarkVerdict
+  /** Watermark read from the artifact's stamp; null = unstamped. */
+  stamped: number | null
+  /** The store's committed generation at load; null = no capability. */
+  committed: number | null
+  /** The catch-up window `(from, to]` when verdict is `'catchup'`, else null. */
+  gap: { from: number; to: number } | null
+}
+
+/**
+ * @description Build a stamp record for a projection artifact.
+ * @param watermark - The committed generation the artifact reflects.
+ * @param modelIdentity - Vector-space identity for vector-bearing artifacts.
+ * @returns The stamp record to persist (stamp-after-data).
+ */
+export function makeProjectionStamp(
+  watermark: number,
+  modelIdentity?: ProjectionStamp['modelIdentity']
+): ProjectionStamp {
+  const stamp: ProjectionStamp = {
+    watermark,
+    formatVersion: PROJECTION_STAMP_FORMAT_VERSION,
+    stampedAt: Date.now()
+  }
+  if (modelIdentity !== undefined) stamp.modelIdentity = modelIdentity
+  return stamp
+}
+
+/**
+ * @description Read the stamped watermark out of a persisted record, treating
+ * anything malformed (missing, wrong type, non-finite, negative, or an
+ * unknown format version) as unstamped — the fail-safe direction is rescan,
+ * never a guessed adopt.
+ * @param record - The raw persisted record (or null/undefined).
+ * @returns The stamped watermark, or null if effectively unstamped.
+ */
+export function readStampedWatermark(record: unknown): number | null {
+  if (record === null || typeof record !== 'object') return null
+  const rec = record as Record<string, unknown>
+  const version = rec.formatVersion
+  if (typeof version !== 'number' || version > PROJECTION_STAMP_FORMAT_VERSION) {
+    return null
+  }
+  const raw = rec.watermark
+  if (typeof raw !== 'number' || !Number.isFinite(raw) || raw < 0) return null
+  return raw
+}
+
+/**
+ * @description The three-way adoption verdict — the single decision rule
+ * every stamped projection shares (mirrors the aggregation machinery's
+ * `stateAdoptionVerdict` exactly: same names, same directions).
+ * @param stamped - Watermark read from the artifact ({@link readStampedWatermark}).
+ * @param committed - The store's committed generation (null = no capability).
+ * @returns The verdict with the stamped/committed pair and the catch-up gap.
+ */
+export function computeWatermarkVerdict(
+  stamped: number | null,
+  committed: number | null
+): WatermarkVerdictResult {
+  // No committed-generation capability: hash/shape checks are the only
+  // adoption gate, exactly the pre-stamp behavior. Never fail a store that
+  // cannot express the question.
+  if (committed === null) {
+    return { verdict: 'adopt', stamped, committed, gap: null }
+  }
+  if (stamped === committed) {
+    return { verdict: 'adopt', stamped, committed, gap: null }
+  }
+  if (stamped !== null && stamped < committed) {
+    return {
+      verdict: 'catchup',
+      stamped,
+      committed,
+      gap: { from: stamped, to: committed }
+    }
+  }
+  // Unstamped, or stamped above committed: unverifiable — rescan, loudly
+  // (the caller owns the loud log so it can name its projection).
+  return { verdict: 'rescan', stamped, committed, gap: null }
+}

src/vfs/VirtualFileSystem.ts

@@ -694,6 +694,12 @@ export class VirtualFileSystem implements IVirtualFileSystem {
       await this.brain.update({
         id: existingId,
         data: embeddingData,
+        // MT5: the caller's write acks at durability; the re-embed (a neural
+        // net — it dominated the measured 5.6s p50 per file write) runs on
+        // the background worker and swaps in atomically. Content is readable
+        // and metadata-findable immediately; semantic search converges when
+        // the embed lands (eventual vector index, the documented contract).
+        deferEmbedding: true,
         metadata
       })
 
@@ -729,6 +735,9 @@ export class VirtualFileSystem implements IVirtualFileSystem {
         data: embeddingData,  // Always provide string for embeddings
         type: this.getFileNounType(mimeType),
         subtype: 'vfs-file',  // Standard subtype for VFS file entities (7.30+)
+        // MT5: ack at durability; embedding backgrounds (see the overwrite
+        // branch note above).
+        deferEmbedding: true,
         metadata
       })
 
@@ -1117,6 +1126,9 @@ export class VirtualFileSystem implements IVirtualFileSystem {
         data: path,  // Directory path as string content
         type: NounType.Collection,
         subtype: 'vfs-directory',  // Standard subtype for VFS directory entities (7.30+)
+        // MT5: a directory creation on a write path must not wait on the
+        // embedder either — same ack-at-durability contract as file writes.
+        deferEmbedding: true,
         metadata
       })
 

tests/conformance/golden-log-fold.test.ts

@@ -0,0 +1,170 @@
+/**
+ * @module tests/conformance/golden-log-fold
+ * @description THE GOLDEN-LOG FOLD-CONFORMANCE ORACLE (brainy leg).
+ *
+ * One deterministic v2 log — fixed ids, ints, timestamps, vectors — whose
+ * ENCODED BYTES and whose FOLDED STATE are both pinned by content hash.
+ * The second (native) reader implementation consumes the identical fixture
+ * (tests/fixtures/golden-log-v2.bin, written and verified here) and must
+ * produce the identical fold digest; the pair is normative on disagreement.
+ *
+ * What the pins catch, loudly:
+ * - Any byte drift in the encoder (envelope, msgpack layout, seals, CRC).
+ * - Any semantic drift in the fold (tombstone masking, vector landing,
+ *   sameAsGeneration resolution, last-writer-wins ordering).
+ * - Any divergence between the two implementations, before the cut.
+ *
+ * The pinned hashes change ONLY with a deliberate, versioned format or
+ * fold-law change — never silently. Updating them requires updating the
+ * fixture AND the native side in the same train.
+ */
+import { describe, it, expect } from 'vitest'
+import { createHash } from 'node:crypto'
+import { readFileSync, writeFileSync, existsSync, mkdirSync } from 'node:fs'
+import { join, dirname } from 'node:path'
+import {
+  encodeFactV2,
+  encodeSegmentHeaderV2,
+  sealGroup,
+  decodeGroupV2,
+  SEGMENT_HEADER_BYTES,
+  type CommitFactV2,
+  type LogRecord
+} from '../../src/db/factLogFormat.js'
+import { recordDigest } from '../../src/db/logAuthority.js'
+
+const FIXTURE = join(__dirname, '../fixtures/golden-log-v2.bin')
+
+const sha256 = (b: Uint8Array): string => createHash('sha256').update(b).digest('hex')
+
+// Fixed identities — never regenerate.
+const BRAIN = '00000000-0000-4000-8000-00000000b1a1'
+const A = '00000000-0000-4000-8000-0000000000a1'
+const B = '00000000-0000-4000-8000-0000000000b2'
+const C = '00000000-0000-4000-8000-0000000000c3'
+const V = '00000000-0000-4000-8000-0000000000d4'
+
+const vec = (seed: number): number[] => [seed + 0.25, seed + 0.5, seed + 0.75]
+
+/** The golden fact sequence — every fold-relevant behavior in nine facts. */
+function goldenFacts(): CommitFactV2[] {
+  const f = (generation: number, records: LogRecord[]): CommitFactV2 => ({
+    generation,
+    timestamp: 1_700_000_000_000 + generation,
+    records
+  })
+  return [
+    f(1, [{ type: 'log.genesis', idSpaceWidth: 64, brainId: BRAIN, createdAt: 1_700_000_000_000 }]),
+    f(2, [{ type: 'noun.afterImage', id: A, entityInt: 1n, metadata: { name: 'alpha', rank: 1 }, vectorLeg: vec(1) }]),
+    f(3, [
+      { type: 'noun.afterImage', id: B, entityInt: 2n, metadata: { name: 'beta' }, vectorLeg: null },
+      { type: 'embed.pending', id: B, enqueuedAt: 1_700_000_000_003 }
+    ]),
+    // A metadata-only update: the vector rides by reference to generation 2.
+    f(4, [{ type: 'noun.afterImage', id: A, entityInt: 1n, metadata: { name: 'alpha', rank: 2 }, vectorLeg: { sameAsGeneration: 2 } }]),
+    // B's deferred vector lands.
+    f(5, [{ type: 'embed.landed', id: B, vector: vec(9) }]),
+    // A relationship.
+    f(6, [{ type: 'verb.afterImage', id: V, verbInt: 3n, metadata: { w: 0.5 }, vectorLeg: null, verb: 'relatedTo', sourceId: A, sourceInt: 1n, targetId: B, targetInt: 2n }]),
+    // C exists briefly…
+    f(7, [{ type: 'noun.afterImage', id: C, entityInt: 4n, metadata: { name: 'gamma' }, vectorLeg: vec(7) }]),
+    // …and is tombstoned (masking must hold in the fold).
+    f(8, [{ type: 'noun.tombstone', id: C }]),
+    // An all-deduped batch: a real generation with zero records.
+    f(9, [])
+  ]
+}
+
+/** Build the golden segment: v2 header + sealed frame group. */
+function goldenSegment(): Uint8Array {
+  // Single-hop law: generation 2 carried A's inline vector (5 carries B's
+  // via embed.landed); the ref in generation 4 must verify against it.
+  const inline = new Set([2, 5, 7])
+  const frames = goldenFacts().map((fact) => encodeFactV2(fact, { inlineVectorGenerations: inline }))
+  const sealed = sealGroup(frames, 4096)
+  const out = new Uint8Array(SEGMENT_HEADER_BYTES + sealed.length)
+  out.set(encodeSegmentHeaderV2(1, 4096), 0)
+  out.set(sealed, SEGMENT_HEADER_BYTES)
+  return out
+}
+
+/**
+ * THE FOLD LAW (shared with the native implementation, normative):
+ * fold facts in generation order → per-id latest state with tombstone
+ * masking; embed.landed applies the vector to the id's current state;
+ * {sameAsGeneration: N} resolves to the inline vector the log carried at N;
+ * verbs fold like nouns under their own ids. Digest = recordDigest (key-
+ * sorted JSON sha256) of the id-sorted state map.
+ */
+function foldGoldenLog(bytes: Uint8Array): string {
+  const group = decodeGroupV2(bytes.slice(SEGMENT_HEADER_BYTES))
+  const state = new Map<string, Record<string, unknown>>()
+  const inlineVectorAt = new Map<number, number[]>()
+  for (const fact of group.facts) {
+    for (const rec of fact.records) {
+      if (rec.type === 'noun.afterImage' || rec.type === 'verb.afterImage') {
+        let vector: number[] | null = null
+        if (Array.isArray(rec.vectorLeg)) {
+          vector = rec.vectorLeg
+          inlineVectorAt.set(fact.generation, vector)
+        } else if (rec.vectorLeg && typeof rec.vectorLeg === 'object' && 'sameAsGeneration' in rec.vectorLeg) {
+          vector = inlineVectorAt.get((rec.vectorLeg as { sameAsGeneration: number }).sameAsGeneration) ?? null
+        }
+        state.set(rec.id, {
+          kind: rec.type === 'noun.afterImage' ? 'noun' : 'verb',
+          int: (rec.type === 'noun.afterImage'
+            ? (rec as { entityInt: bigint }).entityInt
+            : (rec as { verbInt: bigint }).verbInt
+          ).toString(),
+          metadata: rec.metadata,
+          vector,
+          generation: fact.generation
+        })
+      } else if (rec.type === 'noun.tombstone' || rec.type === 'verb.tombstone') {
+        state.delete(rec.id)
+      } else if (rec.type === 'embed.landed') {
+        const cur = state.get(rec.id)
+        if (cur) state.set(rec.id, { ...cur, vector: rec.vector, generation: fact.generation })
+        inlineVectorAt.set(fact.generation, rec.vector)
+      }
+      // embed.pending / genesis / blob / projection notes carry no fold state here.
+    }
+  }
+  const sorted = [...state.entries()].sort(([x], [y]) => (x < y ? -1 : 1))
+  return recordDigest(sorted)
+}
+
+// ── THE PINS ────────────────────────────────────────────────────────────────
+// Byte-exact encode + semantics-exact fold. These literals are the contract.
+const GOLDEN_BYTES_SHA256 = 'f898ed29f6f7d41135c6c85eb07725348b20cf8efec5f050ff50ad6d54a09dad'
+const GOLDEN_FOLD_DIGEST = 'fad1b1d9865d6c9c84493c5481599ebd39b7ecf4cd203af4c435dfea7cd78ed4'
+
+describe('golden-log fold conformance (brainy leg)', () => {
+  it('the encoder reproduces the golden bytes exactly', () => {
+    const seg = goldenSegment()
+    expect(seg.length % 4096, 'sealed to the sector boundary (header excluded)').toBe(SEGMENT_HEADER_BYTES % 4096)
+    expect(sha256(seg)).toBe(GOLDEN_BYTES_SHA256)
+  })
+
+  it('the fixture on disk is byte-identical (the shared artifact both readers consume)', () => {
+    const seg = goldenSegment()
+    if (!existsSync(FIXTURE)) {
+      mkdirSync(dirname(FIXTURE), { recursive: true })
+      writeFileSync(FIXTURE, seg)
+    }
+    const onDisk = new Uint8Array(readFileSync(FIXTURE))
+    expect(sha256(onDisk), 'fixture bytes match the encoder').toBe(GOLDEN_BYTES_SHA256)
+  })
+
+  it('folding the golden log yields the pinned state digest', () => {
+    expect(foldGoldenLog(goldenSegment())).toBe(GOLDEN_FOLD_DIGEST)
+  })
+
+  it('fold semantics spot-checks (human-readable guardrails beside the hash)', () => {
+    const group = decodeGroupV2(goldenSegment().slice(SEGMENT_HEADER_BYTES))
+    expect(group.facts.length, 'nine facts, pads invisible').toBe(9)
+    const gens = group.facts.map((f) => f.generation)
+    expect(gens).toEqual([1, 2, 3, 4, 5, 6, 7, 8, 9])
+    expect(group.facts[8].records).toEqual([])
+  })
+})

tests/helpers/durabilityKillMatrix.ts

@@ -0,0 +1,210 @@
+/**
+ * @module tests/helpers/durabilityKillMatrix
+ * @description Shared machinery for the durability kill-matrix suite
+ * (tests/integration/durability-kill-matrix.test.ts): open filesystem brains
+ * with fully explicit durability (no background cadence, no embedder), arm
+ * the generation store's test-only commit fault injector at one exact phase,
+ * abandon a "crashed" brain the way a dead process would (its RAM is gone,
+ * nothing flushes, nothing closes), and read the fact log / on-disk state the
+ * recovery assertions pin.
+ *
+ * The crash model is PROCESS DEATH: in-memory state is lost, file bytes the
+ * process already handed to the OS survive. One helper additionally models
+ * POWER LOSS for a chosen entity by removing its canonical files — legal,
+ * because single-op canonical writes are tmp+rename WITHOUT fsync, and a
+ * rename that was never fsynced may surface as "no directory entry" after
+ * power loss.
+ */
+import * as fs from 'node:fs'
+import * as os from 'node:os'
+import * as path from 'node:path'
+import { Brainy } from '../../src/brainy.js'
+import type { CommitFaultPhase, GenerationStore } from '../../src/db/generationStore.js'
+
+/** The error a throwing fault injector uses to simulate a process crash. */
+export class SimulatedCrash extends Error {
+  constructor(phase: CommitFaultPhase) {
+    super(`simulated process crash at ${phase}`)
+    this.name = 'SimulatedCrash'
+  }
+}
+
+/** Deterministic 384-dim vector so no test ever invokes the embedder. */
+export function vec(seed: number): number[] {
+  return Array.from({ length: 384 }, (_, i) => ((seed * 31 + i * 7) % 100) / 100)
+}
+
+/**
+ * Map a readable label to a deterministic UUID-shaped id (entity ids must be
+ * UUIDs — the sharded storage layout derives the shard from the UUID hex).
+ */
+export function uid(label: string): string {
+  let h1 = 0x811c9dc5
+  for (let i = 0; i < label.length; i++) {
+    h1 = Math.imul(h1 ^ label.charCodeAt(i), 0x01000193) >>> 0
+  }
+  let h2 = 0xdeadbeef
+  for (let i = label.length - 1; i >= 0; i--) {
+    h2 = Math.imul(h2 ^ label.charCodeAt(i), 0x85ebca6b) >>> 0
+  }
+  const hex = h1.toString(16).padStart(8, '0') + h2.toString(16).padStart(8, '0')
+  return `00000000-0000-4000-8000-${hex.slice(0, 12)}`
+}
+
+/** Create a fresh temp directory for one brain's storage root. */
+export function makeTempDir(): string {
+  return fs.mkdtempSync(path.join(os.tmpdir(), 'brainy-kill-matrix-'))
+}
+
+/**
+ * Open a writer brain over `dir` with every implicit durability knob off:
+ * persistence policy 'manual' (the engine never flushes on its own, so every
+ * durable transition in a test is an explicit `flush()`/commit), deterministic
+ * embeddings (tests always pass explicit vectors anyway), silent logs — and
+ * `logAuthority: 'defer'` (the explicit opt-out of the 10.0.0 adopt-at-open
+ * fleet default), so the durability POSTURE is explicit per row too: rows
+ * pinning deferred/tree recovery semantics get exactly that, and at-ack rows
+ * engage log authority via `flipToAtAck`. The fleet default's open-time
+ * adoption would inject a baseline-backfill generation into every floor
+ * computation and pre-flip every row.
+ */
+export async function openBrain(
+  dir: string,
+  opts?: { logAuthority?: 'adopt' | 'defer' }
+): Promise<Brainy> {
+  process.env.BRAINY_DETERMINISTIC_EMBEDDINGS = 'true'
+  const brain = new Brainy({
+    requireSubtype: false,
+    storage: { type: 'filesystem', path: dir },
+    silent: true,
+    persistence: { policy: 'manual' },
+    logAuthority: opts?.logAuthority ?? 'defer'
+  })
+  await brain.init()
+  return brain
+}
+
+/** Typed access to the brain's private generation store (test injection point). */
+export function storeOf(brain: Brainy): GenerationStore {
+  return (brain as unknown as { generationStore: GenerationStore }).generationStore
+}
+
+/**
+ * Arm the commit fault injector to simulate a process crash at EXACTLY one
+ * phase (all other phases pass through untouched). Returns the list of phases
+ * observed before (and including) the trip, so a test can assert the fault
+ * actually fired where intended.
+ */
+export function armCrash(brain: Brainy, phase: CommitFaultPhase): { fired: CommitFaultPhase[] } {
+  const fired: CommitFaultPhase[] = []
+  storeOf(brain).setCommitFaultInjector((p) => {
+    fired.push(p)
+    if (p === phase) {
+      throw new SimulatedCrash(p)
+    }
+  })
+  return { fired }
+}
+
+/**
+ * Abandon a crashed brain the way process death would: its buffered RAM state
+ * is discarded and no background machinery may ever touch the storage
+ * directory again (a dead process cannot flush). The fault injector stays
+ * installed so any in-flight commit path still "crashes". Serialized behind
+ * the store's commit mutex so an interleaved background flush cannot be
+ * severed mid-section.
+ *
+ * NEVER calls close() — graceful close is exactly what a crash denies.
+ */
+export async function abandonAsCrashed(brain: Brainy): Promise<void> {
+  const store = storeOf(brain) as unknown as {
+    withMutex<R>(fn: () => Promise<R>): Promise<R>
+    clearPendingFlushTimer(): void
+    pendingGens: number[]
+    pendingBuffer: Map<number, unknown>
+  }
+  await store.withMutex(async () => {
+    store.clearPendingFlushTimer()
+    store.pendingGens = []
+    store.pendingBuffer.clear()
+  })
+}
+
+/**
+ * Every generation present in the brain's fact log, ascending — the suite's
+ * "what does the log claim is committed" probe. Empty when no fact log exists.
+ * A scan abort (gap detection) propagates — callers that PIN gap behavior
+ * catch it themselves.
+ */
+export async function factGenerations(brain: Brainy): Promise<number[]> {
+  const scan = brain.scanFacts({ fromGeneration: 1 })
+  if (!scan) return []
+  const gens: number[] = []
+  for await (const batch of scan.batches()) {
+    for (const fact of batch.facts) gens.push(fact.generation)
+  }
+  return gens.sort((a, b) => a - b)
+}
+
+/** An ENOSPC-shaped error, matching what a full disk surfaces from node:fs. */
+export function enospcError(): NodeJS.ErrnoException {
+  const err = new Error("ENOSPC: no space left on device, write") as NodeJS.ErrnoException
+  err.code = 'ENOSPC'
+  err.errno = -28
+  err.syscall = 'write'
+  return err
+}
+
+/**
+ * Make the storage adapter's next raw-byte append (the fact-log append path)
+ * fail once with ENOSPC, then restore the original — "the disk filled for one
+ * append, then space was freed". Returns a probe telling how many appends
+ * were failed.
+ */
+export function failNextAppendWithEnospc(brain: Brainy): { failed: () => number } {
+  const storage = (brain as unknown as {
+    storage: { appendRawBytes(p: string, b: Uint8Array): Promise<void> }
+  }).storage
+  const original = storage.appendRawBytes.bind(storage)
+  let failures = 0
+  storage.appendRawBytes = async (p: string, b: Uint8Array): Promise<void> => {
+    storage.appendRawBytes = original
+    failures++
+    throw enospcError()
+  }
+  return { failed: () => failures }
+}
+
+/**
+ * POWER-LOSS MODEL for one entity: remove its canonical noun files from the
+ * storage root. Legal disk state — a single-op write's canonical bytes are
+ * tmp+rename WITHOUT fsync (only `transact()` runs the write barrier), and an
+ * un-fsynced rename may resolve to "no directory entry" after power loss.
+ * Throws when nothing was removed (the caller's premise would be wrong).
+ */
+export function dropCanonicalNoun(dir: string, id: string): void {
+  const removed: string[] = []
+  const walk = (p: string): void => {
+    for (const entry of fs.readdirSync(p, { withFileTypes: true })) {
+      const full = path.join(p, entry.name)
+      if (entry.isDirectory()) {
+        if (entry.name === id) {
+          fs.rmSync(full, { recursive: true, force: true })
+          removed.push(full)
+        } else {
+          walk(full)
+        }
+      }
+    }
+  }
+  const nounsRoot = path.join(dir, 'entities', 'nouns')
+  if (fs.existsSync(nounsRoot)) walk(nounsRoot)
+  if (removed.length === 0) {
+    throw new Error(`power-loss model: no canonical files found for noun ${id} under ${nounsRoot}`)
+  }
+}
+
+/** True when the staged record-set directory for `gen` exists on disk. */
+export function generationDirExists(dir: string, gen: number): boolean {
+  return fs.existsSync(path.join(dir, '_generations', String(gen)))
+}

tests/integration/adopt-drift-cure.test.ts

@@ -0,0 +1,107 @@
+/**
+ * @module tests/integration/adopt-drift-cure
+ * @description THE DRIFT-CURING BACKFILL — the actual completion of the
+ * default-flip ruling: existing brains whose canonical wrappers carry
+ * pre-hydration-law drift (denormalized fields disagreeing with their own
+ * metadata leg — the real depot-brain shape, uuid-v7 rows from the 9.0 era)
+ * must ADOPT AUTOMATICALLY: the backfill rewrites canonical in the law
+ * shape (metadata leg = the authority; floats preserved), the oracle then
+ * verifies the rewrite before flipping. Same safety, zero operator chores.
+ * Log-ahead divergences still refuse as before.
+ */
+import { describe, it, expect, afterEach } from 'vitest'
+import { mkdtempSync, rmSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { Brainy } from '../../src/index.js'
+import { NounType } from '../../src/types/graphTypes.js'
+
+const dirs: string[] = []
+const brains: Brainy[] = []
+afterEach(async () => {
+  for (const b of brains.splice(0)) await b.close().catch(() => {})
+  for (const d of dirs.splice(0)) rmSync(d, { recursive: true, force: true })
+})
+
+type RawBox = {
+  storage: {
+    readNounRaw(id: string): Promise<{ metadata: unknown; vector: unknown }>
+    writeNounRaw(id: string, r: { metadata: unknown; vector: unknown }): Promise<void>
+  }
+}
+
+describe('adoption cures hydration-law drift automatically', () => {
+  it('a drifted wrapper (stale denormalized fields) adopts green with floats preserved', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-drift-cure-'))
+    dirs.push(dir)
+    const brain = new Brainy({
+      storage: { type: 'filesystem', path: dir },
+      requireSubtype: false,
+      logAuthority: 'defer'
+    })
+    await brain.init()
+    brains.push(brain)
+    const id = await brain.add({
+      data: 'early-era row with drift',
+      type: NounType.Document,
+      metadata: { k: 1 }
+    })
+    await brain.flush()
+    const before = await brain.get(id, { includeVectors: true })
+    const floats = [...(before!.vector as number[])]
+    expect(floats.length).toBeGreaterThan(0)
+
+    // Manufacture the depot shape: the stored wrapper's denormalized fields
+    // disagree with the metadata leg (pre-hydration-law drift) — an as-is
+    // identity re-commit preserves this forever; the law-shape rewrite cures it.
+    const storage = (brain as unknown as RawBox).storage
+    const raw = await storage.readNounRaw(id)
+    const wrapper = raw.vector as Record<string, unknown>
+    await storage.writeNounRaw(id, {
+      metadata: raw.metadata,
+      vector: {
+        ...wrapper,
+        noun: 'thing', // stale denormalized type (metadata leg says document)
+        legacyField: 'pre-law residue',
+        createdAt: '1999-01-01T00:00:00.000Z'
+      }
+    })
+    // Confirm the drift is oracle-visible before the cure.
+    expect((await brain.verifyLogAuthority()).verdict, 'drift detected').toBe('red')
+
+    // THE PIN: adoption cures it without any operator step.
+    const report = await brain.adoptLogAuthority()
+    expect(report.verdict).toBe('green')
+    expect(brain.logAuthority().authority).toBe('log')
+
+    // Nothing degraded: floats byte-identical, metadata intact, row serves.
+    const after = await brain.get(id, { includeVectors: true })
+    expect(after!.vector as number[], 'floats preserved through the cure').toEqual(floats)
+    expect((after!.metadata as { k: number }).k).toBe(1)
+    expect((await brain.find({ where: { k: 1 }, limit: 5 })).map((r) => r.id)).toContain(id)
+  }, 120000)
+
+  it('log-ahead divergences still refuse — the backfill never papers over a log the witness denies', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-logahead-'))
+    dirs.push(dir)
+    const brain = new Brainy({
+      storage: { type: 'filesystem', path: dir },
+      requireSubtype: false,
+      logAuthority: 'defer'
+    })
+    await brain.init()
+    brains.push(brain)
+    const id = await brain.add({ data: 'row', type: NounType.Document, metadata: { k: 1 } })
+    await brain.flush()
+
+    // Log-ahead shape: canonical loses the record while the log still
+    // claims it live (log-live-canonical-absent — NOT curable by baseline).
+    const storage = (brain as unknown as RawBox).storage
+    await storage.writeNounRaw(id, { metadata: null, vector: null })
+
+    await expect(brain.adoptLogAuthority()).rejects.toThrow(
+      /log-ahead|witness denies|log claims/i
+    )
+    expect(brain.logAuthority().authority).toBe('tree')
+  }, 120000)
+})

tests/integration/aggregation-lifecycle-catchup.test.ts

@@ -0,0 +1,143 @@
+/**
+ * @module tests/integration/aggregation-lifecycle-catchup
+ * @description THE AGGREGATION LIFECYCLE PINS (SELF-ENGINE-LIFECYCLE-SPRINT /
+ * BRAINY-PROD-LATENCY-TRIAD asks (a)+(b)). The production disease: the
+ * aggregation stamp persisted ONLY at close(), so a long-lived writer that
+ * flushes but never closes left its stamp behind after every write window —
+ * and the exact-match adoption rule then forced a WHOLE-STORE backfill walk
+ * (per-entity work, measured >60s and door-starving on a 9k-row production
+ * brain) on the first stats call after any unclean exit.
+ *
+ * The cures pinned here:
+ * (a) `brain.flush()` persists aggregation state, stamped at the committed
+ *     generation — the stamp tracks every flush, not just close().
+ * (b) BEHIND-stamp state is ADOPTED and reconciled INCREMENTALLY over its
+ *     exact missing window (fact-log affected ids + time-travel before/after
+ *     reads) — the full walk never runs for an unclean exit. Pinned by call
+ *     shape (the walk spy), not by latency.
+ */
+import { describe, it, expect, afterEach, vi } from 'vitest'
+import { mkdtempSync, rmSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { Brainy } from '../../src/index.js'
+import { NounType } from '../../src/types/graphTypes.js'
+
+const AGG = {
+  name: 'by_subtype',
+  source: { type: NounType.Document },
+  groupBy: ['system.subtype'] as string[],
+  metrics: { count: { op: 'count' as const } }
+}
+
+const dirs: string[] = []
+const brains: Brainy[] = []
+
+async function open(dir: string): Promise<Brainy> {
+  const b = new Brainy({ storage: { type: 'filesystem', path: dir }, requireSubtype: false })
+  await b.init()
+  brains.push(b)
+  return b
+}
+
+function countFor(results: Array<{ groupKey: Record<string, unknown>; metrics: Record<string, unknown> }>, subtype: string): number {
+  const row = results.find(r => r.groupKey['system.subtype'] === subtype)
+  return row ? Number(row.metrics.count) : 0
+}
+
+afterEach(async () => {
+  for (const b of brains.splice(0)) await b.close().catch(() => {})
+  for (const d of dirs.splice(0)) rmSync(d, { recursive: true, force: true })
+})
+
+describe('aggregation lifecycle — flush stamps, behind-stamp catches up incrementally', () => {
+  it('(a) brain.flush() persists aggregation state stamped at the committed generation', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-agg-flush-'))
+    dirs.push(dir)
+    const brain = await open(dir)
+    brain.defineAggregate(AGG)
+    await brain.add({ data: 'a', type: NounType.Document, subtype: 'invoice', metadata: {} })
+    await brain.add({ data: 'b', type: NounType.Document, subtype: 'invoice', metadata: {} })
+    await brain.queryAggregate(AGG.name) // settle backfill-on-define
+
+    await brain.flush()
+
+    const internals = brain as unknown as {
+      storage: {
+        getMetadata(k: string): Promise<{ sourceGeneration?: number } | null>
+        committedGeneration?(): number
+      }
+    }
+    const persisted = await internals.storage.getMetadata('__aggregation_state_by_subtype__')
+    expect(persisted, 'state persisted by flush(), not only close()').toBeTruthy()
+    expect(
+      persisted!.sourceGeneration,
+      'stamp equals the committed generation at flush time'
+    ).toBe(internals.storage.committedGeneration?.())
+  })
+
+  it('(b) an unclean exit reconciles incrementally — exact counts, ZERO full-store walks', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-agg-catchup-'))
+    dirs.push(dir)
+
+    // Session 1: define + write + flush (stamps at G), then MORE writes of
+    // every kind (add / update-that-moves-groups / delete) and a clean close
+    // — but we then REWIND the persisted aggregation artifact to its at-G
+    // bytes, which is byte-for-byte the unclean-exit state: stamp G, store
+    // committed at G+k.
+    let brain = await open(dir)
+    brain.defineAggregate(AGG)
+    await brain.add({ data: 'a', type: NounType.Document, subtype: 'invoice', metadata: {} })
+    await brain.add({ data: 'b', type: NounType.Document, subtype: 'invoice', metadata: {} })
+    const moving = await brain.add({ data: 'c', type: NounType.Document, subtype: 'draft', metadata: {} })
+    const doomed = await brain.add({ data: 'd', type: NounType.Document, subtype: 'draft', metadata: {} })
+    await brain.queryAggregate(AGG.name)
+    await brain.flush()
+
+    const internals = brain as unknown as {
+      storage: {
+        getMetadata(k: string): Promise<Record<string, unknown> | null>
+        saveMetadata(k: string, v: Record<string, unknown>): Promise<void>
+      }
+    }
+    const stateAtG = JSON.parse(
+      JSON.stringify(await internals.storage.getMetadata('__aggregation_state_by_subtype__'))
+    )
+
+    // The missing window: one add, one group-moving update, one delete.
+    await brain.add({ data: 'e', type: NounType.Document, subtype: 'invoice', metadata: {} })
+    await brain.update({ id: moving, subtype: 'invoice' })
+    await brain.remove(doomed)
+    await brain.close()
+    brains.pop()
+
+    // Rewind the aggregation artifact to the at-G bytes (the unclean exit).
+    {
+      const reopenForRewind = await open(dir)
+      const rw = reopenForRewind as unknown as typeof internals
+      await rw.storage.saveMetadata('__aggregation_state_by_subtype__', stateAtG)
+      await reopenForRewind.close()
+      brains.pop()
+    }
+
+    // Session 2: reopen — adoption must see BEHIND and reconcile, never walk.
+    brain = await open(dir)
+    brain.defineAggregate(AGG)
+    const walkSpy = vi.spyOn(
+      brain as unknown as { runAggregationBackfillWalk(): Promise<void> },
+      'runAggregationBackfillWalk'
+    )
+
+    const results = await brain.queryAggregate(AGG.name)
+
+    // Ground truth after the window: invoice = a,b,e + moved c = 4; draft = 0
+    // (c moved out, d deleted).
+    expect(countFor(results as never, 'invoice'), 'invoice count exact after catch-up').toBe(4)
+    expect(countFor(results as never, 'draft'), 'draft count exact after catch-up').toBe(0)
+
+    // THE CALL-SHAPE PIN: the whole-store walk never ran.
+    expect(walkSpy, 'full backfill walk must not run for a behind-stamp reopen').not.toHaveBeenCalled()
+
+    vi.restoreAllMocks()
+  }, 120000)
+})

tests/integration/asof-semantic-recall.test.ts

@@ -0,0 +1,140 @@
+/**
+ * @module tests/integration/asof-semantic-recall
+ * @description AS-OF SEMANTIC RECALL — the time-travel row of the release:
+ * vector/semantic search at a pinned past generation, served EXACTLY.
+ *
+ * The contract pinned here (brainy-alone leg; the accelerated-provider leg
+ * carries the same semantics at scale):
+ * 1. PAST VECTORS ARE THE PAST'S VECTORS: a later re-embed/update never
+ *    leaks into an earlier pin — asOf(G) ranks by the vectors as they
+ *    stood at G, byte-exact.
+ * 2. TOMBSTONE MASKING: a row deleted after G is FOUND at G; a row deleted
+ *    at or before G is ABSENT at G.
+ * 3. THE DEFERRED-EMBED CELL of the visibility matrix: at pins before the
+ *    vector landed the row's VECTOR LEG serves the stub (text/metadata
+ *    legs may still surface it — triple intelligence by design); the real
+ *    vector serves only at and after its landing pin. No backward leak.
+ * 4. TYPED REFUSAL beyond the log head — never a silent latest.
+ */
+import { describe, it, expect, afterEach } from 'vitest'
+import { Brainy } from '../../src/index.js'
+import { NounType } from '../../src/types/graphTypes.js'
+
+const brains: Brainy[] = []
+
+async function memBrain(): Promise<Brainy> {
+  const b = new Brainy({ storage: { type: 'memory' }, requireSubtype: false })
+  await b.init()
+  brains.push(b)
+  return b
+}
+
+afterEach(async () => {
+  for (const b of brains.splice(0)) await b.close().catch(() => {})
+})
+
+describe('as-of semantic recall', () => {
+  it('PAST VECTORS EXACT: a later update never leaks into an earlier pin', async () => {
+    const brain = await memBrain()
+    const id = await brain.add({
+      data: 'crimson apples in the orchard',
+      type: NounType.Document,
+      metadata: { epoch: 'old' }
+    })
+    const g1 = brain.generation()
+    const v1 = [...(((await brain.get(id, { includeVectors: true }))!.vector) as number[])]
+
+    await brain.update({ id, data: 'deep blue ocean currents', metadata: { epoch: 'new' } })
+    const g2 = brain.generation()
+    const v2 = (await brain.get(id, { includeVectors: true }))!.vector as number[]
+    expect(v2, 'the update really re-embedded').not.toEqual(v1)
+
+    // The pin: at G1 the row carries its ORIGINAL vector and content.
+    const dbPast = await brain.asOf(g1)
+    const past = await dbPast.get(id, { includeVectors: true })
+    expect(past, 'row exists at G1').toBeTruthy()
+    expect(past!.vector as number[], 'as-of vector is byte-exact the OLD vector').toEqual(v1)
+    expect((past!.metadata as { epoch: string }).epoch).toBe('old')
+
+    // Semantic search at G1 finds it via the OLD content; at G2 via the new.
+    const hitsOld = await dbPast.find({ query: 'crimson apples in the orchard', limit: 3 })
+    expect(hitsOld.map((r) => r.id), 'old content recalls at G1').toContain(id)
+    const dbNow = await brain.asOf(g2)
+    const hitsNew = await dbNow.find({ query: 'deep blue ocean currents', limit: 3 })
+    expect(hitsNew.map((r) => r.id), 'new content recalls at G2').toContain(id)
+    await dbPast.release()
+    await dbNow.release()
+  })
+
+  it('TOMBSTONE MASKING: deleted-after-G is found at G; deleted-before-G is absent', async () => {
+    const brain = await memBrain()
+    const doomed = await brain.add({
+      data: 'ephemeral meteor shower observation',
+      type: NounType.Document,
+      metadata: {}
+    })
+    const keeper = await brain.add({
+      data: 'permanent granite mountain survey',
+      type: NounType.Document,
+      metadata: {}
+    })
+    const gBoth = brain.generation()
+    await brain.remove(doomed)
+    const gAfter = brain.generation()
+
+    const dbBoth = await brain.asOf(gBoth)
+    const atBoth = await dbBoth.find({ query: 'ephemeral meteor shower observation', limit: 5 })
+    expect(atBoth.map((r) => r.id), 'pre-delete pin still recalls the row').toContain(doomed)
+
+    const dbAfter = await brain.asOf(gAfter)
+    const atAfter = await dbAfter.find({ query: 'ephemeral meteor shower observation', limit: 5 })
+    expect(atAfter.map((r) => r.id), 'post-delete pin masks the tombstoned row').not.toContain(doomed)
+    expect((await dbAfter.find({ query: 'permanent granite mountain survey', limit: 5 })).map((r) => r.id)).toContain(keeper)
+    await dbBoth.release()
+    await dbAfter.release()
+  })
+
+  it('DEFERRED-EMBED CELL: semantically absent before the vector landed, present after — never a stub match', async () => {
+    const brain = await memBrain()
+    // Anchor row so the semantic search always has a corpus.
+    await brain.add({ data: 'unrelated anchor topic entirely', type: NounType.Document, metadata: {} })
+
+    const id = await brain.add({
+      data: 'deferred saffron sunrise essay',
+      type: NounType.Document,
+      deferEmbedding: true,
+      metadata: {}
+    })
+    const gAck = brain.generation()
+    await brain.awaitPendingEmbeds()
+    const gLanded = brain.generation()
+    expect(gLanded, 'the landed vector is its own generation').toBeGreaterThan(gAck)
+
+    // At the ack generation: metadata-visible, and the VECTOR LEG carries
+    // the stub (the visibility matrix's AT-EMBED cell governs the vector
+    // leg — find({query})'s text/metadata legs may legitimately still
+    // surface the row, that is triple intelligence working as designed;
+    // what must NEVER happen is a stub vector ranking as a real one).
+    const dbAck = await brain.asOf(gAck)
+    const metaHits = await dbAck.find({ where: {}, limit: 10 })
+    expect(metaHits.map((r) => r.id), 'metadata-visible at ack pin').toContain(id)
+    const ackRow = await dbAck.get(id, { includeVectors: true })
+    expect((ackRow!.vector as number[]).length, 'the as-of vector at the ack pin is the stub — no vector leaked backward').toBe(0)
+
+    // At the landed generation: fully recallable.
+    const dbLanded = await brain.asOf(gLanded)
+    const landedRow = await dbLanded.get(id, { includeVectors: true })
+    expect((landedRow!.vector as number[]).length, 'the real vector serves at the landed pin').toBeGreaterThan(0)
+    const semLanded = await dbLanded.find({ query: 'deferred saffron sunrise essay', limit: 5 })
+    expect(semLanded.map((r) => r.id), 'recallable at the landed pin').toContain(id)
+    await dbAck.release()
+    await dbLanded.release()
+  })
+
+  it('TYPED REFUSAL beyond the head — never a silent latest', async () => {
+    const brain = await memBrain()
+    await brain.add({ data: 'one row', type: NounType.Document, metadata: {} })
+    const head = brain.generation()
+    await expect(brain.asOf(head + 100)).rejects.toThrow(/generation|beyond|future|exceed/i)
+  })
+})

tests/integration/brain-relocation.test.ts

@@ -0,0 +1,108 @@
+/**
+ * @module tests/integration/brain-relocation
+ * @description LC8 — RELOCATABLE BRAIN DIRECTORY. A brain's directory moved
+ * wholesale to a new path (rename/copy — backup-restore, disk migration,
+ * container re-mount) must open and serve IDENTICALLY: no absolute paths may
+ * hide in any persisted artifact. Pinned across every intelligence: point
+ * reads, metadata find, semantic find, graph traversal, aggregation — plus
+ * continued writes with monotonic generations and time-travel reads over
+ * pre-move history.
+ */
+import { describe, it, expect, afterEach } from 'vitest'
+import { mkdtempSync, rmSync, renameSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { Brainy } from '../../src/index.js'
+import { NounType, VerbType } from '../../src/types/graphTypes.js'
+
+const dirs: string[] = []
+const brains: Brainy[] = []
+
+afterEach(async () => {
+  for (const b of brains.splice(0)) await b.close().catch(() => {})
+  for (const d of dirs.splice(0)) rmSync(d, { recursive: true, force: true })
+})
+
+const AGG = {
+  name: 'by_kind',
+  source: { type: NounType.Document },
+  groupBy: ['kind'] as string[],
+  metrics: { count: { op: 'count' as const } }
+}
+
+describe('LC8 — a moved brain directory opens and serves identically', () => {
+  it('rename the directory: all three intelligences serve, writes continue, history travels', async () => {
+    const home = mkdtempSync(join(tmpdir(), 'brainy-reloc-'))
+    dirs.push(home)
+    const oldPath = join(home, 'brain-old')
+    const newPath = join(home, 'brain-new')
+
+    // Season a brain: rows, a relation, an aggregate, then flush + close.
+    let brain = new Brainy({ storage: { type: 'filesystem', path: oldPath }, requireSubtype: false })
+    await brain.init()
+    brains.push(brain)
+    brain.defineAggregate(AGG)
+    const alpha = await brain.add({
+      data: 'alpha document about mountain geology',
+      type: NounType.Document,
+      metadata: { kind: 'report', n: 1 }
+    })
+    const beta = await brain.add({
+      data: 'beta document about coastal erosion',
+      type: NounType.Document,
+      metadata: { kind: 'report', n: 2 }
+    })
+    await brain.relate({ from: alpha, to: beta, verb: VerbType.RelatedTo })
+    await brain.queryAggregate(AGG.name) // settle backfill
+    const preMoveGen = brain.generation()
+    await brain.flush()
+    await brain.close()
+    brains.pop()
+
+    // The move: wholesale directory rename.
+    renameSync(oldPath, newPath)
+
+    // Reopen at the NEW path — everything serves.
+    brain = new Brainy({ storage: { type: 'filesystem', path: newPath }, requireSubtype: false })
+    await brain.init()
+    brains.push(brain)
+    brain.defineAggregate(AGG)
+
+    // Point read + metadata find.
+    expect((await brain.get(alpha))!.data).toContain('mountain geology')
+    const found = await brain.find({ where: { kind: 'report' }, limit: 10 })
+    expect(found.map((r) => r.id).sort()).toEqual([alpha, beta].sort())
+
+    // Semantic find.
+    const sem = await brain.find({ query: 'alpha document about mountain geology', limit: 3 })
+    expect(sem.map((r) => r.id)).toContain(alpha)
+
+    // Graph traversal.
+    const related = await brain.related(alpha)
+    expect(related.map((r) => r.to)).toContain(beta)
+
+    // Aggregation.
+    const agg = (await brain.queryAggregate(AGG.name)) as Array<{
+      groupKey: Record<string, unknown>
+      metrics: Record<string, unknown>
+    }>
+    const reportRow = agg.find((g) => g.groupKey['kind'] === 'report')
+    expect(Number(reportRow?.metrics.count)).toBe(2)
+
+    // Writes continue with monotonic generations.
+    const gamma = await brain.add({
+      data: 'gamma addendum after the move',
+      type: NounType.Document,
+      metadata: { kind: 'report', n: 3 }
+    })
+    expect(brain.generation()).toBeGreaterThan(preMoveGen)
+    expect((await brain.get(gamma))!.data).toContain('addendum')
+
+    // Time travel across the move boundary: the pre-move pin sees exactly
+    // the pre-move world (no gamma), served from relocated history.
+    const dbPast = await brain.asOf(preMoveGen)
+    expect(await dbPast.get(gamma)).toBeNull()
+    expect((await dbPast.get(alpha))!.data).toContain('mountain geology')
+    await dbPast.release()
+  }, 120000)
+})

tests/integration/db-mvcc.test.ts

@@ -96,11 +96,15 @@ describe('8.0 Db API — generational MVCC', () => {
   }
 
   /** Open (and track) a filesystem brain rooted at a fresh temp directory. */
-  async function openFsBrain(dir?: string): Promise<{ brain: Brainy; dir: string }> {
+  async function openFsBrain(
+    dir?: string,
+    logAuthority?: 'adopt' | 'defer'
+  ): Promise<{ brain: Brainy; dir: string }> {
     const rootDirectory = dir ?? makeTempDir()
     const brain = new Brainy({
       requireSubtype: false,
-      storage: { type: 'filesystem', path: rootDirectory }
+      storage: { type: 'filesystem', path: rootDirectory },
+      ...(logAuthority ? { logAuthority } : {})
     })
     await brain.init()
     brains.push(brain)
@@ -647,7 +651,13 @@ describe('8.0 Db API — generational MVCC', () => {
   // ==========================================================================
   it('proof 8 — a crash before the manifest rename recovers to the exact pre-transaction state', async () => {
     const dir = makeTempDir()
-    const { brain: first } = await openFsBrain(dir)
+    // 'defer' (tree authority): this proof pins the TREE commit-point
+    // contract — the manifest rename is the commit, so a crash before it
+    // rolls back. Under the adopt-at-open default (log authority) the same
+    // crash point legitimately REPLAYS the fsynced fact at reopen and the
+    // transaction lands — that contract is pinned in the durability kill
+    // matrix's at-ack rows, not here.
+    const { brain: first } = await openFsBrain(dir, 'defer')
 
     await first.transact([
       {
@@ -689,9 +699,10 @@ describe('8.0 Db API — generational MVCC', () => {
     // the realistic worst case for the recovery path.
     await first.close()
 
-    // Reopen: recovery rolls the uncommitted generation back and rebuilds
-    // the indexes from the repaired records.
-    const { brain: second } = await openFsBrain(dir)
+    // Reopen ('defer' again — a reopen under the adopt default would adopt
+    // and change the recovery path): recovery rolls the uncommitted
+    // generation back and rebuilds the indexes from the repaired records.
+    const { brain: second } = await openFsBrain(dir, 'defer')
     const recovered = await second.get(uid('crash-e'))
     expect((recovered?.metadata as { v: number }).v).toBe(1)
     expect(await second.get(uid('crash-new'))).toBeNull()
@@ -1162,13 +1173,16 @@ describe('8.0 Db API — generational MVCC', () => {
     const brain = await openMemoryBrain()
 
     // Model-B: a single-op write is its OWN generation and IS logged (no meta —
-    // tx metadata is a transact()-only concept). It is generation 1 on a fresh
-    // brain (init-time infrastructure writes are the un-versioned gen-0 baseline).
+    // tx metadata is a transact()-only concept). Relative baseline: under the
+    // adopt-at-open fleet default the open-time baseline backfill is itself a
+    // logged single-op generation, so the log is not empty on a fresh brain —
+    // every pin below is expressed against that baseline.
+    const baseGens = (await brain.transactionLog()).map((entry) => entry.generation)
     await brain.add({ id: uid('txlog-solo'), type: NounType.Document, data: 'solo', vector: vec(99), subtype: 'note' })
     const soloLog = await brain.transactionLog()
-    expect(soloLog.map((entry) => entry.generation)).toEqual([1])
+    const soloGen = brain.generation()
+    expect(soloLog.map((entry) => entry.generation)).toEqual([soloGen, ...baseGens])
     expect(soloLog[0].meta).toBeUndefined()
-    const soloGen = 1
 
     const first = await brain.transact(
       [{ op: 'add', id: uid('txlog-a'), type: NounType.Document, data: 'a', vector: vec(100), metadata: {} }],
@@ -1181,12 +1195,14 @@ describe('8.0 Db API — generational MVCC', () => {
     const third = await brain.transact([{ op: 'update', id: uid('txlog-a'), metadata: { v: 3 } }])
 
     const entries = await brain.transactionLog()
-    // Newest first: the three transacts, then the single-op solo write (gen 1).
+    // Newest first: the three transacts, then the single-op solo write, then
+    // whatever the open baseline logged (the adopt-at-open backfill).
     expect(entries.map((entry) => entry.generation)).toEqual([
       third.generation,
       second.generation,
       first.generation,
-      soloGen
+      soloGen,
+      ...baseGens
     ])
     expect(entries[1].meta).toEqual({ author: 'job-2' })
     expect(entries[2].meta).toEqual({ author: 'job-1' })
@@ -1238,21 +1254,24 @@ describe('8.0 Db API — generational MVCC', () => {
     const brain = await openMemoryBrain()
     const a = uid('ov-a')
     const b = uid('ov-b')
-    await (
-      await brain.transact([
-        { op: 'add', id: a, type: NounType.Document, data: 'a', vector: vec(1), metadata: { v: 1 } },
-        { op: 'add', id: b, type: NounType.Document, data: 'b', vector: vec(2), metadata: { v: 1 } }
-      ])
-    ).release()
-    const at1 = await brain.asOf(1)
+    // Pin RELATIVELY at the transact's own generation (not an absolute 1 —
+    // the adopt-at-open baseline backfill owns the first generation).
+    const tx = await brain.transact([
+      { op: 'add', id: a, type: NounType.Document, data: 'a', vector: vec(1), metadata: { v: 1 } },
+      { op: 'add', id: b, type: NounType.Document, data: 'b', vector: vec(2), metadata: { v: 1 } }
+    ])
+    const txGen = tx.generation
+    await tx.release()
+    const at1 = await brain.asOf(txGen)
 
     // A single-op REMOVE of `b` lands AFTER the pin and is NOT flushed (pending).
     await brain.remove(b)
 
     const liveIds = (await brain.find({})).map((r) => r.id)
     const pastIds = (await at1.find({})).map((r) => r.id)
-    // Live: `b` is gone. Historical (pinned at gen 1): the un-flushed removal is
-    // overlaid out, so `b` is still present at its pinned state.
+    // Live: `b` is gone. Historical (pinned at the transact's generation): the
+    // un-flushed removal is overlaid out, so `b` is still present at its
+    // pinned state.
     expect(liveIds).toContain(a)
     expect(liveIds).not.toContain(b)
     expect(pastIds).toContain(a)
@@ -1262,11 +1281,14 @@ describe('8.0 Db API — generational MVCC', () => {
 
   it('Model-B retention — explicit caps reclaim single-op history; committed history survives reopen', async () => {
     const { brain, dir } = await openFsBrain()
+    // Relative baseline: the adopt-at-open backfill holds the first
+    // generation(s), so the 6 writes below land at base+1..base+6.
+    const base = brain.generation()
     const a = uid('ret-a')
     await brain.add({ id: a, type: NounType.Document, data: 'a', vector: vec(1), metadata: { v: 1 } })
     for (let v = 2; v <= 6; v++) await brain.update({ id: a, metadata: { v } })
     await brain.flush() // persist the per-write generations to disk
-    expect(brain.generation()).toBe(6)
+    expect(brain.generation()).toBe(base + 6)
 
     // Cap to the 2 most recent generations — older single-op history is reclaimed.
     const res = await brain.compactHistory({ maxGenerations: 2 })

tests/integration/db-temporal.test.ts

@@ -36,6 +36,9 @@ import { GenerationCompactedError } from '../../src/db/errors.js'
 import type { GenerationStore } from '../../src/db/generationStore.js'
 import { NounType } from '../../src/types/graphTypes.js'
 
+/** The VFS root — re-committed by the adopt-at-open baseline backfill. */
+const VFS_ROOT = '00000000-0000-0000-0000-000000000000'
+
 /** Deterministic 384-dim vector so no test ever invokes the embedder. */
 function vec(seed: number): number[] {
   return Array.from({ length: 384 }, (_, i) => ((seed * 31 + i * 7) % 100) / 100)
@@ -133,7 +136,11 @@ describe('8.0 Db API — temporal range verbs', () => {
     expect(viaDb).toEqual(viaGen)
     expect(viaDb.fromGeneration).toBe(g1)
     expect(viaDb.nouns).toEqual([a, b].sort()) // a (updated after g1) + b (added after g1)
-    expect(viaEpoch.nouns).toEqual([a, b].sort()) // (0, now] also includes a's creation, still {a, b}
+    // (0, now] also includes a's creation — still {a, b} among user rows. The
+    // adopt-at-open baseline backfill re-commits the VFS root as a real
+    // generation, so the full-epoch window legitimately reports it too;
+    // filter it to keep this pin about the user writes.
+    expect(viaEpoch.nouns.filter((n) => n !== VFS_ROOT)).toEqual([a, b].sort())
 
     // direction guard: an older view cannot be `since` a newer lower bound
     const older = await brain.asOf(1)
@@ -163,7 +170,11 @@ describe('8.0 Db API — temporal range verbs', () => {
     }
 
     const all = await brain.transactionLog()
-    expect(all.map((e) => e.generation)).toEqual([...gens].reverse()) // newest first
+    // Newest first — compared above the open baseline (the adopt-at-open
+    // backfill logs its own generation(s) below the first user write).
+    expect(all.map((e) => e.generation).filter((g) => g >= gens[0])).toEqual(
+      [...gens].reverse()
+    )
 
     // INCLUSIVE both ends — gens[1] AND gens[3] are present (contrast since's exclusive lower).
     const windowed = await brain.transactionLog({ from: gens[1], to: gens[3] })
@@ -334,19 +345,22 @@ describe('8.0 Db API — temporal range verbs', () => {
   // 7. Granularity (Model-B) ---------------------------------------------------
   it('granularity: single-operation writes ARE versioned and visible to the temporal verbs', async () => {
     const brain = await openMemoryBrain()
+    // Relative baseline: the adopt-at-open backfill already logged its own
+    // generation(s) — pin the DELTA this test's writes add, not a count.
+    const baseCount = (await brain.transactionLog()).length
     const a = uid('gran-a')
     const r1 = await brain.transact([
       { op: 'add', id: a, type: NounType.Document, data: 'a', vector: vec(1), metadata: { v: 1 } }
     ])
     await r1.release()
-    expect((await brain.transactionLog()).length).toBe(1)
+    expect((await brain.transactionLog()).length).toBe(baseCount + 1)
 
     // Model-B: a single-op write is its OWN immutable generation — logged,
     // diffable, and time-travelable, exactly like a transact() of one op.
     await brain.update({ id: a, metadata: { v: 2 } })
 
     // The single-op update appended a generation/log entry.
-    expect((await brain.transactionLog()).length).toBe(2)
+    expect((await brain.transactionLog()).length).toBe(baseCount + 2)
     expect(brain.generation()).toBe(r1.generation + 1)
 
     // diff sees the single-op update as a modification of `a`.

tests/integration/deferred-embedding.test.ts

@@ -0,0 +1,171 @@
+/**
+ * @module tests/integration/deferred-embedding
+ * @description MT5 — THE DEFERRED-EMBEDDING CONTRACT (A3 of the service-class
+ * pair, BRAINY-PROD-LATENCY-TRIAD). The production disease: a VFS file write
+ * ran a neural network synchronously while the caller waited (5.6s p50 per
+ * small file). The contract pinned here:
+ *
+ * 1. ACK AT DURABILITY: a deferred write never calls the embedder on the
+ *    caller's path — the row is id/metadata-findable immediately, with a
+ *    durable pending marker and an honest `pendingEmbeds` gauge.
+ * 2. EVENTUAL VECTOR INDEX: `awaitPendingEmbeds()` is the barrier — after
+ *    it, the vector is real, indexed, and the marker is reaped.
+ * 3. STALE-BEATS-ABSENT on deferred updates: the OLD vector keeps serving
+ *    until the atomic swap (the flicker law, never a dark window).
+ * 4. CRASH-SAFE: markers survive a session that dies mid-defer; the next
+ *    open recovers and lands the vector. A crash DELAYS a vector, never
+ *    loses one.
+ * 5. TYPED REFUSALS: deferEmbedding + vector, and deferEmbedding without
+ *    data, are caller bugs that refuse with the fix in the message.
+ */
+import { describe, it, expect, afterEach, vi } from 'vitest'
+import { mkdtempSync, rmSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { Brainy } from '../../src/index.js'
+import { NounType } from '../../src/types/graphTypes.js'
+
+const dirs: string[] = []
+const brains: Brainy[] = []
+
+async function memBrain(): Promise<Brainy> {
+  const b = new Brainy({ storage: { type: 'memory' }, requireSubtype: false })
+  await b.init()
+  brains.push(b)
+  return b
+}
+
+afterEach(async () => {
+  vi.restoreAllMocks()
+  for (const b of brains.splice(0)) await b.close().catch(() => {})
+  for (const d of dirs.splice(0)) rmSync(d, { recursive: true, force: true })
+})
+
+describe('MT5 — deferred embedding', () => {
+  it('ACK LAW: add({deferEmbedding}) never embeds on the caller path; row findable immediately; barrier lands the vector and reaps the marker', async () => {
+    const brain = await memBrain()
+    const embedSpy = vi.spyOn(brain, 'embed')
+
+    const id = await brain.add({
+      data: 'deferred content',
+      type: NounType.Document,
+      deferEmbedding: true,
+      metadata: { tag: 'deferred' }
+    })
+
+    // The caller's path never ran the embedder.
+    expect(embedSpy, 'no embed on the ack path').not.toHaveBeenCalled()
+
+    // Immediately findable by metadata; vector is the stub; gauge honest.
+    const found = await brain.find({ where: { tag: 'deferred' }, limit: 5 })
+    expect(found.map((r) => r.id)).toContain(id)
+    expect((await brain.getIndexStatus()).pendingEmbeds).toBeGreaterThanOrEqual(1)
+
+    // The barrier: vector lands, marker reaped, index carries the row.
+    await brain.awaitPendingEmbeds()
+    expect(embedSpy).toHaveBeenCalled()
+    const after = await brain.get(id, { includeVectors: true })
+    expect((after!.vector as number[]).length, 'real vector after the barrier').toBeGreaterThan(0)
+    expect(brain.pendingEmbedCount()).toBe(0)
+    expect((await brain.getIndexStatus()).pendingEmbeds).toBe(0)
+  })
+
+  it('STALE-BEATS-ABSENT: a deferred update serves the OLD vector until the atomic swap; data reads NEW immediately', async () => {
+    const brain = await memBrain()
+    const id = await brain.add({ data: 'original content', type: NounType.Document, metadata: {} })
+    const before = await brain.get(id, { includeVectors: true })
+    const oldVector = [...(before!.vector as number[])]
+    expect(oldVector.length).toBeGreaterThan(0)
+
+    await brain.update({ id, data: 'completely different content', deferEmbedding: true })
+
+    // Data is new IMMEDIATELY; the vector is still the old one (present,
+    // never absent) until the worker swaps it.
+    const mid = await brain.get(id, { includeVectors: true })
+    expect(mid!.data).toBe('completely different content')
+    expect(mid!.vector as number[], 'old vector keeps serving').toEqual(oldVector)
+
+    await brain.awaitPendingEmbeds()
+    const after = await brain.get(id, { includeVectors: true })
+    expect((after!.vector as number[]).length).toBeGreaterThan(0)
+    expect(after!.vector as number[], 'vector swapped after the barrier').not.toEqual(oldVector)
+  })
+
+  it('CRASH-SAFE: a session dying mid-defer leaves the durable marker; the next open recovers and lands the vector', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-defer-crash-'))
+    dirs.push(dir)
+
+    // Session 1: the embedder hangs → the worker can never complete; close()
+    // does not wait for it (crash-equivalent for the embed leg).
+    let brain = new Brainy({ storage: { type: 'filesystem', path: dir }, requireSubtype: false })
+    await brain.init()
+    brains.push(brain)
+    vi.spyOn(brain, 'embed').mockImplementation(() => new Promise(() => {}))
+    const id = await brain.add({
+      data: 'survives the crash',
+      type: NounType.Document,
+      deferEmbedding: true,
+      metadata: { k: 1 }
+    })
+    expect(brain.pendingEmbedCount()).toBe(1)
+    await brain.close()
+    brains.pop()
+    vi.restoreAllMocks()
+
+    // Session 2: recovery lists the marker and resumes in the background.
+    brain = new Brainy({ storage: { type: 'filesystem', path: dir }, requireSubtype: false })
+    await brain.init()
+    brains.push(brain)
+    expect(brain.pendingEmbedCount(), 'marker recovered at open').toBe(1)
+
+    await brain.awaitPendingEmbeds()
+    const after = await brain.get(id, { includeVectors: true })
+    expect((after!.vector as number[]).length, 'the delayed vector landed').toBeGreaterThan(0)
+    expect(brain.pendingEmbedCount()).toBe(0)
+  }, 120000)
+
+  it('VFS ACK LAW: writeFile resolves even when the embedder HANGS forever — the ack never depends on a neural net', async () => {
+    const brain = await memBrain()
+    // The strongest form of the pin: an embedder that never resolves. If any
+    // part of the writeFile ack path awaited an embed, this test would hang.
+    // (The background worker legitimately picks the deferred embeds up later
+    // — it may even interleave on the event loop during writeFile's other
+    // awaits — but the CALLER'S promise must never depend on it.)
+    const hang = vi
+      .spyOn(brain, 'embed')
+      .mockImplementation(() => new Promise<number[]>(() => {}))
+
+    await brain.vfs.writeFile('/notes/today.md', '# The day\nA deferred capture.')
+
+    // Acked with the embedder hung: content + metadata fully readable.
+    const content = await brain.vfs.readFile('/notes/today.md')
+    expect(content.toString()).toContain('A deferred capture.')
+    expect(brain.pendingEmbedCount()).toBeGreaterThanOrEqual(1)
+
+    // Un-hang, abandon the poisoned in-flight run (its embed promise never
+    // resolves — production is covered by the worker's 60s hang guard; the
+    // test takes the white-box shortcut for speed), drain, verify.
+    hang.mockRestore()
+    ;(brain as unknown as { _embedWorkerFlight: Promise<void> | null })._embedWorkerFlight = null
+    await brain.awaitPendingEmbeds()
+    expect(brain.pendingEmbedCount()).toBe(0)
+  })
+
+  it('TYPED REFUSALS: defer+vector and defer-without-data both refuse with the fix', async () => {
+    const brain = await memBrain()
+    await expect(
+      brain.add({
+        data: 'x',
+        vector: new Array(384).fill(0.1),
+        type: NounType.Document,
+        deferEmbedding: true,
+        metadata: {}
+      })
+    ).rejects.toThrow(/deferEmbedding cannot be combined/)
+
+    const id = await brain.add({ data: 'y', type: NounType.Document, metadata: {} })
+    await expect(
+      brain.update({ id, deferEmbedding: true, metadata: { z: 1 } })
+    ).rejects.toThrow(/requires new 'data'/)
+  })
+})

tests/integration/durability-kill-matrix.test.ts

@@ -0,0 +1,701 @@
+/**
+ * @module tests/integration/durability-kill-matrix
+ * @description THE DURABILITY KILL MATRIX — for every step of the commit
+ * path, inject a crash AT that step (the generation store's test-only fault
+ * injector), then reopen the same storage directory with a brand-new Brainy
+ * and assert the recovery contract BY CONSTRUCTION, not by timing:
+ *
+ *   - an ACKED write survives the crash (never a lost ack), and
+ *   - an UN-ACKED write leaves no torn state (fully present or fully absent,
+ *     never half).
+ *
+ * The crash simulation is honest process death: the crashed brain is NEVER
+ * closed — `abandonAsCrashed` discards its buffered RAM state exactly as a
+ * dead process would, and recovery on the next open is the only repair that
+ * runs. File bytes already handed to the OS survive (process-crash model);
+ * one row additionally models POWER LOSS by removing an entity's un-fsynced
+ * canonical files (legal: single-op canonical writes are tmp+rename without
+ * fsync).
+ *
+ * Matrix rows (fault point → durability barrier position):
+ *
+ *   BEFORE the barrier (nothing durable records the write):
+ *     singleop-after-execute · singleop-after-fact-append · flush-after-staging
+ *   AFTER partial durability (staged/synced bytes exist, manifest did not advance):
+ *     flush-before-manifest · before-manifest-rename (transact) ·
+ *     transact-after-fact-sync
+ *   AFTER the commit point:
+ *     after-manifest-rename (transact)
+ *   MODE VARIANTS: singleop-after-fact-append under durable-at-ack.
+ *   DISK FULL: one ENOSPC'd append — loud typed rejection, reads keep
+ *     serving, a later write succeeds.
+ *
+ * Where the observed recovery contract differs from the ideal, the pin states
+ * the OBSERVED behavior with a comment; where the observed behavior violates
+ * "never a torn state / never a lost ack", the pin asserts the CONTRACT and
+ * is marked `.fails` — a release-blocking finding, deliberately not weakened.
+ */
+import { describe, it, expect, afterEach } from 'vitest'
+import * as fs from 'node:fs'
+import { join } from 'node:path'
+import { Brainy } from '../../src/brainy.js'
+import { NounType } from '../../src/types/graphTypes.js'
+import {
+  abandonAsCrashed,
+  armCrash,
+  dropCanonicalNoun,
+  factGenerations,
+  failNextAppendWithEnospc,
+  generationDirExists,
+  makeTempDir,
+  openBrain,
+  storeOf,
+  uid,
+  vec
+} from '../helpers/durabilityKillMatrix.js'
+
+describe('durability kill matrix — crash at every commit-path step, recover by reopen', () => {
+  const dirs: string[] = []
+  const liveBrains: Brainy[] = []
+  // Crashed brains are deliberately NEVER closed (a dead process cannot
+  // close); they are severed by abandonAsCrashed inside each test.
+
+  function trackDir(): string {
+    const dir = makeTempDir()
+    dirs.push(dir)
+    return dir
+  }
+
+  async function openLive(dir: string): Promise<Brainy> {
+    const brain = await openBrain(dir)
+    liveBrains.push(brain)
+    return brain
+  }
+
+  afterEach(async () => {
+    for (const brain of liveBrains.splice(0)) {
+      try {
+        await brain.close()
+      } catch {
+        // already closed / crashed mid-close — teardown only
+      }
+    }
+    for (const dir of dirs.splice(0)) {
+      await fs.promises.rm(dir, { recursive: true, force: true })
+    }
+  })
+
+  /** Baseline arrangement: one durable row + explicit flush = the durable floor. */
+  async function arrangeBaseline(label: string): Promise<{
+    dir: string
+    brain: Brainy
+    baselineId: string
+    floor: number
+  }> {
+    const dir = trackDir()
+    const brain = await openBrain(dir) // NOT tracked live — most rows crash it
+    const baselineId = uid(`${label}-baseline`)
+    await brain.add({
+      id: baselineId,
+      data: 'baseline row',
+      type: NounType.Document,
+      vector: vec(1),
+      metadata: { v: 1 }
+    })
+    await brain.flush()
+    return { dir, brain, baselineId, floor: storeOf(brain).committedGeneration() }
+  }
+
+  /**
+   * Flip a brain to durable-at-ack (log-authority) mode.
+   *
+   * NOT via `adoptLogAuthority()` (and the helper opens every brain with
+   * `logAuthority: 'defer'`, opting out of the 10.0.0 adopt-at-open fleet
+   * default): the sanctioned path runs the oracle and a baseline backfill,
+   * which appends its own generation — shifting the floor arithmetic every
+   * row pins. This helper flips the SAME switch the sanctioned path flips
+   * (`setLogDurability('at-ack')`) and persists the SAME authority artifact,
+   * so a reopened brain also runs in log-authority mode. The durability
+   * semantics under test are governed entirely by that switch.
+   */
+  async function flipToAtAck(brain: Brainy): Promise<void> {
+    const storage = (
+      brain as unknown as {
+        storage: {
+          writeRawObject(p: string, d: unknown): Promise<void>
+          syncRawObjects(p: string[]): Promise<void>
+        }
+      }
+    ).storage
+    await storage.writeRawObject('_system/log-authority.json', {
+      authority: 'log',
+      flippedAt: Date.now()
+    })
+    await storage.syncRawObjects(['_system/log-authority.json'])
+    storeOf(brain).setLogDurability('at-ack')
+  }
+
+  // ==========================================================================
+  // Rows BEFORE the durability barrier — the write never became durable-acked
+  // ==========================================================================
+
+  it('singleop-after-execute — un-acked write is atomic (present-whole), baseline and log stay at the floor', async () => {
+    const { dir, brain, baselineId, floor } = await arrangeBaseline('sae')
+    const crashedId = uid('sae-crashed')
+    const arm = armCrash(brain, 'singleop-after-execute')
+    await expect(
+      brain.add({
+        id: crashedId,
+        data: 'never acked',
+        type: NounType.Document,
+        vector: vec(2),
+        metadata: { v: 2 }
+      })
+    ).rejects.toThrow('simulated process crash at singleop-after-execute')
+    expect(arm.fired).toContain('singleop-after-execute')
+    await abandonAsCrashed(brain)
+
+    const reopened = await openLive(dir)
+    // Baseline intact.
+    expect(((await reopened.get(baselineId)) as { metadata: { v: number } }).metadata.v).toBe(1)
+    // The log holds nothing beyond the committed watermark (no fact was ever
+    // appended for the crashed write).
+    expect(await factGenerations(reopened)).toEqual([floor])
+    expect(storeOf(reopened).committedGeneration()).toBe(floor)
+    // The un-acked write: Model-B applies the live canonical write BEFORE the
+    // ack, so under process death its bytes survive — the row is PRESENT and
+    // WHOLE by id (atomic, not torn). Under power loss the same un-fsynced
+    // bytes may instead vanish entirely; both end states are atomic. NOTE the
+    // divergence: the row is get()-visible but find()-invisible (no index
+    // entry survived, no generation/fact records it, and no repair is pending
+    // — a permanent canonical orphan; see the suite report).
+    const orphan = (await reopened.get(crashedId)) as { metadata: { v: number } } | null
+    expect(orphan).not.toBeNull()
+    expect(orphan!.metadata.v).toBe(2) // whole, byte-consistent — never torn
+    const found = (await reopened.find({ type: NounType.Document, limit: 10 })) as Array<{ id: string }>
+    expect(found.map((f) => f.id)).toContain(baselineId)
+    expect(found.map((f) => f.id)).not.toContain(crashedId)
+    // A fresh write succeeds with a monotonic generation. The crashed
+    // generation number is REUSED (nothing durable references it): the
+    // counter reopened at the floor.
+    expect(reopened.generation()).toBe(floor)
+    const freshId = uid('sae-fresh')
+    await reopened.add({
+      id: freshId,
+      data: 'fresh after recovery',
+      type: NounType.Document,
+      vector: vec(3),
+      metadata: { v: 3 }
+    })
+    await reopened.flush()
+    expect(storeOf(reopened).committedGeneration()).toBe(floor + 1)
+    expect(((await reopened.get(freshId)) as { metadata: { v: number } }).metadata.v).toBe(3)
+  })
+
+  it('singleop-after-fact-append (deferred mode) — the appended fact is truncated back at reopen', async () => {
+    const { dir, brain, baselineId, floor } = await arrangeBaseline('sfa')
+    const crashedId = uid('sfa-crashed')
+    const arm = armCrash(brain, 'singleop-after-fact-append')
+    await expect(
+      brain.add({
+        id: crashedId,
+        data: 'never acked',
+        type: NounType.Document,
+        vector: vec(2),
+        metadata: { v: 2 }
+      })
+    ).rejects.toThrow('simulated process crash at singleop-after-fact-append')
+    expect(arm.fired).toContain('singleop-after-fact-append')
+    await abandonAsCrashed(brain)
+
+    const reopened = await openLive(dir)
+    // The fact WAS appended to the log file before the crash (process death
+    // keeps file bytes) — open() must truncate it back to the manifest
+    // watermark, and does.
+    expect(await factGenerations(reopened)).toEqual([floor])
+    expect(storeOf(reopened).committedGeneration()).toBe(floor)
+    // Baseline intact; un-acked row atomic (present-whole via canonical, as
+    // in the singleop-after-execute row).
+    expect(((await reopened.get(baselineId)) as { metadata: { v: number } }).metadata.v).toBe(1)
+    const orphan = (await reopened.get(crashedId)) as { metadata: { v: number } } | null
+    expect(orphan).not.toBeNull()
+    expect(orphan!.metadata.v).toBe(2)
+    // Fresh write with a monotonic generation (crashed number reused — the
+    // truncated fact freed it).
+    expect(reopened.generation()).toBe(floor)
+    const freshId = uid('sfa-fresh')
+    await reopened.add({
+      id: freshId,
+      data: 'fresh',
+      type: NounType.Document,
+      vector: vec(3),
+      metadata: { v: 3 }
+    })
+    await reopened.flush()
+    expect(storeOf(reopened).committedGeneration()).toBe(floor + 1)
+    expect(await factGenerations(reopened)).toEqual([floor, floor + 1])
+  })
+
+  it('flush-after-staging — the ACKED write survives (drop-without-restore); only the window history is lost', async () => {
+    const { dir, brain, baselineId, floor } = await arrangeBaseline('fas')
+    const ackedId = uid('fas-acked')
+    await brain.add({
+      id: ackedId,
+      data: 'acked before flush',
+      type: NounType.Document,
+      vector: vec(2),
+      metadata: { v: 2 }
+    })
+    const ackedGen = storeOf(brain).generation()
+    const arm = armCrash(brain, 'flush-after-staging')
+    await expect(brain.flush()).rejects.toThrow('simulated process crash at flush-after-staging')
+    expect(arm.fired).toContain('flush-after-staging')
+    // The crashed flush left the staged record-set dir on disk, above the manifest.
+    expect(generationDirExists(dir, ackedGen)).toBe(true)
+    await abandonAsCrashed(brain)
+
+    const reopened = await openLive(dir)
+    // Recovery DROPPED the staged group-commit dir WITHOUT restoring its
+    // before-images — restoring would silently revert an acknowledged write.
+    expect(generationDirExists(dir, ackedGen)).toBe(false)
+    expect(storeOf(reopened).committedGeneration()).toBe(floor)
+    // NEVER A LOST ACK: the acknowledged write is present and whole.
+    const acked = (await reopened.get(ackedId)) as { metadata: { v: number } } | null
+    expect(acked).not.toBeNull()
+    expect(acked!.metadata.v).toBe(2)
+    expect(((await reopened.get(baselineId)) as { metadata: { v: number } }).metadata.v).toBe(1)
+    // Recovery rolled generations back → index reconciliation ran → the acked
+    // row is find()-visible too.
+    const found = (await reopened.find({ type: NounType.Document, limit: 10 })) as Array<{ id: string }>
+    expect(found.map((f) => f.id)).toEqual(expect.arrayContaining([baselineId, ackedId]))
+    // The window's HISTORY is the documented cost: its fact is truncated back
+    // (the acked row now lives only in canonical bytes, not the log).
+    expect(await factGenerations(reopened)).toEqual([floor])
+    // The crashed generation number is NOT reused (its dropped dir was seen
+    // at open): fresh writes continue above it.
+    expect(reopened.generation()).toBe(ackedGen)
+    const freshId = uid('fas-fresh')
+    await reopened.add({
+      id: freshId,
+      data: 'fresh',
+      type: NounType.Document,
+      vector: vec(3),
+      metadata: { v: 3 }
+    })
+    await reopened.flush()
+    expect(storeOf(reopened).committedGeneration()).toBe(ackedGen + 1)
+  })
+
+  // ==========================================================================
+  // Rows AFTER partial durability — staged/synced bytes exist, no manifest
+  // ==========================================================================
+
+  it('flush-before-manifest — staged bytes + synced facts above the manifest are dropped/truncated; the acked write stays', async () => {
+    const { dir, brain, baselineId, floor } = await arrangeBaseline('fbm')
+    const ackedId = uid('fbm-acked')
+    await brain.add({
+      id: ackedId,
+      data: 'acked before flush',
+      type: NounType.Document,
+      vector: vec(2),
+      metadata: { v: 2 }
+    })
+    const ackedGen = storeOf(brain).generation()
+    const arm = armCrash(brain, 'flush-before-manifest')
+    await expect(brain.flush()).rejects.toThrow('simulated process crash at flush-before-manifest')
+    // The earlier flush phase passed through untripped before the target fired.
+    expect(arm.fired).toContain('flush-after-staging')
+    expect(arm.fired).toContain('flush-before-manifest')
+    expect(generationDirExists(dir, ackedGen)).toBe(true)
+    await abandonAsCrashed(brain)
+
+    const reopened = await openLive(dir)
+    // Per the recovery contract in open(): groupCommit record-sets above the
+    // manifest are dropped WITHOUT restore, and the (fsynced!) facts above
+    // the manifest are truncated back. The acked live write stays.
+    expect(generationDirExists(dir, ackedGen)).toBe(false)
+    expect(storeOf(reopened).committedGeneration()).toBe(floor)
+    expect(await factGenerations(reopened)).toEqual([floor])
+    const acked = (await reopened.get(ackedId)) as { metadata: { v: number } } | null
+    expect(acked).not.toBeNull() // never a lost ack
+    expect(acked!.metadata.v).toBe(2)
+    expect(((await reopened.get(baselineId)) as { metadata: { v: number } }).metadata.v).toBe(1)
+    // Fresh write above the crashed generation (number not reused).
+    expect(reopened.generation()).toBe(ackedGen)
+    const freshId = uid('fbm-fresh')
+    await reopened.add({
+      id: freshId,
+      data: 'fresh',
+      type: NounType.Document,
+      vector: vec(3),
+      metadata: { v: 3 }
+    })
+    await reopened.flush()
+    expect(storeOf(reopened).committedGeneration()).toBe(ackedGen + 1)
+  })
+
+  it('before-manifest-rename (transact) — fully staged, never committed: rolled back byte-identically', async () => {
+    const { dir, brain, baselineId, floor } = await arrangeBaseline('bmr')
+    const newId = uid('bmr-new')
+    const arm = armCrash(brain, 'before-manifest-rename')
+    await expect(
+      brain.transact([
+        { op: 'update', id: baselineId, metadata: { v: 2 } },
+        {
+          op: 'add',
+          id: newId,
+          type: NounType.Document,
+          data: 'uncommitted',
+          vector: vec(2),
+          metadata: { v: 2 }
+        }
+      ])
+    ).rejects.toThrow('simulated process crash at before-manifest-rename')
+    expect(arm.fired).toContain('before-manifest-rename')
+    const txGen = storeOf(brain).generation()
+    expect(generationDirExists(dir, txGen)).toBe(true)
+    await abandonAsCrashed(brain)
+
+    const reopened = await openLive(dir)
+    // Rolled back cleanly: the update is undone, the add is ABSENT everywhere.
+    expect(((await reopened.get(baselineId)) as { metadata: { v: number } }).metadata.v).toBe(1)
+    expect(await reopened.get(newId)).toBeNull()
+    const found = (await reopened.find({ type: NounType.Document, limit: 10 })) as Array<{ id: string }>
+    expect(found.map((f) => f.id)).not.toContain(newId)
+    expect(generationDirExists(dir, txGen)).toBe(false)
+    expect(storeOf(reopened).committedGeneration()).toBe(floor)
+    expect(await factGenerations(reopened)).toEqual([floor])
+    // The crashed generation number is never reissued (counter persisted
+    // before the crash point).
+    expect(reopened.generation()).toBe(txGen)
+    const freshId = uid('bmr-fresh')
+    await reopened.add({
+      id: freshId,
+      data: 'fresh',
+      type: NounType.Document,
+      vector: vec(3),
+      metadata: { v: 3 }
+    })
+    await reopened.flush()
+    expect(storeOf(reopened).committedGeneration()).toBe(txGen + 1)
+  })
+
+  it('transact-after-fact-sync — the fsynced fact of an uncommitted transact is truncated back; rollback is clean', async () => {
+    const { dir, brain, baselineId, floor } = await arrangeBaseline('tfs')
+    const newId = uid('tfs-new')
+    const arm = armCrash(brain, 'transact-after-fact-sync')
+    await expect(
+      brain.transact([
+        { op: 'update', id: baselineId, metadata: { v: 2 } },
+        {
+          op: 'add',
+          id: newId,
+          type: NounType.Document,
+          data: 'uncommitted',
+          vector: vec(2),
+          metadata: { v: 2 }
+        }
+      ])
+    ).rejects.toThrow('simulated process crash at transact-after-fact-sync')
+    expect(arm.fired).toContain('transact-after-fact-sync')
+    const txGen = storeOf(brain).generation()
+    await abandonAsCrashed(brain)
+
+    const reopened = await openLive(dir)
+    // The batch's fact was appended AND fsynced before the crash — open()
+    // must truncate it back to the manifest watermark (the generation never
+    // committed), and the before-images must restore byte-identically.
+    expect(await factGenerations(reopened)).toEqual([floor])
+    expect(((await reopened.get(baselineId)) as { metadata: { v: number } }).metadata.v).toBe(1)
+    expect(await reopened.get(newId)).toBeNull()
+    expect(storeOf(reopened).committedGeneration()).toBe(floor)
+    expect(generationDirExists(dir, txGen)).toBe(false)
+    // Counter: the staged dir was seen at open, so the number is not reused.
+    expect(reopened.generation()).toBe(txGen)
+    const freshId = uid('tfs-fresh')
+    await reopened.add({
+      id: freshId,
+      data: 'fresh',
+      type: NounType.Document,
+      vector: vec(3),
+      metadata: { v: 3 }
+    })
+    await reopened.flush()
+    expect(storeOf(reopened).committedGeneration()).toBe(txGen + 1)
+  })
+
+  // ==========================================================================
+  // Row AFTER the commit point — the transaction must be kept
+  // ==========================================================================
+
+  it('after-manifest-rename (transact) — the manifest rename landed: the transaction is COMMITTED and fully present', async () => {
+    const { dir, brain, baselineId, floor } = await arrangeBaseline('amr')
+    const newId = uid('amr-new')
+    const arm = armCrash(brain, 'after-manifest-rename')
+    await expect(
+      brain.transact([
+        { op: 'update', id: baselineId, metadata: { v: 2 } },
+        {
+          op: 'add',
+          id: newId,
+          type: NounType.Document,
+          data: 'committed by the rename',
+          vector: vec(2),
+          metadata: { v: 2 }
+        }
+      ])
+    ).rejects.toThrow('simulated process crash at after-manifest-rename')
+    expect(arm.fired).toContain('after-manifest-rename')
+    const txGen = storeOf(brain).generation()
+    await abandonAsCrashed(brain)
+
+    const reopened = await openLive(dir)
+    // COMMITTED: both operations present, atomically.
+    expect(((await reopened.get(baselineId)) as { metadata: { v: number } }).metadata.v).toBe(2)
+    const added = (await reopened.get(newId)) as { metadata: { v: number } } | null
+    expect(added).not.toBeNull()
+    expect(added!.metadata.v).toBe(2)
+    expect(storeOf(reopened).committedGeneration()).toBe(txGen)
+    // The fact was synced before the commit point and sits at/below the
+    // manifest — it is KEPT.
+    expect(await factGenerations(reopened)).toEqual([floor, txGen])
+    // Fresh writes continue above the committed generation.
+    const freshId = uid('amr-fresh')
+    await reopened.add({
+      id: freshId,
+      data: 'fresh',
+      type: NounType.Document,
+      vector: vec(3),
+      metadata: { v: 3 }
+    })
+    await reopened.flush()
+    expect(storeOf(reopened).committedGeneration()).toBe(txGen + 1)
+  })
+
+  // ==========================================================================
+  // Durable-at-ack (log-authority) mode variants
+  // ==========================================================================
+
+  it('singleop-after-fact-append (at-ack mode) — the intact fact is REPLAYED at reopen; the write commits', async () => {
+    const { dir, brain, baselineId, floor } = await arrangeBaseline('aaf')
+    await flipToAtAck(brain)
+    const crashedId = uid('aaf-crashed')
+    const arm = armCrash(brain, 'singleop-after-fact-append')
+    await expect(
+      brain.add({
+        id: crashedId,
+        data: 'fact fsynced, never acked',
+        type: NounType.Document,
+        vector: vec(2),
+        metadata: { v: 2 }
+      })
+    ).rejects.toThrow('simulated process crash at singleop-after-fact-append')
+    expect(arm.fired).toContain('singleop-after-fact-append')
+    await abandonAsCrashed(brain)
+
+    const reopened = await openLive(dir)
+    // LOG-AUTHORITY RECOVERY CONTRACT: under 'log' authority, an intact
+    // fact above the manifest is adopted at open — REPLAYED into canonical
+    // and committed — never truncated. (At-least-once at the fact layer: a
+    // crashed-pre-ack write whose fact survived intact becomes committed;
+    // that is a valid write landing, never a torn or lost state.)
+    expect(await factGenerations(reopened)).toEqual([floor, floor + 1])
+    expect(storeOf(reopened).committedGeneration()).toBe(floor + 1)
+    expect(((await reopened.get(baselineId)) as { metadata: { v: number } }).metadata.v).toBe(1)
+    const replayed = (await reopened.get(crashedId)) as { metadata: { v: number } } | null
+    expect(replayed).not.toBeNull()
+    expect(replayed!.metadata.v).toBe(2)
+    // Fresh write lands monotonically ABOVE the replayed generation.
+    const freshId = uid('aaf-fresh')
+    await reopened.add({
+      id: freshId,
+      data: 'fresh',
+      type: NounType.Document,
+      vector: vec(3),
+      metadata: { v: 3 }
+    })
+    await reopened.flush()
+    expect(storeOf(reopened).committedGeneration()).toBe(floor + 2)
+  })
+
+  // THE AT-ACK CONTRACT, END TO END (was a release-blocking finding; fixed
+  // by log-authority replay-at-open): under power loss the un-fsynced
+  // tmp+rename canonical bytes legally vanish while the fsynced fact
+  // survives — recovery REPLAYS that fact into canonical, so the acked
+  // write lives. This is the sentence 'durable-at-ack' actually promises.
+  it(
+    'at-ack POWER LOSS — an ACKED write whose fact is fsynced SURVIVES reopen via log replay',
+    async () => {
+      const { dir, brain, baselineId } = await arrangeBaseline('apl')
+      await flipToAtAck(brain)
+      const ackedId = uid('apl-acked')
+      // No fault injector: this write ACKS normally — in at-ack mode the ack
+      // returned only after a covering log fsync.
+      await brain.add({
+        id: ackedId,
+        data: 'acked, fact fsynced',
+        type: NounType.Document,
+        vector: vec(2),
+        metadata: { v: 2 }
+      })
+      // Crash before any flush: RAM is gone…
+      await abandonAsCrashed(brain)
+      // …and power loss takes the un-fsynced canonical rename with it. The
+      // fsynced fact log survives — it is the write's only durable copy.
+      dropCanonicalNoun(dir, ackedId)
+
+      const reopened = await openLive(dir)
+      expect(((await reopened.get(baselineId)) as { metadata: { v: number } }).metadata.v).toBe(1)
+      // THE AT-ACK CONTRACT: the acknowledged write survives the crash.
+      // Observed today: open() truncates its fact back to the manifest
+      // watermark and the write is gone everywhere.
+      const acked = (await reopened.get(ackedId)) as { metadata: { v: number } } | null
+      expect(acked).not.toBeNull()
+      expect(acked!.metadata.v).toBe(2)
+    }
+  )
+
+  // ==========================================================================
+  // Disk full — one ENOSPC'd append
+  // ==========================================================================
+
+  it('disk full — an ENOSPC append rejects loudly and typed; reads keep serving; a later write succeeds', async () => {
+    const { dir, brain, baselineId, floor } = await arrangeBaseline('nospc')
+    liveBrains.push(brain) // this row never crashes the brain
+    void dir
+    const failedId = uid('nospc-failed')
+    const probe = failNextAppendWithEnospc(brain)
+    // LOUD, TYPED, never a silent success: the raw ENOSPC surfaces to the
+    // caller with its errno code intact.
+    await expect(
+      brain.add({
+        id: failedId,
+        data: 'no space',
+        type: NounType.Document,
+        vector: vec(2),
+        metadata: { v: 2 }
+      })
+    ).rejects.toMatchObject({ code: 'ENOSPC' })
+    expect(probe.failed()).toBe(1)
+    // The store still serves reads.
+    expect(((await brain.get(baselineId)) as { metadata: { v: number } }).metadata.v).toBe(1)
+    // Space "restored" (the failing patch self-cleared): a later write succeeds
+    // end to end, including its fact and an explicit durability barrier.
+    const laterId = uid('nospc-later')
+    await brain.add({
+      id: laterId,
+      data: 'space restored',
+      type: NounType.Document,
+      vector: vec(3),
+      metadata: { v: 3 }
+    })
+    await brain.flush()
+    expect(((await brain.get(laterId)) as { metadata: { v: number } }).metadata.v).toBe(3)
+    expect(storeOf(brain).committedGeneration()).toBeGreaterThan(floor)
+    // FIXED BEHAVIOR (was: the rejected generation stayed buffered and the
+    // next flush committed it with NO fact — a silent log gap): the failure
+    // path un-buffers the generation and returns the counter reservation,
+    // so the later write takes floor+1 and the log is gap-free.
+    expect(storeOf(brain).committedGeneration()).toBe(floor + 1)
+    expect(await factGenerations(brain)).toEqual([floor, floor + 1])
+    // Canonical residue of the rejected write (execute ran before the
+    // append failed) is the documented Model-B crash-equivalent orphan —
+    // uncommitted, absent from the log, same shape as a crash at execute.
+    expect(((await brain.get(failedId)) as { metadata: { v: number } } | null)?.metadata.v).toBe(2)
+  })
+
+  // THE NO-SILENT-COMMIT CONTRACT (was a release-blocking finding; fixed by
+  // un-buffering on append failure): a loudly-rejected write never becomes
+  // durably committed and the log never carries a gap. Canonical residue
+  // (the execute-before-commit orphan) is the documented Model-B
+  // crash-equivalent, pinned in the row above — NOT a commit.
+  it('disk full — a write rejected for a failed fact append is NOT silently committed', async () => {
+    const { brain, floor } = await arrangeBaseline('nogap')
+    liveBrains.push(brain)
+    const failedId = uid('nogap-failed')
+    failNextAppendWithEnospc(brain)
+    await expect(
+      brain.add({
+        id: failedId,
+        data: 'no space',
+        type: NounType.Document,
+        vector: vec(2),
+        metadata: { v: 2 }
+      })
+    ).rejects.toMatchObject({ code: 'ENOSPC' })
+    await brain.flush()
+    // THE CONTRACT: nothing was committed behind the caller's back — the
+    // log carries no gap and no generation for the rejected write. (get()
+    // still serves the canonical execute-residue orphan — the documented
+    // Model-B crash-equivalent, pinned in the row above.)
+    expect(storeOf(brain).committedGeneration()).toBe(floor)
+    expect(await factGenerations(brain)).toEqual([floor])
+  })
+
+  // ==========================================================================
+  // Block-layer power-loss findings (first dm-flakey run) — the three cures
+  // ==========================================================================
+
+  it('at-ack POWER LOSS BELOW THE MANIFEST — an unclean open folds the WHOLE log; acked writes committed before the flush still survive vanished canonical', async () => {
+    const { dir, brain, baselineId } = await arrangeBaseline('wlf')
+    await flipToAtAck(brain)
+    const ackedA = uid('wlf-a')
+    const ackedB = uid('wlf-b')
+    await brain.add({ id: ackedA, data: 'below manifest one', type: NounType.Document, vector: vec(2), metadata: { v: 2 } })
+    await brain.add({ id: ackedB, data: 'below manifest two', type: NounType.Document, vector: vec(3), metadata: { v: 3 } })
+    // The group-commit flush advances the manifest OVER these generations —
+    // but live canonical bytes are tmp+rename without per-file fsync, so a
+    // power cut can still take them. The fsynced facts are the durable copy.
+    await (brain as unknown as { flush(): Promise<void> }).flush()
+    await abandonAsCrashed(brain) // no clean close → no clean-shutdown marker
+    dropCanonicalNoun(dir, ackedA)
+    dropCanonicalNoun(dir, ackedB)
+
+    const reopened = await openLive(dir)
+    // The whole-log fold restores BOTH rows from facts ≤ manifest.
+    expect(((await reopened.get(ackedA)) as { metadata: { v: number } }).metadata.v).toBe(2)
+    expect(((await reopened.get(ackedB)) as { metadata: { v: number } }).metadata.v).toBe(3)
+    expect(((await reopened.get(baselineId)) as { metadata: { v: number } }).metadata.v).toBe(1)
+  })
+
+  it('clean-shutdown marker: a clean close writes it, the next open consumes it (no fold on the happy path)', async () => {
+    const { dir, brain } = await arrangeBaseline('csm')
+    await flipToAtAck(brain)
+    await brain.close()
+    liveBrains.splice(liveBrains.indexOf(brain), 1)
+    // The adapter stores raw objects gzipped — accept either spelling.
+    const markerExists = () =>
+      fs.existsSync(join(dir, '_system', 'clean-shutdown.json')) ||
+      fs.existsSync(join(dir, '_system', 'clean-shutdown.json.gz'))
+    expect(markerExists(), 'clean close stamps the marker').toBe(true)
+
+    const reopened = await openLive(dir)
+    expect(markerExists(), 'open consumes the marker').toBe(false)
+    await reopened.close()
+    liveBrains.splice(liveBrains.indexOf(reopened), 1)
+    expect(markerExists(), 'the next clean close re-stamps it').toBe(true)
+  })
+
+  it('torn writer lock (empty file) — open treats it as stale and recovers; never a permanent lockout', async () => {
+    const { dir, brain } = await arrangeBaseline('tlk')
+    await brain.close()
+    liveBrains.splice(liveBrains.indexOf(brain), 1)
+    // The power-loss shape: the lock file exists but is EMPTY (torn write).
+    fs.writeFileSync(join(dir, 'locks', '_writer.lock'), '')
+
+    const reopened = await openLive(dir) // must not throw 'contended'
+    const fresh = uid('tlk-fresh')
+    await reopened.add({ id: fresh, data: 'lock recovered', type: NounType.Document, vector: vec(4), metadata: { v: 4 } })
+    expect(await reopened.get(fresh)).not.toBeNull()
+  })
+
+  it('pair guard: a metadata index without stampWatermark never crashes flush', async () => {
+    const { brain } = await arrangeBaseline('psg')
+    liveBrains.push(brain)
+    // The native pair swaps the metadata manager; the replacement may not
+    // carry the stamp method — flush must treat that as verdict-side rescan,
+    // never a TypeError at the fan-out.
+    ;(brain as unknown as { metadataIndex: { stampWatermark?: unknown } }).metadataIndex.stampWatermark = undefined
+    await expect((brain as unknown as { flush(): Promise<void> }).flush()).resolves.toBeUndefined()
+  })
+})

tests/integration/embed-markers-in-log.test.ts

@@ -0,0 +1,320 @@
+/**
+ * @module tests/integration/embed-markers-in-log
+ * @description DEFERRED-EMBED MARKERS ARE LOG RECORDS — the sidecar is dead.
+ * The pending-embed lifecycle lives IN the generation log as first-class v2
+ * records: `embed.pending` rides the deferred write's OWN commit fact (same
+ * generation, one atomic append — a marker can never be orphaned from its
+ * write nor the write from its marker) and `embed.landed` rides the
+ * background worker's landing commit. Recovery is REPLAY, NOT LISTING: the
+ * open-time fold arms every pending without a matching landed (minus rows
+ * the log later tombstoned). The pins:
+ *
+ * (a) SAME-FACT ATOMICITY: a deferred add's commit fact carries the
+ *     embed.pending record BESIDE its noun after-image — one generation,
+ *     one frame — and no sidecar file is ever written.
+ * (b) LANDING: after the barrier, the log carries embed.landed (inline
+ *     vector, per the v2 format) riding the landing commit's own fact, and
+ *     a fresh fold of the whole log nets ZERO pending.
+ * (c) CRASH RECOVERY VIA THE LOG: kill mid-defer (hung embedder, flushed
+ *     durability, crash-style abandon), reopen — the fold re-arms exactly
+ *     one pending with NO sidecar file existing anywhere, and the vector
+ *     then lands.
+ * (d) LEGACY BRIDGE: a sidecar marker file left by a pre-log build is
+ *     folded in at open, migrated into the log as an embed.pending record,
+ *     and the file is deleted — one-time, durable, idempotent.
+ * (e) VFS ACK LAW (unchanged contract, new mechanism): writeFile acks
+ *     under a forever-hung embedder while its pending marker sits durably
+ *     in the log.
+ */
+import { describe, it, expect, afterEach, vi } from 'vitest'
+import * as fs from 'node:fs'
+import * as path from 'node:path'
+import * as zlib from 'node:zlib'
+import { Brainy } from '../../src/brainy.js'
+import { NounType } from '../../src/types/graphTypes.js'
+import type { CommitFact } from '../../src/db/factLog.js'
+import {
+  makeTempDir,
+  openBrain,
+  abandonAsCrashed,
+  vec,
+  uid
+} from '../helpers/durabilityKillMatrix.js'
+
+/** The retired sidecar prefix — asserted ABSENT (or bridged away) on disk. */
+const SIDECAR_DIR = ['_system', 'pending_embeds'] as const
+
+const sidecarDir = (dir: string): string => path.join(dir, ...SIDECAR_DIR)
+
+/** Every committed fact in the brain's log, generation-ascending. */
+async function allFacts(brain: Brainy): Promise<CommitFact[]> {
+  const scan = (
+    brain as unknown as {
+      scanFacts(o?: { fromGeneration?: number }): {
+        batches(): AsyncGenerator<{ facts: CommitFact[] }>
+      } | null
+    }
+  ).scanFacts({ fromGeneration: 1 })
+  expect(scan, 'filesystem storage hosts a fact log').not.toBeNull()
+  const facts: CommitFact[] = []
+  for await (const batch of scan!.batches()) facts.push(...batch.facts)
+  return facts
+}
+
+/** The recovery fold, reimplemented independently: pending arms, landed
+ *  disarms, a noun tombstone disarms (a deleted row owes no vector). */
+function foldPending(facts: CommitFact[]): Set<string> {
+  const pending = new Set<string>()
+  for (const fact of facts) {
+    for (const record of fact.records ?? []) {
+      if (record.type === 'embed.pending') pending.add(record.id)
+      else if (record.type === 'embed.landed') pending.delete(record.id)
+    }
+    for (const op of fact.ops) {
+      if (op.kind === 'noun' && op.record === null) pending.delete(op.id)
+    }
+  }
+  return pending
+}
+
+/** Hang the embedder forever (the ack-law adversary). */
+function hangEmbedder(brain: Brainy): ReturnType<typeof vi.spyOn> {
+  return vi
+    .spyOn(brain as unknown as { embed(d: unknown): Promise<number[]> }, 'embed')
+    .mockImplementation(() => new Promise<number[]>(() => {}))
+}
+
+/** Abandon a hung worker pass (its embed promise never resolves; production
+ *  is covered by the worker's 60s hang guard — the test takes the white-box
+ *  shortcut for speed, same idiom as the deferred-embedding suite). */
+function abandonHungWorker(brain: Brainy): void {
+  ;(brain as unknown as { _embedWorkerFlight: Promise<void> | null })._embedWorkerFlight = null
+}
+
+describe('deferred-embed markers in the log — the sidecar is dead', () => {
+  const dirs: string[] = []
+  const brains: Brainy[] = []
+
+  const trackDir = (): string => {
+    const dir = makeTempDir()
+    dirs.push(dir)
+    return dir
+  }
+  const track = (brain: Brainy): Brainy => {
+    brains.push(brain)
+    return brain
+  }
+
+  afterEach(async () => {
+    vi.restoreAllMocks()
+    for (const b of brains.splice(0)) {
+      abandonHungWorker(b)
+      await b.close().catch(() => {})
+    }
+    for (const d of dirs.splice(0)) fs.rmSync(d, { recursive: true, force: true })
+  })
+
+  it('(a) SAME-FACT ATOMICITY: the deferred add\'s ONE commit fact carries embed.pending beside its after-image; no sidecar file exists', async () => {
+    const dir = trackDir()
+    const brain = track(await openBrain(dir))
+    hangEmbedder(brain) // hold the pending state open for the scan
+
+    const id = await brain.add({
+      data: 'deferred content whose marker rides the fact',
+      type: NounType.Document,
+      deferEmbedding: true,
+      metadata: { pin: 'a' }
+    })
+    expect(brain.pendingEmbedCount()).toBe(1)
+
+    const facts = await allFacts(brain)
+    const carrying = facts.filter((f) =>
+      (f.records ?? []).some((r) => r.type === 'embed.pending' && r.id === id)
+    )
+    expect(carrying, 'exactly ONE fact carries the pending marker').toHaveLength(1)
+    const fact = carrying[0]
+    // The SAME fact (same generation, one atomic append) carries the write's
+    // own after-image — marker and write are inseparable by construction.
+    const afterImage = fact.ops.find((op) => op.kind === 'noun' && op.id === id)
+    expect(afterImage, 'the marker rides the write\'s own fact').toBeDefined()
+    expect(afterImage!.record, 'an after-image, not a tombstone').not.toBeNull()
+    const marker = (fact.records ?? []).find((r) => r.type === 'embed.pending' && r.id === id)
+    expect(marker && marker.type === 'embed.pending' && marker.enqueuedAt).toBeGreaterThan(0)
+
+    // The sidecar is dead: nothing under the retired prefix, ever.
+    expect(fs.existsSync(sidecarDir(dir)), 'no sidecar directory is created').toBe(false)
+  })
+
+  it('(b) LANDING: after the barrier the log carries embed.landed (inline vector) on the landing commit\'s own fact, and a fresh fold nets zero pending', async () => {
+    const dir = trackDir()
+    const brain = track(await openBrain(dir))
+
+    const id = await brain.add({
+      data: 'content that lands in the background',
+      type: NounType.Document,
+      deferEmbedding: true,
+      metadata: { pin: 'b' }
+    })
+    await brain.awaitPendingEmbeds()
+    expect(brain.pendingEmbedCount()).toBe(0)
+
+    const facts = await allFacts(brain)
+    const landingFacts = facts.filter((f) =>
+      (f.records ?? []).some((r) => r.type === 'embed.landed' && r.id === id)
+    )
+    expect(landingFacts, 'exactly ONE landing fact').toHaveLength(1)
+    const landed = (landingFacts[0].records ?? []).find(
+      (r) => r.type === 'embed.landed' && r.id === id
+    )
+    expect(landed && landed.type === 'embed.landed' && landed.vector.length).toBeGreaterThan(0)
+    // The landing commit's own after-image rides the same fact — the worker's
+    // vector swap and its durable "pending consumed" are one atomic append.
+    const landingAfterImage = landingFacts[0].ops.find((op) => op.kind === 'noun' && op.id === id)
+    expect(landingAfterImage, 'the landed marker rides the swap\'s own fact').toBeDefined()
+    expect(landingAfterImage!.record).not.toBeNull()
+
+    // A fresh fold of the WHOLE log — the exact recovery computation — nets zero.
+    expect(foldPending(facts).size).toBe(0)
+    expect(fs.existsSync(sidecarDir(dir))).toBe(false)
+  })
+
+  it('(c) CRASH RECOVERY VIA THE LOG: kill mid-defer, reopen — one pending re-armed from the fold, NO sidecar file anywhere, and the vector then lands', async () => {
+    const dir = trackDir()
+
+    // Session 1: embedder hung, deferred add acked, durability flushed, then
+    // a crash-style abandon (RAM gone, no close, no background machinery).
+    const first = await openBrain(dir)
+    brains.push(first)
+    hangEmbedder(first)
+    const id = await first.add({
+      data: 'survives the kill through the log',
+      type: NounType.Document,
+      deferEmbedding: true,
+      metadata: { pin: 'c' }
+    })
+    expect(first.pendingEmbedCount()).toBe(1)
+    await first.flush() // the durability barrier: fact (with marker) + manifest
+    expect(fs.existsSync(sidecarDir(dir)), 'no sidecar before the kill').toBe(false)
+    await abandonAsCrashed(first)
+    brains.splice(brains.indexOf(first), 1)
+    vi.restoreAllMocks()
+
+    // Session 2: recovery folds the log — embedder hung BEFORE init so the
+    // re-armed pending is observable, not raced away by the fast worker.
+    const second = new Brainy({
+      requireSubtype: false,
+      storage: { type: 'filesystem', path: dir },
+      silent: true,
+      persistence: { policy: 'manual' }
+    })
+    const hang = hangEmbedder(second)
+    await second.init()
+    track(second)
+    expect(second.pendingEmbedCount(), 'the fold re-armed the pending').toBe(1)
+    expect(fs.existsSync(sidecarDir(dir)), 'recovery used the LOG, not files').toBe(false)
+
+    // Un-hang and drain: a crash DELAYED the vector, never lost it.
+    hang.mockRestore()
+    abandonHungWorker(second)
+    await second.awaitPendingEmbeds()
+    expect(second.pendingEmbedCount()).toBe(0)
+    const after = await second.get(id, { includeVectors: true })
+    expect(after, 'the deferred row survived the crash').toBeTruthy()
+    expect((after!.vector as number[]).length, 'the delayed vector landed').toBeGreaterThan(0)
+    expect(foldPending(await allFacts(second)).size, 'the landing is durable in the log').toBe(0)
+  })
+
+  it('(d) LEGACY BRIDGE: a pre-log sidecar marker folds in at open, migrates into the log, and the file dies — one-time and durable', async () => {
+    const dir = trackDir()
+
+    // Session 1: a normal committed row (the entity the legacy marker names).
+    const first = await openBrain(dir)
+    brains.push(first)
+    const id = uid('legacy-defer')
+    await first.add({
+      id,
+      data: 'legacy deferred content',
+      type: NounType.Document,
+      vector: vec(9),
+      metadata: { pin: 'd' }
+    })
+    await first.flush()
+    await first.close()
+    brains.splice(brains.indexOf(first), 1)
+
+    // A pre-log build's sidecar marker, hand-written exactly as the old
+    // writeRawObject persisted it (the filesystem adapter compresses raw
+    // objects by default: gzipped JSON at `<path>.gz`).
+    fs.mkdirSync(sidecarDir(dir), { recursive: true })
+    const sidecarFile = path.join(sidecarDir(dir), id)
+    fs.writeFileSync(
+      `${sidecarFile}.gz`,
+      zlib.gzipSync(JSON.stringify({ id, enqueuedAt: 1234567890 }, null, 2))
+    )
+
+    // Session 2: the bridge fires at open. Embedder hung BEFORE init so the
+    // folded pending is observable.
+    const second = new Brainy({
+      requireSubtype: false,
+      storage: { type: 'filesystem', path: dir },
+      silent: true,
+      persistence: { policy: 'manual' }
+    })
+    const hang = hangEmbedder(second)
+    await second.init()
+    track(second)
+    expect(second.pendingEmbedCount(), 'the legacy marker folded in').toBe(1)
+    expect(fs.existsSync(sidecarFile), 'the sidecar file was deleted').toBe(false)
+    expect(fs.existsSync(`${sidecarFile}.gz`), 'the compressed variant too').toBe(false)
+    const migrated = await allFacts(second)
+    expect(
+      migrated.some((f) => (f.records ?? []).some((r) => r.type === 'embed.pending' && r.id === id)),
+      'the marker now lives IN the log'
+    ).toBe(true)
+
+    // Drain: the bridged pending embeds and lands like any other.
+    hang.mockRestore()
+    abandonHungWorker(second)
+    await second.awaitPendingEmbeds()
+    expect(second.pendingEmbedCount()).toBe(0)
+    const facts = await allFacts(second)
+    expect(
+      facts.some((f) => (f.records ?? []).some((r) => r.type === 'embed.landed' && r.id === id)),
+      'the bridged pending landed durably'
+    ).toBe(true)
+    expect(foldPending(facts).size).toBe(0)
+    await second.flush()
+    await second.close()
+    brains.splice(brains.indexOf(second), 1)
+
+    // Session 3: nothing resurrects — the bridge was one-time, the clear durable.
+    const third = track(await openBrain(dir))
+    expect(third.pendingEmbedCount(), 'no zombie pending on the next open').toBe(0)
+    expect(fs.existsSync(sidecarDir(dir)) && fs.readdirSync(sidecarDir(dir)).length > 0).toBe(false)
+  })
+
+  it('(e) VFS ACK LAW: writeFile acks under a forever-hung embedder while its pending marker sits durably in the log', async () => {
+    const dir = trackDir()
+    const brain = track(await openBrain(dir))
+    const hang = hangEmbedder(brain)
+
+    await brain.vfs.writeFile('/notes/today.md', '# The day\nA deferred capture.')
+
+    // Acked with the embedder hung: content + metadata fully readable.
+    const content = await brain.vfs.readFile('/notes/today.md')
+    expect(content.toString()).toContain('A deferred capture.')
+    expect(brain.pendingEmbedCount()).toBeGreaterThanOrEqual(1)
+
+    // The marker is already durable IN the log while the embedder hangs —
+    // the exact state a crash here would recover from.
+    expect(foldPending(await allFacts(brain)).size).toBeGreaterThanOrEqual(1)
+    expect(fs.existsSync(sidecarDir(dir))).toBe(false)
+
+    // Un-hang, abandon the poisoned pass, drain, verify.
+    hang.mockRestore()
+    abandonHungWorker(brain)
+    await brain.awaitPendingEmbeds()
+    expect(brain.pendingEmbedCount()).toBe(0)
+    expect(foldPending(await allFacts(brain)).size).toBe(0)
+  })
+})

tests/integration/fact-log-contracts.test.ts

@@ -4,14 +4,13 @@
  *
  * (1) FSYNC-BEFORE-ACK: an acknowledged write's fact survives an abrupt
  *     process end (no flush, no close — reopen from disk).
- *     - transact(): HOLDS TODAY — the fact is fsync'd before transact returns.
- *     - single-op: PINNED AS `it.fails` — today's group-commit batches
- *       DURABILITY (ack precedes the group fsync; a hard kill loses the fact
- *       AND the generation together, coherently — the documented Model-B
- *       contract, fine while the tree is authoritative). The destination
- *       (ack-at-log) requires group commit to become LATENCY batching: the
- *       ack waits for the shared fsync. When that lands, this pin flips red —
- *       remove `.fails` and the contract is permanent. No cliff to discover.
+ *     - transact(): HOLDS — the fact is fsync'd before transact returns.
+ *     - single-op: HOLDS (was pinned `it.fails` until the ack-at-log
+ *       destination landed): the 10.0.0 adopt-at-open fleet default flips a
+ *       fresh brain to log authority at open, so single-op acks await the
+ *       covering group fsync (durable-at-ack) and recovery REPLAYS intact
+ *       facts above the manifest at the next open. The contract is now
+ *       permanent on every path.
  *
  * (2) SCAN STABILITY UNDER ROTATION: a scan handle opened before segment
  *     rotation yields exactly its snapshot — byte-identical facts, no gaps,
@@ -63,9 +62,11 @@ describe('fsync-before-ack contract (fact durability at the ack boundary)', () =
     expect(facts.some((f) => f.generation === receipt.generation)).toBe(true)
   })
 
-  // PINNED (flips red when group commit becomes latency batching — then
-  // remove `.fails` and the ack-at-log contract is permanent on every path).
-  it.fails('single-op: the fact is durable the moment the ack returns (the ack-at-log target)', async () => {
+  // THE ACK-AT-LOG CONTRACT, HELD (was `.fails` until it landed): under the
+  // adopt-at-open fleet default this brain runs durable-at-ack from open —
+  // the ack waits for the covering log fsync, and the log-authority recovery
+  // path replays the intact fact at the next open instead of truncating it.
+  it('single-op: the fact is durable the moment the ack returns (the ack-at-log target)', async () => {
     await brain.add({ data: 'acked single-op', type: 'document', metadata: { n: 1 } })
     const ackedHead = brain.scanFacts()!.headGeneration
     // Abrupt end immediately after the ack — before any flush window.

tests/integration/fact-log-v2-cutover.test.ts

@@ -0,0 +1,397 @@
+/**
+ * @module tests/integration/fact-log-v2-cutover
+ * @description The fact log's LIVE WRITE FORMAT cutover to v2, end-to-end
+ * through real brains: (a) a NEW brain's tail segment carries a v2 header
+ * (formatVersion 2, sealSize 4096), opens with the log.genesis record
+ * (id-space width 64 + the manifest-persisted brainId), and scanFacts yields
+ * the same CommitFact shape a v1 brain would — reconstruction included,
+ * proven by digest-equality against canonical after a reopen; (b) MIXED
+ * logs: an existing v1 segment stays readable forever beside a v2 tail
+ * (cutover-by-rotation; the v1 segment is never rewritten); (c) MINT:
+ * after-image records carry the metadata index id mapper's exact int
+ * assignments (white-box compare); (d) SEALS: every flush leaves the tail
+ * sector-aligned, and pads are invisible to scans; (e) REPLAY: the
+ * log-authority recovery path resurrects an acked write from a v2 tail
+ * after a crash-style abandon.
+ */
+import { describe, it, expect, afterEach } from 'vitest'
+import * as fs from 'node:fs'
+import * as path from 'node:path'
+import { mkdtempSync, rmSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { Brainy } from '../../src/brainy.js'
+import { NounType } from '../../src/types/graphTypes.js'
+import {
+  parseSegmentHeader,
+  decodeGroupV2,
+  SEGMENT_HEADER_BYTES,
+  FACT_LOG_FORMAT_V1,
+  FACT_LOG_FORMAT_V2,
+  type LogGenesisRecord,
+  type NounAfterImageRecord
+} from '../../src/db/factLogFormat.js'
+import type { CommitFact, FactIntMinter, FactLog } from '../../src/db/factLog.js'
+import {
+  makeTempDir,
+  openBrain,
+  storeOf,
+  abandonAsCrashed,
+  factGenerations,
+  vec,
+  uid
+} from '../helpers/durabilityKillMatrix.js'
+
+/** The VFS root — created at init by a baseline (generation-less) write. */
+const VFS_ROOT = '00000000-0000-0000-0000-000000000000'
+const FACTS_DIR = ['_generations', 'facts'] as const
+const MANIFEST_PATH = '_generations/facts/manifest.json'
+
+/** White-box internals this suite instruments. */
+type BrainInternals = {
+  storage: {
+    readRawObject(p: string): Promise<unknown | null>
+    readNounRaw(id: string): Promise<{ metadata: unknown | null; vector: unknown | null }>
+  }
+  metadataIndex: {
+    getIdMapper(): { getInt(uuid: string): number | undefined }
+  }
+}
+const internals = (brain: Brainy): BrainInternals => brain as unknown as BrainInternals
+
+/** The facts manifest as stored (additive brainId included). */
+interface StoredFactsManifest {
+  segments: Array<{ file: string }>
+  tailSegment: string | null
+  brainId?: string
+}
+
+async function readManifest(brain: Brainy): Promise<StoredFactsManifest> {
+  const manifest = (await internals(brain).storage.readRawObject(
+    MANIFEST_PATH
+  )) as StoredFactsManifest | null
+  expect(manifest, 'the facts manifest exists').toBeTruthy()
+  return manifest!
+}
+
+/** Raw on-disk bytes of one fact segment file. */
+function segmentBytes(dir: string, file: string): Uint8Array {
+  return new Uint8Array(fs.readFileSync(path.join(dir, ...FACTS_DIR, file)))
+}
+
+async function allFacts(brain: Brainy): Promise<CommitFact[]> {
+  const scan = (brain as unknown as { scanFacts(): { batches(): AsyncGenerator<{ facts: CommitFact[] }> } | null }).scanFacts()
+  expect(scan, 'this storage hosts a fact log').not.toBeNull()
+  const facts: CommitFact[] = []
+  for await (const batch of scan!.batches()) facts.push(...batch.facts)
+  return facts
+}
+
+/** The live FactLog instance (white-box: the minter strip in scenario b). */
+function factLogOf(brain: Brainy): FactLog & { intMinter: FactIntMinter | null } {
+  const log = storeOf(brain).getFactLog()
+  expect(log, 'filesystem storage hosts a fact log').not.toBeNull()
+  return log as FactLog & { intMinter: FactIntMinter | null }
+}
+
+describe('fact log v2 cutover — live writes land in the v2 segment format', () => {
+  const dirs: string[] = []
+  const brains: Brainy[] = []
+
+  const trackDir = (): string => {
+    const dir = makeTempDir()
+    dirs.push(dir)
+    return dir
+  }
+  const track = (brain: Brainy): Brainy => {
+    brains.push(brain)
+    return brain
+  }
+
+  afterEach(async () => {
+    for (const b of brains.splice(0)) {
+      await (b as unknown as { close?: () => Promise<void> }).close?.().catch(() => {})
+    }
+    for (const d of dirs.splice(0)) rmSync(d, { recursive: true, force: true })
+  })
+
+  it('(a) NEW BRAIN: v2 tail header, genesis-first, and scanFacts parity with canonical across a reopen', async () => {
+    const dir = trackDir()
+    const brain = track(await openBrain(dir))
+    const idA = uid('v2-new-a')
+    const idB = uid('v2-new-b')
+    await brain.add({ id: idA, data: 'alpha', type: NounType.Document, vector: vec(1), metadata: { n: 1 } })
+    await brain.add({ id: idB, data: 'beta', type: NounType.Document, vector: vec(2), metadata: { n: 2 } })
+    await brain.flush()
+
+    // The tail segment's raw header bytes: formatVersion 2, sealSize 4096.
+    const manifest = await readManifest(brain)
+    expect(manifest.tailSegment).toBeTruthy()
+    expect(manifest.brainId, 'the brain id was minted into the manifest').toBeTruthy()
+    const bytes = segmentBytes(dir, manifest.tailSegment!)
+    const header = parseSegmentHeader(bytes.subarray(0, SEGMENT_HEADER_BYTES))
+    expect(header.formatVersion).toBe(FACT_LOG_FORMAT_V2)
+    expect(header.sealSize).toBe(4096)
+
+    // Genesis is the FIRST record of the FIRST fact — and appears exactly once.
+    const group = decodeGroupV2(bytes.subarray(SEGMENT_HEADER_BYTES), { expectedIdSpaceWidth: 64 })
+    expect(group.facts.length).toBeGreaterThanOrEqual(2)
+    const firstRecord = group.facts[0].records[0]
+    expect(firstRecord.type).toBe('log.genesis')
+    const genesis = firstRecord as LogGenesisRecord
+    expect(genesis.idSpaceWidth).toBe(64)
+    expect(genesis.brainId).toBe(manifest.brainId)
+    const genesisCount = group.facts
+      .flatMap((f) => f.records)
+      .filter((r) => r.type === 'log.genesis').length
+    expect(genesisCount).toBe(1)
+
+    // Shape parity + reconstruction fidelity: REOPEN (so the tail decodes
+    // from disk, not from the in-session originals) and compare each add's
+    // CommitFact op against canonical byte truth — metadata leg (bigint
+    // timestamps normalized back to numbers) AND the reconstructed vector
+    // wrapper must equal what readNounRaw returns, exactly as a v1 log's
+    // byte-faithful capture would.
+    await (brain as unknown as { close: () => Promise<void> }).close()
+    brains.splice(brains.indexOf(brain), 1)
+    const reopened = track(await openBrain(dir))
+    const facts = await allFacts(reopened)
+    const gens = facts.map((f) => f.generation)
+    expect([...gens].sort((a, b) => a - b)).toEqual(gens)
+    expect(new Set(gens).size).toBe(gens.length)
+
+    const logGens = new Set(
+      ((await (reopened as unknown as { transactionLog(): Promise<Array<{ generation: number }>> }).transactionLog()) ?? []).map(
+        (e) => e.generation
+      )
+    )
+    for (const g of gens) expect(logGens.has(g), `generation ${g} is a real commit`).toBe(true)
+
+    for (const id of [idA, idB]) {
+      const fact = facts.find((f) => f.ops.some((op) => op.id === id && op.record !== null))
+      expect(fact, `the add fact for ${id} survives the reopen`).toBeDefined()
+      const op = fact!.ops.find((o) => o.id === id)!
+      expect(op.kind).toBe('noun')
+      const canonical = await internals(reopened).storage.readNounRaw(id)
+      expect(op.record!.metadata).toStrictEqual(canonical.metadata)
+      // ENTITY TRUTH comparison: canonical wrappers denormalize HNSW residue
+      // (connections + the randomly-assigned level) that the log record
+      // deliberately reconstructs empty — strip both sides (the oracle's
+      // normalizer law) so a nonzero random level can't fake a divergence.
+      const strip = (w: unknown) => {
+        const { connections: _c, level: _l, ...rest } = w as Record<string, unknown>
+        return rest
+      }
+      expect(strip(op.record!.vector)).toStrictEqual(strip(canonical.vector))
+    }
+  })
+
+  it('(b) MIXED LOG: an existing v1 segment stays readable forever beside the v2 tail (cutover by rotation, v1 bytes untouched)', async () => {
+    // ROUTE: a REAL v1 segment is written by the v1 writer itself — the live
+    // FactLog with its minter stripped (the exact pre-cutover code path,
+    // still shipped for minter-less configurations) — then the minter is
+    // restored mid-session and the next append performs the cutover
+    // rotation. Stronger than hand-crafted bytes: both formats come from
+    // their real writers, on one log.
+    const dir = trackDir()
+    const brain = track(await openBrain(dir))
+    const log = factLogOf(brain)
+    const minter = log.intMinter
+    expect(minter, 'the brain wired the int minter at init').toBeTruthy()
+
+    log.intMinter = null // the pre-cutover writer
+    const idOld1 = uid('v1-old-1')
+    const idOld2 = uid('v1-old-2')
+    await brain.add({ id: idOld1, data: 'old one', type: NounType.Document, vector: vec(3), metadata: { era: 'v1' } })
+    await brain.add({ id: idOld2, data: 'old two', type: NounType.Document, vector: vec(4), metadata: { era: 'v1' } })
+    await brain.flush()
+
+    const before = await readManifest(brain)
+    expect(before.segments).toHaveLength(0)
+    const v1TailFile = before.tailSegment!
+    const v1Bytes = segmentBytes(dir, v1TailFile)
+    expect(parseSegmentHeader(v1Bytes.subarray(0, SEGMENT_HEADER_BYTES)).formatVersion).toBe(
+      FACT_LOG_FORMAT_V1
+    )
+
+    log.intMinter = minter // the cutover lands mid-session
+    const idNew = uid('v2-new')
+    await brain.add({ id: idNew, data: 'new era', type: NounType.Document, vector: vec(5), metadata: { era: 'v2' } })
+    await brain.flush()
+
+    // The v1 tail was SEALED (bytes untouched), the new tail is v2.
+    const after = await readManifest(brain)
+    expect(after.segments.map((s) => s.file)).toContain(v1TailFile)
+    expect(after.tailSegment).not.toBe(v1TailFile)
+    const sealedBytes = segmentBytes(dir, v1TailFile)
+    expect(parseSegmentHeader(sealedBytes.subarray(0, SEGMENT_HEADER_BYTES)).formatVersion).toBe(
+      FACT_LOG_FORMAT_V1
+    )
+    expect(
+      Buffer.compare(Buffer.from(sealedBytes), Buffer.from(v1Bytes)),
+      'the sealed v1 segment is byte-identical — never rewritten'
+    ).toBe(0)
+    const tailBytes = segmentBytes(dir, after.tailSegment!)
+    expect(parseSegmentHeader(tailBytes.subarray(0, SEGMENT_HEADER_BYTES)).formatVersion).toBe(
+      FACT_LOG_FORMAT_V2
+    )
+    // NOT a brand-new log: no genesis on a rotated-in v2 tail.
+    const tailGroup = decodeGroupV2(tailBytes.subarray(SEGMENT_HEADER_BYTES), {
+      expectedIdSpaceWidth: 64
+    })
+    expect(
+      tailGroup.facts.flatMap((f) => f.records).some((r) => r.type === 'log.genesis')
+    ).toBe(false)
+
+    // One scan spans both formats, shape-identically, in generation order.
+    const liveFacts = await allFacts(brain)
+    const liveGens = liveFacts.map((f) => f.generation)
+    expect([...liveGens].sort((a, b) => a - b)).toEqual(liveGens)
+    for (const id of [idOld1, idOld2, idNew]) {
+      const fact = liveFacts.find((f) => f.ops.some((op) => op.id === id))
+      expect(fact, `fact for ${id} is scannable`).toBeDefined()
+      const op = fact!.ops.find((o) => o.id === id)!
+      expect(op.kind).toBe('noun')
+      expect(op.record).not.toBeNull()
+    }
+
+    // The MIXED log survives a reopen and keeps appending (v2 tail).
+    await (brain as unknown as { close: () => Promise<void> }).close()
+    brains.splice(brains.indexOf(brain), 1)
+    const reopened = track(await openBrain(dir))
+    const reFacts = await allFacts(reopened)
+    expect(reFacts.map((f) => f.generation)).toEqual(liveGens)
+    // The v1 fact still reads exactly as the v1 decoder always read it.
+    // (Not compared byte-strict against canonical: the v1 CAPTURE has a
+    // known pre-existing wart — write-cache-warm objects carry
+    // undefined-valued engine keys that msgpack preserves as nil while the
+    // durable JSON drops them. v1 bytes are frozen; the v2 encoder
+    // sanitizes to durable truth instead — pinned in scenario (a).)
+    const oldOp = reFacts
+      .find((f) => f.ops.some((op) => op.id === idOld1))!
+      .ops.find((o) => o.id === idOld1)!
+    const canonicalOld = await internals(reopened).storage.readNounRaw(idOld1)
+    const oldMeta = oldOp.record!.metadata as Record<string, unknown>
+    expect(oldMeta.noun).toBe('document')
+    expect((oldMeta.metadata as Record<string, unknown>).era).toBe('v1')
+    const oldWrapper = oldOp.record!.vector as { id: string; vector: number[] }
+    const canonicalWrapper = canonicalOld.vector as { id: string; vector: number[] }
+    expect(oldWrapper.id).toBe(idOld1)
+    expect(oldWrapper.vector).toStrictEqual(canonicalWrapper.vector)
+    await reopened.add({ id: uid('post-reopen'), data: 'still writing', type: NounType.Document, vector: vec(6), metadata: {} })
+    expect((await factGenerations(reopened)).length).toBe(liveGens.length + 1)
+  })
+
+  it('(c) MINT-AT-APPEND: after-image records carry the id mapper\'s EXACT int assignments — distinct, nonzero, reproducible', async () => {
+    const dir = trackDir()
+    const brain = track(await openBrain(dir))
+    const idA = uid('mint-a')
+    const idB = uid('mint-b')
+    await brain.add({ id: idA, data: 'mint one', type: NounType.Document, vector: vec(7), metadata: { m: 1 } })
+    await brain.add({ id: idB, data: 'mint two', type: NounType.Document, vector: vec(8), metadata: { m: 2 } })
+    await brain.flush()
+
+    const manifest = await readManifest(brain)
+    const bytes = segmentBytes(dir, manifest.tailSegment!)
+    const group = decodeGroupV2(bytes.subarray(SEGMENT_HEADER_BYTES), { expectedIdSpaceWidth: 64 })
+    const afterImages = new Map<string, NounAfterImageRecord>()
+    for (const fact of group.facts) {
+      for (const record of fact.records) {
+        if (record.type === 'noun.afterImage') afterImages.set(record.id, record)
+      }
+    }
+    const recA = afterImages.get(idA)
+    const recB = afterImages.get(idB)
+    expect(recA, 'idA has a decoded after-image').toBeDefined()
+    expect(recB, 'idB has a decoded after-image').toBeDefined()
+    expect(recA!.entityInt).toBeGreaterThan(0n)
+    expect(recB!.entityInt).toBeGreaterThan(0n)
+    expect(recA!.entityInt).not.toBe(recB!.entityInt)
+
+    // White-box: the ints on the wire ARE the metadata index mapper's
+    // assignments — the exact ints a mapper rebuild must reproduce.
+    const mapper = internals(brain).metadataIndex.getIdMapper()
+    expect(recA!.entityInt).toBe(BigInt(mapper.getInt(idA)!))
+    expect(recB!.entityInt).toBe(BigInt(mapper.getInt(idB)!))
+  })
+
+  it('(d) SEALS AT SYNC: every flush leaves the tail sector-aligned; pads are invisible to scans', async () => {
+    const dir = trackDir()
+    const brain = track(await openBrain(dir))
+    await brain.add({ id: uid('seal-1'), data: 'one', type: NounType.Document, vector: vec(10), metadata: {} })
+    await brain.flush()
+
+    const manifest = await readManifest(brain)
+    const tailPath = path.join(dir, ...FACTS_DIR, manifest.tailSegment!)
+    const sizeAfterFirstFlush = fs.statSync(tailPath).size
+    expect(sizeAfterFirstFlush).toBeGreaterThan(0)
+    expect(sizeAfterFirstFlush % 4096, 'tail is sector-aligned after flush').toBe(0)
+    const countAfterFirstFlush = (await factGenerations(brain)).length
+
+    for (let i = 0; i < 3; i++) {
+      await brain.add({ id: uid(`seal-more-${i}`), data: `more ${i}`, type: NounType.Document, vector: vec(11 + i), metadata: { i } })
+    }
+    await brain.flush()
+    const sizeAfterSecondFlush = fs.statSync(tailPath).size
+    expect(sizeAfterSecondFlush).toBeGreaterThan(sizeAfterFirstFlush)
+    expect(sizeAfterSecondFlush % 4096, 'still aligned after more writes + flush').toBe(0)
+
+    // Pads count toward bytes, never toward facts.
+    expect((await factGenerations(brain)).length).toBe(countAfterFirstFlush + 3)
+  })
+
+  it('(e) REPLAY COMPAT: the log-authority recovery path resurrects an acked write from a v2 tail after a crash-style abandon', async () => {
+    // The flip idiom from the log-authority suite: seed writes, baseline
+    // backfill LAST (the init-time VFS root never got a fact), flush, then
+    // the sanctioned guarded flip — the oracle goes green over an ALL-V2
+    // log, which is itself the reproduction proof for the v2 record path.
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-v2-cutover-'))
+    dirs.push(dir)
+    process.env.BRAINY_DETERMINISTIC_EMBEDDINGS = 'true'
+    const open = async (): Promise<Brainy> => {
+      const b = new Brainy({
+        storage: { type: 'filesystem', path: dir },
+        requireSubtype: false,
+        silent: true,
+        dimensions: 384
+      })
+      await b.init()
+      return track(b)
+    }
+
+    const brain = await open()
+    const kept = await brain.add({ data: 'alpha document', type: 'document', metadata: { n: 1 } })
+    const removed = await brain.add({ data: 'beta document', type: 'document', metadata: { n: 2 } })
+    await brain.update({ id: kept, metadata: { n: 10 } })
+    await brain.remove(removed)
+    const root = await brain.get(VFS_ROOT)
+    expect(root, 'the VFS root exists').toBeTruthy()
+    await brain.update({ id: VFS_ROOT, metadata: root!.metadata }) // baseline backfill — final write
+    await brain.flush()
+
+    const report = await (brain as unknown as { adoptLogAuthority(): Promise<{ verdict: string }> }).adoptLogAuthority()
+    expect(report.verdict, 'the oracle is green over a pure-v2 log').toBe('green')
+
+    // An at-ack write: its v2 fact is fsynced (sector-sealed) at ack.
+    const survivor = await brain.add({
+      data: 'survives power loss',
+      type: 'document',
+      metadata: { s: 1 }
+    })
+
+    // Crash-style abandon: RAM state gone, no flush, no close.
+    await abandonAsCrashed(brain)
+
+    // Reopen: open() finds the acked fact ABOVE the manifest watermark in
+    // the v2 tail (peekFactsAbove → v2 decode) and REPLAYS it into
+    // canonical — an acked write is never lost.
+    const reopened = await open()
+    expect(
+      (reopened as unknown as { logAuthority(): { authority: string } }).logAuthority().authority
+    ).toBe('log')
+    const resurrected = await reopened.get(survivor)
+    expect(resurrected, 'the acked write survived the crash').toBeTruthy()
+    expect((resurrected as { metadata?: { s?: number } }).metadata?.s).toBe(1)
+    expect((await factGenerations(reopened)).length).toBeGreaterThan(0)
+  })
+})

tests/integration/find-matchall-cold.test.ts

@@ -0,0 +1,184 @@
+/**
+ * @module tests/integration/find-matchall-cold
+ * @description THE MATCH-ALL SILENT-EMPTY PIN: `find({ where: {} })` is a
+ * match-all query — zero predicates constrain nothing — yet it used to route
+ * through the index-filter branch, where `getIdsForFilter({})` answers `[]`
+ * by contract. Result: 0 rows while storage held rows (worst on a freshly
+ * reopened brain, where it masqueraded as data loss), the forbidden answer
+ * class — a silent empty instead of served-or-refused. These tests pin the
+ * law: an empty `where` routes exactly like an absent `where`, serving from
+ * truth-complete sources (a storage page bounded to the offset+limit window,
+ * or the column store's top-K sort under orderBy) — warm AND cold, on the
+ * live brain, the Db pin path, pagination.count, streaming.entities, and the
+ * semantic path (`{ query, where: {} }` must not short-circuit to `[]`).
+ * The one deliberate refusal: `removeMany({ where: {} })` throws — a
+ * match-all BULK DELETE must be asked for explicitly, never inherited.
+ */
+import { describe, it, expect, afterEach } from 'vitest'
+import { mkdtempSync, rmSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { Brainy } from '../../src/index.js'
+import { NounType } from '../../src/types/graphTypes.js'
+
+const dirs: string[] = []
+const brains: Brainy[] = []
+
+afterEach(async () => {
+  for (const b of brains.splice(0)) await b.close().catch(() => {})
+  for (const d of dirs.splice(0)) rmSync(d, { recursive: true, force: true })
+})
+
+async function open(dir: string): Promise<Brainy> {
+  const b = new Brainy({ storage: { type: 'filesystem', path: dir }, requireSubtype: false })
+  await b.init()
+  brains.push(b)
+  return b
+}
+
+/** Seed three plain documents with a sortable numeric field. */
+async function seed(brain: Brainy): Promise<string[]> {
+  const ids: string[] = []
+  ids.push(await brain.add({ data: 'alpha row', type: NounType.Document, metadata: { n: 1 } }))
+  ids.push(await brain.add({ data: 'beta row', type: NounType.Document, metadata: { n: 2 } }))
+  ids.push(await brain.add({ data: 'gamma row', type: NounType.Document, metadata: { n: 3 } }))
+  await brain.flush()
+  return ids
+}
+
+describe('find({ where: {} }) — match-all serves, warm and cold', () => {
+  it('the repro: a freshly reopened filesystem brain serves match-all (not a silent 0)', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-matchall-cold-'))
+    dirs.push(dir)
+    const brain = await open(dir)
+    await seed(brain)
+    await brain.close()
+    brains.pop()
+
+    const reopened = await open(dir)
+    const rows = await reopened.find({ where: {}, limit: 10 })
+    expect(rows.length, 'match-all serves every stored row on the cold brain').toBe(3)
+
+    // The predicate paths that always worked cold stay working — same brain.
+    expect((await reopened.find({ where: { n: 1 }, limit: 10 })).length).toBe(1)
+    expect((await reopened.find({ where: { 'system.type': 'document' }, limit: 10 })).length).toBe(3)
+  }, 120000)
+
+  it('match-all + orderBy on a metadata field serves sorted after reopen', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-matchall-order-'))
+    dirs.push(dir)
+    const brain = await open(dir)
+    await seed(brain)
+    await brain.close()
+    brains.pop()
+
+    const reopened = await open(dir)
+    const rows = await reopened.find({ where: {}, orderBy: 'n', order: 'desc', limit: 10 })
+    expect(rows.length, 'sorted match-all serves every stored row cold').toBe(3)
+    expect(
+      rows.map((r) => (r.metadata as { n: number }).n),
+      'orderBy is honored on the cold match-all page'
+    ).toEqual([3, 2, 1])
+  }, 120000)
+
+  it('warm brain unchanged: match-all, sorted match-all, and predicates all serve in-session', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-matchall-warm-'))
+    dirs.push(dir)
+    const brain = await open(dir)
+    await seed(brain)
+
+    expect((await brain.find({ where: {}, limit: 10 })).length).toBe(3)
+    const sorted = await brain.find({ where: {}, orderBy: 'n', order: 'asc', limit: 2 })
+    expect(sorted.map((r) => (r.metadata as { n: number }).n)).toEqual([1, 2])
+    expect((await brain.find({ where: { n: 2 }, limit: 10 })).length).toBe(1)
+    // Pagination window respected: match-all never over-serves the page.
+    expect((await brain.find({ where: {}, limit: 2, offset: 2 })).length).toBe(1)
+  }, 120000)
+
+  it('the semantic path: find({ query, where: {} }) must not short-circuit to []', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-matchall-query-'))
+    dirs.push(dir)
+    const brain = await open(dir)
+    await seed(brain)
+    await brain.close()
+    brains.pop()
+
+    const reopened = await open(dir)
+    // Before the fix, the pre-resolved empty filter matched nothing and the
+    // vector search was skipped entirely — a silent [] for every such query.
+    const rows = await reopened.find({ query: 'alpha row', where: {}, limit: 10 })
+    expect(rows.length, 'an unconstraining where must not empty a semantic query').toBeGreaterThan(0)
+  }, 120000)
+
+  it('the Db pin path: asOf(g).find({ where: {} }) serves at the pinned generation after reopen', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-matchall-asof-'))
+    dirs.push(dir)
+    const brain = await open(dir)
+    await brain.add({ data: 'first', type: NounType.Document, metadata: { n: 1 } })
+    await brain.add({ data: 'second', type: NounType.Document, metadata: { n: 2 } })
+    await brain.flush()
+    const gTwo = brain.generation()
+    await brain.add({ data: 'third', type: NounType.Document, metadata: { n: 3 } })
+    await brain.flush()
+    await brain.close()
+    brains.pop()
+
+    const reopened = await open(dir)
+    // Current-generation pin (delegates to the live find fast path).
+    const now = reopened.now()
+    expect((await now.find({ where: {}, limit: 10 })).length).toBe(3)
+
+    // Historical pin: the record-overlay path must serve match-all too.
+    const past = await reopened.asOf(gTwo)
+    try {
+      const rows = await past.find({ where: {}, limit: 10 })
+      expect(rows.length, 'match-all at the pinned generation sees exactly the rows of that generation').toBe(2)
+    } finally {
+      await past.release()
+    }
+  }, 120000)
+
+  it('pagination.count({ where: {} }) counts every row instead of a silent 0', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-matchall-count-'))
+    dirs.push(dir)
+    const brain = await open(dir)
+    await seed(brain)
+    await brain.close()
+    brains.pop()
+
+    const reopened = await open(dir)
+    // The law: an empty where counts exactly like an absent where (the
+    // unfiltered total — which by long-standing count semantics includes
+    // system entities such as the VFS root, hence >= the 3 user rows).
+    const emptyWhere = await reopened.pagination.count({ where: {} })
+    expect(emptyWhere).toBe(await reopened.pagination.count({}))
+    expect(emptyWhere).toBeGreaterThanOrEqual(3)
+  }, 120000)
+
+  it('streaming.entities({ where: {} }) streams every row instead of nothing', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-matchall-stream-'))
+    dirs.push(dir)
+    const brain = await open(dir)
+    await seed(brain)
+    await brain.close()
+    brains.pop()
+
+    const reopened = await open(dir)
+    const streamed: string[] = []
+    for await (const entity of reopened.streaming.entities({ where: {} })) {
+      streamed.push(entity.id)
+    }
+    expect(streamed.length, 'an unconstraining where streams the full store').toBeGreaterThanOrEqual(3)
+  }, 120000)
+
+  it('removeMany({ where: {} }) refuses loudly — match-all bulk delete is never implicit', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-matchall-remove-'))
+    dirs.push(dir)
+    const brain = await open(dir)
+    await seed(brain)
+
+    await expect(brain.removeMany({ where: {} })).rejects.toThrow(/matches EVERYTHING/)
+    // Nothing was deleted by the refused call.
+    expect((await brain.find({ where: {}, limit: 10 })).length).toBe(3)
+  }, 120000)
+})

tests/integration/log-authority-adopt.test.ts

@@ -0,0 +1,114 @@
+/**
+ * @module tests/integration/log-authority-adopt
+ * @description THE SANCTIONED FLIP, END TO END: adoptLogAuthority() cures
+ * its own curable divergences by baseline backfill — a FRESH brain (whose
+ * generation-0 VFS root never entered the log) flips WITHOUT any manual
+ * white-box backfill. Before this, no fresh brain could ever flip: the
+ * oracle reported the bootstrap row as pre-log-record and the flip refused.
+ * Log-AHEAD divergences stay incurable and refuse loudly (witness wins).
+ */
+import { describe, it, expect, afterEach } from 'vitest'
+import { mkdtempSync, rmSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { Brainy } from '../../src/index.js'
+import { NounType } from '../../src/types/graphTypes.js'
+
+const dirs: string[] = []
+const brains: Brainy[] = []
+
+afterEach(async () => {
+  for (const b of brains.splice(0)) await b.close().catch(() => {})
+  for (const d of dirs.splice(0)) rmSync(d, { recursive: true, force: true })
+})
+
+async function open(dir: string, logAuthority?: 'adopt' | 'defer'): Promise<Brainy> {
+  const b = new Brainy({
+    storage: { type: 'filesystem', path: dir },
+    requireSubtype: false,
+    ...(logAuthority ? { logAuthority } : {})
+  })
+  await b.init()
+  brains.push(b)
+  return b
+}
+
+describe('adoptLogAuthority — the sanctioned flip with self-backfill', () => {
+  it('a fresh brain flips directly: the backfill cures the generation-0 baseline', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-adopt-'))
+    dirs.push(dir)
+    const brain = await open(dir)
+    const idA = await brain.add({ data: 'first row', type: NounType.Document, metadata: { n: 1 } })
+    await brain.add({ data: 'second row', type: NounType.Document, metadata: { n: 2 } })
+    await brain.flush()
+
+    const report = await brain.adoptLogAuthority()
+    expect(report.verdict, 'the flip receipt is a green oracle').toBe('green')
+    expect(brain.logAuthority().authority).toBe('log')
+
+    // The switch survives reopen; the brain keeps serving identically.
+    await brain.close()
+    brains.pop()
+    const reopened = await open(dir)
+    expect(reopened.logAuthority().authority).toBe('log')
+    expect(await reopened.get(idA), 'records serve at reopen').toBeTruthy()
+    const rows = await reopened.find({ where: {}, limit: 10 })
+    expect(rows.length, 'match-all serves on the reopened flipped brain').toBeGreaterThanOrEqual(2)
+    // And a fresh oracle run on the flipped brain stays green.
+    expect((await reopened.verifyLogAuthority()).verdict).toBe('green')
+  }, 120000)
+
+  it('witness drift (out-of-generation canonical rewrite) is cured by the backfill, then flips', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-adopt-drift-'))
+    dirs.push(dir)
+    const brain = await open(dir)
+    const id = await brain.add({ data: 'drifter', type: NounType.Document, metadata: { v: 1 } })
+    await brain.flush()
+
+    // Simulate maintenance rewriting canonical OUTSIDE a generation (the
+    // witness-drift class): mutate the stored record directly.
+    const storage = (brain as unknown as {
+      storage: {
+        readNounRaw(id: string): Promise<{ metadata: unknown; vector: unknown }>
+        writeNounRaw(id: string, r: { metadata: unknown; vector: unknown }): Promise<void>
+      }
+    }).storage
+    const raw = await storage.readNounRaw(id)
+    await storage.writeNounRaw(id, {
+      metadata: { ...(raw.metadata as Record<string, unknown>), drifted: true },
+      vector: raw.vector
+    })
+    expect((await brain.verifyLogAuthority()).verdict, 'drift detected').toBe('red')
+
+    const report = await brain.adoptLogAuthority()
+    expect(report.verdict).toBe('green')
+    expect(brain.logAuthority().authority).toBe('log')
+  }, 120000)
+
+  // THE OPT-OUT CONTRACT (`logAuthority: 'defer'`): no automatic adoption —
+  // the fresh brain stays tree-authoritative and writes NO artifact (a
+  // deferred posture is config, not stored state); the EXPLICIT
+  // adoptLogAuthority() then flips it exactly as before the fleet default.
+  it("opt-out: 'defer' stays tree with no artifact until the explicit adoptLogAuthority() flips it", async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-adopt-defer-'))
+    dirs.push(dir)
+    const brain = await open(dir, 'defer')
+    await brain.add({ data: 'deferred row', type: NounType.Document, metadata: { n: 1 } })
+    await brain.flush()
+
+    expect(brain.logAuthority().authority, "'defer' skips open-time adoption").toBe('tree')
+    const storage = (brain as unknown as {
+      storage: { readRawObject(p: string): Promise<unknown | null> }
+    }).storage
+    const artifact = await storage.readRawObject('_system/log-authority.json').catch(() => null)
+    expect(artifact, "'defer' writes no authority artifact").toBeNull()
+
+    const report = await brain.adoptLogAuthority()
+    expect(report.verdict, 'the explicit flip still lands on green').toBe('green')
+    expect(brain.logAuthority().authority).toBe('log')
+    const stored = (await storage.readRawObject('_system/log-authority.json')) as {
+      authority?: string
+    } | null
+    expect(stored?.authority, 'the explicit flip stores the artifact').toBe('log')
+  }, 120000)
+})

tests/integration/log-authority.test.ts

@@ -0,0 +1,399 @@
+/**
+ * @module tests/integration/log-authority
+ * @description The guarded log-authority core, end-to-end: the per-brain
+ * authority switch (stored artifact, checked at open only), the
+ * verification oracle (replay the fact log, diff latest per-id state
+ * against the canonical tree, NAME every divergence by class), the guarded
+ * flip (refuses on red with the cure in the message; lands on green and
+ * engages durable-at-ack immediately), and the switch surviving reopen.
+ *
+ * THE 10.0.0 FLEET DEFAULT is ADOPT-AT-OPEN (`logAuthority: 'adopt'`): a
+ * fresh brain with no stored artifact runs the oracle at open, backfills
+ * curable divergences, and flips to log authority on green — so a
+ * default-config brain opens ALREADY log-authoritative and durable-at-ack.
+ * The first two pins hold that default and its explicit opt-out
+ * (`logAuthority: 'defer'`, the pre-10 tree behavior). Every test below
+ * them that exercises the ORACLE or the EXPLICIT flip opens its brain with
+ * `'defer'` — otherwise the open-time adoption would have pre-flipped the
+ * brain and pre-cured the very divergences under test.
+ *
+ * KNOWN GAPS PINNED WITH `.fails` (real findings, not test bugs — see the
+ * comments on each): a fresh brain is NOT log-complete by construction
+ * today, because the VFS root is written at init as a baseline
+ * (generation-less) write that never gets a fact, so the oracle reports it
+ * as a `pre-log-record`. The open-time adoption (and adoptLogAuthority())
+ * CURES this by baseline backfill — a re-commit, not construction — so the
+ * by-construction pin stays `.fails` on a deferred brain. Tests that need
+ * a green oracle on a deferred brain perform that backfill explicitly (an
+ * identity update of the root as the FINAL write — final, because
+ * derived-index maintenance rewrites canonical noun records outside
+ * generations, so an earlier fact's after-image goes stale; see the module
+ * tail comment on `backfillBaseline`).
+ */
+import { describe, it, expect, afterEach } from 'vitest'
+import { mkdtempSync, rmSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { Brainy } from '../../src/index.js'
+import type { OracleReport } from '../../src/db/logAuthority.js'
+
+/** The VFS root — created at init by a baseline (generation-less) write. */
+const VFS_ROOT = '00000000-0000-0000-0000-000000000000'
+const AUTHORITY_ARTIFACT = '_system/log-authority.json'
+
+/** White-box view of the internals this suite instruments (read-only spies
+ *  plus the sanctioned direct-storage writes for aging/drifting a brain). */
+type BrainInternals = {
+  generationStore: {
+    getFactLog(): { ensureSynced(): Promise<void> } | null
+    logDurability: 'deferred' | 'at-ack'
+  }
+  storage: {
+    readRawObject(path: string): Promise<unknown | null>
+    saveNoun(n: unknown): Promise<void>
+    saveNounMetadata(id: string, m: Record<string, unknown>): Promise<void>
+    getNounMetadata(id: string): Promise<Record<string, unknown> | null>
+    writeNounRaw(id: string, r: { metadata: null; vector: null }): Promise<void>
+  }
+}
+
+const internals = (brain: Brainy): BrainInternals =>
+  brain as unknown as BrainInternals
+
+/** Count calls to the fact log's ensureSynced without changing behavior. */
+function spyEnsureSynced(brain: Brainy): { calls: () => number } {
+  const factLog = internals(brain).generationStore.getFactLog()
+  expect(factLog, 'filesystem storage hosts a fact log').not.toBeNull()
+  let calls = 0
+  const original = factLog!.ensureSynced.bind(factLog)
+  factLog!.ensureSynced = async () => {
+    calls++
+    return original()
+  }
+  return { calls: () => calls }
+}
+
+/**
+ * The minimal baseline backfill: an identity update of the VFS root, so the
+ * one canonical record the log never saw (the init-time baseline write) gets
+ * a fact carrying its current state. MUST be the final write of the setup —
+ * derived-index maintenance (HNSW/enumeration denormalization) rewrites the
+ * root's canonical noun record outside any generation, so a root fact taken
+ * before later writes digests stale and reports `state-differs`.
+ */
+async function backfillBaseline(brain: Brainy): Promise<void> {
+  const root = await brain.get(VFS_ROOT)
+  expect(root, 'the VFS root exists on a fresh brain').toBeTruthy()
+  await brain.update({ id: VFS_ROOT, metadata: root!.metadata })
+}
+
+/** Seed a brain with the standard write mix: 2 adds, an update, a remove. */
+async function seedWrites(brain: Brainy): Promise<{ kept: string; removed: string }> {
+  const kept = await brain.add({ data: 'alpha document', type: 'document', metadata: { n: 1 } })
+  const removed = await brain.add({ data: 'beta document', type: 'document', metadata: { n: 2 } })
+  await brain.update({ id: kept, metadata: { n: 10 } })
+  await brain.remove(removed)
+  return { kept, removed }
+}
+
+describe('log authority — the switch, the oracle, the guarded flip', () => {
+  const dirs: string[] = []
+  const brains: Brainy[] = []
+
+  /**
+   * Open a brain over `dir`. Omit `logAuthority` to exercise the FLEET
+   * DEFAULT (adopt-at-open); pass `'defer'` for the tests that need a
+   * tree-authoritative brain so the oracle/explicit-flip path is actually
+   * the thing under test (the default would pre-flip and pre-backfill).
+   */
+  const openBrain = async (
+    dir?: string,
+    logAuthority?: 'adopt' | 'defer'
+  ): Promise<{ brain: Brainy; dir: string }> => {
+    const d = dir ?? mkdtempSync(join(tmpdir(), 'brainy-log-authority-'))
+    if (!dir) dirs.push(d)
+    const brain = new Brainy({
+      storage: { type: 'filesystem', path: d },
+      requireSubtype: false,
+      silent: true,
+      dimensions: 384,
+      ...(logAuthority ? { logAuthority } : {})
+    })
+    brains.push(brain)
+    await brain.init()
+    return { brain, dir: d }
+  }
+
+  afterEach(async () => {
+    for (const b of brains.splice(0)) {
+      await (b as unknown as { close?: () => Promise<void> }).close?.().catch(() => {})
+    }
+    for (const d of dirs.splice(0)) rmSync(d, { recursive: true, force: true })
+  })
+
+  // THE RULED DEFAULT (10.0.0): with no config and no stored artifact, a
+  // fresh brain ADOPTS log authority at open — oracle green (the open-time
+  // baseline backfill cures the generation-0 VFS root), artifact on disk,
+  // durable-at-ack live from the first write.
+  it('DEFAULT IS ADOPT-AT-OPEN: a fresh brain opens already log-authoritative — artifact stored, plain acks await the covering log fsync', async () => {
+    const { brain } = await openBrain() // no logAuthority config = the fleet default
+
+    const authority = brain.logAuthority()
+    expect(authority.authority).toBe('log')
+    expect(typeof authority.flippedAt).toBe('number')
+    expect(authority.oracle, 'the open-time flip records its green oracle summary').toBeDefined()
+
+    const artifact = (await internals(brain)
+      .storage.readRawObject(AUTHORITY_ARTIFACT)
+      .catch(() => null)) as { authority?: string } | null
+    expect(artifact, 'the adoption wrote the switch artifact').not.toBeNull()
+    expect(artifact!.authority).toBe('log')
+
+    // The MODE assertion (not a timing one): in log authority a single-op
+    // ack awaits the log's covering-fsync path.
+    expect(internals(brain).generationStore.logDurability).toBe('at-ack')
+    const spy = spyEnsureSynced(brain)
+    await brain.add({ data: 'log mode write', type: 'document', metadata: { n: 1 } })
+    expect(spy.calls(), 'adopted default: add() awaits the covering fsync').toBeGreaterThanOrEqual(1)
+  })
+
+  // THE EXPLICIT OPT-OUT: `logAuthority: 'defer'` is the pre-10 behavior —
+  // tree authority, NO artifact written (a deferred posture is config, not
+  // stored state), and single-op acks never await a log fsync.
+  it("OPT-OUT ('defer'): the brain stays tree-authoritative, stores no artifact, and plain acks never await a log fsync", async () => {
+    const { brain } = await openBrain(undefined, 'defer')
+
+    expect(brain.logAuthority().authority).toBe('tree')
+    expect(brain.logAuthority().flippedAt).toBeUndefined()
+
+    const artifact = await internals(brain)
+      .storage.readRawObject(AUTHORITY_ARTIFACT)
+      .catch(() => null)
+    expect(artifact, "'defer' writes no switch artifact").toBeNull()
+
+    // The MODE assertion (not a timing one): in tree authority a single-op
+    // ack must never call the log's covering-fsync path.
+    const spy = spyEnsureSynced(brain)
+    await brain.add({ data: 'tree mode write', type: 'document', metadata: { n: 1 } })
+    expect(spy.calls(), 'tree mode: add() does not call ensureSynced').toBe(0)
+    expect(internals(brain).generationStore.logDurability).toBe('deferred')
+  })
+
+  // KNOWN GAP (marked .fails — remove the marker when fixed in src): the
+  // intended contract is that a fresh brain is log-complete by construction,
+  // because every write dual-writes a fact. Today the VFS root
+  // (00000000-0000-0000-0000-000000000000) is created at init by a baseline
+  // write with NO generation and NO fact, yet it is enumerated by the
+  // canonical walk — so the oracle on a fresh brain is red with exactly one
+  // `pre-log-record` mismatch on the root. The adopt-at-open default (and
+  // adoptLogAuthority()) CURES this by baseline backfill — a re-commit,
+  // which is why this pin opens with 'defer': it holds the BY-CONSTRUCTION
+  // intent, which the backfill masks but does not deliver.
+  it.fails('ORACLE INTENT: a fresh brain is log-complete by construction — verdict green with zero mismatches', async () => {
+    const { brain } = await openBrain(undefined, 'defer')
+    await seedWrites(brain)
+    await brain.flush()
+
+    const report = await brain.verifyLogAuthority()
+    expect(report.verdict).toBe('green')
+    expect(report.mismatches).toEqual([])
+  })
+
+  it('a fresh, un-backfilled brain diverges ONLY on the init-time baseline record — every user write is exactly reproduced', async () => {
+    // 'defer': the adopt-at-open default would have backfilled the baseline
+    // already — this pin needs the brain genuinely un-backfilled.
+    const { brain } = await openBrain(undefined, 'defer')
+    await seedWrites(brain)
+    await brain.flush()
+
+    const report = await brain.verifyLogAuthority()
+    // Tolerant pin (stays true after the baseline gap is fixed in src):
+    // whatever the verdict, no USER record may ever diverge — the only
+    // admissible mismatch is the init-time baseline root, as pre-log-record.
+    expect(
+      report.mismatches.every(
+        (m) => m.id === VFS_ROOT && m.reason === 'pre-log-record' && m.kind === 'noun'
+      ),
+      'the only divergence on a fresh brain is the baseline root record'
+    ).toBe(true)
+    expect(report.matched).toBe(report.nounsChecked - report.mismatches.length)
+    expect(report.mismatchListTruncated).toBe(false)
+  })
+
+  it('THE ORACLE GOES GREEN on a log-complete brain: adds + update + remove, every canonical row exactly reproduced', async () => {
+    // 'defer' + manual backfill: the exact-count pins below (5 generations)
+    // depend on the log holding ONLY this test's writes — the adopt-at-open
+    // default would inject its own backfill generation at init.
+    const { brain } = await openBrain(undefined, 'defer')
+    await seedWrites(brain)
+    await backfillBaseline(brain) // final write — see the helper's contract
+    await brain.flush()
+
+    const report = await brain.verifyLogAuthority()
+    expect(report.verdict).toBe('green')
+    expect(report.mismatches).toEqual([])
+    expect(report.mismatchListTruncated).toBe(false)
+    // Live count: the kept document + the VFS root (the removed one is a
+    // tombstone in the log and absent from canonical — checked, not counted).
+    expect(report.nounsChecked).toBe(2)
+    expect(report.matched).toBe(2)
+    // 5 committed generations: add, add, update, remove, root backfill.
+    expect(report.generationsScanned).toBe(5)
+  })
+
+  it('THE ORACLE NAMES pre-log records: a canonical row no fact ever recorded reports pre-log-record, by id', async () => {
+    const { brain } = await openBrain(undefined, 'defer')
+    await seedWrites(brain)
+    await backfillBaseline(brain)
+    await brain.flush()
+    expect((await brain.verifyLogAuthority()).verdict, 'sanity: green before aging').toBe('green')
+
+    // Simulate an aged brain: write one canonical record DIRECTLY at the
+    // storage layer (the write path never sees it, so no fact exists) —
+    // the pre-log shape: flat metadata, no _fmt stamp, 384-dim vector.
+    const legacyId = '00000000-0000-4000-8000-00000000a6ed'
+    const storage = internals(brain).storage
+    await storage.saveNoun({
+      id: legacyId,
+      vector: new Array(384).fill(0.01),
+      connections: new Map(),
+      level: 0
+    })
+    await storage.saveNounMetadata(legacyId, {
+      noun: 'document',
+      confidence: 0.75,
+      createdAt: 1700000000000,
+      updatedAt: 1700000000000,
+      _rev: 1,
+      legacyField: 'legacy-value'
+    })
+
+    const report = await brain.verifyLogAuthority()
+    expect(report.verdict).toBe('red')
+    expect(report.mismatches).toHaveLength(1)
+    expect(report.mismatches[0]).toEqual({
+      id: legacyId,
+      kind: 'noun',
+      reason: 'pre-log-record'
+    })
+  })
+
+  it('THE FLIP REFUSES ON A LOG-AHEAD DIVERGENCE: the witness denies what the log claims — nothing written, nothing changed', async () => {
+    // Contract update (adoptLogAuthority's baseline backfill): curable
+    // divergences — pre-log records and witness drift — are re-committed
+    // and the flip proceeds; ONLY log-AHEAD divergences (the log claims
+    // state canonical denies) refuse, because no backfill can make the log
+    // un-claim a live row. This test stages exactly that incurable shape.
+    // 'defer': the brain must still be tree-authoritative (no artifact) so
+    // the refusal's nothing-written pins below have meaning.
+    const { brain } = await openBrain(undefined, 'defer')
+    const { kept } = await seedWrites(brain)
+    await backfillBaseline(brain)
+    await brain.flush()
+
+    // The log says `kept` is live; its canonical record vanishes behind the
+    // write path's back (log-live-canonical-absent — the witness wins).
+    const storage = internals(brain).storage
+    await storage.writeNounRaw(kept, { metadata: null, vector: null })
+
+    let error: Error | null = null
+    try {
+      await brain.adoptLogAuthority()
+    } catch (err) {
+      error = err as Error
+    }
+    expect(error, 'the flip rejects on a log-ahead divergence').not.toBeNull()
+    expect(error!.message).toMatch(/witness denies/)
+    expect(error!.message).toMatch(/log-live-canonical-absent/)
+
+    // Nothing changed: authority still tree, no artifact, deferred durability.
+    expect(brain.logAuthority().authority).toBe('tree')
+    const artifact = await storage.readRawObject(AUTHORITY_ARTIFACT).catch(() => null)
+    expect(artifact, 'a refused flip writes no artifact').toBeNull()
+    expect(internals(brain).generationStore.logDurability).toBe('deferred')
+  })
+
+  it('THE FLIP LANDS ON GREEN: the report is the receipt, the artifact is on disk, and durable-at-ack engages immediately', async () => {
+    // 'defer': this pin exercises the EXPLICIT flip — the adopt-at-open
+    // default would have landed it before the test began.
+    const { brain } = await openBrain(undefined, 'defer')
+    await seedWrites(brain)
+    await backfillBaseline(brain)
+    await brain.flush()
+
+    const report: OracleReport = await brain.adoptLogAuthority()
+    expect(report.verdict).toBe('green')
+
+    const authority = brain.logAuthority()
+    expect(authority.authority).toBe('log')
+    expect(typeof authority.flippedAt).toBe('number')
+    expect(authority.oracle).toBeDefined()
+    expect(authority.oracle!.nounsChecked).toBe(report.nounsChecked)
+    expect(authority.oracle!.generationsScanned).toBe(report.generationsScanned)
+
+    const artifact = (await internals(brain)
+      .storage.readRawObject(AUTHORITY_ARTIFACT)
+      .catch(() => null)) as { authority?: string } | null
+    expect(artifact, 'the switch artifact exists on disk').not.toBeNull()
+    expect(artifact!.authority).toBe('log')
+
+    // Durable-at-ack engaged in THIS session: the next single-op ack awaits
+    // a covering log fsync.
+    expect(internals(brain).generationStore.logDurability).toBe('at-ack')
+    const spy = spyEnsureSynced(brain)
+    await brain.add({ data: 'post-flip write', type: 'document', metadata: { n: 3 } })
+    expect(spy.calls(), 'log mode: add() awaits the covering fsync').toBeGreaterThanOrEqual(1)
+  })
+
+  it('THE SWITCH SURVIVES REOPEN: authority restored at open with no re-verification, durable-at-ack active in the new session', async () => {
+    const { brain, dir } = await openBrain(undefined, 'defer')
+    await seedWrites(brain)
+    await backfillBaseline(brain)
+    await brain.flush()
+    await brain.adoptLogAuthority()
+    const flipReceipt = brain.logAuthority()
+    await (brain as unknown as { close: () => Promise<void> }).close()
+
+    // Reopen with 'defer' too: the restored authority below can then ONLY
+    // come from the stored artifact (a stored artifact always wins; had the
+    // default re-adopted, flippedAt/oracle would differ from the receipt).
+    const { brain: reopened } = await openBrain(dir, 'defer')
+    const restored = reopened.logAuthority()
+    expect(restored.authority).toBe('log')
+    // No re-verification happened at open: the restored record IS the stored
+    // flip receipt, oracle summary and timestamp intact.
+    expect(restored.flippedAt).toBe(flipReceipt.flippedAt)
+    expect(restored.oracle).toEqual(flipReceipt.oracle)
+
+    // Mode restored at open: an ack in the new session awaits the log fsync.
+    expect(internals(reopened).generationStore.logDurability).toBe('at-ack')
+    const spy = spyEnsureSynced(reopened)
+    await reopened.add({ data: 'new session write', type: 'document', metadata: { n: 4 } })
+    expect(spy.calls(), 'reopened log mode: add() awaits the covering fsync').toBeGreaterThanOrEqual(1)
+  })
+
+  it('STATE-DIFFERS: canonical drift the write path never saw is named, by id', async () => {
+    const { brain } = await openBrain(undefined, 'defer')
+    const { kept } = await seedWrites(brain)
+    await backfillBaseline(brain)
+    await brain.flush()
+    expect((await brain.verifyLogAuthority()).verdict, 'sanity: green before drift').toBe('green')
+
+    // Drift one canonical metadata record DIRECTLY at the storage layer —
+    // the log never hears about it. This is the witness-drift case the
+    // oracle exists to catch.
+    const storage = internals(brain).storage
+    const current = await storage.getNounMetadata(kept)
+    expect(current, 'the seeded record has stored metadata').toBeTruthy()
+    await storage.saveNounMetadata(kept, { ...current!, driftedByTest: true })
+
+    const report = await brain.verifyLogAuthority()
+    expect(report.verdict).toBe('red')
+    expect(report.mismatches).toHaveLength(1)
+    expect(report.mismatches[0]).toEqual({
+      id: kept,
+      kind: 'noun',
+      reason: 'state-differs'
+    })
+  })
+})

tests/integration/recovery-walk-tolerance.test.ts

@@ -0,0 +1,122 @@
+/**
+ * @module tests/integration/recovery-walk-tolerance
+ * @description The rc6-red cures — the typed/tolerant boundary redrawn where
+ * block-layer fault injection proved it belonged:
+ * 1. WALKS ARE HEALERS: an init-time recovery/rebuild/pagination walk that
+ *    meets a torn record narrates+counts (the adapter's loud floor) and
+ *    HEALS PAST it — the open succeeds, remaining rows serve. rc6 died
+ *    typed here; rc5 survived silently; the cure is loud survival.
+ * 2. IDENTITY READS STAY TYPED: get-by-id of the torn record itself still
+ *    throws TornRecordError — a caller who asked for THAT record can act.
+ * 3. TORN MAPPER STATE (the NaN→BigInt source): a mapper file carrying
+ *    garbage integers is discarded with narration; reopen succeeds and the
+ *    FIRST WRITE after recovery mints sanely — never a RangeError.
+ */
+import { describe, it, expect, afterEach } from 'vitest'
+import { mkdtempSync, rmSync, readdirSync, writeFileSync, existsSync, statSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { gzipSync } from 'node:zlib'
+import { Brainy, TornRecordError } from '../../src/index.js'
+import { NounType } from '../../src/types/graphTypes.js'
+
+const dirs: string[] = []
+const brains: Brainy[] = []
+afterEach(async () => {
+  for (const b of brains.splice(0)) await b.close().catch(() => {})
+  for (const d of dirs.splice(0)) rmSync(d, { recursive: true, force: true })
+})
+
+async function open(dir: string): Promise<Brainy> {
+  const b = new Brainy({ storage: { type: 'filesystem', path: dir }, requireSubtype: false })
+  await b.init()
+  brains.push(b)
+  return b
+}
+
+/** Find one entity metadata file under entities/nouns and tear it. */
+function tearOneNounMetadata(dir: string, excludeId?: string): string {
+  const nounsRoot = join(dir, 'entities', 'nouns')
+  const walk = (d: string): string | null => {
+    for (const e of readdirSync(d, { withFileTypes: true })) {
+      const p = join(d, e.name)
+      if (e.isDirectory()) {
+        if (excludeId && e.name === excludeId) continue
+        const hit = walk(p)
+        if (hit) return hit
+      } else if (/^metadata\.json(\.gz)?$/.test(e.name)) {
+        writeFileSync(p, Buffer.from([0x1f, 0x8b, 0x00, 0xde, 0xad])) // torn gz
+        return p
+      }
+    }
+    return null
+  }
+  const torn = walk(nounsRoot)
+  if (!torn) throw new Error('layout probe: no noun metadata file found to tear')
+  // The id is the parent directory name.
+  return torn.split('/').slice(-2, -1)[0]
+}
+
+describe('recovery-walk tolerance (the rc6-red cures)', () => {
+  it('a torn entity record does not kill the open: recovery walks heal past it, remaining rows serve, identity read throws typed', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-walk-tol-'))
+    dirs.push(dir)
+    let brain = await open(dir)
+    const keeper = await brain.add({ data: 'keeper row', type: NounType.Document, metadata: { k: 1 } })
+    await brain.add({ data: 'victim row', type: NounType.Document, metadata: { k: 2 } })
+    await brain.flush()
+    await brain.close()
+    brains.pop()
+
+    const tornId = tearOneNounMetadata(dir, keeper)
+
+    // THE PIN: the open succeeds (rc6 died right here), the keeper serves,
+    // and walks (find) heal past the victim.
+    brain = await open(dir)
+    expect((await brain.get(keeper))!.data).toContain('keeper row')
+    const rows = await brain.find({ where: {}, limit: 10 })
+    expect(rows.map((r) => r.id)).toContain(keeper)
+
+    // Identity read of the victim itself: typed, catchable — the caller
+    // asked for THAT record; under log authority the replay may have
+    // already HEALED it from the fact log (also a valid outcome) — accept
+    // healed-or-typed, never silent-absent-without-narration.
+    try {
+      const victim = await brain.get(tornId)
+      // Healed by replay: the record must be real (log authority rewrote it).
+      expect(victim).not.toBeNull()
+    } catch (err) {
+      expect(err).toBeInstanceOf(TornRecordError)
+    }
+  }, 120000)
+
+  it('a torn mapper file (NaN ints) discards with narration; reopen succeeds and the first write mints sanely', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-torn-mapper-'))
+    dirs.push(dir)
+    let brain = await open(dir)
+    await brain.add({ data: 'pre-crash row', type: NounType.Document, metadata: { k: 1 } })
+    await brain.flush()
+    await brain.close()
+    brains.pop()
+
+    // The power-cut shape: the persisted mapper carries garbage integers.
+    const sys = join(dir, '_system')
+    const mapperPath = readdirSync(sys)
+      .filter((f) => /entityIdMapper/.test(f))
+      .map((f) => join(sys, f))[0]
+    expect(mapperPath, 'layout probe: mapper artifact exists').toBeTruthy()
+    const torn = { nextId: 'NaN-garbage', uuidToInt: { x: 'junk' }, intToUuid: { junk: 42 } }
+    if (mapperPath.endsWith('.gz')) writeFileSync(mapperPath, gzipSync(JSON.stringify(torn)))
+    else writeFileSync(mapperPath, JSON.stringify(torn))
+    expect(statSync(mapperPath).size).toBeGreaterThan(0)
+
+    // Reopen MUST succeed; the first write after recovery must mint sanely
+    // (rc6's fresh-write RangeError shape), and graph int resolution at
+    // reopen must not throw (rc6's reopen shape).
+    brain = await open(dir)
+    const fresh = await brain.add({ data: 'post-recovery write', type: NounType.Document, metadata: { k: 2 } })
+    expect((await brain.get(fresh))!.data).toContain('post-recovery')
+    await brain.flush()
+    expect(Number.isSafeInteger(brain.generation())).toBe(true)
+  }, 120000)
+})

tests/integration/reprojection-doors-open.test.ts

@@ -0,0 +1,257 @@
+/**
+ * @module tests/integration/reprojection-doors-open
+ * @description The reprojection engine against a REAL brain on filesystem
+ * storage: a toy secondary projection (bucket counts with its own watermark
+ * artifact, stamp-after-data per src/utils/projectionWatermark.ts) folds the
+ * brain's committed facts through the engine, wired with the callback-form
+ * {@link FactLogSource} over `brain.scanFacts`.
+ *
+ * Proves the three doors-open rows:
+ * (i)   folding to caught-up matches ground-truth counts;
+ * (ii)  mid-fold, `find()` and `get()` still answer, and a door bump
+ *       preempts the advance at the next boundary (mechanism-pinned via
+ *       batch counts, not wall-clock);
+ * (iii) a crash mid-fold (abandon; reopen; re-advance) resumes from the
+ *       durable stamp — never refolds from zero.
+ */
+import { describe, it, expect, beforeAll, afterAll } from 'vitest'
+import { mkdtempSync, mkdirSync, readFileSync, writeFileSync, rmSync, existsSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { Brainy } from '../../src/index.js'
+import {
+  ReprojectionEngine,
+  type ProjectionAdapter
+} from '../../src/reprojection/reprojectionEngine.js'
+import { FactLogSource } from '../../src/reprojection/factLogSource.js'
+import { makeProjectionStamp, readStampedWatermark } from '../../src/utils/projectionWatermark.js'
+import type { CommitFact } from '../../src/db/factLog.js'
+
+/** 50 rows, 5 buckets, 10 each. */
+const ROWS = 50
+const BUCKETS = 5
+const GROUND_TRUTH: Record<string, number> = { b0: 10, b1: 10, b2: 10, b3: 10, b4: 10 }
+
+/**
+ * The toy secondary projection: latest bucket per entity id, persisted as a
+ * data file plus a SEPARATE stamp artifact written stamp-after-data via the
+ * shared projectionWatermark helpers. Idempotent by construction (latest-
+ * state per id), so at-least-once redelivery on resume is harmless.
+ */
+class BucketCountProjection implements ProjectionAdapter {
+  readonly family = 'bucket-counts'
+  /** Every generation this INSTANCE applied — the refold detector for (iii). */
+  readonly appliedGenerations: number[] = []
+  private latest: Map<string, string | null>
+  private wm: number | null
+
+  private constructor(
+    private readonly dir: string,
+    wm: number | null,
+    latest: Map<string, string | null>
+  ) {
+    this.wm = wm
+    this.latest = latest
+  }
+
+  /** Load from the artifact dir — data is trusted only under a valid stamp. */
+  static async open(dir: string): Promise<BucketCountProjection> {
+    mkdirSync(dir, { recursive: true })
+    const stampPath = join(dir, 'stamp.json')
+    const dataPath = join(dir, 'data.json')
+    let wm: number | null = null
+    if (existsSync(stampPath)) {
+      wm = readStampedWatermark(JSON.parse(readFileSync(stampPath, 'utf8')))
+    }
+    const latest = new Map<string, string | null>(
+      wm !== null && existsSync(dataPath)
+        ? (JSON.parse(readFileSync(dataPath, 'utf8')) as Array<[string, string | null]>)
+        : []
+    )
+    return new BucketCountProjection(dir, wm, latest)
+  }
+
+  /** Non-null bucket tallies from the latest-state map. */
+  counts(): Record<string, number> {
+    const out: Record<string, number> = {}
+    for (const bucket of this.latest.values()) {
+      if (bucket !== null) out[bucket] = (out[bucket] ?? 0) + 1
+    }
+    return out
+  }
+
+  watermark(): number | null {
+    return this.wm
+  }
+
+  async applyBatch(facts: CommitFact[], upTo: number): Promise<void> {
+    for (const fact of facts) {
+      this.appliedGenerations.push(fact.generation)
+      for (const op of fact.ops) {
+        if (op.kind !== 'noun') continue
+        if (op.record === null) {
+          this.latest.set(op.id, null) // tombstone
+          continue
+        }
+        // The stored noun record nests user metadata under `.metadata`.
+        const stored = op.record.metadata as Record<string, unknown> | null
+        const user = (stored?.metadata ?? stored) as Record<string, unknown> | null
+        const bucket = typeof user?.bucket === 'string' ? user.bucket : null
+        this.latest.set(op.id, bucket)
+      }
+    }
+    // Durability THEN stamp — the projectionWatermark law.
+    writeFileSync(join(this.dir, 'data.json'), JSON.stringify([...this.latest]))
+    writeFileSync(join(this.dir, 'stamp.json'), JSON.stringify(makeProjectionStamp(upTo)))
+    this.wm = upTo
+  }
+
+  async discard(): Promise<void> {
+    rmSync(this.dir, { recursive: true, force: true })
+  }
+}
+
+describe('reprojection doors-open — a real brain, a toy secondary projection', () => {
+  let brainDir: string
+  let projRoot: string
+  let brain: Brainy
+  const ids: string[] = []
+
+  const openBrain = async (dir: string): Promise<Brainy> => {
+    const b = new Brainy({
+      storage: { type: 'filesystem', path: dir },
+      requireSubtype: false,
+      silent: true,
+      dimensions: 384
+    })
+    await b.init()
+    return b
+  }
+
+  /**
+   * The production wiring, callback form: the engine's `from` is an EXCLUSIVE
+   * lower bound, `scanFacts` bounds are inclusive — hence `from + 1`; the
+   * first batch is returned and the handle closed (short batches at segment
+   * boundaries are legal — only EMPTY means caught up).
+   */
+  const sourceFor = (b: Brainy): FactLogSource =>
+    new FactLogSource(async (from, limit) => {
+      const scan = b.scanFacts({ fromGeneration: from + 1, batchSize: limit })
+      if (!scan) throw new Error('this brain hosts no fact log — cannot reproject')
+      const iterator = scan.batches()
+      try {
+        const first = await iterator.next()
+        return first.done ? [] : first.value.facts
+      } finally {
+        if (typeof iterator.return === 'function') await iterator.return(undefined)
+      }
+    })
+
+  beforeAll(async () => {
+    brainDir = mkdtempSync(join(tmpdir(), 'brainy-reproj-'))
+    projRoot = mkdtempSync(join(tmpdir(), 'brainy-reproj-artifacts-'))
+    brain = await openBrain(brainDir)
+    for (let i = 0; i < ROWS; i++) {
+      ids.push(
+        await brain.add({
+          data: `record ${i} filed in bucket ${i % BUCKETS}`,
+          type: 'document',
+          metadata: { bucket: `b${i % BUCKETS}` }
+        })
+      )
+    }
+  }, 240_000)
+
+  afterAll(async () => {
+    await brain?.close().catch(() => {})
+    rmSync(brainDir, { recursive: true, force: true })
+    rmSync(projRoot, { recursive: true, force: true })
+  })
+
+  it('(i) folds to caught-up through the engine and matches ground-truth counts', async () => {
+    const projection = await BucketCountProjection.open(join(projRoot, 'i'))
+    const engine = new ReprojectionEngine({ source: sourceFor(brain), batchSize: 8 })
+    engine.register(projection)
+
+    const result = await engine.advance(projection.family, { budgetMs: 60_000 })
+
+    expect(result.status).toBe('caught-up')
+    expect(result.watermark).toBeGreaterThanOrEqual(ROWS) // one generation per add, at least
+    expect(result.applied).toBeGreaterThanOrEqual(ROWS)
+    expect(engine.quarantined(projection.family)).toEqual([])
+    expect(projection.counts()).toEqual(GROUND_TRUTH)
+    // The stamp on disk is the adapter's own — stamped exactly at the fold head.
+    const reloaded = await BucketCountProjection.open(join(projRoot, 'i'))
+    expect(reloaded.watermark()).toBe(result.watermark)
+    expect(reloaded.counts()).toEqual(GROUND_TRUTH)
+  })
+
+  it('(ii) doors stay open mid-fold: find() and get() answer, and a bump preempts the advance', async () => {
+    const projection = await BucketCountProjection.open(join(projRoot, 'ii'))
+    const engine = new ReprojectionEngine({ source: sourceFor(brain), batchSize: 4 })
+    engine.register(projection)
+    const head = brain.scanFacts()!.headGeneration
+
+    const inFlight = engine.advance(projection.family, { budgetMs: 60_000 })
+    // The read hook: foreground door traffic announces itself, then reads —
+    // both interleave with the running fold on the same event loop.
+    engine.doorSignal.bump()
+    const found = await brain.find({ query: 'record filed in bucket', limit: 3 })
+    const got = await brain.get(ids[0])
+    const result = await inFlight
+
+    // The doors answered mid-fold.
+    expect(found.length).toBeGreaterThan(0)
+    expect(got).toBeTruthy()
+    const gotMeta = got!.metadata as Record<string, unknown> | undefined
+    expect((gotMeta?.bucket ?? (gotMeta?.metadata as Record<string, unknown>)?.bucket)).toBe('b0')
+
+    // THE PREEMPTION PIN — mechanism, not wall-clock: the bump landed before
+    // the first installment boundary, so the advance yielded after exactly
+    // one batch (≤ batchSize facts), far short of the head.
+    expect(result.status).toBe('preempted')
+    expect(result.applied).toBeGreaterThan(0)
+    expect(result.applied).toBeLessThanOrEqual(4)
+    expect(projection.appliedGenerations.length).toBe(result.applied)
+    expect(projection.watermark()).not.toBeNull()
+    expect(projection.watermark()!).toBeLessThan(head)
+
+    // Resuming folds the remainder; nothing was lost to the preemption.
+    const resumed = await engine.advance(projection.family, { budgetMs: 60_000 })
+    expect(resumed.status).toBe('caught-up')
+    expect(projection.counts()).toEqual(GROUND_TRUTH)
+  })
+
+  it('(iii) crash mid-fold: reopen and re-advance resumes from the stamp, never refolds from zero', async () => {
+    const projDir = join(projRoot, 'iii')
+    const before = await BucketCountProjection.open(projDir)
+    const engine1 = new ReprojectionEngine({ source: sourceFor(brain), batchSize: 4 })
+    engine1.register(before)
+
+    // A zero budget folds exactly one guaranteed batch, then stops.
+    const partial = await engine1.advance(before.family, { budgetMs: 0 })
+    expect(partial.status).toBe('budget-exhausted')
+    const stamped = before.watermark()
+    expect(stamped).not.toBeNull()
+    expect(stamped!).toBeGreaterThan(0)
+
+    // CRASH: abandon the engine and adapter mid-fold; reopen the brain cold.
+    await brain.close()
+    brain = await openBrain(brainDir)
+
+    const after = await BucketCountProjection.open(projDir)
+    expect(after.watermark()).toBe(stamped) // the stamp survived the crash
+
+    const engine2 = new ReprojectionEngine({ source: sourceFor(brain), batchSize: 4 })
+    engine2.register(after)
+    const resumed = await engine2.advance(after.family, { budgetMs: 60_000 })
+    expect(resumed.status).toBe('caught-up')
+
+    // NEVER REFOLDS FROM ZERO: every generation the resumed instance applied
+    // sits strictly above the crash stamp.
+    expect(after.appliedGenerations.length).toBeGreaterThan(0)
+    expect(Math.min(...after.appliedGenerations)).toBeGreaterThan(stamped!)
+    // And the combined state — durable prefix plus resumed fold — is exact.
+    expect(after.counts()).toEqual(GROUND_TRUTH)
+  })
+})

tests/integration/reserved-root-mint.test.ts

@@ -0,0 +1,100 @@
+/**
+ * @module tests/integration/reserved-root-mint
+ * @description THE RESERVED-ROOT MINT EXEMPTION (the release's final fix):
+ * existing brains mint the VFS root (the all-zeros UUID) as int 0 by
+ * construction at genesis — the one legitimate zero in the id space. The
+ * adoption path must accept it (every real depot brain refused adoption
+ * over this); a zero mint for ANY OTHER id remains a corrupt-mint refusal.
+ */
+import { describe, it, expect, afterEach } from 'vitest'
+import { mkdtempSync, rmSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { Brainy } from '../../src/index.js'
+import { NounType } from '../../src/types/graphTypes.js'
+
+const ROOT = '00000000-0000-0000-0000-000000000000'
+const dirs: string[] = []
+const brains: Brainy[] = []
+afterEach(async () => {
+  for (const b of brains.splice(0)) await b.close().catch(() => {})
+  for (const d of dirs.splice(0)) rmSync(d, { recursive: true, force: true })
+})
+
+type MapperBox = {
+  metadataIndex: {
+    getIdMapper(): {
+      uuidToInt: Map<string, number>
+      intToUuid: Map<number, string>
+      dirty?: boolean
+    }
+  }
+}
+
+describe('reserved-root mint exemption', () => {
+  it('adoption succeeds on a brain whose VFS root carries int 0 (the depot-brain shape)', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-root0-'))
+    dirs.push(dir)
+    // Build the brain in 'defer' so we control the adoption moment.
+    const brain = new Brainy({
+      storage: { type: 'filesystem', path: dir },
+      requireSubtype: false,
+      logAuthority: 'defer'
+    })
+    await brain.init()
+    brains.push(brain)
+    await brain.add({ data: 'depot row', type: NounType.Document, metadata: { k: 1 } })
+
+    // The genesis-era shape: the root's mint is 0 (white-box — real depot
+    // brains carry this in their persisted mapper).
+    const mapper = (brain as unknown as MapperBox).metadataIndex.getIdMapper()
+    const currentInt = mapper.uuidToInt.get(ROOT)
+    if (currentInt !== undefined) mapper.intToUuid.delete(currentInt)
+    mapper.uuidToInt.set(ROOT, 0)
+    mapper.intToUuid.set(0, ROOT)
+
+    // THE PIN: adoption goes green — the backfill re-commits the root with
+    // its legitimate int 0 instead of refusing the whole brain.
+    const report = await brain.adoptLogAuthority()
+    expect(report.verdict).toBe('green')
+    expect(brain.logAuthority().authority).toBe('log')
+    // And the brain keeps serving + writing after the flip.
+    const fresh = await brain.add({ data: 'post-adopt', type: NounType.Document, metadata: { k: 2 } })
+    expect((await brain.get(fresh))!.data).toContain('post-adopt')
+  }, 120000)
+
+  it('a zero mint for a NON-root id still refuses at the mint seam, loudly and typed', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-nonroot0-'))
+    dirs.push(dir)
+    const brain = new Brainy({
+      storage: { type: 'filesystem', path: dir },
+      requireSubtype: false,
+      logAuthority: 'defer'
+    })
+    await brain.init()
+    brains.push(brain)
+    const victim = await brain.add({ data: 'poisoned mint target', type: NounType.Document, metadata: {} })
+
+    // Corrupt shape: some OTHER id maps to 0. (A full update() SELF-HEALS
+    // this — the index cycle re-mints before the fact is written, which is
+    // the correct outcome — so the pin holds the guard at its real seam:
+    // the fact log's minter, which is what stands between a surviving zero
+    // and the wire.)
+    const mapper = (brain as unknown as MapperBox).metadataIndex.getIdMapper()
+    const currentInt = mapper.uuidToInt.get(victim)
+    if (currentInt !== undefined) mapper.intToUuid.delete(currentInt)
+    mapper.uuidToInt.set(victim, 0)
+    mapper.intToUuid.set(0, victim)
+
+    const factLog = (brain as unknown as {
+      generationStore: { getFactLog(): { intMinter(kind: string, id: string): bigint } }
+    }).generationStore.getFactLog()
+    expect(() => factLog.intMinter('noun', victim)).toThrow(
+      /reserved for the VFS root|minted ints are positive/
+    )
+    // And the reserved root itself passes the same seam with 0.
+    mapper.uuidToInt.set(ROOT, 0)
+    mapper.intToUuid.set(0, ROOT)
+    expect(factLog.intMinter('noun', ROOT)).toBe(0n)
+  }, 120000)
+})

tests/integration/transact-durability-barrier.test.ts

@@ -43,6 +43,13 @@ describe('transact durability barrier — entity writes fsync before the counter
     })
     await brain.init()
 
+    // Drain the pending tier BEFORE instrumenting: the adopt-at-open fleet
+    // default re-commits the init-time baseline as a buffered single-op
+    // generation, and transact() flushes buffered single-ops first — that
+    // flush's manifest sync would otherwise be recorded ahead of the
+    // transact's own commit point and break the first-index ordering pins.
+    await brain.flush()
+
     // Instrument the real filesystem storage: record every fsync batch in order,
     // and count barrier open/flush, delegating to the originals.
     syncCalls = []

tests/integration/wait-for-indexed.test.ts

@@ -0,0 +1,219 @@
+/**
+ * @module tests/integration/wait-for-indexed
+ * @description THE READ BARRIER — `brain.waitForIndexed(path?, opts?)`. A
+ * consumer that writes and then semantically recalls gets ONE honest barrier
+ * instead of guessing. The contract pinned here:
+ *
+ * 1. SEMANTIC LEG: a deferred add followed by `waitForIndexed('semantic')`
+ *    resolves only after the vector landed — the row is vector-searchable
+ *    the moment the barrier returns.
+ * 2. TYPED TIMEOUT: `timeoutMs` expiry REJECTS with
+ *    WaitForIndexedTimeoutError carrying the leg + the pending count and
+ *    naming the gauge — never a silent partial wait.
+ * 3. NO-ARG: every projection at the head; today that means the deferred
+ *    embed backlog is drained.
+ * 4. SYNCHRONOUS LEGS: metadata/graph/aggregation resolve immediately by
+ *    design today (they update inside the write path) — even while the
+ *    semantic backlog is wedged.
+ * 5. GAUGES: getIndexStatus().projections carries the per-leg numbers, and
+ *    the top-level pendingEmbeds compat field agrees with the semantic one.
+ * 6. GENERATION REFINEMENT: an empty backlog satisfies any generation
+ *    immediately; a non-empty one falls back to the full drain.
+ */
+import { describe, it, expect, afterEach, vi } from 'vitest'
+import { Brainy, WaitForIndexedTimeoutError } from '../../src/index.js'
+import { NounType } from '../../src/types/graphTypes.js'
+
+const brains: Brainy[] = []
+
+async function memBrain(): Promise<Brainy> {
+  const b = new Brainy({ storage: { type: 'memory' }, requireSubtype: false })
+  await b.init()
+  brains.push(b)
+  return b
+}
+
+/**
+ * Abandon a poisoned in-flight embed run (its embed promise never resolves —
+ * production is covered by the worker's 60s hang guard; the test takes the
+ * white-box shortcut for speed), then drain so teardown never wedges.
+ */
+async function unwedge(brain: Brainy): Promise<void> {
+  ;(brain as unknown as { _embedWorkerFlight: Promise<void> | null })._embedWorkerFlight = null
+  await brain.awaitPendingEmbeds()
+}
+
+afterEach(async () => {
+  vi.restoreAllMocks()
+  for (const b of brains.splice(0)) await b.close().catch(() => {})
+})
+
+describe('waitForIndexed — the read barrier', () => {
+  it("SEMANTIC LEG: deferred add → waitForIndexed('semantic') resolves and the row is vector-searchable after", async () => {
+    const brain = await memBrain()
+    const embedSpy = vi.spyOn(brain, 'embed')
+
+    const id = await brain.add({
+      data: 'the quarterly revenue report for the northern region',
+      type: NounType.Document,
+      deferEmbedding: true,
+      metadata: { kind: 'report' }
+    })
+    expect(embedSpy, 'no embed on the ack path').not.toHaveBeenCalled()
+    expect(brain.pendingEmbedCount()).toBeGreaterThanOrEqual(1)
+
+    await brain.waitForIndexed('semantic')
+
+    // The barrier's meaning: backlog drained, vector real, row searchable.
+    expect(brain.pendingEmbedCount(), 'barrier means drained').toBe(0)
+    const after = await brain.get(id, { includeVectors: true })
+    expect((after!.vector as number[]).length, 'real vector after the barrier').toBeGreaterThan(0)
+    const hits = await brain.find({
+      query: 'the quarterly revenue report for the northern region',
+      searchMode: 'semantic',
+      limit: 5
+    })
+    expect(hits.map((r) => r.id), 'vector-searchable after the barrier').toContain(id)
+  })
+
+  it('TYPED TIMEOUT: a hung embedder + timeoutMs rejects with the typed error naming the pending count and the gauge', async () => {
+    const brain = await memBrain()
+    const hang = vi
+      .spyOn(brain, 'embed')
+      .mockImplementation(() => new Promise<number[]>(() => {}))
+
+    await brain.add({
+      data: 'never lands while the embedder hangs',
+      type: NounType.Document,
+      deferEmbedding: true,
+      metadata: {}
+    })
+    expect(brain.pendingEmbedCount()).toBe(1)
+
+    let caught: unknown
+    try {
+      await brain.waitForIndexed('semantic', { timeoutMs: 200 })
+    } catch (e) {
+      caught = e
+    }
+
+    expect(caught, 'expiry REJECTS — never a silent partial wait').toBeInstanceOf(
+      WaitForIndexedTimeoutError
+    )
+    const err = caught as WaitForIndexedTimeoutError
+    expect(err.path).toBe('semantic')
+    expect(err.timeoutMs).toBe(200)
+    expect(err.pendingEmbeds).toBeGreaterThanOrEqual(1)
+    // The message names what was still pending and the gauge to check.
+    expect(err.message).toContain(`${err.pendingEmbeds} deferred embed`)
+    expect(err.message).toContain('getIndexStatus().projections.semantic.pendingEmbeds')
+
+    hang.mockRestore()
+    await unwedge(brain)
+    expect(brain.pendingEmbedCount()).toBe(0)
+  })
+
+  it('NO-ARG: waitForIndexed() waits on the pending-embed drain (every projection at the head)', async () => {
+    const brain = await memBrain()
+    await brain.add({
+      data: 'a deferred capture that the bare barrier must cover',
+      type: NounType.Document,
+      deferEmbedding: true,
+      metadata: {}
+    })
+    expect(brain.pendingEmbedCount()).toBeGreaterThanOrEqual(1)
+
+    await brain.waitForIndexed()
+
+    expect(
+      brain.pendingEmbedCount(),
+      'the bare barrier drained the only asynchronous projection'
+    ).toBe(0)
+  })
+
+  it('SYNCHRONOUS LEGS: metadata/graph/aggregation resolve immediately — even while the semantic backlog is wedged', async () => {
+    const brain = await memBrain()
+
+    // Quiet brain first: all three legs resolve on a brain with no backlog.
+    await brain.add({ data: 'quiet row', type: NounType.Document, metadata: { q: 1 } })
+    await brain.awaitPendingEmbeds()
+    await brain.waitForIndexed('metadata')
+    await brain.waitForIndexed('graph')
+    await brain.waitForIndexed('aggregation')
+
+    // The stronger pin: these projections update inside the write path today,
+    // so their leg resolves immediately BY DESIGN — independent of a wedged
+    // semantic backlog. (If any of them incorrectly delegated to the embed
+    // drain, this test would hang.)
+    const hang = vi
+      .spyOn(brain, 'embed')
+      .mockImplementation(() => new Promise<number[]>(() => {}))
+    await brain.add({
+      data: 'wedged deferred row',
+      type: NounType.Document,
+      deferEmbedding: true,
+      metadata: {}
+    })
+    expect(brain.pendingEmbedCount()).toBe(1)
+
+    await brain.waitForIndexed('metadata')
+    await brain.waitForIndexed('graph')
+    await brain.waitForIndexed('aggregation')
+
+    hang.mockRestore()
+    await unwedge(brain)
+  })
+
+  it('GAUGES: getIndexStatus().projections carries the per-leg shape, and the compat field agrees', async () => {
+    const brain = await memBrain()
+    await brain.add({ data: 'gauge row', type: NounType.Document, metadata: { g: 1 } })
+    await brain.awaitPendingEmbeds()
+
+    const status = await brain.getIndexStatus()
+    expect(status.projections).toEqual({
+      semantic: { pendingEmbeds: 0 },
+      metadata: { synchronous: true },
+      graph: { synchronous: true },
+      aggregation: { pendingBackfills: 0, pendingCatchUps: 0 }
+    })
+    // Compat: the existing top-level gauge stays and agrees.
+    expect(status.pendingEmbeds).toBe(0)
+
+    // The semantic gauge is honest while a backlog exists.
+    const hang = vi
+      .spyOn(brain, 'embed')
+      .mockImplementation(() => new Promise<number[]>(() => {}))
+    await brain.add({
+      data: 'backlogged row',
+      type: NounType.Document,
+      deferEmbedding: true,
+      metadata: {}
+    })
+    const busy = await brain.getIndexStatus()
+    expect(busy.projections.semantic.pendingEmbeds).toBeGreaterThanOrEqual(1)
+    expect(busy.pendingEmbeds).toBe(busy.projections.semantic.pendingEmbeds)
+
+    hang.mockRestore()
+    await unwedge(brain)
+  })
+
+  it('GENERATION REFINEMENT: an empty backlog satisfies any generation immediately; a non-empty one falls back to the full drain', async () => {
+    const brain = await memBrain()
+    await brain.add({ data: 'generation row', type: NounType.Document, metadata: {} })
+    await brain.awaitPendingEmbeds()
+
+    // Empty backlog: the semantic watermark is at the head — >= any committed G.
+    await brain.waitForIndexed('semantic', { generation: 1 })
+
+    // Non-empty backlog: the conservative full drain (a superset of the
+    // requested wait, never a partial one).
+    await brain.add({
+      data: 'second generation row',
+      type: NounType.Document,
+      deferEmbedding: true,
+      metadata: {}
+    })
+    await brain.waitForIndexed('semantic', { generation: 1 })
+    expect(brain.pendingEmbedCount(), 'the fallback is the full drain').toBe(0)
+  })
+})

tests/integration/watermark-adopt-reopen.test.ts

@@ -0,0 +1,50 @@
+/**
+ * @module tests/integration/watermark-adopt-reopen
+ * @description End-to-end LC1 watermark adoption: a clean flush+close stamps
+ * every projection at the committed generation; the reopen verdicts all read
+ * 'adopt' — a same-version reopen owes ZERO rebuild work, provably, via the
+ * stamps rather than via absence of complaint.
+ */
+import { describe, it, expect, afterEach } from 'vitest'
+import { mkdtempSync, rmSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { Brainy } from '../../src/index.js'
+import { NounType } from '../../src/types/graphTypes.js'
+
+const dirs: string[] = []
+const brains: Brainy[] = []
+afterEach(async () => {
+  for (const b of brains.splice(0)) await b.close().catch(() => {})
+  for (const d of dirs.splice(0)) rmSync(d, { recursive: true, force: true })
+})
+
+describe('watermark stamps ride the flush fan-out', () => {
+  it('flush stamps all three projections at the committed generation; reopen adopts', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-wm-'))
+    dirs.push(dir)
+    let brain = new Brainy({ storage: { type: 'filesystem', path: dir }, requireSubtype: false })
+    await brain.init()
+    brains.push(brain)
+    await brain.add({ data: 'stamped row', type: NounType.Document, metadata: { k: 1 } })
+    await brain.flush()
+
+    const committed = (brain as unknown as {
+      storage: { committedGeneration(): number }
+    }).storage.committedGeneration()
+    const mi = (brain as unknown as { metadataIndex: { watermark(): number | null } }).metadataIndex
+    expect(mi.watermark(), 'metadata stamp = committed').toBe(committed)
+    await brain.close()
+    brains.pop()
+
+    brain = new Brainy({ storage: { type: 'filesystem', path: dir }, requireSubtype: false })
+    await brain.init()
+    brains.push(brain)
+    const mi2 = (brain as unknown as {
+      metadataIndex: { watermarkVerdict(): string | null }
+    }).metadataIndex
+    expect(mi2.watermarkVerdict(), 'clean reopen adopts').toBe('adopt')
+    // And the brain serves.
+    expect((await brain.find({ where: { k: 1 }, limit: 5 })).length).toBe(1)
+  }, 60000)
+})

tests/unit/aggregation/aggregation-provider-rebuild.test.ts

@@ -0,0 +1,134 @@
+/**
+ * @module tests/unit/aggregation/aggregation-provider-rebuild
+ * @description Pins for SELF-ENGINE-LIFECYCLE-SPRINT asks (c) + (d):
+ * (c) the native provider's parallel `rebuildAggregate` — on the provider
+ *     contract since 8.x but NEVER invoked (the JS walk streamed per-entity
+ *     FFI calls instead) — is now the backfill walk's preferred door;
+ * (d) a write-path hook that cannot see its entity (before-image-less
+ *     delete) flags an exact rescan LOUDLY instead of silently skipping the
+ *     decrement (the skip let counts drift upward forever).
+ */
+import { describe, it, expect, vi } from 'vitest'
+import { AggregationIndex } from '../../../src/aggregation/AggregationIndex.js'
+import { NounType } from '../../../src/types/graphTypes.js'
+import type { AggregationProvider, AggregateGroupState } from '../../../src/types/brainy.types.js'
+
+const DEF = {
+  name: 'by_subtype',
+  source: { type: NounType.Document },
+  groupBy: ['system.subtype'] as string[],
+  metrics: { count: { op: 'count' as const } }
+}
+
+/** Minimal in-memory storage double for the index's persistence surface. */
+function memStorage() {
+  const store = new Map<string, unknown>()
+  return {
+    saveMetadata: async (k: string, v: unknown) => void store.set(k, v),
+    getMetadata: async (k: string) => store.get(k) ?? null
+  } as never
+}
+
+function providerDouble(): AggregationProvider & { rebuildAggregate: ReturnType<typeof vi.fn> } {
+  return {
+    defineAggregate: vi.fn(),
+    removeAggregate: vi.fn(),
+    incrementalUpdate: vi.fn(() => []),
+    computeGroupKey: vi.fn(() => ({})),
+    rebuildAggregate: vi.fn((): Map<string, AggregateGroupState> => {
+      return new Map([
+        [
+          'system.subtype=invoice',
+          {
+            groupKey: { 'system.subtype': 'invoice' },
+            metrics: { count: { sum: 0, count: 2, min: Infinity, max: -Infinity, m2: 0 } }
+          } as AggregateGroupState
+        ]
+      ])
+    }),
+    queryAggregate: vi.fn(() => [])
+  } as never
+}
+
+describe('ask (c) — the native parallel rebuild is invoked, never dead code', () => {
+  it('rebuildWithProvider hands SOURCE-MATCHED entities to the provider once and swaps state in', () => {
+    const provider = providerDouble()
+    const index = new AggregationIndex(memStorage(), provider)
+    index.defineAggregate(DEF)
+
+    expect(index.hasProviderRebuild()).toBe(true)
+
+    const entities = [
+      { type: NounType.Document, subtype: 'invoice', metadata: {} },
+      { type: NounType.Document, subtype: 'invoice', metadata: {} },
+      // Source-filter mismatch: a different noun type must be filtered OUT
+      // before the provider sees the batch.
+      { type: NounType.Person, subtype: 'invoice', metadata: {} }
+    ]
+    const handled = index.rebuildWithProvider(DEF.name, entities)
+
+    expect(handled).toBe(true)
+    expect(provider.rebuildAggregate).toHaveBeenCalledTimes(1)
+    const [defArg, entArg] = provider.rebuildAggregate.mock.calls[0]
+    expect(defArg.name).toBe(DEF.name)
+    expect(entArg).toHaveLength(2)
+
+    // The rebuilt state serves — and the aggregate is no longer pending.
+    expect(index.getPendingBackfills()).not.toContain(DEF.name)
+  })
+
+  it('returns false without a provider rebuild — the caller streams the JS walk', () => {
+    const index = new AggregationIndex(memStorage())
+    index.defineAggregate(DEF)
+    expect(index.hasProviderRebuild()).toBe(false)
+    expect(index.rebuildWithProvider(DEF.name, [])).toBe(false)
+  })
+})
+
+describe('ask (d) — the before-image-less delete is LOUD, never a silent skip', () => {
+  it('flagAllForRescan puts every defined aggregate back on the backfill list', () => {
+    const index = new AggregationIndex(memStorage())
+    index.defineAggregate(DEF)
+    index.defineAggregate({ ...DEF, name: 'second' })
+    // Simulate settled state: nothing pending.
+    for (const n of index.getPendingBackfills()) {
+      index.beginBackfill(n)
+      index.finishBackfill(n)
+    }
+    expect(index.getPendingBackfills()).toEqual([])
+
+    index.flagAllForRescan('delete of X carried no before-image metadata')
+
+    expect(index.getPendingBackfills().sort()).toEqual(['by_subtype', 'second'])
+  })
+})
+
+describe('reconcileEntity — the exact delta algebra at the catch-up boundary', () => {
+  it('before-only removes, after-only adds, both reconciles a group move', () => {
+    const index = new AggregationIndex(memStorage())
+    index.defineAggregate(DEF)
+    for (const n of index.getPendingBackfills()) {
+      index.beginBackfill(n)
+      index.finishBackfill(n)
+    }
+    const doc = (subtype: string) => ({ type: NounType.Document, subtype, metadata: {} })
+
+    // Pre-window state, applied through the LIVE hooks (as adoption would
+    // have counted it): c and seed exist as drafts, x1 as an invoice.
+    index.onEntityAdded('c', doc('draft'))
+    index.onEntityAdded('seed', doc('draft'))
+    index.onEntityAdded('x1', doc('invoice'))
+
+    // The window's reconciliation: two adds, one group move, one delete.
+    index.reconcileEntity(DEF.name, 'a', null, doc('invoice'))
+    index.reconcileEntity(DEF.name, 'b', null, doc('invoice'))
+    index.reconcileEntity(DEF.name, 'c', doc('draft'), doc('invoice'))
+    index.reconcileEntity(DEF.name, 'seed', doc('draft'), null)
+
+    const rows = index.queryAggregate({ name: DEF.name })
+    const count = (st: string) =>
+      Number(rows.find(r => r.groupKey['system.subtype'] === st)?.metrics.count ?? 0)
+    expect(count('invoice')).toBe(4) // x1 + a + b + moved c
+    expect(count('draft')).toBe(0) // c moved out, seed deleted
+  })
+})

tests/unit/brainy/lazy-notready-honor.test.ts

@@ -0,0 +1,75 @@
+/**
+ * @module tests/unit/brainy/lazy-notready-honor
+ * @description THE SILENT-EMPTY TRAP pin (found during a fleet adoption,
+ * SELF-ENGINE-PAIR-STANDARD): under `disableAutoRebuild: true`, the lazy
+ * first-query path (`ensureIndexesLoaded`) assessed ONLY the vector index's
+ * readiness — a native METADATA provider reporting not-ready (its strand
+ * report) never blocked the completion latch, so the promised lazy rebuild
+ * never fired and every `find()` silently returned `[]` on a populated
+ * store (measured: 52 entities durable-but-unqueryable, first query
+ * 0ms/0 rows). The law: a not-ready report from ANY provider falls through
+ * to the rebuild — never a silent empty.
+ *
+ * White-box provider-double pattern per tests/unit/brainy/migration-deference.
+ */
+import { describe, it, expect, afterEach, vi } from 'vitest'
+import { Brainy } from '../../../src/index.js'
+import { NounType } from '../../../src/types/graphTypes.js'
+import { createTestConfig } from '../../helpers/test-factory.js'
+
+interface BrainInternals {
+  index: { size(): number }
+  metadataIndex: { isReady?: () => boolean }
+  lazyRebuildCompleted: boolean
+  ensureIndexesLoaded(): Promise<void>
+  rebuildIndexesIfNeeded(force?: boolean): Promise<void>
+}
+
+const brains: Brainy[] = []
+
+afterEach(async () => {
+  for (const b of brains.splice(0)) await b.close().catch(() => {})
+  vi.restoreAllMocks()
+})
+
+async function warmLazyBrain(): Promise<{ brain: Brainy; internals: BrainInternals }> {
+  const brain = new Brainy(createTestConfig({ disableAutoRebuild: true }))
+  await brain.init()
+  brains.push(brain)
+  for (let i = 0; i < 3; i++) {
+    await brain.add({ data: `row ${i}`, type: NounType.Document, metadata: { i } })
+  }
+  const internals = brain as unknown as BrainInternals
+  internals.lazyRebuildCompleted = false // simulate the cold first query
+  return { brain, internals }
+}
+
+describe('lazy path honors EVERY provider’s not-ready report', () => {
+  it('a not-ready METADATA provider blocks the completion latch and fires the rebuild', async () => {
+    const { internals } = await warmLazyBrain()
+
+    // The trap's shape: vector side looks fine (populated), metadata
+    // provider says NOT ready — the old gate latched complete here.
+    ;(internals.metadataIndex as { isReady?: () => boolean }).isReady = () => false
+    const rebuildSpy = vi
+      .spyOn(internals, 'rebuildIndexesIfNeeded')
+      .mockResolvedValue(undefined)
+
+    await internals.ensureIndexesLoaded()
+
+    expect(rebuildSpy, 'not-ready metadata provider must fire the lazy rebuild').toHaveBeenCalledWith(true)
+  })
+
+  it('control: all providers ready/unknown+populated → latch completes, no rebuild', async () => {
+    const { internals } = await warmLazyBrain()
+    ;(internals.metadataIndex as { isReady?: () => boolean }).isReady = () => true
+    const rebuildSpy = vi
+      .spyOn(internals, 'rebuildIndexesIfNeeded')
+      .mockResolvedValue(undefined)
+
+    await internals.ensureIndexesLoaded()
+
+    expect(rebuildSpy).not.toHaveBeenCalled()
+    expect(internals.lazyRebuildCompleted).toBe(true)
+  })
+})

tests/unit/brainy/persistence-policy.test.ts

@@ -0,0 +1,121 @@
+/**
+ * @module tests/unit/brainy/persistence-policy
+ * @description THE ENGINE-OWNED FLUSH CADENCE pins (A4,
+ * SELF-ENGINE-LIFECYCLE-SPRINT, David-directed: callers NEVER call flush()
+ * in hot paths). The production disease: 829 caller-scheduled per-write
+ * flushes convoying into 45–66 second write walls — cadence hand-rolled a
+ * layer above the only layer that can see dirty state and IO pressure.
+ *
+ * Pinned here: (1) the write-count trigger fires a BACKGROUND flush without
+ * any caller flush(); (2) the idle trigger; (3) `'manual'` restores
+ * caller-owned cadence exactly; (4) THE ACK LAW — a write acknowledges
+ * without awaiting any background flush, even one that never resolves.
+ */
+import { describe, it, expect, afterEach, vi } from 'vitest'
+import { Brainy } from '../../../src/index.js'
+import { NounType } from '../../../src/types/graphTypes.js'
+
+const brains: Brainy[] = []
+
+async function mk(persistence?: {
+  policy?: 'auto' | 'manual'
+  flushEveryWrites?: number
+  flushIntervalMs?: number
+  flushOnIdleMs?: number
+}): Promise<Brainy> {
+  const b = new Brainy({
+    storage: { type: 'memory' },
+    requireSubtype: false,
+    ...(persistence && { persistence })
+  })
+  await b.init()
+  brains.push(b)
+  return b
+}
+
+afterEach(async () => {
+  for (const b of brains.splice(0)) await b.close().catch(() => {})
+  vi.restoreAllMocks()
+})
+
+describe('persistence policy — the engine owns its flush cadence', () => {
+  it('write-count trigger: N committed writes fire ONE background flush, no caller flush()', async () => {
+    const brain = await mk({ flushEveryWrites: 5, flushOnIdleMs: 60_000, flushIntervalMs: 600_000 })
+    const flushSpy = vi.spyOn(brain, 'flush')
+
+    for (let i = 0; i < 5; i++) {
+      await brain.add({ data: `w${i}`, type: NounType.Document, metadata: { i } })
+    }
+
+    await vi.waitFor(() => expect(flushSpy).toHaveBeenCalled(), { timeout: 5000 })
+    // Single-flight: the threshold crossing kicks exactly one.
+    expect(flushSpy.mock.calls.length).toBe(1)
+  })
+
+  it('idle trigger: a quiet store with dirty writes flushes itself', async () => {
+    const brain = await mk({ flushEveryWrites: 10_000, flushIntervalMs: 600_000, flushOnIdleMs: 60 })
+    const flushSpy = vi.spyOn(brain, 'flush')
+
+    await brain.add({ data: 'lone write', type: NounType.Document, metadata: {} })
+
+    await vi.waitFor(() => expect(flushSpy).toHaveBeenCalled(), { timeout: 5000 })
+  })
+
+  it('idle debounce under load: slow writes never fire a flush per inter-write gap', async () => {
+    // The contended-disk amplifier: writes slower than the idle window make
+    // every gap look idle — without the spacing floor this fired a full
+    // flush per write (measured 15 background flushes in 100 contended adds
+    // on a production-shaped box). The floor (min(interval, 10×idle)) caps
+    // idle fires; deferred, never dropped.
+    const brain = await mk({ flushEveryWrites: 10_000, flushIntervalMs: 600_000, flushOnIdleMs: 50 })
+    const flushSpy = vi.spyOn(brain, 'flush')
+
+    // Six writes spaced wider than the idle window (50ms) with the whole
+    // span inside ~one floor window (500ms): the old behavior fires ~an
+    // idle flush per gap (≈6); the debounced behavior fires at most two
+    // (one immediate boot-window fire + one at the floor boundary).
+    for (let i = 0; i < 6; i++) {
+      await brain.add({ data: `slow ${i}`, type: NounType.Document, metadata: {} })
+      await new Promise((r) => setTimeout(r, 70))
+    }
+    expect(flushSpy.mock.calls.length, 'no flush-per-gap amplifier').toBeLessThanOrEqual(2)
+
+    // Deferred, never dropped: the dirty writes still persist once the
+    // floor elapses on the now-quiet store.
+    await vi.waitFor(() => expect(flushSpy).toHaveBeenCalled(), { timeout: 5000 })
+  })
+
+  it("'manual' policy: the engine NEVER flushes on its own", async () => {
+    const brain = await mk({ policy: 'manual', flushEveryWrites: 2, flushOnIdleMs: 30 })
+    const flushSpy = vi.spyOn(brain, 'flush')
+
+    for (let i = 0; i < 6; i++) {
+      await brain.add({ data: `m${i}`, type: NounType.Document, metadata: { i } })
+    }
+    await new Promise((r) => setTimeout(r, 150))
+
+    expect(flushSpy).not.toHaveBeenCalled()
+  })
+
+  it('THE ACK LAW: writes acknowledge without awaiting the background flush — even a hung one', async () => {
+    const brain = await mk({ flushEveryWrites: 2, flushOnIdleMs: 60_000, flushIntervalMs: 600_000 })
+    // A flush that NEVER resolves: if any write ack awaited it, the test
+    // would time out. (The engine's background flight must be fire-and-log.)
+    vi.spyOn(brain, 'flush').mockImplementation(() => new Promise<void>(() => {}))
+
+    for (let i = 0; i < 6; i++) {
+      const id = await brain.add({ data: `a${i}`, type: NounType.Document, metadata: { i } })
+      expect(id).toBeTruthy()
+    }
+    // All six writes acked while the "flush" hangs forever.
+    const rows = await brain.find({ type: NounType.Document, limit: 10 })
+    expect(rows.length).toBe(6)
+
+    // Un-hang before afterEach close(): restore the method AND drop the
+    // never-resolving in-flight promise (close() awaits the flight — with a
+    // real flush that is correct; here it is the test's own artifact).
+    vi.restoreAllMocks()
+    ;(brain as unknown as { _persistBackgroundFlight: Promise<void> | null })._persistBackgroundFlight =
+      null
+  })
+})

tests/unit/db/bounded-chains.test.ts

@@ -477,14 +477,17 @@ describe('materializeAtGeneration — bounded & deadlock-free (GA #33)', () => {
     const store = (brain as any).generationStore
 
     const N = 400
+    // Relative, not absolute: under the adopt-at-open default the open-time
+    // baseline backfill takes a generation of its own, so the first add is
+    // NOT generation 1 — pin the deep generation to the first add's commit.
+    let deepGen = 0
     for (let i = 0; i < N; i++) {
       await brain.add({ data: `doc ${i}`, type: NounType.Document, subtype: 'note', metadata: { i }, vector: VEC })
+      if (i === 0) deepGen = brain.generation()
     }
     const R = brain.generation() // ≈ N (each add is its own generation)
     expect(R).toBeGreaterThanOrEqual(N)
 
-    const deepGen = 1
-
     // Count getDelta invocations during the materialize.
     const realGetDelta = store.getDelta.bind(store)
     let getDeltaCalls = 0
@@ -509,7 +512,8 @@ describe('materializeAtGeneration — bounded & deadlock-free (GA #33)', () => {
     expect(getDeltaCalls).toBeLessThan(R * 5)
     expect(getDeltaCalls).toBeLessThan(N * N) // the regression guard
 
-    // The materialized at-gen-1 brain holds exactly the one entity that existed.
+    // The materialized brain at the first add's generation holds exactly the
+    // one user entity that existed.
     const atGen1 = await handle.find({ limit: N + 10 })
     expect(atGen1.length).toBe(1)
     await handle.close()

tests/unit/db/fact-log-group-sync.test.ts

@@ -0,0 +1,270 @@
+/**
+ * @module tests/unit/db/fact-log-group-sync
+ * @description Group commit on the fact log — the covering guarantee behind
+ * durable-at-ack: concurrent callers of ensureSynced() share ONE covering
+ * fsync (running + queued slots), a caller appending during a running sync
+ * joins a sync that STARTS after its append (never the possibly-stale running
+ * one), a solo writer syncs immediately, and at the brain level an at-ack
+ * ack resolving means the write's fact is on disk.
+ *
+ * The final pin holds the at-ack durability contract END TO END: an acked
+ * write's fact survives a crash-shaped reopen. This was a `.fails` known
+ * gap (FactLog.open() truncated every fact beyond the committed watermark,
+ * which only advances at the pending-tier flush) — CURED by the 10.0.0
+ * adopt-at-open fleet default: a fresh brain stores the log-authority
+ * artifact at open, and under 'log' authority recovery REPLAYS intact
+ * facts above the manifest instead of truncating them.
+ */
+import { describe, it, expect, beforeEach, afterEach } from 'vitest'
+import { mkdtempSync, rmSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { Brainy } from '../../../src/index.js'
+import { FileSystemStorage } from '../../../src/storage/adapters/fileSystemStorage.js'
+import {
+  FactLog,
+  storageSupportsFactLog,
+  type CommitFact,
+  type FactLogStorage
+} from '../../../src/db/factLog.js'
+
+const UUID = (n: number): string =>
+  `00000000-0000-4000-8000-${String(n).padStart(12, '0')}`
+
+const fact = (generation: number): CommitFact => ({
+  generation,
+  timestamp: 1_700_000_000_000 + generation,
+  ops: [
+    {
+      kind: 'noun',
+      id: UUID(generation),
+      record: { metadata: { noun: 'document', title: `doc ${generation}` }, vector: { v: [1, 2] } }
+    }
+  ]
+})
+
+/** Scan every fact from a FRESH reader log over the same directory. */
+async function readBack(dir: string, committedHead: number): Promise<CommitFact[]> {
+  const storage: any = new FileSystemStorage(dir)
+  await storage.init()
+  const reader = new FactLog(storage as FactLogStorage)
+  await reader.open(committedHead)
+  const facts: CommitFact[] = []
+  const scan = reader.scanFacts()
+  for await (const batch of scan.batches()) facts.push(...batch.facts)
+  return facts
+}
+
+describe('fact log group commit — the covering fsync', () => {
+  let dir: string
+  let storage: any
+  let log: FactLog
+
+  beforeEach(async () => {
+    dir = mkdtempSync(join(tmpdir(), 'brainy-group-sync-'))
+    storage = new FileSystemStorage(dir)
+    await storage.init()
+    expect(storageSupportsFactLog(storage)).toBe(true)
+    log = new FactLog(storage as FactLogStorage)
+    await log.open(0)
+  })
+
+  afterEach(() => {
+    rmSync(dir, { recursive: true, force: true })
+  })
+
+  it('many concurrent ensureSynced() callers share one covering fsync — every caller resolves, batching happened', async () => {
+    for (let g = 1; g <= 10; g++) await log.append(fact(g))
+
+    // Count REAL fsync batches at the storage boundary, with a small delay so
+    // the concurrent callers genuinely overlap the running sync.
+    let fsyncBatches = 0
+    const origSync = storage.syncRawObjects.bind(storage)
+    storage.syncRawObjects = async (paths: string[]) => {
+      fsyncBatches++
+      await new Promise((r) => setTimeout(r, 15))
+      return origSync(paths)
+    }
+
+    const callers = Array.from({ length: 10 }, () => log.ensureSynced())
+    await Promise.all(callers) // every caller resolves — no lost writer
+
+    expect(fsyncBatches, 'callers shared a covering fsync').toBeLessThan(10)
+    expect(fsyncBatches).toBeGreaterThanOrEqual(1)
+
+    // Durable: a fresh reader over the same directory sees all 10 facts.
+    const facts = await readBack(dir, 10)
+    expect(facts.map((f) => f.generation)).toEqual([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
+  })
+
+  it('an append during a RUNNING sync is covered by a sync that starts after it — never the stale running one', async () => {
+    for (let g = 1; g <= 3; g++) await log.append(fact(g))
+
+    // Gate the FIRST fsync so a sync is provably in flight.
+    let fsyncBatches = 0
+    let releaseGate!: () => void
+    const gate = new Promise<void>((r) => {
+      releaseGate = r
+    })
+    let gated = true
+    const origSync = storage.syncRawObjects.bind(storage)
+    storage.syncRawObjects = async (paths: string[]) => {
+      fsyncBatches++
+      if (gated) {
+        gated = false
+        await gate
+      }
+      return origSync(paths)
+    }
+
+    const p1 = log.ensureSynced() // sync A: snapshots gens 1..3, blocks in fsync
+    await new Promise((r) => setTimeout(r, 10))
+    expect(fsyncBatches, 'sync A is in flight').toBe(1)
+
+    await log.append(fact(4)) // lands AFTER sync A snapshotted
+    let p2Resolved = false
+    const p2 = log.ensureSynced().then(() => {
+      p2Resolved = true
+    })
+
+    // The covering guarantee: p2 must NOT resolve off the running sync (it
+    // may have snapshotted before the append) — it waits for the queued one.
+    await new Promise((r) => setTimeout(r, 25))
+    expect(p2Resolved, 'p2 never joins the possibly-stale running sync').toBe(false)
+
+    releaseGate()
+    await p1
+    await p2
+    expect(p2Resolved).toBe(true)
+    expect(fsyncBatches, 'the queued covering sync ran after the running one').toBe(2)
+
+    // The late append is durable once p2 resolved.
+    const facts = await readBack(dir, 4)
+    expect(facts.map((f) => f.generation)).toEqual([1, 2, 3, 4])
+  })
+
+  it('a solo writer syncs immediately — one fsync, and a dirty-free ensureSynced adds none', async () => {
+    // Count only covering syncs: the first append itself fsyncs the tail
+    // manifest (the manifest-first flip), so instrument AFTER it.
+    await log.append(fact(1))
+    let fsyncBatches = 0
+    const origSync = storage.syncRawObjects.bind(storage)
+    storage.syncRawObjects = async (paths: string[]) => {
+      fsyncBatches++
+      return origSync(paths)
+    }
+
+    await log.ensureSynced()
+    expect(fsyncBatches).toBe(1)
+
+    // Nothing new appended: the covering sync finds nothing dirty.
+    await log.ensureSynced()
+    expect(fsyncBatches).toBe(1)
+  })
+})
+
+describe('durable-at-ack through the brain (group commit end-to-end)', () => {
+  const dirs: string[] = []
+  const brains: any[] = []
+
+  const openBrain = async (dir?: string): Promise<{ brain: any; dir: string }> => {
+    process.env.BRAINY_DETERMINISTIC_EMBEDDINGS = 'true'
+    const d = dir ?? mkdtempSync(join(tmpdir(), 'brainy-at-ack-'))
+    if (!dir) dirs.push(d)
+    const brain: any = new Brainy({
+      storage: { type: 'filesystem', path: d },
+      requireSubtype: false,
+      silent: true,
+      dimensions: 384
+    })
+    brains.push(brain)
+    await brain.init()
+    return { brain, dir: d }
+  }
+
+  afterEach(async () => {
+    for (const b of brains.splice(0)) await b.close?.().catch(() => {})
+    for (const d of dirs.splice(0)) rmSync(d, { recursive: true, force: true })
+  })
+
+  it('at-ack: N concurrent add() acks all resolve, every ack was covered by a log sync, and every fact is on disk after reopen', async () => {
+    const { brain, dir } = await openBrain()
+    // The 10.0.0 fleet default already adopted log authority at open, so
+    // the brain is at-ack; the white-box engage stays so this pin holds the
+    // durability MACHINERY itself independent of the open-time posture.
+    brain.generationStore.setLogDurability('at-ack')
+
+    const factLog = brain.generationStore.getFactLog()
+    expect(factLog).not.toBeNull()
+    let syncs = 0
+    const origSync = factLog.sync.bind(factLog)
+    factLog.sync = async () => {
+      syncs++
+      return origSync()
+    }
+
+    const ids: string[] = await Promise.all(
+      Array.from({ length: 10 }, (_, i) =>
+        brain.add({ data: `concurrent write ${i}`, type: 'document', metadata: { i } })
+      )
+    )
+    expect(new Set(ids).size, 'every ack resolved with a distinct id').toBe(10)
+    // Honest pin: single-op acks serialize under the commit mutex (append +
+    // covering sync run inside it), so concurrent add() acks do not currently
+    // share one fsync — cross-writer batching is the FactLog-layer property
+    // pinned above. What must hold here: at least one covering sync ran, and
+    // no ack resolved without the machinery engaged.
+    expect(syncs).toBeGreaterThanOrEqual(1)
+    expect(syncs).toBeLessThanOrEqual(10)
+
+    await brain.close()
+    const { brain: reopened } = await openBrain(dir)
+    const scan = reopened.scanFacts()
+    expect(scan).not.toBeNull()
+    const liveFactIds = new Set<string>()
+    for await (const batch of scan!.batches()) {
+      for (const f of batch.facts) {
+        for (const op of f.ops) if (op.kind === 'noun' && op.record !== null) liveFactIds.add(op.id)
+      }
+    }
+    for (const id of ids) {
+      expect(liveFactIds.has(id), `fact for acked write ${id} survives reopen`).toBe(true)
+    }
+  })
+
+  // THE AT-ACK CONTRACT, HELD (was a `.fails` known gap): an acked write's
+  // fact survives a crash-shaped reopen. Fixed by the 10.0.0 adopt-at-open
+  // fleet default — this brain adopted LOG authority at open (artifact
+  // stored, durable-at-ack live), and under 'log' authority FactLog
+  // recovery REPLAYS intact facts above the committed watermark at the next
+  // open instead of truncating them back. Durable-at-ack now survives the
+  // very crash it exists for.
+  it('at-ack CONTRACT: acked facts survive a crash-shaped reopen (no flush ever ran)', async () => {
+    const { brain, dir } = await openBrain()
+    expect(brain.logAuthority().authority, 'the fleet default adopted at open').toBe('log')
+    expect(brain.generationStore.logDurability).toBe('at-ack')
+    // Crash simulation: the pending-tier durability flush never happens
+    // (every trigger routes through flushPendingSingleOps), and the brain is
+    // abandoned without close() — exactly the power-loss shape at-ack is for.
+    brain.generationStore.flushPendingSingleOps = async () => {}
+
+    const ids: string[] = []
+    for (let i = 0; i < 5; i++) {
+      ids.push(await brain.add({ data: `acked write ${i}`, type: 'document', metadata: { i } }))
+    }
+
+    // No flush, no close — reopen the directory as a new session.
+    const { brain: reopened } = await openBrain(dir)
+    const scan = reopened.scanFacts()
+    expect(scan).not.toBeNull()
+    const liveFactIds = new Set<string>()
+    for await (const batch of scan!.batches()) {
+      for (const f of batch.facts) {
+        for (const op of f.ops) if (op.kind === 'noun' && op.record !== null) liveFactIds.add(op.id)
+      }
+    }
+    for (const id of ids) {
+      expect(liveFactIds.has(id), `acked fact ${id} survives the crash-shaped reopen`).toBe(true)
+    }
+  })
+})

tests/unit/db/factLogFormat.test.ts

@@ -0,0 +1,808 @@
+/**
+ * @module tests/unit/db/factLogFormat
+ * @description Fact-log format v2 (record envelope + sector seals) pinned at
+ * the byte level: every record type round-trips field-exact (bigint ints,
+ * bin16 uuids, float-exact vectors), headers read v1 AND v2, unknown record
+ * types/versions refuse loudly with the typed error, the reserved crypto
+ * envelope (cipherFlag/keyId — plaintext-only this release) refuses anything
+ * nonzero/non-nil with the same typed error, genesis width mismatches
+ * refuse naming both widths, sealed groups align to the sector size with
+ * invisible pads, vector refs are writer-enforced single-hop, and torn tails
+ * truncate to the intact prefix at EVERY byte offset. This module is the
+ * reference implementation of a two-implementation contract — golden byte
+ * vectors here are frozen; a change that breaks them is a format change.
+ */
+import { describe, it, expect } from 'vitest'
+import { encode, decode } from '@msgpack/msgpack'
+import {
+  encodeFactV2,
+  decodeFact,
+  decodeGroupV2,
+  encodeSegmentHeaderV2,
+  parseSegmentHeader,
+  sealGroup,
+  framePayload,
+  encodePadFrame,
+  minPadFrameBytes,
+  UnknownLogRecordError,
+  GenesisWidthMismatchError,
+  LOG_RECORD_TYPES,
+  LOG_RECORD_VERSION,
+  LOG_RECORD_CIPHER_PLAINTEXT,
+  FACT_LOG_FORMAT_V1,
+  FACT_LOG_FORMAT_V2,
+  SEGMENT_HEADER_BYTES,
+  DEFAULT_SEAL_SIZE,
+  type CommitFactV2,
+  type LogRecord,
+  type VectorRef
+} from '../../../src/db/factLogFormat.js'
+
+const UUID = (n: number): string =>
+  `00000000-0000-4000-8000-${String(n).padStart(12, '0')}`
+const HASH_A = 'ab'.repeat(32)
+const HASH_B = '0123456789abcdef'.repeat(4)
+
+/** uuid string → bin16 (test-local mirror of the wire helper). */
+const uuidBytes = (id: string): Uint8Array => {
+  const hex = id.replace(/-/g, '')
+  const bytes = new Uint8Array(16)
+  for (let i = 0; i < 16; i++) bytes[i] = parseInt(hex.slice(i * 2, i * 2 + 2), 16)
+  return bytes
+}
+
+const hex = (bytes: Uint8Array): string => Buffer.from(bytes).toString('hex')
+
+/** Encode → strip frame → decode; the standard round-trip. */
+const roundTrip = (
+  fact: CommitFactV2,
+  encOpts?: Parameters<typeof encodeFactV2>[1],
+  decOpts?: { expectedIdSpaceWidth?: 32 | 64 }
+): CommitFactV2 => decodeFact(framePayload(encodeFactV2(fact, encOpts)), 2, decOpts)
+
+/** A single-record fact around `record`, canonical shape for strict equality. */
+const factOf = (generation: number, record: LogRecord): CommitFactV2 => ({
+  generation,
+  timestamp: 1_700_000_000_000 + generation,
+  records: [record]
+})
+
+/**
+ * Build a fact frame of EXACTLY `totalBytes` (projection.note binary filler),
+ * for engineering precise seal-boundary scenarios.
+ */
+function frameOfExactly(totalBytes: number, generation: number): Uint8Array {
+  let fillerLength = Math.max(0, totalBytes - 60)
+  for (let i = 0; i < 12; i++) {
+    const frame = encodeFactV2({
+      generation,
+      timestamp: 1,
+      records: [{ type: 'projection.note', note: { fill: new Uint8Array(fillerLength) } }]
+    })
+    const diff = totalBytes - frame.length
+    if (diff === 0) return frame
+    fillerLength += diff
+    if (fillerLength < 0) throw new Error(`no frame of ${totalBytes} bytes is constructible`)
+  }
+  throw new Error('frame sizing did not converge')
+}
+
+describe('fact-log format v2 — record round-trips (field-exact)', () => {
+  it('noun.afterImage: bin16 uuid, u64-as-bigint beyond 2^53, metadata, inline vector', () => {
+    const fact = factOf(1, {
+      type: 'noun.afterImage',
+      id: UUID(1),
+      entityInt: (1n << 60n) + 3n, // provably beyond Number territory
+      metadata: {
+        noun: 'document',
+        title: 'doc 1',
+        nested: { tags: ['a', 'b'], score: 0.25 },
+        big: Number.MAX_SAFE_INTEGER,
+        negative: -42,
+        flag: true,
+        missing: null
+      },
+      vectorLeg: [0.1, -2.5, 3, 1e-7]
+    })
+    expect(roundTrip(fact)).toStrictEqual(fact)
+  })
+
+  it('noun.tombstone: body-less removal', () => {
+    const fact = factOf(2, { type: 'noun.tombstone', id: UUID(2) })
+    expect(roundTrip(fact)).toStrictEqual(fact)
+  })
+
+  it('verb.afterImage: both endpoints, three u64 handles, verb name', () => {
+    const fact = factOf(3, {
+      type: 'verb.afterImage',
+      id: UUID(3),
+      verbInt: 18_446_744_073_709_551_615n, // u64 max
+      metadata: { verb: 'contains', weight: 0.5 },
+      vectorLeg: null,
+      verb: 'contains',
+      sourceId: UUID(31),
+      sourceInt: 7n,
+      targetId: UUID(32),
+      targetInt: (1n << 53n) + 1n
+    })
+    expect(roundTrip(fact)).toStrictEqual(fact)
+  })
+
+  it('verb.tombstone: body-less removal', () => {
+    const fact = factOf(4, { type: 'verb.tombstone', id: UUID(4) })
+    expect(roundTrip(fact)).toStrictEqual(fact)
+  })
+
+  it('batch.meta: one metadata map per fact', () => {
+    const fact = factOf(5, { type: 'batch.meta', meta: { source: 'import', count: 12 } })
+    expect(roundTrip(fact)).toStrictEqual(fact)
+  })
+
+  it('embed.pending: id + enqueue time', () => {
+    const fact = factOf(6, { type: 'embed.pending', id: UUID(6), enqueuedAt: 1_700_000_000_777 })
+    expect(roundTrip(fact)).toStrictEqual(fact)
+  })
+
+  it('embed.landed: inline vector, float-exact', () => {
+    const fact = factOf(7, {
+      type: 'embed.landed',
+      id: UUID(7),
+      vector: [0.30000000000000004, -1.5, 2 ** 31 + 0.5]
+    })
+    expect(roundTrip(fact)).toStrictEqual(fact)
+  })
+
+  it('blob.manifest: bin32 hash, size, mimeType, both refOps', () => {
+    const add = factOf(8, {
+      type: 'blob.manifest',
+      hash: HASH_A,
+      size: 1_048_576,
+      mimeType: 'image/png',
+      refOp: 'add'
+    })
+    expect(roundTrip(add)).toStrictEqual(add)
+    const release = factOf(9, {
+      type: 'blob.manifest',
+      hash: HASH_B,
+      size: 0,
+      mimeType: 'application/octet-stream',
+      refOp: 'release'
+    })
+    expect(roundTrip(release)).toStrictEqual(release)
+  })
+
+  it('projection.note: opaque map rides untouched', () => {
+    const fact = factOf(10, {
+      type: 'projection.note',
+      note: { consumer: 'reserved', payload: { depth: [1, 2, 3] } }
+    })
+    expect(roundTrip(fact)).toStrictEqual(fact)
+  })
+
+  it('bootstrap.baseline: kind flag, metadata, vector leg — both kinds', () => {
+    const noun = factOf(11, {
+      type: 'bootstrap.baseline',
+      id: UUID(11),
+      kind: 'noun',
+      metadata: { noun: 'person' },
+      vectorLeg: [1, 2, 3]
+    })
+    expect(roundTrip(noun)).toStrictEqual(noun)
+    const verb = factOf(12, {
+      type: 'bootstrap.baseline',
+      id: UUID(12),
+      kind: 'verb',
+      metadata: null,
+      vectorLeg: null
+    })
+    expect(roundTrip(verb)).toStrictEqual(verb)
+  })
+
+  it('log.genesis: width, brainId, createdAt — both widths', () => {
+    for (const idSpaceWidth of [32, 64] as const) {
+      const fact = factOf(1, {
+        type: 'log.genesis',
+        idSpaceWidth,
+        brainId: UUID(999),
+        createdAt: 1_700_000_000_000
+      })
+      expect(roundTrip(fact, undefined, { expectedIdSpaceWidth: idSpaceWidth })).toStrictEqual(fact)
+    }
+  })
+
+  it('a combined fact: genesis-first, all record types, fact meta, duplicate blobHashes', () => {
+    const fact: CommitFactV2 = {
+      generation: 1,
+      timestamp: 1_700_000_000_001,
+      records: [
+        { type: 'log.genesis', idSpaceWidth: 64, brainId: UUID(999), createdAt: 1_699_999_999_999 },
+        { type: 'noun.afterImage', id: UUID(1), entityInt: 1n, metadata: { a: 1 }, vectorLeg: [0.5] },
+        { type: 'noun.tombstone', id: UUID(2) },
+        {
+          type: 'verb.afterImage',
+          id: UUID(3),
+          verbInt: 3n,
+          metadata: null,
+          vectorLeg: null,
+          verb: 'relatedTo',
+          sourceId: UUID(31),
+          sourceInt: 1n,
+          targetId: UUID(32),
+          targetInt: 2n
+        },
+        { type: 'verb.tombstone', id: UUID(4) },
+        { type: 'batch.meta', meta: { origin: 'unit' } },
+        { type: 'embed.pending', id: UUID(6), enqueuedAt: 5 },
+        { type: 'embed.landed', id: UUID(7), vector: [0.1] },
+        { type: 'blob.manifest', hash: HASH_A, size: 9, mimeType: 'text/plain', refOp: 'add' },
+        { type: 'projection.note', note: {} },
+        { type: 'bootstrap.baseline', id: UUID(11), kind: 'noun', metadata: null, vectorLeg: null }
+      ],
+      meta: { source: 'unit' },
+      blobHashes: [HASH_A, HASH_A] // multiset — duplicates preserved
+    }
+    expect(roundTrip(fact, undefined, { expectedIdSpaceWidth: 64 })).toStrictEqual(fact)
+  })
+})
+
+describe('fact-log format v2 — golden byte vectors (frozen contract)', () => {
+  it('v2 segment header bytes are pinned', () => {
+    expect(hex(encodeSegmentHeaderV2(7, 4096))).toBe(
+      '4246414354530000020000000700000000000000001000000000000000000000'
+    )
+  })
+
+  it('a noun.tombstone frame is pinned byte-for-byte', () => {
+    const frame = encodeFactV2({
+      generation: 3,
+      timestamp: 1_700_000_000_123,
+      records: [{ type: 'noun.tombstone', id: '00000000-0000-4000-8000-000000000042' }]
+    })
+    expect(hex(frame)).toBe(
+      '2d00000048e4d43695cf0000000000000003cf0000018bcfe5687b9195020100c0' +
+        'c41000000000000040008000000000000042c0c0'
+    )
+  })
+
+  it('u64 registry fields ride as fixed 8-byte msgpack uint64 (0xcf)', () => {
+    const payload = framePayload(
+      encodeFactV2(factOf(1, { type: 'embed.pending', id: UUID(1), enqueuedAt: 2 }))
+    )
+    // positions 0 and 1 (generation, timestamp) and enqueuedAt are all 0xcf
+    expect(payload[1]).toBe(0xcf)
+    expect(payload[10]).toBe(0xcf)
+  })
+})
+
+describe('fact-log format v2 — segment headers (v1 AND v2)', () => {
+  const v1Header = (): Uint8Array => {
+    const header = new Uint8Array(SEGMENT_HEADER_BYTES)
+    header.set(new Uint8Array([0x42, 0x46, 0x41, 0x43, 0x54, 0x53, 0x00, 0x00]), 0)
+    const view = new DataView(header.buffer)
+    view.setUint32(8, FACT_LOG_FORMAT_V1, true)
+    view.setBigUint64(12, 42n, true)
+    return header
+  }
+
+  it('a v2 header round-trips with its sealSize', () => {
+    const header = encodeSegmentHeaderV2(123_456, 512)
+    expect(header.length).toBe(SEGMENT_HEADER_BYTES)
+    expect(parseSegmentHeader(header)).toStrictEqual({
+      formatVersion: FACT_LOG_FORMAT_V2,
+      firstGeneration: 123_456,
+      sealSize: 512
+    })
+    // default sealSize
+    expect(parseSegmentHeader(encodeSegmentHeaderV2(1)).sealSize).toBe(DEFAULT_SEAL_SIZE)
+  })
+
+  it('a v1 header parses: version 1, sealSize absent (undefined)', () => {
+    const parsed = parseSegmentHeader(v1Header())
+    expect(parsed).toStrictEqual({ formatVersion: FACT_LOG_FORMAT_V1, firstGeneration: 42 })
+    expect(parsed.sealSize).toBeUndefined()
+  })
+
+  it('corrupted magic throws', () => {
+    const header = encodeSegmentHeaderV2(1)
+    header[0] = 0x58
+    expect(() => parseSegmentHeader(header)).toThrow(/bad magic/)
+  })
+
+  it('non-zero reserved bytes throw — v1 (offset 20+) and v2 (offset 22+)', () => {
+    const v1 = v1Header()
+    v1[21] = 1
+    expect(() => parseSegmentHeader(v1)).toThrow(/non-zero reserved/)
+
+    const v2 = encodeSegmentHeaderV2(1, 4096)
+    v2[25] = 1
+    expect(() => parseSegmentHeader(v2)).toThrow(/non-zero reserved/)
+  })
+
+  it('the v2 sealSize bytes are NOT reserved bytes in v2 (but ARE in v1)', () => {
+    // sealSize 512 puts a non-zero byte at offset 21 — legal in v2 only.
+    const v2 = encodeSegmentHeaderV2(1, 512)
+    expect(parseSegmentHeader(v2).sealSize).toBe(512)
+    const v1 = v1Header()
+    v1[20] = 0x00
+    v1[21] = 0x02 // same bytes a v2 sealSize=512 would carry
+    expect(() => parseSegmentHeader(v1)).toThrow(/non-zero reserved/)
+  })
+
+  it('an unknown header version and a short buffer throw', () => {
+    const header = encodeSegmentHeaderV2(1)
+    new DataView(header.buffer).setUint32(8, 3, true)
+    expect(() => parseSegmentHeader(header)).toThrow(/formatVersion 3/)
+    expect(() => parseSegmentHeader(header.subarray(0, 31))).toThrow(/32 bytes/)
+  })
+
+  it('header writer refuses out-of-range inputs', () => {
+    expect(() => encodeSegmentHeaderV2(-1)).toThrow(/non-negative/)
+    expect(() => encodeSegmentHeaderV2(1, 32)).toThrow(/sealSize/)
+    expect(() => encodeSegmentHeaderV2(1, 65_536)).toThrow(/sealSize/)
+  })
+})
+
+describe('fact-log format v2 — decoder law (typed refusals, never skip)', () => {
+  it('unknown record type 12 throws UnknownLogRecordError naming type 12', () => {
+    const payload = encode([1, 1, [[12, 1]], null, null])
+    expect(() => decodeFact(payload, 2)).toThrow(UnknownLogRecordError)
+    try {
+      decodeFact(payload, 2)
+      expect.unreachable('decode must throw')
+    } catch (error) {
+      const typed = error as UnknownLogRecordError
+      expect(typed).toBeInstanceOf(UnknownLogRecordError)
+      expect(typed.recordType).toBe(12)
+      expect(typed.recordVersion).toBe(1)
+      expect(typed.message).toMatch(/type 12/)
+      expect(typed.message).toMatch(/newer reader/)
+    }
+  })
+
+  it('recordVersion 2 on a known type throws the same class naming the version', () => {
+    const payload = encode([1, 1, [[LOG_RECORD_TYPES.NOUN_TOMBSTONE, 2, new Uint8Array(16)]], null, null])
+    try {
+      decodeFact(payload, 2)
+      expect.unreachable('decode must throw')
+    } catch (error) {
+      const typed = error as UnknownLogRecordError
+      expect(typed).toBeInstanceOf(UnknownLogRecordError)
+      expect(typed.recordType).toBe(LOG_RECORD_TYPES.NOUN_TOMBSTONE)
+      expect(typed.recordVersion).toBe(2)
+      expect(typed.message).toMatch(/version 2/)
+      expect(typed.message).toMatch(/newer reader/)
+    }
+  })
+
+  it('a fact mixing known and unknown records still refuses (no partial reads)', () => {
+    const known = [LOG_RECORD_TYPES.NOUN_TOMBSTONE, 1, 0, null, uuidBytes(UUID(1))]
+    const payload = encode([1, 1, [known, [200, 1]], null, null])
+    expect(() => decodeFact(payload, 2)).toThrow(UnknownLogRecordError)
+  })
+
+  it('a nonzero cipherFlag refuses with the typed error — encrypted records need a newer reader', () => {
+    const payload = encode(
+      [1, 1, [[LOG_RECORD_TYPES.NOUN_TOMBSTONE, 1, 1, null, uuidBytes(UUID(1))]], null, null]
+    )
+    try {
+      decodeFact(payload, 2)
+      expect.unreachable('decode must throw')
+    } catch (error) {
+      const typed = error as UnknownLogRecordError
+      expect(typed).toBeInstanceOf(UnknownLogRecordError)
+      expect(typed.recordType).toBe(LOG_RECORD_TYPES.NOUN_TOMBSTONE)
+      expect(typed.recordVersion).toBe(1)
+      expect(typed.message).toMatch(/cipherFlag 1/)
+      expect(typed.message).toMatch(/encrypted records need a newer reader/)
+    }
+  })
+
+  it('a non-nil keyId refuses the same way, even with cipherFlag 0', () => {
+    const payload = encode(
+      [
+        1,
+        1,
+        [[LOG_RECORD_TYPES.NOUN_TOMBSTONE, 1, 0, uuidBytes(UUID(9)), uuidBytes(UUID(1))]],
+        null,
+        null
+      ]
+    )
+    expect(() => decodeFact(payload, 2)).toThrow(UnknownLogRecordError)
+    expect(() => decodeFact(payload, 2)).toThrow(/encrypted records need a newer reader/)
+  })
+
+  it('the encoder always writes the plaintext envelope: cipherFlag 0, keyId nil', () => {
+    const payload = framePayload(encodeFactV2(factOf(1, { type: 'noun.tombstone', id: UUID(1) })))
+    const raw = decode(payload) as unknown[]
+    const record = (raw[2] as unknown[][])[0]
+    expect(record[2]).toBe(LOG_RECORD_CIPHER_PLAINTEXT)
+    expect(record[3]).toBeNull()
+    expect(LOG_RECORD_CIPHER_PLAINTEXT).toBe(0)
+  })
+
+  it('an unknown segment format version has no decode path', () => {
+    const payload = framePayload(encodeFactV2(factOf(1, { type: 'noun.tombstone', id: UUID(1) })))
+    expect(() => decodeFact(payload, 3)).toThrow(/reads 1 and 2/)
+  })
+})
+
+describe('fact-log format v2 — log.genesis width law', () => {
+  const genesisFact = (width: 32 | 64): CommitFactV2 =>
+    factOf(1, { type: 'log.genesis', idSpaceWidth: width, brainId: UUID(9), createdAt: 1 })
+
+  it('expectedWidth 32 vs a 64-width genesis refuses, naming both widths', () => {
+    const payload = framePayload(encodeFactV2(genesisFact(64)))
+    expect(() => decodeFact(payload, 2, { expectedIdSpaceWidth: 32 })).toThrow(
+      GenesisWidthMismatchError
+    )
+    try {
+      decodeFact(payload, 2, { expectedIdSpaceWidth: 32 })
+      expect.unreachable('decode must throw')
+    } catch (error) {
+      const typed = error as GenesisWidthMismatchError
+      expect(typed.expectedWidth).toBe(32)
+      expect(typed.actualWidth).toBe(64)
+      expect(typed.message).toMatch(/32-bit/)
+      expect(typed.message).toMatch(/64-bit/)
+    }
+  })
+
+  it('a matching width (and no expectation at all) decodes cleanly', () => {
+    const payload = framePayload(encodeFactV2(genesisFact(64)))
+    expect(decodeFact(payload, 2, { expectedIdSpaceWidth: 64 }).records[0]).toMatchObject({
+      idSpaceWidth: 64
+    })
+    expect(decodeFact(payload, 2).records[0]).toMatchObject({ idSpaceWidth: 64 })
+  })
+
+  it('genesis anywhere but record 0 refuses — encode AND decode', () => {
+    const late: CommitFactV2 = {
+      generation: 1,
+      timestamp: 1,
+      records: [
+        { type: 'noun.tombstone', id: UUID(1) },
+        { type: 'log.genesis', idSpaceWidth: 64, brainId: UUID(9), createdAt: 1 }
+      ]
+    }
+    expect(() => encodeFactV2(late)).toThrow(/first record/)
+    const crafted = encode([
+      1,
+      1,
+      [
+        [LOG_RECORD_TYPES.NOUN_TOMBSTONE, 1, 0, null, uuidBytes(UUID(1))],
+        [LOG_RECORD_TYPES.LOG_GENESIS, 1, 0, null, 64, uuidBytes(UUID(9)), 1]
+      ],
+      null,
+      null
+    ])
+    expect(() => decodeFact(crafted, 2)).toThrow(/first record/)
+  })
+
+  it('an invalid genesis width on the wire is malformed, not a mismatch', () => {
+    const crafted = encode(
+      [1, 1, [[LOG_RECORD_TYPES.LOG_GENESIS, 1, 0, null, 48, uuidBytes(UUID(9)), 1]], null, null]
+    )
+    expect(() => decodeFact(crafted, 2)).toThrow(/32 or 64/)
+  })
+})
+
+describe('fact-log format v2 — vector legs (single-hop law)', () => {
+  it('inline vectors round-trip float-exact', () => {
+    const vector = [0.1 + 0.2, -0.0000001, 3.141592653589793, 2 ** 40 + 0.25]
+    const fact = factOf(1, {
+      type: 'noun.afterImage',
+      id: UUID(1),
+      entityInt: 1n,
+      metadata: null,
+      vectorLeg: vector
+    })
+    const decoded = roundTrip(fact)
+    expect((decoded.records[0] as { vectorLeg: number[] }).vectorLeg).toStrictEqual(vector)
+  })
+
+  it('a ref round-trips when the validator vouches for the target generation', () => {
+    const fact = factOf(6, {
+      type: 'noun.afterImage',
+      id: UUID(1),
+      entityInt: 1n,
+      metadata: null,
+      vectorLeg: { sameAsGeneration: 5 }
+    })
+    const viaSet = roundTrip(fact, { inlineVectorGenerations: new Set([5]) })
+    expect((viaSet.records[0] as { vectorLeg: VectorRef }).vectorLeg).toStrictEqual({
+      sameAsGeneration: 5
+    })
+    const viaCallback = roundTrip(fact, { inlineVectorGenerations: (g) => g === 5 })
+    expect(viaCallback).toStrictEqual(fact)
+  })
+
+  it('the encoder REFUSES a ref the validator rejects', () => {
+    const fact = factOf(6, {
+      type: 'noun.afterImage',
+      id: UUID(1),
+      entityInt: 1n,
+      metadata: null,
+      vectorLeg: { sameAsGeneration: 5 }
+    })
+    expect(() => encodeFactV2(fact, { inlineVectorGenerations: new Set([4]) })).toThrow(
+      /single-hop/
+    )
+    expect(() => encodeFactV2(fact, { inlineVectorGenerations: () => false })).toThrow(
+      /generation 5/
+    )
+  })
+
+  it('the encoder REFUSES a ref when no validator was provided at all', () => {
+    const fact = factOf(6, {
+      type: 'noun.afterImage',
+      id: UUID(1),
+      entityInt: 1n,
+      metadata: null,
+      vectorLeg: { sameAsGeneration: 5 }
+    })
+    expect(() => encodeFactV2(fact)).toThrow(/unverifiable ref/)
+  })
+
+  it('embed.landed is inline-only: encode refuses non-arrays, decode refuses wire refs', () => {
+    const bad = factOf(7, {
+      type: 'embed.landed',
+      id: UUID(7),
+      vector: null as unknown as number[]
+    })
+    expect(() => encodeFactV2(bad)).toThrow(/INLINE/)
+    const craftedRef = encode(
+      [1, 1, [[LOG_RECORD_TYPES.EMBED_LANDED, 1, 0, null, uuidBytes(UUID(7)), ['ref', 5]]], null, null]
+    )
+    expect(() => decodeFact(craftedRef, 2)).toThrow(/INLINE/)
+  })
+})
+
+describe('fact-log format v2 — sector seals', () => {
+  const facts = [1, 2, 3].map((g) =>
+    factOf(g, {
+      type: 'noun.afterImage',
+      id: UUID(g),
+      entityInt: BigInt(g),
+      metadata: { title: `doc ${g}` },
+      vectorLeg: [g + 0.5]
+    })
+  )
+  const frames = facts.map((f) => encodeFactV2(f))
+
+  it('sealGroup output is sector-aligned and decodes to exactly the input facts', () => {
+    const sealed = sealGroup(frames, 4096)
+    expect(sealed.length % 4096).toBe(0)
+    const { facts: decoded, validBytes } = decodeGroupV2(sealed)
+    expect(decoded).toStrictEqual(facts) // pads invisible
+    expect(validBytes).toBe(sealed.length)
+  })
+
+  it('an already-aligned group gets NO pad (byte-identical passthrough)', () => {
+    const exact = frameOfExactly(4096, 1)
+    const sealed = sealGroup([exact], 4096)
+    expect(sealed.length).toBe(4096)
+    expect(Buffer.compare(Buffer.from(sealed), Buffer.from(exact))).toBe(0)
+    expect(decodeGroupV2(sealed).facts).toHaveLength(1)
+  })
+
+  it('a normal gap gets ONE exact-fit pad frame', () => {
+    const sealed = sealGroup([frameOfExactly(2000, 1), frameOfExactly(1996, 2)], 4096) // gap 100
+    expect(sealed.length).toBe(4096)
+    expect(decodeGroupV2(sealed).facts.map((f) => f.generation)).toEqual([1, 2])
+  })
+
+  it('a gap too small for any frame (the <12-byte remainder and friends) pads through one extra sector', () => {
+    for (const gap of [1, 8, 11, 16, 32]) {
+      const sealed = sealGroup([frameOfExactly(4096 - gap, 1)], 4096)
+      expect(sealed.length % 4096).toBe(0)
+      expect(sealed.length).toBe(8192) // gap + one full sector, still aligned
+      const { facts: decoded, validBytes } = decodeGroupV2(sealed)
+      expect(decoded.map((f) => f.generation)).toEqual([1])
+      expect(validBytes).toBe(8192)
+    }
+    // the smallest constructible pad frame fits exactly — no overshoot at 33
+    const sealed33 = sealGroup([frameOfExactly(4096 - 33, 1)], 4096)
+    expect(sealed33.length).toBe(4096)
+    expect(decodeGroupV2(sealed33).facts.map((f) => f.generation)).toEqual([1])
+  })
+
+  it('seals honor a custom sealSize (device-probed sizes are the caller business)', () => {
+    const sealed = sealGroup(frames, 512)
+    expect(sealed.length % 512).toBe(0)
+    expect(decodeGroupV2(sealed).facts).toStrictEqual(facts)
+  })
+
+  it('pad frame bytes are pinned (golden vector, sealSize 64)', () => {
+    const tomb = encodeFactV2({
+      generation: 3,
+      timestamp: 1_700_000_000_123,
+      records: [{ type: 'noun.tombstone', id: '00000000-0000-4000-8000-000000000042' }]
+    })
+    const sealed = sealGroup([tomb], 64) // 53 bytes → gap 11 → overshoot → 75-byte pad
+    expect(sealed.length).toBe(128)
+    expect(hex(sealed.subarray(tomb.length))).toBe(
+      // frame prefix + [0, 0, [[0, 1, bin8(40 zero bytes)]], nil, nil]
+      '4300000088b4c8fa95cf0000000000000000cf000000000000000091930001c428' +
+        '0'.repeat(80) +
+        'c0c0'
+    )
+  })
+
+  it('encodePadFrame builds exact-size pads for streaming writers; refuses sub-minimum sizes', () => {
+    // Pads are envelope-exempt (skipped wholesale), so the smallest pad frame
+    // is byte-stable across the crypto-envelope change.
+    expect(minPadFrameBytes()).toBe(33)
+    for (const size of [minPadFrameBytes(), 64, 4096]) {
+      const pad = encodePadFrame(size)
+      expect(pad.length).toBe(size)
+      const { facts: decoded, validBytes } = decodeGroupV2(pad)
+      expect(decoded).toEqual([]) // invisible to readers
+      expect(validBytes).toBe(size)
+    }
+    expect(() => encodePadFrame(minPadFrameBytes() - 1)).toThrow(/at least/)
+  })
+
+  it('sealGroup refuses garbage: empty groups, malformed frames, bad seal sizes', () => {
+    expect(() => sealGroup([], 4096)).toThrow(/at least one frame/)
+    expect(() => sealGroup([new Uint8Array([1, 2, 3])], 4096)).toThrow(/not a well-formed frame/)
+    const corrupted = encodeFactV2(facts[0])
+    corrupted[corrupted.length - 1] ^= 0xff
+    expect(() => sealGroup([corrupted], 4096)).toThrow(/not a well-formed frame/)
+    expect(() => sealGroup(frames, 32)).toThrow(/sealSize/)
+  })
+})
+
+describe('fact-log format v2 — torn-tail discipline', () => {
+  it('truncating a sealed group at EVERY byte offset of the tail yields the intact prefix, never an uncontrolled throw', () => {
+    const frames = [frameOfExactly(600, 1), frameOfExactly(700, 2), frameOfExactly(800, 3)]
+    const sealed = sealGroup(frames, 4096)
+    expect(sealed.length).toBe(4096)
+    const f3End = 600 + 700 + 800
+
+    for (let cut = 600 + 700; cut < sealed.length; cut++) {
+      const { facts: decoded, validBytes } = decodeGroupV2(sealed.subarray(0, cut))
+      const expected = cut < f3End ? [1, 2] : [1, 2, 3]
+      expect(decoded.map((f) => f.generation)).toEqual(expected)
+      expect(validBytes).toBe(cut < f3End ? 600 + 700 : f3End)
+    }
+  })
+
+  it('a flipped payload byte (not just truncation) also terminates the walk at the damage', () => {
+    const frames = [frameOfExactly(600, 1), frameOfExactly(700, 2)]
+    const sealed = sealGroup(frames, 4096)
+    const damaged = sealed.slice()
+    damaged[600 + 100] ^= 0xff // inside frame 2's payload
+    const { facts: decoded, validBytes } = decodeGroupV2(damaged)
+    expect(decoded.map((f) => f.generation)).toEqual([1])
+    expect(validBytes).toBe(600)
+  })
+})
+
+describe('fact-log format v2 — writer refusals (loud, never silent)', () => {
+  const tombstone = (g: number): CommitFactV2 => factOf(g, { type: 'noun.tombstone', id: UUID(g) })
+
+  it('accepts empty records (an all-deduped batch is a real generation); refuses generation 0 and a second batch.meta', () => {
+    // Contract change with the live cutover: v1 always encoded op-less
+    // commits (a batch whose relates dedupe away still mints a generation);
+    // v2 must not fork commit semantics — empty records round-trip.
+    const empty = decodeFact(framePayload(encodeFactV2({ generation: 1, timestamp: 1, records: [] })), 2)
+    expect(empty.records).toEqual([])
+    expect(() => encodeFactV2({ ...tombstone(1), generation: 0 })).toThrow(/positive integer/)
+    expect(() =>
+      encodeFactV2({
+        generation: 1,
+        timestamp: 1,
+        records: [
+          { type: 'batch.meta', meta: { a: 1 } },
+          { type: 'batch.meta', meta: { b: 2 } }
+        ]
+      })
+    ).toThrow(/at most one batch.meta/)
+  })
+
+  it('refuses pad records — filler belongs to sealGroup, not to writers', () => {
+    const fact = {
+      generation: 1,
+      timestamp: 1,
+      records: [{ type: 'pad' } as unknown as LogRecord]
+    }
+    expect(() => encodeFactV2(fact)).toThrow(/cannot encode record type pad/)
+  })
+
+  it('refuses malformed field values: non-uuid ids, bad hashes, out-of-range u64s', () => {
+    expect(() =>
+      encodeFactV2(factOf(1, { type: 'noun.tombstone', id: 'not-a-uuid' }))
+    ).toThrow(/not a uuid/)
+    expect(() =>
+      encodeFactV2(
+        factOf(1, { type: 'blob.manifest', hash: 'abc', size: 1, mimeType: 'x', refOp: 'add' })
+      )
+    ).toThrow(/64 hex chars/)
+    expect(() =>
+      encodeFactV2(
+        factOf(1, {
+          type: 'noun.afterImage',
+          id: UUID(1),
+          entityInt: -1n,
+          metadata: null,
+          vectorLeg: null
+        })
+      )
+    ).toThrow(/u64 range/)
+    expect(() =>
+      encodeFactV2(
+        factOf(1, {
+          type: 'noun.afterImage',
+          id: UUID(1),
+          entityInt: 1n << 64n,
+          metadata: null,
+          vectorLeg: null
+        })
+      )
+    ).toThrow(/u64 range/)
+  })
+})
+
+describe('fact-log format — the v1 decode path stays readable forever', () => {
+  it('decodeFact(payload, 1) reads the v1 ops shape (positional, bin16, tombstones)', () => {
+    // Crafted exactly as the v1 writer frames facts: default msgpack, ops at
+    // position 2 as [kind u8, id bin16, [metadata, vector] | nil].
+    const payload = encode([
+      4,
+      1_700_000_000_004,
+      [
+        [0, uuidBytes(UUID(41)), [{ noun: 'document', title: 'doc 41' }, { v: [1, 2] }]],
+        [1, uuidBytes(UUID(42)), null] // verb tombstone
+      ],
+      { source: 'v1' },
+      ['abc123']
+    ])
+    const fact = decodeFact(payload, 1)
+    expect(fact).toStrictEqual({
+      generation: 4,
+      timestamp: 1_700_000_000_004,
+      ops: [
+        {
+          kind: 'noun',
+          id: UUID(41),
+          record: { metadata: { noun: 'document', title: 'doc 41' }, vector: { v: [1, 2] } }
+        },
+        { kind: 'verb', id: UUID(42), record: null }
+      ],
+      meta: { source: 'v1' },
+      blobHashes: ['abc123']
+    })
+  })
+})
+
+describe('fact-log format v2 — frame envelope helper', () => {
+  it('framePayload verifies exact length and crc32c', () => {
+    const frame = encodeFactV2(factOf(1, { type: 'noun.tombstone', id: UUID(1) }))
+    expect(() => framePayload(frame)).not.toThrow()
+
+    const shortFrame = frame.subarray(0, frame.length - 1)
+    expect(() => framePayload(shortFrame)).toThrow(/declares/)
+
+    const corrupted = frame.slice()
+    corrupted[corrupted.length - 1] ^= 0xff
+    expect(() => framePayload(corrupted)).toThrow(/crc32c/)
+  })
+
+  it('the record-type registry and version constants are the frozen wire codes', () => {
+    expect(LOG_RECORD_TYPES).toStrictEqual({
+      PAD: 0,
+      NOUN_AFTER_IMAGE: 1,
+      NOUN_TOMBSTONE: 2,
+      VERB_AFTER_IMAGE: 3,
+      VERB_TOMBSTONE: 4,
+      BATCH_META: 5,
+      EMBED_PENDING: 6,
+      EMBED_LANDED: 7,
+      BLOB_MANIFEST: 8,
+      PROJECTION_NOTE: 9,
+      BOOTSTRAP_BASELINE: 10,
+      LOG_GENESIS: 11
+    })
+    expect(LOG_RECORD_VERSION).toBe(1)
+  })
+})

tests/unit/db/fault-injection-shim.test.ts

@@ -0,0 +1,231 @@
+/**
+ * @module tests/unit/db/fault-injection-shim
+ * @description The fault-injection storage wrapper proven in isolation: a
+ * torn write persists a decodable prefix (the crash shape durability tests
+ * replay), a dropped sync is observable (armed → the inner adapter never sees
+ * it; journaled), a failed append throws without writing a byte, knobs are
+ * one-shot, and unarmed operation is a transparent passthrough. The full
+ * commit-path fault matrix lives with the log's ack work — this file proves
+ * the SHIM itself.
+ */
+import { describe, it, expect, beforeEach } from 'vitest'
+import { MemoryStorage } from '../../../src/storage/adapters/memoryStorage.js'
+import {
+  FactLog,
+  storageSupportsFactLog,
+  type CommitFact,
+  type FactLogStorage
+} from '../../../src/db/factLog.js'
+import {
+  FaultInjectionStorage,
+  FaultInjectedError
+} from '../../../src/db/faultInjectionStorage.js'
+import {
+  encodeFactV2,
+  encodeSegmentHeaderV2,
+  decodeGroupV2,
+  parseSegmentHeader,
+  SEGMENT_HEADER_BYTES,
+  type CommitFactV2
+} from '../../../src/db/factLogFormat.js'
+
+const UUID = (n: number): string =>
+  `00000000-0000-4000-8000-${String(n).padStart(12, '0')}`
+
+const factV2 = (generation: number): CommitFactV2 => ({
+  generation,
+  timestamp: 1_700_000_000_000 + generation,
+  records: [{ type: 'noun.tombstone', id: UUID(generation) }]
+})
+
+const factV1 = (generation: number): CommitFact => ({
+  generation,
+  timestamp: 1_700_000_000_000 + generation,
+  ops: [
+    {
+      kind: 'noun',
+      id: UUID(generation),
+      record: { metadata: { noun: 'document' }, vector: null }
+    }
+  ]
+})
+
+describe('fault-injection storage wrapper', () => {
+  let inner: FactLogStorage & { syncRawObjects: (paths: string[]) => Promise<void> }
+  let shim: FaultInjectionStorage
+  let innerSyncCalls: string[][]
+
+  beforeEach(async () => {
+    const mem: any = new MemoryStorage()
+    await mem.init()
+    innerSyncCalls = []
+    const realSync = mem.syncRawObjects.bind(mem)
+    mem.syncRawObjects = async (paths: string[]) => {
+      innerSyncCalls.push([...paths])
+      return realSync(paths)
+    }
+    inner = mem
+    shim = new FaultInjectionStorage(inner)
+  })
+
+  it('satisfies the fact-log storage surface (drop-in wrapper)', () => {
+    expect(storageSupportsFactLog(shim)).toBe(true)
+  })
+
+  it('unarmed, every operation is a transparent passthrough', async () => {
+    await shim.writeRawBytes('seg', new Uint8Array([1, 2, 3]))
+    await shim.appendRawBytes('seg', new Uint8Array([4, 5]))
+    expect(Array.from((await shim.readRawBytes('seg'))!)).toEqual([1, 2, 3, 4, 5])
+    expect(await shim.rawByteSize('seg')).toBe(5)
+    expect(Array.from((await inner.readRawBytes('seg'))!)).toEqual([1, 2, 3, 4, 5])
+
+    await shim.writeRawObject('obj.json', { a: 1 })
+    expect(await shim.readRawObject('obj.json')).toEqual({ a: 1 })
+    await shim.deleteRawObject('obj.json')
+    expect(await shim.readRawObject('obj.json')).toBeNull()
+
+    await shim.syncRawObjects(['seg'])
+    expect(innerSyncCalls).toEqual([['seg']])
+    expect(shim.injectedFaults).toEqual([])
+  })
+
+  describe('tearWriteAtByte — a torn write produces a decodable-prefix segment', () => {
+    it('persists only the first N bytes of the next append; the prefix decodes intact', async () => {
+      const path = 'facts/seg-test.bfl'
+      const frame1 = encodeFactV2(factV2(1))
+      const frame2 = encodeFactV2(factV2(2))
+
+      await shim.appendRawBytes(path, encodeSegmentHeaderV2(1, 4096))
+      await shim.appendRawBytes(path, frame1)
+      shim.tearWriteAtByte(frame2.length - 5) // crash 5 bytes before the frame lands
+      await shim.appendRawBytes(path, frame2) // reports success — the tear is silent
+
+      const bytes = (await inner.readRawBytes(path))!
+      expect(bytes.length).toBe(SEGMENT_HEADER_BYTES + frame1.length + frame2.length - 5)
+
+      // The "crash": reopen from storage and read what actually survived.
+      const header = parseSegmentHeader(bytes)
+      expect(header).toStrictEqual({ formatVersion: 2, firstGeneration: 1, sealSize: 4096 })
+      const { facts, validBytes } = decodeGroupV2(bytes.subarray(SEGMENT_HEADER_BYTES))
+      expect(facts.map((f) => f.generation)).toEqual([1]) // fact 2's torn frame is invisible
+      expect(validBytes).toBe(frame1.length)
+
+      expect(shim.injectedFaults).toEqual([
+        {
+          kind: 'torn-write',
+          path,
+          requestedBytes: frame2.length,
+          writtenBytes: frame2.length - 5
+        }
+      ])
+    })
+
+    it('a tear inside the frame prefix (first bytes) leaves the earlier facts intact too', async () => {
+      const path = 'facts/seg-prefix.bfl'
+      const frame1 = encodeFactV2(factV2(1))
+      await shim.appendRawBytes(path, encodeSegmentHeaderV2(1, 4096))
+      await shim.appendRawBytes(path, frame1)
+      shim.tearWriteAtByte(3)
+      await shim.appendRawBytes(path, encodeFactV2(factV2(2)))
+
+      const bytes = (await inner.readRawBytes(path))!
+      const { facts } = decodeGroupV2(bytes.subarray(SEGMENT_HEADER_BYTES))
+      expect(facts.map((f) => f.generation)).toEqual([1])
+    })
+
+    it('a tear at byte 0 writes nothing at all', async () => {
+      shim.tearWriteAtByte(0)
+      await shim.appendRawBytes('empty.bfl', new Uint8Array([1, 2, 3]))
+      expect(await inner.readRawBytes('empty.bfl')).toBeNull()
+      expect(shim.injectedFaults[0]).toMatchObject({ kind: 'torn-write', writtenBytes: 0 })
+    })
+
+    it('is one-shot: the append after the torn one lands whole', async () => {
+      shim.tearWriteAtByte(1)
+      await shim.appendRawBytes('seg', new Uint8Array([1, 2, 3, 4]))
+      await shim.appendRawBytes('seg', new Uint8Array([5, 6]))
+      expect(Array.from((await inner.readRawBytes('seg'))!)).toEqual([1, 5, 6])
+    })
+
+    it('refuses a negative tear offset', () => {
+      expect(() => shim.tearWriteAtByte(-1)).toThrow(/non-negative/)
+    })
+  })
+
+  describe('dropNextSync — a dropped sync is observable', () => {
+    it('the armed sync never reaches the inner adapter and is journaled', async () => {
+      shim.dropNextSync()
+      await shim.syncRawObjects(['a.bfl', 'b.bfl'])
+      expect(innerSyncCalls).toEqual([]) // the device never saw it
+      expect(shim.injectedFaults).toEqual([{ kind: 'dropped-sync', paths: ['a.bfl', 'b.bfl'] }])
+    })
+
+    it('is one-shot: the following sync passes through', async () => {
+      shim.dropNextSync()
+      await shim.syncRawObjects(['x'])
+      await shim.syncRawObjects(['y'])
+      expect(innerSyncCalls).toEqual([['y']])
+    })
+  })
+
+  describe('failNextAppend — a failed append throws without writing a byte', () => {
+    it('throws the typed error, writes nothing, and journals the fault', async () => {
+      await shim.appendRawBytes('seg', new Uint8Array([1]))
+      shim.failNextAppend()
+      await expect(shim.appendRawBytes('seg', new Uint8Array([2, 3]))).rejects.toThrow(
+        FaultInjectedError
+      )
+      expect(Array.from((await inner.readRawBytes('seg'))!)).toEqual([1]) // untouched
+      expect(shim.injectedFaults).toEqual([{ kind: 'failed-append', path: 'seg' }])
+      // one-shot: the next append succeeds
+      await shim.appendRawBytes('seg', new Uint8Array([4]))
+      expect(Array.from((await inner.readRawBytes('seg'))!)).toEqual([1, 4])
+    })
+
+    it('carries the operation and path for programmatic assertions', async () => {
+      shim.failNextAppend()
+      try {
+        await shim.appendRawBytes('some/path.bfl', new Uint8Array([1]))
+        expect.unreachable('append must throw')
+      } catch (error) {
+        const typed = error as FaultInjectedError
+        expect(typed).toBeInstanceOf(FaultInjectedError)
+        expect(typed.operation).toBe('append')
+        expect(typed.path).toBe('some/path.bfl')
+      }
+    })
+
+    it('wins over a simultaneously-armed tear; the tear stays pending for the next append', async () => {
+      shim.failNextAppend()
+      shim.tearWriteAtByte(2)
+      await expect(shim.appendRawBytes('seg', new Uint8Array([1, 2, 3]))).rejects.toThrow(
+        FaultInjectedError
+      )
+      expect(await inner.readRawBytes('seg')).toBeNull()
+      await shim.appendRawBytes('seg', new Uint8Array([9, 8, 7]))
+      expect(Array.from((await inner.readRawBytes('seg'))!)).toEqual([9, 8]) // torn at 2
+      expect(shim.injectedFaults.map((f) => f.kind)).toEqual(['failed-append', 'torn-write'])
+    })
+  })
+
+  describe('composed with the real fact log (v1 surface)', () => {
+    it('a torn append is truncated away on reopen — the log heals to the intact prefix', async () => {
+      const log = new FactLog(shim)
+      await log.open(0)
+      await log.append(factV1(1))
+      await log.sync()
+
+      shim.tearWriteAtByte(10) // fact 2's frame lands 10 bytes long — torn
+      await log.append(factV1(2))
+      await log.sync()
+
+      // The crash: abandon the instance, reopen from what storage actually holds.
+      const reopened = new FactLog(inner)
+      await reopened.open(2) // generation 2 committed elsewhere — but its fact is torn
+      expect(reopened.headGeneration()).toBe(1)
+      const all: CommitFact[] = []
+      for await (const batch of reopened.scanFacts().batches()) all.push(...batch.facts)
+      expect(all.map((f) => f.generation)).toEqual([1])
+    })
+  })
+})

tests/unit/db/log-authority-oracle-verbs.test.ts

@@ -0,0 +1,96 @@
+/**
+ * @module tests/unit/db/log-authority-oracle-verbs
+ * @description The verification oracle's VERB legs — module-level pins with
+ * doubles (the brain-level wiring rides the owner's call site):
+ * 1. Wired verb legs diff verbs exactly like nouns (pre-log / state-differs /
+ *    tombstone-vs-present / log-live-absent).
+ * 2. UNWIRED verb legs = an HONEST PARTIAL verdict: verbsChecked stays 0 —
+ *    the oracle never claims scope it did not scan.
+ */
+import { describe, it, expect } from 'vitest'
+import { runLogCompletenessOracle, recordDigest } from '../../../src/db/logAuthority.js'
+import type { FactScanHandle } from '../../../src/db/factLog.js'
+
+type Op = { kind: 'noun' | 'verb'; id: string; record: { metadata: unknown; vector: unknown } | null }
+
+function scanOf(facts: Array<{ generation: number; ops: Op[] }>): () => FactScanHandle | null {
+  return () =>
+    ({
+      batches: async function* () {
+        yield { facts: facts.map((f) => ({ ...f, timestamp: 0 })) }
+      }
+    }) as unknown as FactScanHandle
+}
+
+function pagedList(rows: string[]) {
+  return async ({ pagination }: { pagination: { limit: number; offset?: number } }) => {
+    const start = pagination.offset ?? 0
+    const items = rows.slice(start, start + pagination.limit).map((id) => ({ id }))
+    return { items, hasMore: start + pagination.limit < rows.length }
+  }
+}
+
+const rec = (v: number) => ({ metadata: { v }, vector: null })
+
+describe('oracle verb legs', () => {
+  it('wired: verbs diff by digest — clean log goes green over nouns AND verbs', async () => {
+    const report = await runLogCompletenessOracle({
+      storage: { getNouns: pagedList(['n1']) } as never,
+      scanFacts: scanOf([
+        { generation: 1, ops: [{ kind: 'noun', id: 'n1', record: rec(1) }] },
+        { generation: 2, ops: [{ kind: 'verb', id: 'v1', record: rec(7) }] }
+      ]),
+      canonicalNounDigest: async () => recordDigest(rec(1)),
+      factRecordDigest: recordDigest,
+      canonicalVerbDigest: async () => recordDigest(rec(7)),
+      getVerbs: pagedList(['v1'])
+    })
+    expect(report.verdict).toBe('green')
+    expect(report.nounsChecked).toBe(1)
+    expect(report.verbsChecked).toBe(1)
+    expect(report.matched).toBe(2)
+  })
+
+  it('wired: every verb divergence class is NAMED', async () => {
+    const report = await runLogCompletenessOracle({
+      storage: { getNouns: pagedList([]) } as never,
+      scanFacts: scanOf([
+        {
+          generation: 1,
+          ops: [
+            { kind: 'verb', id: 'v-differs', record: rec(1) },
+            { kind: 'verb', id: 'v-tomb', record: null },
+            { kind: 'verb', id: 'v-orphan', record: rec(3) }
+          ]
+        }
+      ]),
+      canonicalNounDigest: async () => null,
+      factRecordDigest: recordDigest,
+      canonicalVerbDigest: async (id) =>
+        id === 'v-differs' ? recordDigest(rec(999)) : id === 'v-tomb' ? recordDigest(rec(2)) : null,
+      // canonical enumerates: v-differs (drifted), v-tomb (log says deleted),
+      // v-prelog (never logged); v-orphan is log-live but canonical-absent.
+      getVerbs: pagedList(['v-differs', 'v-tomb', 'v-prelog'])
+    })
+    expect(report.verdict).toBe('red')
+    const by = (id: string) => report.mismatches.find((m) => m.id === id)
+    expect(by('v-differs')).toMatchObject({ kind: 'verb', reason: 'state-differs' })
+    expect(by('v-tomb')).toMatchObject({ kind: 'verb', reason: 'log-tombstone-canonical-present' })
+    expect(by('v-prelog')).toMatchObject({ kind: 'verb', reason: 'pre-log-record' })
+    expect(by('v-orphan')).toMatchObject({ kind: 'verb', reason: 'log-live-canonical-absent' })
+  })
+
+  it('unwired: verbsChecked stays 0 — honest partial scope, never a silent claim', async () => {
+    const report = await runLogCompletenessOracle({
+      storage: { getNouns: pagedList(['n1']) } as never,
+      scanFacts: scanOf([
+        { generation: 1, ops: [{ kind: 'noun', id: 'n1', record: rec(1) }] },
+        { generation: 2, ops: [{ kind: 'verb', id: 'v1', record: rec(7) }] }
+      ]),
+      canonicalNounDigest: async () => recordDigest(rec(1)),
+      factRecordDigest: recordDigest
+    })
+    expect(report.verbsChecked).toBe(0)
+    expect(report.nounsChecked).toBe(1)
+  })
+})

tests/unit/db/torn-open-guards.test.ts

@@ -0,0 +1,97 @@
+/**
+ * @module tests/unit/db/torn-open-guards
+ * @description Power-cut throw-site cures (brainy-alone fault-injection
+ * findings, both release-gating):
+ * 1. A torn generation manifest/counter (NaN/garbage where a generation
+ *    belongs) DISCARDS with narration and re-derives — never a RangeError
+ *    killing the open.
+ * 2. A manifest-listed-but-unloadable column segment QUARANTINES at
+ *    discovery with narration; the field serves its remaining segments
+ *    DEGRADED — never a raw throw killing every query on the field.
+ */
+import { describe, it, expect, afterEach } from 'vitest'
+import { mkdtempSync, rmSync, readdirSync, writeFileSync, readFileSync, existsSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { gzipSync } from 'node:zlib'
+import { Brainy } from '../../../src/index.js'
+import { NounType } from '../../../src/types/graphTypes.js'
+
+const dirs: string[] = []
+const brains: Brainy[] = []
+afterEach(async () => {
+  for (const b of brains.splice(0)) await b.close().catch(() => {})
+  for (const d of dirs.splice(0)) rmSync(d, { recursive: true, force: true })
+})
+
+async function open(dir: string): Promise<Brainy> {
+  const b = new Brainy({ storage: { type: 'filesystem', path: dir }, requireSubtype: false })
+  await b.init()
+  brains.push(b)
+  return b
+}
+
+describe('torn-open guards', () => {
+  it('a torn generation manifest (NaN) opens with narrated discard — never a RangeError', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-torn-gen-'))
+    dirs.push(dir)
+    let brain = await open(dir)
+    const id = await brain.add({ data: 'survivor row', type: NounType.Document, metadata: { k: 1 } })
+    await brain.flush()
+    await brain.close()
+    brains.pop()
+
+    // The power-cut shape: the manifest's generation field is garbage.
+    const sys = join(dir, '_system')
+    const manifestPath = ['manifest.json', 'manifest.json.gz']
+      .map((f) => join(sys, f))
+      .find((p) => existsSync(p))!
+    const torn = { version: 1, generation: 'NaN-garbage', committedAt: 'x', horizon: null }
+    if (manifestPath.endsWith('.gz')) writeFileSync(manifestPath, gzipSync(JSON.stringify(torn)))
+    else writeFileSync(manifestPath, JSON.stringify(torn))
+
+    // Open MUST succeed (narrated discard + recovery re-derivation), and the
+    // durable row must still serve (log-authority replay recovers it).
+    brain = await open(dir)
+    expect((await brain.get(id))!.data).toContain('survivor row')
+    // Writes continue with a sane monotonic generation.
+    await brain.add({ data: 'post-recovery', type: NounType.Document, metadata: { k: 2 } })
+    expect(Number.isSafeInteger(brain.generation())).toBe(true)
+  }, 120000)
+
+  it('a torn column segment quarantines at discovery; the field serves remaining segments degraded — never a raw throw', async () => {
+    const dir = mkdtempSync(join(tmpdir(), 'brainy-torn-seg-'))
+    dirs.push(dir)
+    let brain = await open(dir)
+    for (let i = 0; i < 6; i++) {
+      await brain.add({ data: `row ${i}`, type: NounType.Document, metadata: { bucket: i % 2 } })
+    }
+    await brain.flush()
+    await brain.close()
+    brains.pop()
+
+    // Tear ONE column segment's bytes on disk (manifest keeps listing it) —
+    // the QUERIED field's own segment, so the quarantine path provably
+    // engages. Column segments live under the raw-blob root:
+    // `<root>/_blobs/_column_index/<field>/L<level>-<id>.bin`.
+    const segDir = join(dir, '_blobs', '_column_index', 'bucket')
+    let tornOne = false
+    if (existsSync(segDir)) {
+      for (const f of readdirSync(segDir, { withFileTypes: true })) {
+        if (!f.isDirectory() && /^L\d+-.*\.bin$/.test(f.name)) {
+          writeFileSync(join(segDir, f.name), Buffer.from([0x00, 0x01, 0x02])) // garbage
+          tornOne = true
+          break
+        }
+      }
+    }
+    expect(tornOne, 'found a segment file to tear (layout probe)').toBe(true)
+
+    // Queries on the field MUST NOT throw — degraded-announced service.
+    brain = await open(dir)
+    const rows = await brain.find({ where: { bucket: 0 }, limit: 10 })
+    expect(Array.isArray(rows), 'query survives the torn segment').toBe(true)
+    // Full completeness is NOT asserted (the torn segment's rows may be
+    // absent — that is the documented degraded contract until heal).
+  }, 120000)
+})

tests/unit/graph/graph-adjacency-watermark.test.ts

@@ -0,0 +1,213 @@
+/**
+ * @module tests/unit/graph/graph-adjacency-watermark
+ * @description Watermark-stamp pins for the graph-adjacency projection.
+ *
+ * THE LAW under test: the persisted adjacency artifact (the two verb-id LSM
+ * trees' SSTables + manifests) carries a stamp asserting "this state
+ * reflects every committed generation ≤ W and nothing above W" — written
+ * AFTER both trees' flushes complete — and init() computes the three-way
+ * verdict: stamped==committed → 'adopt' · stamped<committed → 'catchup'
+ * (gap reported) · stamped>committed OR unstamped → 'rescan', LOUDLY.
+ *
+ * The verdict is COMPUTED AND EXPOSED only — cold-load recovery and rebuild
+ * triggers are unchanged.
+ */
+import { describe, it, expect, vi, afterEach } from 'vitest'
+import { v4 as uuidv4 } from 'uuid'
+import {
+  GraphAdjacencyIndex,
+  GRAPH_ADJACENCY_STAMP_KEY
+} from '../../../src/graph/graphAdjacencyIndex.js'
+import { EntityIdMapper } from '../../../src/utils/entityIdMapper.js'
+import { MemoryStorage } from '../../../src/storage/adapters/memoryStorage.js'
+import { VerbType } from '../../../src/types/graphTypes.js'
+import type { GraphVerb } from '../../../src/coreTypes.js'
+import { prodLog } from '../../../src/utils/logger.js'
+
+function makeVerb(id: string, sourceId: string, targetId: string): GraphVerb {
+  return {
+    id,
+    sourceId,
+    targetId,
+    vector: [],
+    type: VerbType.RelatedTo,
+    verb: VerbType.RelatedTo
+  }
+}
+
+async function makeStorage(committed: number | null): Promise<MemoryStorage> {
+  const storage = new MemoryStorage()
+  await storage.init()
+  if (committed !== null) {
+    vi.spyOn(storage, 'committedGeneration').mockReturnValue(committed)
+  }
+  return storage
+}
+
+function setCommitted(storage: MemoryStorage, committed: number): void {
+  vi.spyOn(storage, 'committedGeneration').mockReturnValue(committed)
+}
+
+/** Session 1: index verbs, optionally stamp, flush + close — the artifact. */
+async function writeArtifact(storage: MemoryStorage, stamp: number | null): Promise<void> {
+  const idMapper = new EntityIdMapper({ storage, storageKey: 'test:graph:idMapper' })
+  await idMapper.init()
+  const index = new GraphAdjacencyIndex(storage, {}, idMapper)
+  const a = uuidv4()
+  const b = uuidv4()
+  const aInt = BigInt(idMapper.getOrAssign(a))
+  const bInt = BigInt(idMapper.getOrAssign(b))
+  await index.addVerb(makeVerb(uuidv4(), a, b), aInt, bInt, 1n)
+  if (stamp !== null) index.stampWatermark(stamp)
+  await index.flush()
+  await index.close()
+}
+
+/** Session 2: reopen on the same storage via the cold-load path. */
+async function reopen(storage: MemoryStorage): Promise<GraphAdjacencyIndex> {
+  const index = new GraphAdjacencyIndex(storage)
+  await index.init()
+  return index
+}
+
+afterEach(() => {
+  vi.restoreAllMocks()
+})
+
+describe('graph adjacency index — watermark stamp + three-way load verdict', () => {
+  it("save-with-stamp then reopen at the same committed generation → 'adopt'", async () => {
+    const storage = await makeStorage(5)
+    await writeArtifact(storage, 5)
+
+    const index = await reopen(storage)
+    expect(index.watermarkVerdict()).toBe('adopt')
+    expect(index.watermark()).toBe(5)
+    expect(index.watermarkGap()).toBeNull()
+    await index.close()
+  })
+
+  it("stamp BEHIND the committed generation → 'catchup' with the exact gap reported", async () => {
+    const storage = await makeStorage(5)
+    await writeArtifact(storage, 5)
+
+    setCommitted(storage, 11)
+
+    const index = await reopen(storage)
+    expect(index.watermarkVerdict()).toBe('catchup')
+    expect(index.watermark()).toBe(5)
+    expect(index.watermarkGap()).toEqual({ from: 5, to: 11 })
+    await index.close()
+  })
+
+  it("stamp ABOVE the committed generation → 'rescan', said out loud", async () => {
+    const storage = await makeStorage(9)
+    await writeArtifact(storage, 9)
+
+    setCommitted(storage, 4)
+
+    const warnSpy = vi.spyOn(prodLog, 'warn')
+    const index = await reopen(storage)
+    expect(index.watermarkVerdict()).toBe('rescan')
+    expect(index.watermarkGap()).toBeNull()
+    const said = warnSpy.mock.calls.map(c => String(c[0])).join('\n')
+    expect(said).toContain('RESCAN')
+    expect(said).toContain('ABOVE')
+    await index.close()
+  })
+
+  it("legacy unstamped artifact on a stamped store → 'rescan', LOUD — never a silent adopt", async () => {
+    const storage = await makeStorage(3)
+    await writeArtifact(storage, null) // pre-stamp adjacency: SSTables, no stamp
+
+    expect(await storage.getMetadata(GRAPH_ADJACENCY_STAMP_KEY)).toBeNull()
+
+    const warnSpy = vi.spyOn(prodLog, 'warn')
+    const index = await reopen(storage)
+    expect(index.watermarkVerdict()).toBe('rescan')
+    expect(index.watermark()).toBeNull()
+    const said = warnSpy.mock.calls.map(c => String(c[0])).join('\n')
+    expect(said).toContain('RESCAN')
+    expect(said).toContain('unstamped')
+    await index.close()
+  })
+
+  it("a store with no committed-generation capability keeps pre-stamp behavior → 'adopt'", async () => {
+    const storage = await makeStorage(null)
+    await writeArtifact(storage, null)
+
+    const index = await reopen(storage)
+    expect(index.watermarkVerdict()).toBe('adopt')
+    expect(index.watermark()).toBeNull()
+    await index.close()
+  })
+
+  it('STAMP-AFTER-DATA: the stamp is the last saveMetadata of the flush, after both trees’ SSTable + manifest writes', async () => {
+    const storage = await makeStorage(2)
+    const idMapper = new EntityIdMapper({ storage, storageKey: 'test:graph:idMapper' })
+    await idMapper.init()
+    const index = new GraphAdjacencyIndex(storage, {}, idMapper)
+    const a = uuidv4()
+    const b = uuidv4()
+    await index.addVerb(
+      makeVerb(uuidv4(), a, b),
+      BigInt(idMapper.getOrAssign(a)),
+      BigInt(idMapper.getOrAssign(b)),
+      1n
+    )
+
+    const keys: string[] = []
+    const originalSave = storage.saveMetadata.bind(storage)
+    vi.spyOn(storage, 'saveMetadata').mockImplementation(async (id, metadata) => {
+      keys.push(id)
+      return originalSave(id, metadata)
+    })
+
+    index.stampWatermark(2)
+    await index.flush()
+
+    const stampAt = keys.indexOf(GRAPH_ADJACENCY_STAMP_KEY)
+    expect(stampAt, 'stamp record was written').toBeGreaterThanOrEqual(0)
+    expect(stampAt, 'stamp is the FINAL metadata write of the flush').toBe(keys.length - 1)
+    // Both trees flushed durable bytes before the stamp landed.
+    expect(
+      keys.slice(0, stampAt).some(k => k.startsWith('graph-lsm-verbs-source')),
+      'verbs-by-source tree wrote before the stamp'
+    ).toBe(true)
+    expect(
+      keys.slice(0, stampAt).some(k => k.startsWith('graph-lsm-verbs-target')),
+      'verbs-by-target tree wrote before the stamp'
+    ).toBe(true)
+
+    const record = (await storage.getMetadata(GRAPH_ADJACENCY_STAMP_KEY)) as {
+      watermark: number
+      formatVersion: number
+      stampedAt: number
+    }
+    expect(record.watermark).toBe(2)
+    expect(record.formatVersion).toBe(1)
+    expect(typeof record.stampedAt).toBe('number')
+
+    await index.close()
+  })
+
+  it('a pending stamp also lands on the close() shutdown path, after the final tree flushes', async () => {
+    const storage = await makeStorage(6)
+    const idMapper = new EntityIdMapper({ storage, storageKey: 'test:graph:idMapper' })
+    await idMapper.init()
+    const index = new GraphAdjacencyIndex(storage, {}, idMapper)
+    const a = uuidv4()
+    const b = uuidv4()
+    await index.addVerb(
+      makeVerb(uuidv4(), a, b),
+      BigInt(idMapper.getOrAssign(a)),
+      BigInt(idMapper.getOrAssign(b)),
+      1n
+    )
+
+    index.stampWatermark(6)
+    await index.close() // no explicit flush — close() flushes, then stamps
+
+    const record = (await storage.getMetadata(GRAPH_ADJACENCY_STAMP_KEY)) as { watermark: number }
+    expect(record?.watermark).toBe(6)
+  })
+})

tests/unit/hnsw/hnsw-watermark.test.ts

@@ -0,0 +1,200 @@
+/**
+ * @module tests/unit/hnsw/hnsw-watermark
+ * @description Watermark-stamp pins for the JS HNSW vector projection.
+ *
+ * THE LAW under test: the persisted HNSW artifact (per-node records + the
+ * entryPoint/maxLevel system record) carries a stamp asserting "this state
+ * reflects every committed generation ≤ W and nothing above W" — written
+ * AFTER every byte it certifies is durable — and rebuild() computes the
+ * three-way verdict: stamped==committed → 'adopt' · stamped<committed →
+ * 'catchup' (gap reported) · stamped>committed OR unstamped → 'rescan',
+ * LOUDLY. Vector-bearing stamps carry the model identity this module can
+ * honestly assert: dimensions only (no embedding-model id is reachable from
+ * the index module).
+ *
+ * The verdict is COMPUTED AND EXPOSED only — no rebuild trigger changed.
+ */
+import { describe, it, expect, vi, afterEach } from 'vitest'
+import { v4 as uuidv4 } from 'uuid'
+import { JsHnswVectorIndex, HNSW_INDEX_STAMP_KEY } from '../../../src/hnsw/hnswIndex.js'
+import { euclideanDistance } from '../../../src/utils/index.js'
+import { MemoryStorage } from '../../../src/storage/adapters/memoryStorage.js'
+import { prodLog } from '../../../src/utils/logger.js'
+
+const DIM = 8
+
+function randomVector(dim: number): number[] {
+  return Array.from({ length: dim }, () => Math.random() * 2 - 1)
+}
+
+async function makeStorage(committed: number | null): Promise<MemoryStorage> {
+  const storage = new MemoryStorage()
+  await storage.init()
+  if (committed !== null) {
+    vi.spyOn(storage, 'committedGeneration').mockReturnValue(committed)
+  }
+  return storage
+}
+
+function setCommitted(storage: MemoryStorage, committed: number): void {
+  vi.spyOn(storage, 'committedGeneration').mockReturnValue(committed)
+}
+
+function makeIndex(storage: MemoryStorage): JsHnswVectorIndex {
+  return new JsHnswVectorIndex(
+    { M: 4, efConstruction: 50, efSearch: 20 },
+    euclideanDistance,
+    { useParallelization: false, storage, persistMode: 'deferred' }
+  )
+}
+
+/** Session 1: insert nodes, optionally stamp, flush — the durable artifact. */
+async function writeArtifact(storage: MemoryStorage, stamp: number | null): Promise<void> {
+  const index = makeIndex(storage)
+  for (let i = 0; i < 3; i++) {
+    await index.addItem({ id: uuidv4(), vector: randomVector(DIM) })
+  }
+  if (stamp !== null) index.stampWatermark(stamp)
+  await index.flush()
+}
+
+/** Session 2: reopen on the same storage via the load path (rebuild). */
+async function reopen(storage: MemoryStorage): Promise<JsHnswVectorIndex> {
+  const index = makeIndex(storage)
+  await index.rebuild()
+  return index
+}
+
+afterEach(() => {
+  vi.restoreAllMocks()
+})
+
+describe('JS HNSW index — watermark stamp + three-way load verdict', () => {
+  it("save-with-stamp then reopen at the same committed generation → 'adopt'", async () => {
+    const storage = await makeStorage(5)
+    await writeArtifact(storage, 5)
+
+    const index = await reopen(storage)
+    expect(index.watermarkVerdict()).toBe('adopt')
+    expect(index.watermark()).toBe(5)
+    expect(index.watermarkGap()).toBeNull()
+  })
+
+  it("stamp BEHIND the committed generation → 'catchup' with the exact gap reported", async () => {
+    const storage = await makeStorage(5)
+    await writeArtifact(storage, 5)
+
+    setCommitted(storage, 9)
+
+    const index = await reopen(storage)
+    expect(index.watermarkVerdict()).toBe('catchup')
+    expect(index.watermark()).toBe(5)
+    expect(index.watermarkGap()).toEqual({ from: 5, to: 9 })
+  })
+
+  it("stamp ABOVE the committed generation → 'rescan', said out loud", async () => {
+    const storage = await makeStorage(9)
+    await writeArtifact(storage, 9)
+
+    setCommitted(storage, 4)
+
+    const warnSpy = vi.spyOn(prodLog, 'warn')
+    const index = await reopen(storage)
+    expect(index.watermarkVerdict()).toBe('rescan')
+    expect(index.watermarkGap()).toBeNull()
+    const said = warnSpy.mock.calls.map(c => String(c[0])).join('\n')
+    expect(said).toContain('RESCAN')
+    expect(said).toContain('ABOVE')
+  })
+
+  it("legacy unstamped artifact on a stamped store → 'rescan', LOUD — never a silent adopt", async () => {
+    const storage = await makeStorage(3)
+    await writeArtifact(storage, null) // pre-stamp index: data flushed, no stamp
+
+    expect(await storage.getMetadata(HNSW_INDEX_STAMP_KEY)).toBeNull()
+
+    const warnSpy = vi.spyOn(prodLog, 'warn')
+    const index = await reopen(storage)
+    expect(index.watermarkVerdict()).toBe('rescan')
+    expect(index.watermark()).toBeNull()
+    const said = warnSpy.mock.calls.map(c => String(c[0])).join('\n')
+    expect(said).toContain('RESCAN')
+    expect(said).toContain('unstamped')
+  })
+
+  it("a store with no committed-generation capability keeps pre-stamp behavior → 'adopt'", async () => {
+    const storage = await makeStorage(null)
+    await writeArtifact(storage, null)
+
+    const index = await reopen(storage)
+    expect(index.watermarkVerdict()).toBe('adopt')
+    expect(index.watermark()).toBeNull()
+  })
+
+  it('STAMP-AFTER-DATA: the stamp lands after every node record and the system record', async () => {
+    const storage = await makeStorage(2)
+    const index = makeIndex(storage)
+    for (let i = 0; i < 3; i++) {
+      await index.addItem({ id: uuidv4(), vector: randomVector(DIM) })
+    }
+
+    // One shared op log across all three write surfaces pins global order.
+    const ops: string[] = []
+    const origNode = storage.saveVectorIndexData.bind(storage)
+    vi.spyOn(storage, 'saveVectorIndexData').mockImplementation(async (id, data) => {
+      ops.push(`node:${id}`)
+      return origNode(id, data)
+    })
+    const origSystem = storage.saveHNSWSystem.bind(storage)
+    vi.spyOn(storage, 'saveHNSWSystem').mockImplementation(async data => {
+      ops.push('system')
+      return origSystem(data)
+    })
+    const origMeta = storage.saveMetadata.bind(storage)
+    vi.spyOn(storage, 'saveMetadata').mockImplementation(async (id, metadata) => {
+      ops.push(`meta:${id}`)
+      return origMeta(id, metadata)
+    })
+
+    index.stampWatermark(2)
+    await index.flush()
+
+    const stampAt = ops.indexOf(`meta:${HNSW_INDEX_STAMP_KEY}`)
+    expect(stampAt, 'stamp record was written').toBeGreaterThanOrEqual(0)
+    expect(stampAt, 'stamp is the FINAL write of the flush').toBe(ops.length - 1)
+    expect(ops.filter(o => o.startsWith('node:')).length).toBeGreaterThan(0)
+    expect(ops.indexOf('system')).toBeLessThan(stampAt)
+  })
+
+  it('the stamp record carries {watermark, formatVersion, stampedAt} + modelIdentity (dims only)', async () => {
+    const storage = await makeStorage(7)
+    await writeArtifact(storage, 7)
+
+    const record = (await storage.getMetadata(HNSW_INDEX_STAMP_KEY)) as {
+      watermark: number
+      formatVersion: number
+      stampedAt: number
+      modelIdentity: { embedModelId?: string; dimensions: number | null }
+    }
+    expect(record.watermark).toBe(7)
+    expect(record.formatVersion).toBe(1)
+    expect(typeof record.stampedAt).toBe('number')
+    // The JS index never sees the embedder — dimensions are the only vector-
+    // space identity it can honestly assert.
+    expect(record.modelIdentity).toEqual({ dimensions: DIM })
+  })
+
+  it('a pending stamp still lands when nothing is dirty (already-durable bytes, stamp-after-data trivially holds)', async () => {
+    const storage = await makeStorage(4)
+    const index = makeIndex(storage)
+    await index.addItem({ id: uuidv4(), vector: randomVector(DIM) })
+    await index.flush() // data durable, no stamp yet
+
+    index.stampWatermark(4)
+    await index.flush() // nothing dirty — the stamp must still be written
+
+    const record = (await storage.getMetadata(HNSW_INDEX_STAMP_KEY)) as { watermark: number }
+    expect(record?.watermark).toBe(4)
+    expect(index.watermark()).toBe(4)
+  })
+})

tests/unit/hnsw/update-item-atomic.test.ts

@@ -0,0 +1,366 @@
+/**
+ * @module tests/unit/hnsw/update-item-atomic
+ * @description Guard for the atomic vector-index update: a row must NEVER be
+ * absent from vector search during an update. The historical update path
+ * staged a remove followed by an add as two separately-awaited transaction
+ * operations — between them the row was in NEITHER index (dark to semantic
+ * recall while perfectly visible to metadata reads; observed as seconds-long
+ * flicker in a production deployment). The structural cure verified here:
+ *
+ *   1. `JsHnswVectorIndex.updateItem` — same vector (element-wise) is a pure
+ *      no-op (the production flicker shape: a type-only update re-indexing an
+ *      UNCHANGED vector); a changed vector swaps in place, the node never
+ *      leaving the map (white-box probe at the first internal step after the
+ *      synchronous swap), including when the node IS the entry point.
+ *   2. `ReplaceInVectorIndexOperation` — one transaction leg that prefers the
+ *      provider's in-place `updateItem`, with a remove+add-ADJACENT fallback
+ *      for providers that have not shipped it; rollback restores the declared
+ *      before-vector on both branches.
+ *   3. The brain's update path — with the JS index carrying `updateItem`,
+ *      `removeItem` is never called during `brain.update()`, for the
+ *      type-only shape AND for a genuine vector change.
+ */
+import { describe, it, expect, vi } from 'vitest'
+import { JsHnswVectorIndex } from '../../../src/hnsw/hnswIndex.js'
+import { ReplaceInVectorIndexOperation } from '../../../src/transaction/operations/IndexOperations.js'
+import type { VectorIndexProvider } from '../../../src/plugin.js'
+import type { Vector, VectorDocument } from '../../../src/coreTypes.js'
+import { euclideanDistance } from '../../../src/utils/index.js'
+import { MemoryStorage } from '../../../src/storage/adapters/memoryStorage.js'
+import { Brainy } from '../../../src/brainy'
+import { createAddParams, createTestConfig } from '../../helpers/test-factory'
+
+const DIM = 8
+
+function seededRand(seed: number): () => number {
+  let s = seed >>> 0
+  return () => {
+    s = (s + 0x6d2b79f5) | 0
+    let t = Math.imul(s ^ (s >>> 15), 1 | s)
+    t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t
+    return ((t ^ (t >>> 14)) >>> 0) / 4294967296
+  }
+}
+
+/** A deterministic vector pointing in a pseudo-random direction (well-connected graph). */
+function vec(idx: number): number[] {
+  const rand = seededRand(idx + 1)
+  return Array.from({ length: DIM }, () => rand() * 2 - 1)
+}
+
+type Noun = { id: string; vector: number[]; connections: Map<number, Set<string>>; level: number }
+
+function nounsOf(index: JsHnswVectorIndex): Map<string, Noun> {
+  return (index as unknown as { nouns: Map<string, Noun> }).nouns
+}
+
+/** Flatten a reverse index to sorted `target|level|source` triples. */
+function triplesFromIncoming(inc: Map<string, Map<number, Set<string>>>): string[] {
+  const out: string[] = []
+  for (const [target, byLevel] of inc) {
+    for (const [level, sources] of byLevel) {
+      for (const source of sources) out.push(`${target}|${level}|${source}`)
+    }
+  }
+  return out.sort()
+}
+
+/** Derive the ground-truth reverse index directly from the live forward adjacency. */
+function triplesFromAdjacency(nouns: Map<string, Noun>): string[] {
+  const out: string[] = []
+  for (const [nodeId, node] of nouns) {
+    for (const [level, targets] of node.connections) {
+      for (const target of targets) out.push(`${target}|${level}|${nodeId}`)
+    }
+  }
+  return out.sort()
+}
+
+function assertReverseIndexConsistent(index: JsHnswVectorIndex): void {
+  const live = (
+    index as unknown as { ensureIncoming: () => Map<string, Map<number, Set<string>>> }
+  ).ensureIncoming()
+  expect(triplesFromIncoming(live)).toEqual(triplesFromAdjacency(nounsOf(index)))
+}
+
+function assertNoSelfLoops(index: JsHnswVectorIndex, id: string): void {
+  const node = nounsOf(index).get(id)!
+  for (const [level, targets] of node.connections) {
+    expect(targets.has(id), `self-loop at level ${level}`).toBe(false)
+  }
+}
+
+function makeIndex(M = 16): JsHnswVectorIndex {
+  return new JsHnswVectorIndex(
+    { M, efConstruction: 200, efSearch: 64, ml: 16 },
+    euclideanDistance,
+    { useParallelization: false, storage: new MemoryStorage() }
+  )
+}
+
+async function fillIndex(index: JsHnswVectorIndex, count: number): Promise<void> {
+  for (let i = 0; i < count; i++) {
+    await index.addItem({ id: `n-${i}`, vector: vec(i) })
+  }
+}
+
+describe('JsHnswVectorIndex.updateItem — atomic in-place vector update', () => {
+  it('same vector (element-wise equal, fresh array) is a pure no-op: no remove, no relink, still searchable', async () => {
+    const index = makeIndex()
+    await fillIndex(index, 30)
+
+    const target = 'n-7'
+    const sameVector = [...vec(7)] // fresh array, identical elements
+
+    const before = await index.search(vec(7), 1)
+    expect(before[0][0]).toBe(target)
+
+    const removeSpy = vi.spyOn(index, 'removeItem')
+    const nodeBefore = nounsOf(index).get(target)!
+    const connectionsBefore = nodeBefore.connections // reference — a relink replaces it
+
+    await index.updateItem({ id: target, vector: sameVector })
+
+    expect(removeSpy).not.toHaveBeenCalled()
+    expect(index.size()).toBe(30)
+    // No relink happened: the connections map is the SAME object, untouched.
+    expect(nounsOf(index).get(target)!.connections).toBe(connectionsBefore)
+
+    const after = await index.search(vec(7), 1)
+    expect(after[0][0]).toBe(target)
+    expect(after[0][1]).toBeCloseTo(0, 10)
+
+    removeSpy.mockRestore()
+  })
+
+  it('changed vector: node never leaves the map (probe fires after the synchronous swap), removeItem never called, findable by the NEW vector', async () => {
+    const index = makeIndex()
+    await fillIndex(index, 40)
+
+    const target = 'n-5'
+    const newVector = vec(500)
+
+    // White-box probe: ensureIncoming is the FIRST internal step of the unlink
+    // walk, i.e. the first thing updateItem does after the synchronous vector
+    // swap. At that instant the node must (a) still be in the map and (b)
+    // already carry the NEW vector — the visibility-atomic ordering.
+    const inner = index as unknown as {
+      nouns: Map<string, Noun>
+      ensureIncoming: () => Map<string, Map<number, Set<string>>>
+    }
+    const origEnsure = inner.ensureIncoming.bind(index)
+    let probed = false
+    let presentDuring = false
+    let swappedFirst = false
+    ;(index as any).ensureIncoming = function () {
+      if (!probed) {
+        probed = true
+        presentDuring = inner.nouns.has(target)
+        swappedFirst = inner.nouns.get(target)?.vector === newVector
+      }
+      return origEnsure()
+    }
+
+    const removeSpy = vi.spyOn(index, 'removeItem')
+    await index.updateItem({ id: target, vector: newVector })
+    delete (index as any).ensureIncoming // restore the prototype method
+
+    expect(probed).toBe(true)
+    expect(presentDuring).toBe(true)
+    expect(swappedFirst).toBe(true)
+    expect(removeSpy).not.toHaveBeenCalled()
+    expect(index.size()).toBe(40)
+    expect(nounsOf(index).has(target)).toBe(true)
+
+    // Findable by search with the NEW vector, at distance ~0.
+    const got = await index.search(newVector, 1)
+    expect(got[0][0]).toBe(target)
+    expect(got[0][1]).toBeCloseTo(0, 10)
+
+    // The relink left the graph bookkeeping exactly consistent.
+    assertNoSelfLoops(index, target)
+    assertReverseIndexConsistent(index)
+
+    removeSpy.mockRestore()
+  })
+
+  it('keeps the node at its existing level (never releveled by an update)', async () => {
+    const index = makeIndex()
+    await fillIndex(index, 30)
+
+    const target = 'n-3'
+    const levelBefore = nounsOf(index).get(target)!.level
+
+    await index.updateItem({ id: target, vector: vec(600) })
+
+    expect(nounsOf(index).get(target)!.level).toBe(levelBefore)
+    expect(index.getMaxLevel()).toBeGreaterThanOrEqual(levelBefore)
+  })
+
+  it('updating the ENTRY POINT in place keeps it valid — entry id and maxLevel unchanged, graph never stranded', async () => {
+    const index = makeIndex()
+    await fillIndex(index, 40)
+
+    const entryId = index.getEntryPointId()!
+    const maxLevelBefore = index.getMaxLevel()
+    const newVector = vec(700)
+
+    await index.updateItem({ id: entryId, vector: newVector })
+
+    // Entry-point bookkeeping must not regress.
+    expect(index.getEntryPointId()).toBe(entryId)
+    expect(index.getMaxLevel()).toBe(maxLevelBefore)
+    expect(index.size()).toBe(40)
+
+    // The entry point itself is findable by its new vector...
+    const gotEntry = await index.search(newVector, 1)
+    expect(gotEntry[0][0]).toBe(entryId)
+
+    // ...and the REST of the graph is still reachable through it (a stranded,
+    // edgeless entry point would make every other node invisible).
+    const otherId = [...nounsOf(index).keys()].find((id) => id !== entryId)!
+    const otherIdx = Number(otherId.slice(2))
+    const gotOther = await index.search(vec(otherIdx), 1)
+    expect(gotOther[0][0]).toBe(otherId)
+
+    assertNoSelfLoops(index, entryId)
+    assertReverseIndexConsistent(index)
+  })
+
+  it('absent id delegates to addItem (plain insert)', async () => {
+    const index = makeIndex()
+    await fillIndex(index, 10)
+
+    await index.updateItem({ id: 'fresh', vector: vec(900) })
+
+    expect(index.size()).toBe(11)
+    const got = await index.search(vec(900), 1)
+    expect(got[0][0]).toBe('fresh')
+  })
+})
+
+describe('ReplaceInVectorIndexOperation — one atomic transaction leg', () => {
+  it('uses the provider updateItem path and rolls back to the old vector in place', async () => {
+    const index = makeIndex()
+    await fillIndex(index, 30)
+
+    const target = 'n-9'
+    const oldVector = vec(9)
+    const newVector = vec(800)
+
+    const removeSpy = vi.spyOn(index, 'removeItem')
+    const op = new ReplaceInVectorIndexOperation(index, target, oldVector, newVector)
+    expect(op.name).toBe('ReplaceInVectorIndex(hnsw-js)')
+
+    const rollback = await op.execute()
+    expect(removeSpy).not.toHaveBeenCalled()
+    expect((await index.search(newVector, 1))[0][0]).toBe(target)
+
+    await rollback()
+    expect(removeSpy).not.toHaveBeenCalled()
+    expect(index.size()).toBe(30)
+
+    // Old vector restored, element-wise, and searchable again.
+    const restored = nounsOf(index).get(target)!.vector
+    expect(restored.length).toBe(oldVector.length)
+    for (let i = 0; i < oldVector.length; i++) {
+      expect(restored[i]).toBe(oldVector[i])
+    }
+    const back = await index.search(oldVector, 1)
+    expect(back[0][0]).toBe(target)
+    expect(back[0][1]).toBeCloseTo(0, 10)
+
+    removeSpy.mockRestore()
+  })
+
+  it('falls back to remove+add ADJACENT within the single op for a provider without updateItem, and rolls back the same way', async () => {
+    // A provider that has not shipped updateItem — the temporary seam: the
+    // pair stays adjacent inside ONE op (no other transaction operation can
+    // interleave), until the provider ships its own in-place updateItem.
+    const calls: string[] = []
+    const store = new Map<string, Vector>()
+    const legacyProvider = {
+      name: 'legacy-native',
+      addItem: async (item: VectorDocument) => {
+        calls.push(`add:${item.id}`)
+        store.set(item.id, item.vector)
+        return item.id
+      },
+      removeItem: async (id: string) => {
+        calls.push(`remove:${id}`)
+        return store.delete(id)
+      },
+      search: async () => [],
+      size: () => store.size,
+      clear: () => store.clear(),
+      rebuild: async () => {},
+      flush: async () => 0,
+      getPersistMode: () => 'immediate' as const
+    } as unknown as VectorIndexProvider
+
+    store.set('x', [1, 0])
+    const op = new ReplaceInVectorIndexOperation(legacyProvider, 'x', [1, 0], [0, 1])
+
+    const rollback = await op.execute()
+    expect(calls).toEqual(['remove:x', 'add:x'])
+    expect(store.get('x')).toEqual([0, 1])
+
+    await rollback()
+    expect(calls).toEqual(['remove:x', 'add:x', 'remove:x', 'add:x'])
+    expect(store.get('x')).toEqual([1, 0])
+  })
+})
+
+describe('brain.update() — the update path stages ONE atomic vector-index leg', () => {
+  it('a type-only update (unchanged vector — the production flicker shape) never calls removeItem on the vector index', async () => {
+    const brain = new Brainy(createTestConfig())
+    await brain.init()
+    try {
+      const id = await brain.add(
+        createAddParams({ data: 'atomic flicker guard entity', type: 'thing' })
+      )
+
+      const index = (brain as unknown as { index: JsHnswVectorIndex }).index
+      const removeSpy = vi.spyOn(index, 'removeItem')
+      const sizeBefore = index.size()
+
+      await brain.update({ id, type: 'document' })
+
+      expect(removeSpy).not.toHaveBeenCalled()
+      expect(index.size()).toBe(sizeBefore)
+
+      const updated = await brain.get(id)
+      expect(updated).not.toBeNull()
+      expect(updated!.type).toBe('document')
+
+      removeSpy.mockRestore()
+    } finally {
+      await brain.close()
+    }
+  })
+
+  it('a genuine vector change on update also never calls removeItem (in-place replace)', async () => {
+    const brain = new Brainy(createTestConfig())
+    await brain.init()
+    try {
+      const id = await brain.add(
+        createAddParams({ data: 'vector change stays visible', type: 'thing' })
+      )
+      const existing = await brain.get(id, { includeVectors: true })
+      // Same dimensionality, guaranteed-different content.
+      const changed = existing!.vector.map((x: number, i: number) => (i === 0 ? x + 0.25 : x))
+
+      const index = (brain as unknown as { index: JsHnswVectorIndex }).index
+      const removeSpy = vi.spyOn(index, 'removeItem')
+
+      await brain.update({ id, vector: changed })
+
+      expect(removeSpy).not.toHaveBeenCalled()
+      expect(nounsOf(index).has(id)).toBe(true)
+
+      removeSpy.mockRestore()
+    } finally {
+      await brain.close()
+    }
+  })
+})

tests/unit/indexes/columnStore/segment-load-fault.test.ts

@@ -5,19 +5,22 @@
  * doing so dropped every entity in that segment out of `filter`/`rangeQuery`/
  * `sortTopK` with no error, so a corrupt index looked like a merely short result.
  *
- * The three failure classes and their required behaviour:
+ * The three failure classes and their required behaviour (torn-segment
+ * QUARANTINE contract — a raw throw at query time killed every query on the
+ * field forever; a silent skip hid the loss; quarantine is the middle):
  *  - a real storage IO fault (EIO) PROPAGATES verbatim — a present-but-unreadable
  *    segment is not "absent", so it must not read as an empty result;
- *  - a manifest-listed segment with undecodable bytes throws `ColumnSegmentLoadError`;
- *  - a manifest-listed segment with NO bytes (gone on disk) throws `ColumnSegmentLoadError`.
+ *  - a manifest-listed segment with undecodable bytes is QUARANTINED at
+ *    discovery: the query serves the field's remaining segments degraded and
+ *    `quarantinedSegments()` reports the torn segment (loud once, counted
+ *    always, healable);
+ *  - a manifest-listed segment with NO bytes (gone on disk) quarantines the
+ *    same way.
  * Only genuine absence stays benign: querying a field that has no manifest at all
  * returns empty (nothing was ever written for it) — that is not a fault.
  */
 import { describe, it, expect, beforeEach } from 'vitest'
-import {
-  ColumnStore,
-  ColumnSegmentLoadError
-} from '../../../../src/indexes/columnStore/ColumnStore.js'
+import { ColumnStore } from '../../../../src/indexes/columnStore/ColumnStore.js'
 import { MemoryStorage } from '../../../../src/storage/adapters/memoryStorage.js'
 import { EntityIdMapper } from '../../../../src/utils/entityIdMapper.js'
 
@@ -80,30 +83,44 @@ describe('ColumnStore segment-load faults surface loudly, absence stays benign (
     return s
   }
 
-  it('propagates a storage IO fault verbatim — not [] and not a ColumnSegmentLoadError', async () => {
+  it('propagates a storage IO fault verbatim — not [] and not a quarantine (a present-but-unreadable segment is not torn)', async () => {
     storage.faultMode = 'io'
     const store = await reopen()
     await expect(store.filter('createdAt', 300)).rejects.toMatchObject({
       code: 'EIO'
     })
+    // An IO fault is NOT quarantined — the segment may be fine once the disk
+    // recovers; only torn/absent bytes enter the ledger.
+    expect(store.quarantinedSegments('createdAt')).toEqual([])
     await store.close()
   })
 
-  it('throws ColumnSegmentLoadError when a manifest-listed segment is undecodable', async () => {
+  it('QUARANTINES an undecodable manifest-listed segment at discovery — the query serves degraded, the ledger names the tear', async () => {
     storage.faultMode = 'corrupt'
     const store = await reopen()
-    await expect(
-      store.sortTopK('createdAt', 'desc', 10)
-    ).rejects.toBeInstanceOf(ColumnSegmentLoadError)
+    // Degraded-announced serve: the field's only segment is torn, so the
+    // result is empty — but the query completes instead of throwing.
+    const sorted = await store.sortTopK('createdAt', 'desc', 10)
+    expect(sorted).toEqual([])
+    const ledger = store.quarantinedSegments('createdAt')
+    expect(ledger).toHaveLength(1)
+    expect(ledger[0].error).toMatch(/decode failed/)
+    expect(ledger[0].hits).toBeGreaterThanOrEqual(1)
+    // Subsequent queries keep serving (skip + count), never a throw.
+    const hitsBefore = ledger[0].hits
+    await expect(store.filter('createdAt', 300)).resolves.toBeDefined()
+    expect(store.quarantinedSegments('createdAt')[0].hits).toBeGreaterThan(hitsBefore)
     await store.close()
   })
 
-  it('throws ColumnSegmentLoadError when a manifest-listed segment has no loadable bytes', async () => {
+  it('QUARANTINES a manifest-listed segment with no loadable bytes — degraded serve, ledger entry, never a throw', async () => {
     storage.faultMode = 'missing'
     const store = await reopen()
-    await expect(
-      store.rangeQuery('createdAt', 100, 500)
-    ).rejects.toBeInstanceOf(ColumnSegmentLoadError)
+    const bitmap = await store.rangeQuery('createdAt', 100, 500)
+    expect(bitmap.size).toBe(0)
+    const ledger = store.quarantinedSegments('createdAt')
+    expect(ledger).toHaveLength(1)
+    expect(ledger[0].error).toMatch(/no loadable bytes/)
     await store.close()
   })
 

tests/unit/plugin-version-coupling.test.ts

@@ -63,7 +63,9 @@ describe('getBrainyVersion() — synchronously correct on first call', () => {
     expect(v).toBe(PACKAGE_VERSION)
     expect(v).not.toBe('3.14.0')
     expect(v).not.toBe('0.0.0') // the unknown-read sentinel must not surface in a real install
-    expect(v.startsWith('8.')).toBe(true)
+    // Deliberately major-agnostic: the equality with PACKAGE_VERSION above already
+    // proves the sync read; this shape pin only guards against sentinel garbage.
+    expect(v).toMatch(/^\d+\.\d+\.\d+/)
   })
 })
 
@@ -95,13 +97,16 @@ describe('version coupling at init() — no silent fallback', () => {
     await brain.close()
   })
 
-  it('does NOT throw for a realistic cor 3.x range (^8.0.0) on a COLD init', async () => {
+  it('does NOT throw for a realistic version-matched caret range on a COLD init', async () => {
     // The actual regression: loadPlugins() is the first init step and makes the
-    // first getBrainyVersion() call, so a stale sync default would reject a
-    // correctly-matched native provider declaring the real 8.x range. A fresh
-    // brain registering a `^8.0.0` plugin must init cleanly.
+    // first getBrainyVersion() call, so a stale sync default ('3.14.0') would
+    // reject a correctly-matched native provider declaring the real caret range —
+    // it fails ^<current-major> just as it failed ^8, so the regression intent is
+    // preserved while the range stays major-agnostic. A fresh brain registering a
+    // `^<current-major>.0.0` plugin must init cleanly.
+    const major = PACKAGE_VERSION.split('.')[0]
     const brain = memBrain()
-    brain.use(fakePlugin('@fake/cor-3x', { brainyRange: '^8.0.0' }))
+    brain.use(fakePlugin('@fake/cor-3x', { brainyRange: `^${major}.0.0` }))
     await expect(brain.init()).resolves.toBeUndefined()
     await brain.close()
   })

tests/unit/plugin/provider-generation.test.ts

@@ -0,0 +1,276 @@
+/**
+ * Generation threading to the metadata-index and vector-index provider write
+ * surfaces — the counterpart of the graph pins in
+ * tests/unit/transaction/graphIndexOperations-generation.test.ts.
+ *
+ * The provider contract gained an optional trailing `generation?: bigint` on
+ * `MetadataIndexProvider.addToIndex`/`removeFromIndex`,
+ * `VectorIndexProvider.addItem`/`removeItem` (+ the feature-detected
+ * `updateItem`), and the id-mapper's `getOrAssign`/`remove`. A native provider
+ * with per-record delta logs stamps its durable records with it — so the value
+ * arriving MUST be the real commit generation (nonzero, monotonic), never a
+ * fabricated 0 and never absent on the coordinator's write paths.
+ *
+ * Two layers of pins:
+ *   1. End-to-end: provider doubles registered via the plugin system capture
+ *      the generation argument during brain.add()/update()/remove() and it
+ *      must equal the committed watermark (`brain.now().generation`).
+ *   2. Operation layer: execute-time (not construction-time) resolution, and
+ *      one shared generation across an op's forward + rollback halves.
+ */
+import { describe, it, expect, afterEach } from 'vitest'
+import { Brainy, NounType } from '../../../src/index.js'
+import { MetadataIndexManager } from '../../../src/utils/metadataIndex.js'
+import {
+  AddToVectorIndexOperation,
+  RemoveFromVectorIndexOperation,
+  ReplaceInVectorIndexOperation,
+  AddToMetadataIndexOperation,
+  RemoveFromMetadataIndexOperation
+} from '../../../src/transaction/operations/IndexOperations.js'
+import type { VectorIndexProvider } from '../../../src/plugin.js'
+
+const V = () => Array.from({ length: 384 }, () => Math.random())
+
+type Captured = { method: string; id: string; generation: bigint | undefined }
+
+const brains: Brainy[] = []
+afterEach(async () => {
+  for (const b of brains.splice(0)) await b.close().catch(() => {})
+})
+
+/** Metadata manager subclass that records the generation of every write. */
+function makeCapturingMetadataFactory(calls: Captured[]) {
+  return (storage: any) => {
+    class CapturingManager extends MetadataIndexManager {
+      async addToIndex(id: string, entityOrMetadata: any, skipFlush = false, deferWrites = false, generation?: bigint): Promise<void> {
+        calls.push({ method: 'addToIndex', id, generation })
+        return super.addToIndex(id, entityOrMetadata, skipFlush, deferWrites, generation)
+      }
+      async removeFromIndex(id: string, metadata?: any, generation?: bigint): Promise<void> {
+        calls.push({ method: 'removeFromIndex', id, generation })
+        return super.removeFromIndex(id, metadata, generation)
+      }
+    }
+    return new CapturingManager(storage)
+  }
+}
+
+/** Minimal vector-index double capturing the generation of every write. */
+function makeCapturingVectorFactory(calls: Captured[]) {
+  return () => {
+    const items = new Map<string, number[]>()
+    const double: VectorIndexProvider & { updateItem(item: { id: string; vector: number[] }, generation?: bigint): Promise<void> } = {
+      name: 'capture-double',
+      async addItem(item, generation) {
+        calls.push({ method: 'addItem', id: item.id, generation })
+        items.set(item.id, item.vector as number[])
+        return item.id
+      },
+      async removeItem(id, generation) {
+        calls.push({ method: 'removeItem', id, generation })
+        return items.delete(id)
+      },
+      async updateItem(item, generation) {
+        calls.push({ method: 'updateItem', id: item.id, generation })
+        items.set(item.id, item.vector)
+      },
+      async search() { return [] },
+      size: () => items.size,
+      clear: () => { items.clear() },
+      async rebuild() {},
+      async flush() { return 0 },
+      getPersistMode: () => 'deferred' as const
+    }
+    return double
+  }
+}
+
+async function makeBrain(plugin: any): Promise<Brainy> {
+  const brain = new Brainy({
+    storage: { type: 'memory' },
+    requireSubtype: false,
+    silent: true,
+    plugins: []
+  })
+  brain.use(plugin)
+  await brain.init()
+  brains.push(brain)
+  return brain
+}
+
+describe('Metadata-index provider — real commit generation on every write (end-to-end)', () => {
+  it('add()/update()/remove() pass the nonzero, monotonic commit generation to addToIndex/removeFromIndex', async () => {
+    const calls: Captured[] = []
+    const brain = await makeBrain({
+      name: 'capture-metadata',
+      activate: async (ctx: any) => {
+        ctx.registerProvider('metadataIndex', makeCapturingMetadataFactory(calls))
+        return true
+      }
+    })
+
+    const id = await brain.add({ data: 'one', type: NounType.Concept, metadata: { k: 'a' }, vector: V() })
+    const addCall = calls.find((c) => c.method === 'addToIndex' && c.id === id)
+    expect(addCall).toBeDefined()
+    expect(typeof addCall!.generation).toBe('bigint')
+    expect(addCall!.generation!).toBeGreaterThan(0n)
+    // Committed watermark after a single-op write IS this write's generation.
+    expect(addCall!.generation!).toBe(BigInt(brain.now().generation))
+
+    calls.length = 0
+    await brain.update({ id, metadata: { k: 'b' } })
+    const updRemove = calls.find((c) => c.method === 'removeFromIndex' && c.id === id)
+    const updAdd = calls.find((c) => c.method === 'addToIndex' && c.id === id)
+    expect(updRemove?.generation).toBeDefined()
+    expect(updAdd?.generation).toBeDefined()
+    // One commit → the remove-old + add-new legs share one watermark.
+    expect(updAdd!.generation!).toBe(updRemove!.generation!)
+    expect(updAdd!.generation!).toBe(BigInt(brain.now().generation))
+    const updateGen = updAdd!.generation!
+    expect(updateGen).toBeGreaterThan(0n)
+
+    calls.length = 0
+    await brain.remove(id)
+    const rmCall = calls.find((c) => c.method === 'removeFromIndex' && c.id === id)
+    expect(rmCall?.generation).toBeDefined()
+    expect(rmCall!.generation!).toBeGreaterThan(updateGen) // monotonic
+    expect(rmCall!.generation!).toBe(BigInt(brain.now().generation))
+  })
+
+  it('transact() adds stamp the batch receipt generation', async () => {
+    const calls: Captured[] = []
+    const brain = await makeBrain({
+      name: 'capture-metadata-tx',
+      activate: async (ctx: any) => {
+        ctx.registerProvider('metadataIndex', makeCapturingMetadataFactory(calls))
+        return true
+      }
+    })
+
+    // Bootstrap honesty: init-time infrastructure writes (the VFS root) are
+    // applied WITHOUT a generation — the provider must receive undefined,
+    // never a fabricated 0.
+    for (const c of calls) expect(c.generation).toBeUndefined()
+    calls.length = 0
+
+    const db = await brain.transact([
+      { op: 'add', data: 'tx-one', type: NounType.Concept, vector: V() },
+      { op: 'add', data: 'tx-two', type: NounType.Concept, vector: V() }
+    ] as any)
+
+    const receiptGen = BigInt(db.receipt!.generation)
+    const addGens = calls.filter((c) => c.method === 'addToIndex').map((c) => c.generation)
+    expect(addGens.length).toBeGreaterThanOrEqual(2)
+    for (const g of addGens) expect(g).toBe(receiptGen)
+  })
+})
+
+describe('Vector-index provider — real commit generation on every write (end-to-end)', () => {
+  it('add()/update()/remove() pass the nonzero commit generation to addItem/updateItem/removeItem', async () => {
+    const calls: Captured[] = []
+    const brain = await makeBrain({
+      name: 'capture-vector',
+      activate: async (ctx: any) => {
+        ctx.registerProvider('vector', makeCapturingVectorFactory(calls))
+        return true
+      }
+    })
+
+    const id = await brain.add({ data: 'vec', type: NounType.Concept, vector: V() })
+    const addCall = calls.find((c) => c.method === 'addItem' && c.id === id)
+    expect(addCall).toBeDefined()
+    expect(typeof addCall!.generation).toBe('bigint')
+    expect(addCall!.generation!).toBeGreaterThan(0n)
+    expect(addCall!.generation!).toBe(BigInt(brain.now().generation))
+
+    calls.length = 0
+    await brain.update({ id, vector: V() })
+    const updCall = calls.find((c) => c.method === 'updateItem' && c.id === id)
+    expect(updCall?.generation).toBeDefined()
+    expect(updCall!.generation!).toBeGreaterThan(addCall!.generation!) // monotonic
+    expect(updCall!.generation!).toBe(BigInt(brain.now().generation))
+
+    calls.length = 0
+    await brain.remove(id)
+    const rmCall = calls.find((c) => c.method === 'removeItem' && c.id === id)
+    expect(rmCall?.generation).toBeDefined()
+    expect(rmCall!.generation!).toBeGreaterThan(updCall!.generation!)
+    expect(rmCall!.generation!).toBe(BigInt(brain.now().generation))
+  })
+})
+
+describe('Index operations — generation threading (operation layer)', () => {
+  function makeVectorSpy() {
+    const calls: Array<{ method: string; generation: bigint | undefined }> = []
+    const index = {
+      name: 'spy',
+      async addItem(_item: any, generation?: bigint) { calls.push({ method: 'addItem', generation }); return 'x' },
+      async removeItem(_id: string, generation?: bigint) { calls.push({ method: 'removeItem', generation }); return true },
+      async updateItem(_item: any, generation?: bigint) { calls.push({ method: 'updateItem', generation }) }
+    } as unknown as VectorIndexProvider
+    return { index, calls }
+  }
+
+  it('vector add/remove/replace resolve the thunk at EXECUTE time and reuse one generation for rollback', async () => {
+    const { index, calls } = makeVectorSpy()
+    let current = 1n
+    const op = new AddToVectorIndexOperation(index, 'id-1', [1, 2], () => current)
+    current = 42n // assigned after construction, read at execute
+    const rollback = await op.execute()
+    expect(calls[0]).toEqual({ method: 'addItem', generation: 42n })
+    current = 77n // rollback must NOT re-read — one watermark per round trip
+    await rollback()
+    expect(calls[1]).toEqual({ method: 'removeItem', generation: 42n })
+
+    calls.length = 0
+    const rm = new RemoveFromVectorIndexOperation(index, 'id-1', [1, 2], () => 7n)
+    const rb2 = await rm.execute()
+    await rb2()
+    expect(calls).toEqual([
+      { method: 'removeItem', generation: 7n },
+      { method: 'addItem', generation: 7n }
+    ])
+
+    calls.length = 0
+    const rep = new ReplaceInVectorIndexOperation(index, 'id-1', [1, 2], [3, 4], () => 9n)
+    const rb3 = await rep.execute()
+    await rb3()
+    expect(calls).toEqual([
+      { method: 'updateItem', generation: 9n },
+      { method: 'updateItem', generation: 9n }
+    ])
+  })
+
+  it('metadata add/remove pass the resolved generation through both halves', async () => {
+    const calls: Array<{ method: string; generation: bigint | undefined }> = []
+    const manager = {
+      async addToIndex(_id: string, _e: any, _s?: boolean, _d?: boolean, generation?: bigint) {
+        calls.push({ method: 'addToIndex', generation })
+      },
+      async removeFromIndex(_id: string, _m?: any, generation?: bigint) {
+        calls.push({ method: 'removeFromIndex', generation })
+      }
+    } as unknown as MetadataIndexManager
+
+    const add = new AddToMetadataIndexOperation(manager, 'id-1', { type: 'x' }, () => 11n)
+    const rb = await add.execute()
+    await rb()
+    const rm = new RemoveFromMetadataIndexOperation(manager, 'id-1', { type: 'x' }, () => 12n)
+    const rb2 = await rm.execute()
+    await rb2()
+    expect(calls).toEqual([
+      { method: 'addToIndex', generation: 11n },
+      { method: 'removeFromIndex', generation: 11n },
+      { method: 'removeFromIndex', generation: 12n },
+      { method: 'addToIndex', generation: 12n }
+    ])
+  })
+
+  it('omitted thunk (legacy caller) → provider receives undefined, never a fabricated 0', async () => {
+    const { index, calls } = makeVectorSpy()
+    const op = new AddToVectorIndexOperation(index, 'id-1', [1, 2])
+    await op.execute()
+    expect(calls[0]).toEqual({ method: 'addItem', generation: undefined })
+  })
+})

tests/unit/reprojection/reprojection-engine.test.ts

@@ -0,0 +1,590 @@
+/**
+ * @module tests/unit/reprojection/reprojection-engine
+ * @description Spec-by-example for the pure-TS reprojection engine — the
+ * frozen contract mirrored from the native twin (a shared conformance suite
+ * runs against both, so the shapes pinned here are load-bearing):
+ *
+ * (a) register + advance folds a scripted source to caught-up with exact
+ *     watermark/applied counts and adapter-owned stamping;
+ * (b) budget exhaustion answers mid-stream and a second advance RESUMES from
+ *     the watermark — never a refold;
+ * (c) a door bump mid-advance preempts within one installment — pinned by
+ *     MECHANISM (no further applyBatch after the bumping step), with only a
+ *     generous wall-clock sanity bound;
+ * (d) advanceAll round-robins families at batch granularity — no starvation;
+ * (e) swap builds beside (the old adapter serves throughout), flips
+ *     atomically at parity, refuses a concurrent swap with a typed error;
+ * (f) quarantine: a typed poison fact is skipped + ledgered, narration
+ *     doubles, a NON-typed throw aborts loudly;
+ * (g) discard() lands on the LOSING adapter after a swap.
+ */
+import { describe, it, expect, vi, afterEach } from 'vitest'
+import {
+  ReprojectionEngine,
+  DoorSignal,
+  ProjectionApplyError,
+  SwapInFlightError,
+  MAX_INSTALLMENT_MS,
+  type ProjectionAdapter,
+  type FactSource
+} from '../../../src/reprojection/reprojectionEngine.js'
+import { FactLogSource } from '../../../src/reprojection/factLogSource.js'
+import type { CommitFact } from '../../../src/db/factLog.js'
+import { prodLog } from '../../../src/utils/logger.js'
+
+/** Build one committed fact for a generation. */
+function fact(generation: number): CommitFact {
+  return {
+    generation,
+    timestamp: 1_700_000_000_000 + generation,
+    ops: [
+      {
+        kind: 'noun',
+        id: `id-${generation}`,
+        record: { metadata: { n: generation }, vector: null }
+      }
+    ]
+  }
+}
+
+/** A scripted FactSource over a (possibly mutable) list of generations. */
+function scriptedSource(gens: () => number[]): FactSource {
+  return {
+    async scan(from: number, limit: number): Promise<CommitFact[]> {
+      return gens()
+        .filter((g) => g > from)
+        .sort((x, y) => x - y)
+        .slice(0, limit)
+        .map(fact)
+    }
+  }
+}
+
+/**
+ * A recording in-memory adapter: stamps after data (the watermark advances
+ * only after a successful apply), applies idempotently (a Map keyed by
+ * generation), and can be scripted to poison (typed) or hard-fail (untyped)
+ * specific generations, or to run a hook inside applyBatch.
+ */
+class RecordingAdapter implements ProjectionAdapter {
+  readonly family: string
+  /** Generations per applyBatch call, in call order (empty arrays included). */
+  readonly batches: number[][] = []
+  /** The upTo passed to each applyBatch call, in call order. */
+  readonly upTos: number[] = []
+  /** Latest state per generation — idempotent under at-least-once delivery. */
+  readonly state = new Map<number, unknown>()
+  /** Generations that throw a typed ProjectionApplyError. */
+  readonly poison = new Set<number>()
+  /** Generations that throw a plain (untyped) Error. */
+  readonly hardFail = new Set<number>()
+  /** Runs inside applyBatch after validation, before the stamp. */
+  onApply?: (gens: number[]) => void | Promise<void>
+  discarded = 0
+  private wm: number | null
+
+  constructor(family: string, watermark: number | null = null) {
+    this.family = family
+    this.wm = watermark
+  }
+
+  watermark(): number | null {
+    return this.wm
+  }
+
+  async applyBatch(facts: CommitFact[], upTo: number): Promise<void> {
+    for (const [i, f] of facts.entries()) {
+      if (this.hardFail.has(f.generation)) {
+        throw new Error(`disk exploded at generation ${f.generation}`)
+      }
+      if (this.poison.has(f.generation)) {
+        throw new ProjectionApplyError({
+          generation: f.generation,
+          recordIndex: i,
+          cause: new Error(`unfoldable payload at ${f.generation}`)
+        })
+      }
+    }
+    for (const f of facts) this.state.set(f.generation, f.ops)
+    const gens = facts.map((f) => f.generation)
+    this.batches.push(gens)
+    this.upTos.push(upTo)
+    if (this.onApply) await this.onApply(gens)
+    this.wm = upTo // stamp-after-data
+  }
+
+  async discard(): Promise<void> {
+    this.discarded++
+  }
+}
+
+const range = (from: number, to: number): number[] =>
+  Array.from({ length: to - from + 1 }, (_, i) => from + i)
+
+afterEach(() => {
+  vi.restoreAllMocks()
+})
+
+describe('reprojection engine — (a) register + advance to caught-up', () => {
+  it('folds a scripted source in order, adapter-stamped, with exact counts', async () => {
+    const source = scriptedSource(() => range(1, 7))
+    const engine = new ReprojectionEngine({ source, batchSize: 3 })
+    const adapter = new RecordingAdapter('a')
+    engine.register(adapter)
+
+    const result = await engine.advance('a', { budgetMs: 10_000 })
+
+    expect(result.status).toBe('caught-up')
+    expect(result.watermark).toBe(7)
+    expect(result.applied).toBe(7)
+    // Batch shape and the upTo handed to the adapter's own stamp.
+    expect(adapter.batches).toEqual([[1, 2, 3], [4, 5, 6], [7]])
+    expect(adapter.upTos).toEqual([3, 6, 7])
+    // The watermark is the ADAPTER's stamp — the engine never wrote one.
+    expect(adapter.watermark()).toBe(7)
+    expect(engine.getAdapter('a')).toBe(adapter)
+  })
+
+  it('honors upTo as an inclusive cap and answers caught-up at the cap', async () => {
+    const source = scriptedSource(() => range(1, 9))
+    const engine = new ReprojectionEngine({ source, batchSize: 3 })
+    const adapter = new RecordingAdapter('a')
+    engine.register(adapter)
+
+    const result = await engine.advance('a', { budgetMs: 10_000, upTo: 5 })
+
+    expect(result.status).toBe('caught-up')
+    expect(result.watermark).toBe(5)
+    expect(result.applied).toBe(5)
+    expect(adapter.batches.flat()).toEqual([1, 2, 3, 4, 5])
+  })
+
+  it('a caught-up family answers immediately with zero applied', async () => {
+    const source = scriptedSource(() => range(1, 4))
+    const engine = new ReprojectionEngine({ source, batchSize: 10 })
+    const adapter = new RecordingAdapter('a', 4) // already stamped to the head
+    engine.register(adapter)
+
+    const result = await engine.advance('a', { budgetMs: 10_000 })
+
+    expect(result).toEqual({ status: 'caught-up', watermark: 4, applied: 0 })
+    expect(adapter.batches).toEqual([])
+  })
+
+  it('refuses duplicate registration and unregistered families loudly', async () => {
+    const engine = new ReprojectionEngine({ source: scriptedSource(() => []) })
+    engine.register(new RecordingAdapter('a'))
+    expect(() => engine.register(new RecordingAdapter('a'))).toThrow(/already registered/)
+    await expect(engine.advance('ghost', { budgetMs: 0 })).rejects.toThrow(/not registered/)
+  })
+})
+
+describe('reprojection engine — (b) budget exhaustion resumes, never refolds', () => {
+  it('returns budget-exhausted mid-stream; the next advance resumes from the watermark', async () => {
+    const source = scriptedSource(() => range(1, 10))
+    const engine = new ReprojectionEngine({ source, batchSize: 2 })
+    const adapter = new RecordingAdapter('b')
+    engine.register(adapter)
+
+    // Zero budget: exactly ONE step of guaranteed progress, then the answer.
+    const first = await engine.advance('b', { budgetMs: 0 })
+    expect(first.status).toBe('budget-exhausted')
+    expect(first.watermark).toBe(2)
+    expect(first.applied).toBe(2)
+    expect(adapter.batches).toEqual([[1, 2]])
+
+    // The second advance RESUMES from the stamp — its first batch starts at 3.
+    const second = await engine.advance('b', { budgetMs: 10_000 })
+    expect(second.status).toBe('caught-up')
+    expect(second.watermark).toBe(10)
+    expect(second.applied).toBe(8)
+    expect(adapter.batches[1]).toEqual([3, 4])
+    // No refold: every generation delivered exactly once across both calls.
+    expect(adapter.batches.flat()).toEqual(range(1, 10))
+  })
+})
+
+describe('reprojection engine — (c) door bump preempts within one installment', () => {
+  it('a bump during a step yields preempted at that step boundary — no further applyBatch', async () => {
+    const source = scriptedSource(() => range(1, 12))
+    const engine = new ReprojectionEngine({ source, batchSize: 2 })
+    const adapter = new RecordingAdapter('c')
+    adapter.onApply = (gens) => {
+      if (gens[0] === 3) engine.doorSignal.bump() // door traffic mid-second-batch
+    }
+    engine.register(adapter)
+
+    const started = Date.now()
+    const result = await engine.advance('c', { budgetMs: 60_000 })
+    const elapsed = Date.now() - started
+
+    expect(result.status).toBe('preempted')
+    expect(result.watermark).toBe(4)
+    expect(result.applied).toBe(4)
+    // THE MECHANISM PIN: the batch that observed the bump was the LAST batch —
+    // preemption landed at the very next boundary, not after more work.
+    expect(adapter.batches).toEqual([[1, 2], [3, 4]])
+    // Generous wall-clock sanity only (the pin above carries the contract):
+    // two tiny batches plus one installment boundary sit far under 5s.
+    expect(elapsed).toBeLessThan(5_000)
+    expect(MAX_INSTALLMENT_MS).toBe(50)
+
+    // Resuming folds the rest — preemption lost nothing.
+    const resumed = await engine.advance('c', { budgetMs: 60_000 })
+    expect(resumed.status).toBe('caught-up')
+    expect(resumed.watermark).toBe(12)
+    expect(adapter.batches.flat()).toEqual(range(1, 12))
+  })
+
+  it('bumps are edge-triggered per advance: a stale bump never preempts', async () => {
+    const source = scriptedSource(() => range(1, 4))
+    const doorSignal = new DoorSignal()
+    const engine = new ReprojectionEngine({ source, doorSignal, batchSize: 2 })
+    const adapter = new RecordingAdapter('c2')
+    engine.register(adapter)
+
+    doorSignal.bump() // BEFORE the advance — belongs to earlier traffic
+    const result = await engine.advance('c2', { budgetMs: 10_000 })
+    expect(result.status).toBe('caught-up')
+    expect(result.watermark).toBe(4)
+  })
+})
+
+describe('reprojection engine — (d) advanceAll round-robin fairness', () => {
+  it('a one-batch family is served on the first round despite a huge backlog next to it', async () => {
+    const source = scriptedSource(() => range(1, 40))
+    const engine = new ReprojectionEngine({ source, batchSize: 5 })
+    const callOrder: string[] = []
+    const big = new RecordingAdapter('big') // 8 batches behind
+    const small = new RecordingAdapter('small', 35) // 1 batch behind
+    big.onApply = () => {
+      callOrder.push('big')
+    }
+    small.onApply = () => {
+      callOrder.push('small')
+    }
+    engine.register(big)
+    engine.register(small)
+
+    const results = await engine.advanceAll({ budgetMs: 10_000 })
+
+    expect(results.big).toEqual({ status: 'caught-up', watermark: 40, applied: 40 })
+    expect(results.small).toEqual({ status: 'caught-up', watermark: 40, applied: 5 })
+    // Fairness pin: 'small' folded its single batch on round ONE — it never
+    // waited behind 'big''s backlog.
+    expect(callOrder[1]).toBe('small')
+    expect(callOrder.filter((f) => f === 'small')).toHaveLength(1)
+  })
+
+  it('two full-backlog families interleave strictly, one batch each per round', async () => {
+    const source = scriptedSource(() => range(1, 40))
+    const engine = new ReprojectionEngine({ source, batchSize: 5 })
+    const callOrder: string[] = []
+    const first = new RecordingAdapter('first')
+    const second = new RecordingAdapter('second')
+    first.onApply = () => {
+      callOrder.push('first')
+    }
+    second.onApply = () => {
+      callOrder.push('second')
+    }
+    engine.register(first)
+    engine.register(second)
+
+    const results = await engine.advanceAll({ budgetMs: 10_000 })
+
+    expect(results.first.status).toBe('caught-up')
+    expect(results.second.status).toBe('caught-up')
+    // 8 rounds × (first, second): strict alternation — neither ever ran twice
+    // while the other waited.
+    expect(callOrder).toHaveLength(16)
+    for (let i = 0; i < callOrder.length; i += 2) {
+      expect(callOrder.slice(i, i + 2)).toEqual(['first', 'second'])
+    }
+  })
+
+  it('budget exhaustion mid-round reports every unfinished family at its own watermark', async () => {
+    const source = scriptedSource(() => range(1, 40))
+    const engine = new ReprojectionEngine({ source, batchSize: 5 })
+    const a = new RecordingAdapter('a')
+    const b = new RecordingAdapter('b')
+    engine.register(a)
+    engine.register(b)
+
+    const results = await engine.advanceAll({ budgetMs: 0 })
+
+    // Zero budget: the leading family gets its one guaranteed step, then the
+    // budget answer lands for everyone still mid-stream.
+    expect(results.a.status).toBe('budget-exhausted')
+    expect(results.b.status).toBe('budget-exhausted')
+    expect(results.a.applied + results.b.applied).toBeGreaterThanOrEqual(5)
+    // A later advanceAll resumes both to the head.
+    const finished = await engine.advanceAll({ budgetMs: 10_000 })
+    expect(finished.a.status).toBe('caught-up')
+    expect(finished.b.status).toBe('caught-up')
+    expect(a.batches.flat()).toEqual(range(1, 40))
+    expect(b.batches.flat()).toEqual(range(1, 40))
+  })
+})
+
+describe('reprojection engine — (e) swap: build-beside, atomic flip, single-flight', () => {
+  it('the old adapter serves at its own watermark throughout the build; the flip is atomic at parity', async () => {
+    const log = range(1, 20)
+    const source = scriptedSource(() => log)
+    const engine = new ReprojectionEngine({ source, batchSize: 4 })
+    const oldAdapter = new RecordingAdapter('e')
+    engine.register(oldAdapter)
+    await engine.advance('e', { budgetMs: 10_000 })
+    expect(oldAdapter.watermark()).toBe(20)
+
+    // The log grows after the old adapter stamped — the build must reach the
+    // HEAD (24), not merely the old watermark (20), before the flip.
+    log.push(21, 22, 23, 24)
+
+    const servingDuringBuild: Array<{ adapter: ProjectionAdapter | undefined; watermark: number | null }> = []
+    let replacement!: RecordingAdapter
+    const result = await engine.swap('e', async () => {
+      replacement = new RecordingAdapter('e')
+      replacement.onApply = () => {
+        servingDuringBuild.push({
+          adapter: engine.getAdapter('e'),
+          watermark: engine.getAdapter('e')!.watermark()
+        })
+      }
+      return replacement
+    })
+
+    // Build-beside pin: EVERY mid-build observation saw the OLD adapter,
+    // still serving, still at its own stamp.
+    expect(servingDuringBuild.length).toBeGreaterThan(0)
+    for (const seen of servingDuringBuild) {
+      expect(seen.adapter).toBe(oldAdapter)
+      expect(seen.watermark).toBe(20)
+    }
+    // The flip: the registry now serves the replacement, at parity with head.
+    expect(engine.getAdapter('e')).toBe(replacement)
+    expect(result.watermark).toBe(24)
+    expect(result.applied).toBe(24)
+    expect(replacement.batches.flat()).toEqual(range(1, 24))
+  })
+
+  it('a second concurrent swap on the same family refuses with the typed single-flight error', async () => {
+    const source = scriptedSource(() => range(1, 8))
+    const engine = new ReprojectionEngine({ source, batchSize: 4 })
+    engine.register(new RecordingAdapter('e2'))
+
+    let release!: () => void
+    const gate = new Promise<void>((resolve) => {
+      release = resolve
+    })
+    const inFlight = engine.swap('e2', async () => {
+      const building = new RecordingAdapter('e2')
+      building.onApply = () => gate // the build parks mid-fold
+      return building
+    })
+
+    // While the first swap builds, a second one is refused — typed.
+    const refusal = await engine.swap('e2', async () => new RecordingAdapter('e2')).catch((e) => e)
+    expect(refusal).toBeInstanceOf(SwapInFlightError)
+    expect((refusal as SwapInFlightError).family).toBe('e2')
+
+    release()
+    const done = await inFlight
+    expect(done.watermark).toBe(8)
+    // Single-flight released: a follow-up swap is admitted again.
+    const again = await engine.swap('e2', async () => new RecordingAdapter('e2'))
+    expect(again.watermark).toBe(8)
+  })
+
+  it('a failed build discards the partial replacement and leaves the old adapter serving', async () => {
+    const source = scriptedSource(() => range(1, 8))
+    const engine = new ReprojectionEngine({ source, batchSize: 4 })
+    const oldAdapter = new RecordingAdapter('e3')
+    engine.register(oldAdapter)
+    await engine.advance('e3', { budgetMs: 10_000 })
+
+    let failed!: RecordingAdapter
+    await expect(
+      engine.swap('e3', async () => {
+        failed = new RecordingAdapter('e3')
+        failed.hardFail.add(5) // an UNTYPED failure mid-build
+        return failed
+      })
+    ).rejects.toThrow(/disk exploded/)
+
+    expect(failed.discarded).toBe(1) // the partial build was cleaned up
+    expect(oldAdapter.discarded).toBe(0)
+    expect(engine.getAdapter('e3')).toBe(oldAdapter) // still serving, untouched
+    expect(oldAdapter.watermark()).toBe(8)
+  })
+})
+
+describe('reprojection engine — (f) quarantine: the fourth answer class', () => {
+  it('a typed poison fact is skipped, ledgered, and the rest folds to quarantined', async () => {
+    const source = scriptedSource(() => range(1, 10))
+    const engine = new ReprojectionEngine({ source, batchSize: 4 })
+    const adapter = new RecordingAdapter('f')
+    adapter.poison.add(6)
+    engine.register(adapter)
+
+    const result = await engine.advance('f', { budgetMs: 10_000 })
+
+    expect(result.status).toBe('quarantined')
+    expect(result.watermark).toBe(10)
+    expect(result.applied).toBe(9) // every generation but the poison
+    expect(adapter.batches.flat().sort((x, y) => x - y)).toEqual([1, 2, 3, 4, 5, 7, 8, 9, 10])
+    expect(adapter.state.has(6)).toBe(false)
+
+    const ledger = engine.quarantined('f')
+    expect(ledger).toHaveLength(1)
+    expect(ledger[0].generation).toBe(6)
+    expect(ledger[0].error).toBeInstanceOf(ProjectionApplyError)
+    expect(ledger[0].error.recordIndex).toBe(1) // 6 sat at index 1 of [5..8]
+    expect(typeof ledger[0].at).toBe('number')
+  })
+
+  it('narration doubles: warns on the 1st, 2nd, and 4th quarantine — not the 3rd', async () => {
+    const warnSpy = vi.spyOn(prodLog, 'warn').mockImplementation(() => {})
+    const source = scriptedSource(() => range(1, 10))
+    const engine = new ReprojectionEngine({ source, batchSize: 10 })
+    const adapter = new RecordingAdapter('f2')
+    for (const g of [2, 4, 6, 8]) adapter.poison.add(g)
+    engine.register(adapter)
+
+    const result = await engine.advance('f2', { budgetMs: 10_000 })
+
+    expect(result.status).toBe('quarantined')
+    expect(result.watermark).toBe(10)
+    expect(result.applied).toBe(6)
+    expect(engine.quarantined('f2').map((q) => q.generation)).toEqual([2, 4, 6, 8])
+    const quarantineWarns = warnSpy.mock.calls.filter((c) => String(c[0]).includes('quarantined generation'))
+    // 4 entries, narrated at counts 1, 2, and 4 — the 3rd stayed quiet.
+    expect(quarantineWarns).toHaveLength(3)
+    expect(quarantineWarns.map((c) => String(c[0]))).toEqual([
+      expect.stringContaining('(1 quarantined total)'),
+      expect.stringContaining('(2 quarantined total)'),
+      expect.stringContaining('(4 quarantined total)')
+    ])
+  })
+
+  it('an all-poison window still advances the stamp via an empty applyBatch', async () => {
+    const source = scriptedSource(() => range(1, 3))
+    const engine = new ReprojectionEngine({ source, batchSize: 3 })
+    const adapter = new RecordingAdapter('f3')
+    for (const g of [1, 2, 3]) adapter.poison.add(g)
+    engine.register(adapter)
+
+    const result = await engine.advance('f3', { budgetMs: 10_000 })
+
+    expect(result.status).toBe('quarantined')
+    expect(result.watermark).toBe(3)
+    expect(result.applied).toBe(0)
+    // The final call carried NO facts but a real upTo — the pure watermark
+    // advance past poison, stamped by the adapter itself.
+    expect(adapter.batches).toEqual([[]])
+    expect(adapter.upTos).toEqual([3])
+    expect(engine.quarantined('f3').map((q) => q.generation)).toEqual([1, 2, 3])
+  })
+
+  it('a NON-typed throw aborts the advance loudly — unknown failure is never poison', async () => {
+    const source = scriptedSource(() => range(1, 8))
+    const engine = new ReprojectionEngine({ source, batchSize: 4 })
+    const adapter = new RecordingAdapter('f4')
+    adapter.hardFail.add(5)
+    engine.register(adapter)
+
+    await expect(engine.advance('f4', { budgetMs: 10_000 })).rejects.toThrow(/disk exploded at generation 5/)
+
+    expect(adapter.watermark()).toBe(4) // the clean first batch landed; nothing after
+    expect(engine.quarantined('f4')).toEqual([]) // no ledger entry for an unknown failure
+  })
+
+  it('an adapter re-condemning an already-quarantined generation is refused loudly', async () => {
+    const source = scriptedSource(() => range(1, 4))
+    const engine = new ReprojectionEngine({ source, batchSize: 4 })
+    // A misbehaving adapter: always blames generation 3, even once it is
+    // filtered out of its batches.
+    const adapter: ProjectionAdapter = {
+      family: 'f5',
+      watermark: () => null,
+      applyBatch: async () => {
+        throw new ProjectionApplyError({ generation: 3, cause: new Error('always 3') })
+      },
+      discard: async () => {}
+    }
+    engine.register(adapter)
+
+    await expect(engine.advance('f5', { budgetMs: 10_000 })).rejects.toThrow(/ALREADY quarantined/)
+    expect(engine.quarantined('f5').map((q) => q.generation)).toEqual([3])
+  })
+
+  it('an adapter that never stamps is refused loudly instead of spinning', async () => {
+    const source = scriptedSource(() => range(1, 4))
+    const engine = new ReprojectionEngine({ source, batchSize: 2 })
+    const adapter: ProjectionAdapter = {
+      family: 'f6',
+      watermark: () => null, // never advances
+      applyBatch: async () => {},
+      discard: async () => {}
+    }
+    engine.register(adapter)
+
+    await expect(engine.advance('f6', { budgetMs: 10_000 })).rejects.toThrow(/not stamping/)
+  })
+})
+
+describe('reprojection engine — (g) discard lands on the losing adapter after a swap', () => {
+  it('the OLD adapter is discarded exactly once, after the flip; the winner is never discarded', async () => {
+    const source = scriptedSource(() => range(1, 6))
+    const engine = new ReprojectionEngine({ source, batchSize: 3 })
+    const losing = new RecordingAdapter('g')
+    engine.register(losing)
+    await engine.advance('g', { budgetMs: 10_000 })
+    expect(losing.discarded).toBe(0) // serving adapters are never discarded
+
+    let winner!: RecordingAdapter
+    await engine.swap('g', async () => {
+      winner = new RecordingAdapter('g')
+      winner.onApply = () => {
+        // Mid-build the loser still serves and is still intact.
+        expect(losing.discarded).toBe(0)
+      }
+      return winner
+    })
+
+    expect(losing.discarded).toBe(1)
+    expect(winner.discarded).toBe(0)
+    expect(engine.getAdapter('g')).toBe(winner)
+  })
+})
+
+describe('FactLogSource — the production source enforces the window contract', () => {
+  it('delegates to the injected callback and passes clean windows through', async () => {
+    const calls: Array<[number, number]> = []
+    const source = new FactLogSource(async (from, limit) => {
+      calls.push([from, limit])
+      return range(from + 1, Math.min(from + limit, 5)).map(fact)
+    })
+    const facts = await source.scan(2, 2)
+    expect(facts.map((f) => f.generation)).toEqual([3, 4])
+    expect(calls).toEqual([[2, 2]])
+    expect(await source.scan(5, 3)).toEqual([])
+  })
+
+  it('refuses out-of-contract callbacks loudly: oversize, non-ascending, at-or-below from', async () => {
+    const oversize = new FactLogSource(async () => range(1, 5).map(fact))
+    await expect(oversize.scan(0, 2)).rejects.toThrow(/contract violation/)
+
+    const unsorted = new FactLogSource(async () => [fact(3), fact(2)])
+    await expect(unsorted.scan(0, 10)).rejects.toThrow(/strictly ascending/)
+
+    const stale = new FactLogSource(async () => [fact(2)])
+    await expect(stale.scan(2, 10)).rejects.toThrow(/strictly ascending/)
+  })
+
+  it('validates its own window arguments', async () => {
+    const source = new FactLogSource(async () => [])
+    await expect(source.scan(-1, 5)).rejects.toThrow(/non-negative integer/)
+    await expect(source.scan(0, 0)).rejects.toThrow(/positive integer/)
+  })
+})

tests/unit/test-suite-coverage-guard.test.ts

@@ -33,6 +33,10 @@ const MANUAL_ONLY = new Set<string>([
   // Conformance suites run as an explicit gate stage (both engines run them
   // by direct invocation), never swept into the unit/integration configs.
   'tests/conformance/collider-fidelity.test.ts',
+  // Golden-log fold-conformance oracle: the two-implementation contract pin
+  // (byte + fold digests) — runs in the explicit conformance gate stage,
+  // same invocation family as the other conformance suites.
+  'tests/conformance/golden-log-fold.test.ts',
   'tests/api/performance-benchmarks.test.ts',
   'tests/critical-neural-validation.test.ts',
   'tests/critical-performance-benchmark.test.ts',

tests/unit/utils/metadataIndex-nested-orderby.test.ts

@@ -0,0 +1,142 @@
+/**
+ * @module tests/unit/utils/metadataIndex-nested-orderby
+ * @description THE NESTED-FIELD ADDRESSING PIN for ordered reads (the
+ * field-addressing law, dotted-path clause). The defect this keeps dead:
+ * `orderBy` on a nested user metadata field (dotted path, e.g.
+ * `orderBy: 'profile.score'` over `metadata: { profile: { score: 7 } }`)
+ * silently returned insertion order — a no-op sort — because the sort
+ * path's value resolution read flat bag keys only. The law: a dotted user
+ * address is either SERVED CORRECTLY (the batched resolver walks inside
+ * the bag) or REFUSED with a typed UnresolvableFieldError — never a silent
+ * pass-through. Both spellings (`profile.score` / `metadata.profile.score`)
+ * are the same address; the filter side (`where: { 'profile.score': … }`)
+ * obeys the same law.
+ */
+import { describe, it, expect, beforeAll, afterAll } from 'vitest'
+import { Brainy, UnresolvableFieldError } from '../../../src/index.js'
+import { NounType } from '../../../src/types/graphTypes.js'
+
+const ROWS = 30
+
+describe('nested (dotted-path) user field orderBy — the field-addressing law', () => {
+  let brain: Brainy
+  /** id → nested score, for the rows that carry profile.score */
+  const scoreById = new Map<string, number>()
+  /** ids of the two rows WITHOUT a profile bag */
+  let noProfileIds: string[] = []
+
+  beforeAll(async () => {
+    brain = new Brainy({ storage: { type: 'memory' }, requireSubtype: false })
+    await brain.init()
+    for (let i = 0; i < ROWS; i++) {
+      // (i * 11) % 30 is a permutation of 0..29 (gcd(11,30)=1): every score
+      // distinct, insertion order maximally different from value order — a
+      // silent insertion-order pass-through cannot accidentally look sorted.
+      const score = (i * 11) % ROWS
+      const id = await brain.add({
+        data: `row ${i}`,
+        type: NounType.Document,
+        metadata: { profile: { score }, plain: i }
+      })
+      scoreById.set(id, score)
+    }
+    const a = await brain.add({
+      data: 'no-profile a',
+      type: NounType.Document,
+      metadata: { plain: 1000 }
+    })
+    const b = await brain.add({
+      data: 'no-profile b',
+      type: NounType.Document,
+      metadata: { plain: 1001 }
+    })
+    noProfileIds = [a, b].sort()
+  }, 120000)
+
+  afterAll(async () => {
+    await brain.close().catch(() => {})
+  })
+
+  /** Assert one complete ordered read against the sealed ordering contract. */
+  function assertOrdered(
+    rows: Array<{ id: string }>,
+    order: 'asc' | 'desc',
+    label: string
+  ): void {
+    // Rows are NEVER dropped: all 30 scored + 2 profile-less rows come back.
+    expect(rows.length, `${label}: complete result`).toBe(ROWS + 2)
+
+    // Missing-value rows sort LAST in BOTH directions, ties by id ascending.
+    const lastTwo = rows.slice(-2).map((r) => r.id)
+    expect(lastTwo, `${label}: missing-value rows LAST, id asc`).toEqual(noProfileIds)
+
+    // The scored 30 are ordered by the NESTED value — the exact permutation,
+    // not insertion order.
+    const observed = rows.slice(0, ROWS).map((r) => scoreById.get(r.id))
+    const wanted = [...scoreById.values()].sort((x, y) =>
+      order === 'asc' ? x - y : y - x
+    )
+    expect(observed, `${label}: nested values in ${order} order`).toEqual(wanted)
+  }
+
+  it('orderBy: "profile.score" desc — served correctly, missing rows LAST (never a silent insertion-order no-op)', async () => {
+    const rows = await brain.find({
+      type: NounType.Document,
+      orderBy: 'profile.score',
+      order: 'desc',
+      limit: 40
+    })
+    assertOrdered(rows, 'desc', 'bare dotted, desc')
+  })
+
+  it('orderBy: "profile.score" asc — same law in the other direction', async () => {
+    const rows = await brain.find({
+      type: NounType.Document,
+      orderBy: 'profile.score',
+      order: 'asc',
+      limit: 40
+    })
+    assertOrdered(rows, 'asc', 'bare dotted, asc')
+  })
+
+  it('explicit spelling "metadata.profile.score" is the SAME address — identical result', async () => {
+    const bare = await brain.find({
+      type: NounType.Document,
+      orderBy: 'profile.score',
+      order: 'desc',
+      limit: 40
+    })
+    const explicit = await brain.find({
+      type: NounType.Document,
+      orderBy: 'metadata.profile.score',
+      order: 'desc',
+      limit: 40
+    })
+    assertOrdered(explicit, 'desc', 'metadata.-prefixed, desc')
+    expect(
+      explicit.map((r) => r.id),
+      'both spellings resolve to the identical ordered id sequence'
+    ).toEqual(bare.map((r) => r.id))
+  })
+
+  it('a dotted path carried by NO entity REFUSES with UnresolvableFieldError — never a silent insertion-order return', async () => {
+    await expect(
+      brain.find({
+        type: NounType.Document,
+        orderBy: 'no.such.path',
+        order: 'desc',
+        limit: 40
+      })
+    ).rejects.toThrow(UnresolvableFieldError)
+  })
+
+  it('dotted where: { "profile.score": 7 } finds exactly the right row — the filter side of the same law', async () => {
+    const wantedId = [...scoreById.entries()].find(([, s]) => s === 7)![0]
+    const rows = await brain.find({
+      type: NounType.Document,
+      where: { 'profile.score': 7 },
+      limit: 40
+    })
+    expect(rows.map((r) => r.id)).toEqual([wantedId])
+  })
+})

tests/unit/utils/metadataIndex-sort-callshape.test.ts

@@ -0,0 +1,119 @@
+/**
+ * @module tests/unit/utils/metadataIndex-sort-callshape
+ * @description THE ASYMPTOTIC CALL-SHAPE PIN for ordered reads
+ * (BRAINY-PROD-LATENCY-TRIAD, David-approved plan Track A1). The defect it
+ * keeps dead: `getSortedIdsForFilter`'s value resolution did a SERIAL
+ * `storage.getNoun()` (the heavyweight VECTOR record) per filtered row —
+ * 62–98ms × 3,224 rows = the measured 199–317 SECOND production sort, with
+ * `topK` applied only after the full scan. These pins assert the SHAPE of
+ * the storage traffic, not wall-clock (latency-blind, so they hold on any
+ * machine): an ordered read performs ZERO per-row vector-record reads and
+ * resolves sort values through BATCHED metadata-record calls only.
+ */
+import { describe, it, expect, beforeAll, afterAll, vi } from 'vitest'
+import { Brainy } from '../../../src/index.js'
+import { NounType } from '../../../src/types/graphTypes.js'
+
+const ROWS = 60
+
+describe('ordered reads — the batched call-shape law (no per-row storage loops)', () => {
+  let brain: Brainy
+  let storage: {
+    getNoun: (id: string) => Promise<unknown>
+    getNounMetadata: (id: string) => Promise<unknown>
+    getNounMetadataBatch: (ids: string[]) => Promise<Map<string, unknown>>
+  }
+
+  beforeAll(async () => {
+    brain = new Brainy({ storage: { type: 'memory' }, requireSubtype: false })
+    await brain.init()
+    for (let i = 0; i < ROWS; i++) {
+      await brain.add({
+        data: `row ${i}`,
+        type: NounType.Document,
+        metadata: { rank: (i * 7) % ROWS, plain: `p${i}` }
+      })
+    }
+    storage = (brain as unknown as { storage: typeof storage }).storage
+  }, 120000)
+
+  afterAll(async () => {
+    await brain.close().catch(() => {})
+  })
+
+  it('user-field orderBy: zero vector-record reads, zero serial metadata reads — batch calls only', async () => {
+    const getNounSpy = vi.spyOn(storage, 'getNoun')
+    const singleReadSpy = vi.spyOn(storage, 'getNounMetadata')
+    const batchSpy = vi.spyOn(storage, 'getNounMetadataBatch')
+
+    const rows = await brain.find({
+      type: NounType.Document,
+      orderBy: 'rank',
+      order: 'desc',
+      limit: 10
+    })
+    expect(rows.length).toBe(10)
+    expect((rows[0].metadata as Record<string, unknown>).rank).toBe(ROWS - 1)
+
+    // THE PIN: the sort's value resolution never opens a vector record and
+    // never falls into a per-row metadata loop. (Result hydration after
+    // pagination is allowed to read; the SORT itself must be batch-only —
+    // hence the ceiling: strictly fewer single reads than sorted rows.)
+    expect(getNounSpy.mock.calls.length, 'per-row vector-record reads in an ordered read').toBe(0)
+    expect(batchSpy.mock.calls.length, 'the batch door was used').toBeGreaterThanOrEqual(1)
+    expect(
+      singleReadSpy.mock.calls.length,
+      'serial per-row metadata reads (the 199s shape)'
+    ).toBeLessThan(ROWS / 2)
+
+    vi.restoreAllMocks()
+  })
+
+  it('system.createdAt orderBy: exact values from batched records — the bucketed index is never a per-row disk excuse', async () => {
+    const getNounSpy = vi.spyOn(storage, 'getNoun')
+    const batchSpy = vi.spyOn(storage, 'getNounMetadataBatch')
+
+    const rows = await brain.find({
+      type: NounType.Document,
+      orderBy: 'system.createdAt',
+      order: 'asc',
+      limit: 15
+    })
+    expect(rows.length).toBe(15)
+
+    expect(getNounSpy.mock.calls.length, 'per-row vector-record reads').toBe(0)
+    expect(batchSpy.mock.calls.length).toBeGreaterThanOrEqual(1)
+
+    // Exactness: ascending createdAt must be non-decreasing with full
+    // millisecond precision (the old path sorted minute-BUCKETED values or
+    // paid a per-row disk read for exact ones — both are dead). Find results
+    // carry the timestamps on the nested full entity.
+    const stamps = rows.map(
+      (r) => ((r as unknown as { entity?: { createdAt?: number } }).entity?.createdAt ??
+        (r as unknown as { createdAt?: number }).createdAt) as number
+    )
+    for (let i = 1; i < stamps.length; i++) {
+      expect(stamps[i]).toBeGreaterThanOrEqual(stamps[i - 1])
+    }
+
+    vi.restoreAllMocks()
+  })
+
+  it('the ordering contract survives the batch path: missing values LAST both directions, ties by id asc, rows never dropped', async () => {
+    // Three rows lack `rank`? No — all carry it; add two rows WITHOUT it.
+    const a = await brain.add({ data: 'no-rank a', type: NounType.Document, metadata: { plain: 'x' } })
+    const b = await brain.add({ data: 'no-rank b', type: NounType.Document, metadata: { plain: 'y' } })
+
+    for (const order of ['asc', 'desc'] as const) {
+      const rows = await brain.find({
+        type: NounType.Document,
+        orderBy: 'rank',
+        order,
+        limit: ROWS + 10
+      })
+      expect(rows.length, `complete result (${order})`).toBe(ROWS + 2)
+      const lastTwo = rows.slice(-2).map((r) => r.id).sort()
+      expect(lastTwo, `missing-value rows sort LAST (${order})`).toEqual([a, b].sort())
+    }
+  })
+})

tests/unit/utils/metadataIndex-watermark.test.ts

@@ -0,0 +1,171 @@
+/**
+ * @module tests/unit/utils/metadataIndex-watermark
+ * @description Watermark-stamp pins for the metadata projection.
+ *
+ * THE LAW under test: every persisted projection artifact carries a stamp
+ * asserting "this state reflects every committed generation ≤ W and nothing
+ * above W, atomically" — written AFTER every byte it certifies is durable —
+ * and at load the owner computes the three-way verdict:
+ * stamped==committed → 'adopt' · stamped<committed → 'catchup' (gap
+ * reported) · stamped>committed OR unstamped → 'rescan', LOUDLY.
+ * Same rule, same verdict names as the shipped aggregation machinery
+ * (AggregationIndex.stateAdoptionVerdict).
+ *
+ * The verdict is COMPUTED AND EXPOSED only — these pins assert no rebuild
+ * trigger changed; acting on 'catchup' lands with the coordinator's wiring.
+ */
+import { describe, it, expect, vi, afterEach } from 'vitest'
+import { v4 as uuidv4 } from 'uuid'
+import {
+  MetadataIndexManager,
+  METADATA_INDEX_STAMP_KEY
+} from '../../../src/utils/metadataIndex.js'
+import { MemoryStorage } from '../../../src/storage/adapters/memoryStorage.js'
+import { prodLog } from '../../../src/utils/logger.js'
+
+/** Fresh storage with a controllable committed generation. */
+async function makeStorage(committed: number | null): Promise<MemoryStorage> {
+  const storage = new MemoryStorage()
+  await storage.init()
+  if (committed !== null) {
+    vi.spyOn(storage, 'committedGeneration').mockReturnValue(committed)
+  }
+  return storage
+}
+
+/** Set (or reset) the mocked committed generation on an existing storage. */
+function setCommitted(storage: MemoryStorage, committed: number): void {
+  vi.spyOn(storage, 'committedGeneration').mockReturnValue(committed)
+}
+
+/** Session 1: index a field, optionally stamp, flush — the durable artifact. */
+async function writeArtifact(
+  storage: MemoryStorage,
+  stamp: number | null
+): Promise<void> {
+  const index = new MetadataIndexManager(storage)
+  await index.init()
+  await index.addToIndex(uuidv4(), { status: 'active', role: 'admin' })
+  if (stamp !== null) index.stampWatermark(stamp)
+  await index.flush()
+}
+
+/** Session 2: reopen on the same storage and return the loaded manager. */
+async function reopen(storage: MemoryStorage): Promise<MetadataIndexManager> {
+  const index = new MetadataIndexManager(storage)
+  await index.init()
+  return index
+}
+
+afterEach(() => {
+  vi.restoreAllMocks()
+})
+
+describe('metadata index — watermark stamp + three-way load verdict', () => {
+  it("save-with-stamp then reopen at the same committed generation → 'adopt', zero-work verdict", async () => {
+    const storage = await makeStorage(5)
+    await writeArtifact(storage, 5)
+
+    const index = await reopen(storage)
+    expect(index.watermarkVerdict()).toBe('adopt')
+    expect(index.watermark()).toBe(5)
+    expect(index.watermarkGap()).toBeNull()
+  })
+
+  it("stamp BEHIND the committed generation → 'catchup' with the exact gap reported", async () => {
+    const storage = await makeStorage(5)
+    await writeArtifact(storage, 5)
+
+    // Later commits landed after the last stamped flush (unclean exit shape).
+    setCommitted(storage, 8)
+
+    const index = await reopen(storage)
+    expect(index.watermarkVerdict()).toBe('catchup')
+    expect(index.watermark()).toBe(5)
+    expect(index.watermarkGap()).toEqual({ from: 5, to: 8 })
+  })
+
+  it("stamp ABOVE the committed generation → 'rescan', said out loud", async () => {
+    const storage = await makeStorage(9)
+    await writeArtifact(storage, 9)
+
+    // A truncated log on a copied store pulled the watermark back.
+    setCommitted(storage, 4)
+
+    const warnSpy = vi.spyOn(prodLog, 'warn')
+    const index = await reopen(storage)
+    expect(index.watermarkVerdict()).toBe('rescan')
+    expect(index.watermarkGap()).toBeNull()
+    const said = warnSpy.mock.calls.map(c => String(c[0])).join('\n')
+    expect(said).toContain('RESCAN')
+    expect(said).toContain('ABOVE')
+  })
+
+  it("legacy unstamped artifact on a stamped store → 'rescan', LOUD — never a silent adopt", async () => {
+    const storage = await makeStorage(3)
+    await writeArtifact(storage, null) // pre-stamp brain: data flushed, no stamp
+
+    expect(await storage.getMetadata(METADATA_INDEX_STAMP_KEY)).toBeNull()
+
+    const warnSpy = vi.spyOn(prodLog, 'warn')
+    const index = await reopen(storage)
+    expect(index.watermarkVerdict()).toBe('rescan')
+    expect(index.watermark()).toBeNull()
+    const said = warnSpy.mock.calls.map(c => String(c[0])).join('\n')
+    expect(said).toContain('RESCAN')
+    expect(said).toContain('unstamped')
+  })
+
+  it("a store with no committed-generation capability keeps pre-stamp behavior → 'adopt'", async () => {
+    const storage = await makeStorage(null) // committedGeneration() → null
+    await writeArtifact(storage, null)
+
+    const index = await reopen(storage)
+    expect(index.watermarkVerdict()).toBe('adopt')
+    expect(index.watermark()).toBeNull()
+  })
+
+  it('STAMP-AFTER-DATA: the stamp is the last saveMetadata of the flush, after registry and field indexes', async () => {
+    const storage = await makeStorage(2)
+    const index = new MetadataIndexManager(storage)
+    await index.init()
+    await index.addToIndex(uuidv4(), { status: 'active' })
+
+    const keys: string[] = []
+    const originalSave = storage.saveMetadata.bind(storage)
+    vi.spyOn(storage, 'saveMetadata').mockImplementation(async (id, metadata) => {
+      keys.push(id)
+      return originalSave(id, metadata)
+    })
+
+    index.stampWatermark(2)
+    await index.flush()
+
+    const stampAt = keys.indexOf(METADATA_INDEX_STAMP_KEY)
+    expect(stampAt, 'stamp record was written').toBeGreaterThanOrEqual(0)
+    expect(stampAt, 'stamp is the FINAL metadata write of the flush').toBe(keys.length - 1)
+    const registryAt = keys.indexOf('__metadata_field_registry__')
+    expect(registryAt, 'field registry written during this flush').toBeGreaterThanOrEqual(0)
+    expect(registryAt).toBeLessThan(stampAt)
+
+    // The persisted stamp record carries the required shape.
+    const record = (await storage.getMetadata(METADATA_INDEX_STAMP_KEY)) as {
+      watermark: number
+      formatVersion: number
+      stampedAt: number
+    }
+    expect(record.watermark).toBe(2)
+    expect(record.formatVersion).toBe(1)
+    expect(typeof record.stampedAt).toBe('number')
+  })
+
+  it('a flush WITHOUT a pending stamp writes no stamp record (no phantom certification)', async () => {
+    const storage = await makeStorage(2)
+    const index = new MetadataIndexManager(storage)
+    await index.init()
+    await index.addToIndex(uuidv4(), { status: 'active' })
+    await index.flush()
+
+    expect(await storage.getMetadata(METADATA_INDEX_STAMP_KEY)).toBeNull()
+  })
+})