feat: two-tier history reads + the repacker + generationDigest — D1+D3 wired end-to-end

The packed tier goes live inside GenerationStore:

- Two-tier reads: getDelta / readBeforeImage / readGenerationRecords
  fall through live-tier → sealed segments (live-tier-wins: a crash
  mid-fold leaves a duplicate representation, never a gap). Cold-open
  seeds committedRanges from the segment manifest via interval merge —
  packed generations resolve without their directories existing.
- repackHistory({timeBudgetMs, batchGenerations}): folds cold
  generations (older than the newest 1024) oldest-first into sealed
  segments, deleting per-generation directories only after segment +
  manifest are durable. Public API + automatic time-bounded pass at
  close() (before compaction, so reclaim can drop whole segments);
  re-representation only — the sole history transform under the
  archival profile. Early stop = consistent prefix, next pass resumes.
- compact(): packed generations reclaim logically in the loop and
  physically at whole-segment boundaries via dropSegmentsBelow (the
  frozen partial-segments-wait rule).
- generationDigest(g) (D8): deterministic content digest through g —
  sealed-segment checksum chain + live-tier delta hashes; O(segments +
  live window); RangeError out of range, GenerationCompactedError
  below the horizon (a gate can never silently pin reclaimed history).

Four end-to-end pins: asOf answers byte-identical across fold + cold
reopen with folded dirs physically gone; repack+reclaim composition;
digest reopen-stability/divergence/loud-horizon; budget no-op+resume.

CHANGELOG.md

@@ -2,6 +2,84 @@
 
 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.
 
+### [8.9.0](https://github.com/soulcraftlabs/brainy/compare/v8.8.2...v8.9.0) (2026-07-19)
+
+- docs: measured performance envelopes v1 (per-op p50/p95 at 1k and 10k, pure-JS floor) (5cabd78)
+- fix: release drains in-flight writer-lock heartbeat — no phantom lock after unlink (70e4bc8)
+- feat: flush() never compacts — history maintenance moves to close() with bounded passes (300d9f2)
+
+
+### [8.8.2](https://github.com/soulcraftlabs/brainy/compare/v8.8.1...v8.8.2) (2026-07-19)
+
+- fix: one field-resolution law across aggregation hooks, source.where, removeMany, and find() spellings (945d92d)
+- chore: push public docs to the soulcraft.com ingest door on release (42037d0)
+
+
+### [8.8.1](https://github.com/soulcraftlabs/brainy/compare/v8.8.0...v8.8.1) (2026-07-18)
+
+- fix: O(1) adaptive retention accounting + historyStats fleet audit (6207e48)
+- fix: import dedup off-switch honesty + brain-owned lifecycle for the background pass (4fcef7b)
+
+
+### [8.8.0](https://github.com/soulcraftlabs/brainy/compare/v8.7.1...v8.8.0) (2026-07-17)
+
+- feat: OS-limit detection for pool-scale deployments (16a73b8)
+
+
+### [8.7.1](https://github.com/soulcraftlabs/brainy/compare/v8.7.0...v8.7.1) (2026-07-17)
+
+- fix: race-proof writer-lock acquisition + machine-readable conflict through init (01a3b46)
+
+
+### [8.7.0](https://github.com/soulcraftlabs/brainy/compare/v8.6.0...v8.7.0) (2026-07-17)
+
+- feat: scaled transact budgets + labeled timeout diagnostics + envelope docs (6ef9fcb)
+
+
+### [8.6.0](https://github.com/soulcraftlabs/brainy/compare/v8.5.2...v8.6.0) (2026-07-17)
+
+- feat: brain.auditGraph() — read-only graph-truth audit (2a03fae)
+
+
+### [8.5.2](https://github.com/soulcraftlabs/brainy/compare/v8.5.1...v8.5.2) (2026-07-17)
+
+- fix: exception-safe aggregation backfill + generation-verified adoption + loud open-path guards (a77b064)
+
+
+### [8.5.1](https://github.com/soulcraftlabs/brainy/compare/v8.5.0...v8.5.1) (2026-07-17)
+
+- fix: aggregation state adoption on reopen + single-flight backfill + query-cap ratchet removal (da55be7)
+- docs: external-backups/sparse-storage guide + generation fact log concept (593bb8b)
+
+
+### [8.5.0](https://github.com/soulcraftlabs/brainy/compare/v8.4.0...v8.5.0) (2026-07-15)
+
+- test: tolerant timing assertion in the execution-time measure test (4dc0a92)
+- feat: committedGeneration capability + pinned durability/stability contracts (d1ecee1)
+- docs: RELEASES.md entry for 8.5.0 (provider fact-log access + shared verifier) (e4f37cd)
+- feat: provider access to the fact log + shared stamp verifier via internals (352e356)
+
+
+### [8.4.0](https://github.com/soulcraftlabs/brainy/compare/v8.3.3...v8.4.0) (2026-07-15)
+
+- docs: RELEASES.md entry for 8.4.0 (generation fact log + family stamp) (4a60b43)
+- feat: entity-tree family stamp — sourceGeneration + rollup coherence at open (2888ae6)
+- feat: generation fact log — after-image commit records, dual-written at every commit point (38b0041)
+
+
+### [8.3.3](https://github.com/soulcraftlabs/brainy/compare/v8.3.2...v8.3.3) (2026-07-15)
+
+- docs: RELEASES.md entry for 8.3.3 (rename containment fix + repair) (c3feafd)
+- test: lens-consistency regression — combined vs subtype-only vs canonical ground truth (4fb41f9)
+- fix: VFS rename moves the containment edge — no ghost in the old directory (af8c179)
+
+
+### [8.3.2](https://github.com/soulcraftlabs/brainy/compare/v8.3.1...v8.3.2) (2026-07-14)
+
+- docs: RELEASES.md entry for 8.3.2 (honest counters) (0932ecd)
+- fix: honest counters — removal never re-reads the removed record + repairIndex recounts and persists all rollups (2e2ba9c)
+
+
 ### [8.3.1](https://github.com/soulcraftlabs/brainy/compare/v8.3.0...v8.3.1) (2026-07-14)
 
 - docs: RELEASES.md entry for 8.3.1 (full-removal deletes + family-scoped gate) (c0c68ac)

RELEASES.md

@@ -8,8 +8,392 @@ Full auto-generated changelog: `CHANGELOG.md` · Releases: https://github.com/so
 - Debugging data, query, or storage behaviour
 - A new Brainy feature is available that you want to adopt
 
+## Removed APIs — 7.x → 8.x (the complete ledger)
+
+Every public API removed at the 8.0 major, with its sanctioned replacement. If your code
+still calls a left-column name on 8.x it throws (or the config key is rejected) — the
+replacement is always a one-line change. (Standing contract from 8.9.0 forward: removals
+happen only at majors, after ≥1 minor of loud runtime deprecation naming the replacement.)
+
+| Removed (7.x) | Replacement (8.x) |
+|---|---|
+| `brain.search(query, k)` | `find({ query })` — semantic; `find({ query, searchMode })` for hybrid |
+| `brain.getRelations({...})` | `related(id, opts)` for adjacency; `find({ connected: {...} })` for scoped traversal |
+| `brain.neural()` clustering | `find({ vector })` + aggregation `GROUP BY` |
+| `Db.search()` | `db.find({ vector })` |
+| Pre-8.0 storage path aliases (`directory`, `basePath`, …) | one `storage.path` key (old aliases throw) |
+| Reserved keys inside `metadata` bags (silently remapped in 7.x) | top-level params (`subtype`, `visibility`, `confidence`, `weight`, …) — reserved-in-bag throws |
+| 7.x COW branches layout (`branches/main/`) | generational MVCC (`asOf()`, `now()`, `db.persist(path)`) — on-disk migration is automatic at first 8.x open |
+
+The fork/snapshot family (`brain.snapshot()`, `createSnapshot()`, `restoreSnapshot()`)
+is sometimes cited as a 7.x removal — those methods never existed on 7.x; the 8.0 Db API
+(`asOf`/`persist`/`restore({confirm})`) is their first real implementation.
+
 ---
 
+## v8.9.0 — 2026-07-19 (flush is durability-only: history maintenance moves to close())
+
+The write path stops paying maintenance costs — the last structural piece of the
+flush-storm class (a production deployment measured single writes blocked 25–191s behind
+history reclaim running inline on flush under memory pressure):
+
+- **`flush()` never compacts history.** It persists the current window's deltas and
+  nothing else — its cost no longer depends on history backlog or retention mode, in any
+  configuration. **`close()` is the auto-compaction site** (time-bounded per pass, ~5s;
+  an early stop is a consistent prefix and the next pass resumes).
+- **`compactHistory()` gains `timeBudgetMs`** — bound your own maintenance windows; the
+  same resumable-prefix guarantee applies.
+- **The documented trade**: a long-lived writer that never closes accumulates history
+  until its next explicit `compactHistory()`. Predictable writes, explicit maintenance.
+  If you run bounded retention on an always-on service, schedule a periodic
+  `compactHistory({ ...caps, timeBudgetMs })` in your maintenance window.
+- **New public doc: `docs/performance-envelopes.md`** — measured per-op envelopes
+  (p50/p95 at stated scales, hardware, and backend, with the measuring script cited).
+  Refresh rule going forward: any release touching a measured path re-runs that op's
+  benchmark and updates the envelope in the same release.
+- **New in this file: the Removed APIs 7.x→8.x table** (top of this document) — every
+  removal with its sanctioned replacement, one place, per the engine-currency contract.
+  Standing from here: removals only at majors, after ≥1 minor of loud runtime deprecation.
+
+## v8.8.2 — 2026-07-19 (one field-resolution law: reserved-field aggregates stop drifting)
+
+Four fixes from a consumer conformance audit, all rooted in the same disease — two field-resolution
+regimes where there must be one:
+
+- **Aggregates grouped by a RESERVED field (`subtype`, `visibility`, …) now decrement on
+  delete.** The delete/update hooks fed the aggregation engine a partial entity view (type,
+  service, data, metadata only), so a reserved-field `groupBy` resolved to a nonexistent group
+  on the way DOWN — counts drifted upward forever after any delete, and updates that moved an
+  entity between reserved-field groups double-counted it. The hooks now pass the full-fidelity
+  entity view (every reserved field top-level, the same shape the add path uses). If your
+  deployment derives stats from reserved-field aggregates, re-define those aggregates once
+  after upgrading (a changed definition triggers one rescan) or run them fresh — the drifted
+  persisted counts do not self-heal retroactively.
+- **Aggregation `source.where` on reserved fields now filters** instead of silently matching
+  nothing: the matcher resolves fields through the same resolver `groupBy` uses (top-level
+  standard fields + custom metadata), so `where: { subtype: 'note' }` means what it says.
+- **`removeMany()` refuses empty/invalid selectors loudly.** A bare array passed positionally
+  (`removeMany([id])` instead of `removeMany({ ids: [id] })`), an empty params object, or
+  `ids: []` used to resolve successfully having deleted nothing. All three now throw.
+- **`find()` accepts both where-key spellings.** Metadata is flattened at index time
+  (`metadata.entry.title` indexes as `entry.title`); a `metadata.`-prefixed where key now
+  falls back to its flattened spelling when the prefixed one isn't indexed — the
+  "unindexed field(s), returning []" confusion for storage-shaped spellings is gone. (A
+  literal nested custom key named `metadata` still wins when indexed as spelled.)
+
+## v8.8.1 — 2026-07-18 (flush no longer walks the whole generation history + the import dedup off-switch is now honest)
+
+### The flush-storm fix (production incident, reported by a long-running deployment)
+
+Under the default adaptive retention, **every `flush()` re-walked the entire committed
+generation history** to compute total history bytes for the budget check — O(all
+generations) with disk re-reads past the 4,096-entry delta-cache bound. On a brain with
+70,000+ accumulated generations that turned every write into a full-tail scan (60-100s
+writes), even though the budget (free-RAM-based) never tripped and nothing was ever
+reclaimed. Fixed:
+
+- `historyBytes()` now maintains a **running total**: seeded by one walk on first use,
+  then updated incrementally at every commit and reclaim — the adaptive retention check
+  on every flush is O(1). Invariant regression-pinned (running total ≡ fresh walk through
+  both commit paths and compaction).
+- New **`brain.historyStats()`** (read-only, exported `HistoryStats`): generation count,
+  total on-disk bytes, generation/timestamp range, compaction horizon, retention mode,
+  and the effective adaptive budget — the one-call fleet-audit for sizing retention
+  exposure per brain.
+- Interim guidance for keep-everything deployments already affected: `retention: 'all'`
+  skips the adaptive accounting entirely (and is the correct policy if you never want
+  history reclaimed). The accumulated files are harmless at rest; this release removes
+  the per-write cost of their existence.
+
+### The import dedup off-switch (lifecycle honesty)
+
+The post-import background deduplication pass (a merge-DELETE writer that runs ~5 minutes
+after an import, merging entities judged duplicates by id / name / vector similarity) had
+three lifecycle defects, all fixed:
+
+- **`enableDeduplication: false` now actually disables it.** The background pass was
+  scheduled unconditionally — an import that explicitly opted out could still have
+  entities auto-removed 5 minutes later. The flag now gates BOTH the inline merge and
+  the background pass (regression-pinned).
+- **One deduplicator per brain, owned by the brain.** Each `import()` call constructed its
+  own coordinator + deduplicator, so the "debounced" timer never actually debounced across
+  imports (N imports = N delete timers). The brain now owns a single instance — the
+  debounce genuinely spans imports — and `close()` cancels pending work, so a delete pass
+  can never fire against a closed brain.
+- **The 5-minute timer is unref'd** — a pending pass no longer holds the process open
+  (the exit-hang class; this timer had escaped the earlier sweep).
+
+Retention note for keep-everything deployments: with `enableDeduplication: false` on
+import calls and `retention: 'all'` in config, no engine path removes records
+automatically.
+
+## v8.8.0 — 2026-07-17 (OS-limit detection for pool-scale deployments)
+
+Small minor: brains now detect the two OS limits that bite at pool scale and warn **before**
+the incident instead of during it.
+
+- At open (once per process, Linux-only, measurement-only), Brainy reads `RLIMIT_NOFILE`
+  (soft/hard, from `/proc/self/limits`) and `vm.max_map_count`, and warns loudly when either
+  sits below the pool-scale floors (soft NOFILE < 65 536; max_map_count < 262 144) — with the
+  exact raise commands (`ulimit -n` / `LimitNOFILE=` / `sysctl vm.max_map_count`). On stock
+  defaults the failure otherwise arrives as `EMFILE` or a failed mmap deep inside an index
+  open, long after the real cause stopped being visible. An unreadable limit produces **no**
+  warning — no measurement, no claim (non-Linux platforms stay silent).
+- Exported for ops doors: `checkOsLimits()` returns the full `OsLimitsReport`
+  (values + warnings) programmatically, with the floors exported as constants.
+
+## v8.7.1 — 2026-07-17 (writer-lock acquisition is race-proof + machine-readable through init)
+
+Two hardenings of the multi-process writer lock (the `locks/_writer.lock` lease that makes a
+second writer on the same brain directory fail loudly):
+
+- **Lock acquisition claims atomically.** The acquire path used read-then-write, leaving a
+  window where two processes racing an *absent* lock could both "succeed" — and the loser
+  kept running unlocked, silently. The claim is now an atomic create-exclusive write
+  (`O_EXCL`): exactly one racer wins; the loser re-evaluates and either fails loudly with
+  the winner's details or performs a verified stale-takeover. Bounded retries; contention
+  beyond them fails loudly rather than degrading into a lockless open.
+- **`BRAINY_WRITER_LOCKED` survives `init()`.** The conflict error documents a
+  machine-readable contract (`err.code`, `err.lockInfo` with the holder's pid/host/
+  heartbeat), but init's error wrapping silently stripped both, leaving consumers a message
+  to regex against. The error now passes through unwrapped.
+
+Measured while verifying (for operators sizing audits): `brain.auditGraph()` at a
+production-consumer scale of ~2,600 relationships / 800 entities costs ~0.1 s warm and
+~0.5 s cold, with exact scar counting across reopen.
+
+## v8.7.0 — 2026-07-17 (bulk-transact ergonomics: scaled budgets + timeout telemetry)
+
+The bulk-import ergonomics release, from a consumer's measured production incident (a serial
+import on network-attached storage at ~2 s/op met a flat 30 s transaction budget):
+
+- **The transact apply budget now scales with the batch** — `max(30 s, opCount × 2 s)` — or
+  is exactly what you pass as the new `TransactOptions.timeoutMs`. A flat 30 s cap silently
+  limited honest bulk work to ~15 operations on slow disks while looking generous for small
+  batches. Internal batch paths (e.g. `removeMany` chunks) get the same scaling.
+- **`TransactionTimeoutError` is a diagnosis, not just a failure**: it now reports the
+  operation it stopped at as `i/N` with the operation's name, elapsed vs budgeted time, and
+  states the batch rolled back atomically and is retryable. Its `context` carries the same
+  fields programmatically.
+- **The transact envelope is documented** — batch sizing, budget math, chunking with
+  `ifAbsent` idempotency, and the precompute pattern (`embedBatch` + per-op `vector`) that
+  keeps model inference out of the commit path. Guide: `docs/guides/optimistic-concurrency.md`.
+- Note: `brain.embed()` / `brain.embedBatch()` (the precompute APIs) already ship — public,
+  with native-provider passthrough, verified end-to-end (batch and single paths produce
+  bit-identical vectors; a vector-supplied `add` is fully searchable). Honest measurement:
+  on the default WASM engine, batch throughput ≈ sequential (~160 ms/text) — the precompute
+  win is keeping inference out of the budgeted commit path, not raw embedding speed.
+
+## v8.6.0 — 2026-07-17 (brain.auditGraph — the graph-truth verification instrument)
+
+A minor release adding one new public API, from the fleet's graph-trust program: a read-only
+audit that **proves whether relationship reads return stored truth** on a given brain.
+
+- **`brain.auditGraph(options?)`** walks every canonical relationship record, queries the same
+  read path applications use (`related()` / VFS `readdir`) with all visibility tiers included,
+  and classifies every discrepancy into its failure family: `missingFromReads` (records the
+  read path omits — a stale adjacency index), `danglingEndpoints` (relationships whose endpoint
+  entity no longer exists — the historical partial-delete scar class), and `readOnlyVerbIds`
+  (read-path edges with no stored record — ghosts). Design-hidden internal/system edges are
+  counted separately so intentional hiding is never misclassified as loss. Counts are exact;
+  example lists cap at `maxExamples` with an explicit `truncatedExamples` flag; the result is
+  narrated loudly on incoherence. Mutates nothing — safe on a live brain.
+- The operational pairing: audit → if incoherent, `repairIndex()` → audit again. A `coherent`
+  report after the repair is the verified all-clear. Run it after any engine upgrade, restore,
+  or migration. Guide: `docs/guides/inspection.md`.
+- Also: `getNounIds` pagination now refuses an undecodable resume cursor loudly (the same
+  contract `getNouns`/`getVerbs` gained in 8.5.2 — the third and final walk brought under it).
+- Types exported: `GraphAuditReport`, `GraphAuditDiscrepancy`.
+
+## v8.5.2 — 2026-07-17 (aggregation backfill: exception-safe, generation-verified, and loud)
+
+Hardening patch from a migration incident (a byte-copied store on new hardware; the service
+entered a silent full-CPU loop at boot). Four changes, all in the aggregation engine's
+backfill/adoption path:
+
+- **Backfill walks are exception-safe and non-destructive.** A rescan now builds into a
+  staging map and swaps in atomically on completion; a mid-walk failure drops the staging map,
+  keeps the previous live state serving, and surfaces the storage error to the failing query.
+  Previously the walk wiped live state *before* a scan that could throw, never cleared the
+  pending flag on failure, and re-ran a full walk on every subsequent query — a silent
+  wipe/walk/throw loop at the caller's retry rate.
+- **Failed walks are latched.** After a walk fails, retries within a 30-second cooldown rethrow
+  the recorded error instantly instead of re-walking — a tight caller-side retry loop now costs
+  one loud error per query, never a full store walk per query.
+- **Adoption is generation-verified.** Persisted aggregation state is stamped with the store's
+  committed generation at flush; reopen adoption requires the stamp to equal the current
+  watermark. Stale state (unclean shutdown) or over-counting state (a fact-log truncation on a
+  copied store pulled the watermark back) triggers exactly one loud rescan — never a silent
+  adopt. Pre-8.5.2 state on generation-aware stores rescans once after upgrade, then is stamped.
+- **The path narrates.** Adoption decisions, no-adoptable-state outcomes, walk start/finish
+  (entity count + duration), and walk failures all log by default; a non-advancing storage
+  pagination cursor aborts the walk loudly instead of looping forever.
+
+Plus three guards from a full audit of every loop in the open/init path:
+
+- **Invalid pagination cursors fail loudly.** A supplied-but-undecodable resume token to
+  `getNouns`/`getVerbs` used to silently restart the walk at offset 0 — to a `while(hasMore)`
+  caller that re-serves page 1 forever (an unbounded silent CPU loop). It now throws with a
+  clear message instead.
+- **The graph cold-load verb walk has a stall guard.** `hasMore=true` with a missing or
+  non-advancing cursor aborts loudly instead of re-reading the same page forever.
+- **A derived index AHEAD of the store is named at open.** Brainy already surfaced a provider
+  generation *behind* the committed watermark; the *ahead* direction (the signature of a
+  byte-copy of a live service, or a log truncation during crash recovery) now logs a loud
+  warning explaining what happened and that `brain.repairIndex()` forces a heal — instead of
+  passing unnamed into whatever the derived index does next.
+
+## v8.5.1 — 2026-07-17 (aggregation state survives restarts + the query-cap ratchet removed)
+
+Patch release from a production incident (aggregate/count paths taking 40–90 s on an idle box
+while vector search stayed fast, and every `find({ limit: 5000 })` suddenly failing against an
+"auto-configured query limit of 1000"). Three fixes, one cosmetic:
+
+- **Aggregation state is actually adopted on reopen.** The boot pattern `defineAggregate()` →
+  query raced the engine's async state load: the synchronous define always won, flagged a
+  backfill, and the first query then wiped the just-loaded persisted state and re-walked the
+  entire store — every restart, forever. Reopening with an unchanged definition now adopts the
+  persisted state directly (zero scans); a backfill runs only on a real definition change, a
+  missing/failed state load, or a write that landed before adoption (exactness wins). Apps that
+  rely on persisted definitions without re-defining at boot also no longer race a spurious
+  "Aggregate not defined".
+- **Backfills are single-flight and batched.** Concurrent queries on a cold aggregate used to
+  each wipe the others' partial state and start their own full store walk — under steady query
+  arrival the store never converged (the 40–90 s loop). Now all concurrent queries share one
+  walk, and one walk fills every aggregate pending backfill (M aggregates ≠ M scans).
+- **The query-cap "learning" ratchet is removed.** `maxLimit` is a memory-protection bound, but
+  a hidden tuner shrank it 20 % per recorded query while the lifetime-average query time
+  exceeded 1 s — down to a floor of 1000, below the documented 10 000 auto floor, with no
+  practical recovery, and the resulting error blamed "available free memory" (stale basis
+  label). The cap now comes from its construction-time basis (or your explicit
+  `maxQueryLimit` / `reservedQueryMemory`) alone and never changes at runtime; query timing is
+  recorded for diagnostics only.
+- **Cosmetic:** the engine's own persistence keys (`__aggregation_*`, `brainy:entityIdMapper`)
+  no longer log `[Storage] Unknown key format` at boot — they were always routed correctly;
+  they're now recognized before the warning fires.
+
+Operationally: if a host was bitten, upgrading and restarting is the whole fix — no repair
+ritual needed. Setting `maxQueryLimit` explicitly remains the valve that bypasses auto-detection
+entirely.
+
+## v8.5.0 — 2026-07-15 (provider access to the fact log + the shared stamp verifier)
+
+Small additive follow-up to 8.4.0, from the native accelerator's first consumption pass:
+
+- **Index providers can now reach the fact log through the storage adapter** — new optional
+  capability `storage.scanFacts()` / `storage.factLogHeadGeneration()` / `storage.factSegmentPaths()`,
+  wired by the host brain at init as a closure over its live log. Providers hold only `storage` and
+  must never construct their own fact-log reader (the log's open path is writer-side); `null` means
+  "no fact log here — use the enumeration walk."
+- **The family-stamp verifier is shared** via `@soulcraft/brainy/internals`
+  (`readFamilyStamp` / `writeFamilyStamp` / `verifyFamilyStamp` + types) so first-party native
+  providers run literally the same verification function, never a synchronized copy.
+- **Rollup stamp invariants accept strings** (`number | string`) — content fingerprints such as a
+  per-tree SHA-256 are valid invariant values; a type mismatch reads as incoherence, never a pass.
+- **`storage.committedGeneration()`** — the committed watermark as a capability, so a provider
+  compares its stamp's `sourceGeneration` against the store's truth without parsing the private
+  manifest format.
+- **Two durability/stability contracts pinned in the suite:** fsync-before-ack (holds for
+  `transact()` today; the single-op path is pinned as the documented future target — group commit
+  becomes latency batching, never durability skipping) and scan-stability-under-rotation (a scan
+  snapshot yields exactly its facts — no gaps, duplicates, or bleed-in — while segments rotate
+  beneath it).
+
+No behavior change for applications; all additions.
+
+## v8.4.0 — 2026-07-15 (the generation fact log — a sequential, self-verifying commit stream)
+
+A minor release, fully backward-compatible (all additions; no behavior change for existing APIs).
+This is infrastructure: it changes nothing about how you query today, and lays the substrate that
+makes index heals and incremental catch-up sequential-read problems instead of directory walks.
+
+- **Every committed write now also appends a "fact" — an after-image commit record.** Alongside the
+  existing before-image history, each committed generation (single-op and `transact()` alike) appends
+  what each touched entity/relationship *became* — or a body-less tombstone for a removal — to an
+  append-only, checksummed segment log under `_generations/facts/`. Crash-safe by construction: a
+  torn tail is detected and ignored; on open the log is reconciled to committed truth, so an absent
+  generation always means "never committed." `transact()` facts are durable when `transact()`
+  returns; single-op facts ride the same group-commit flush as their history.
+
+- **New: `brain.scanFacts()`** — stream committed facts in commit order, in batches, with heal-grade
+  telemetry (total scope up front; per-batch generation range, byte size, and segment; a summary
+  cross-check at the end; loud abort on any gap — never a silent skip). **`brain.factSegmentPaths()`**
+  hands zero-copy consumers the immutable sealed segment files directly. New exported types:
+  `CommitFact`, `FactOp`, `FactScanBatch`, `FactScanHandle`. Facts accumulate from the first write
+  after upgrading — pre-existing history is not retroactively converted (enumeration remains the
+  fallback for old data).
+
+- **New: the entity-tree family stamp.** At every flush/close, brainy stamps which committed
+  generation the canonical entity files reflect plus the rollup invariants (entity/relationship
+  counts) that verify the tree whole. At open, coherence is a comparison — a genuine divergence is
+  loud and names the failing invariant; `repairIndex()` recounts from canonical and re-stamps. New
+  exports: `readFamilyStamp`, `verifyFamilyStamp`, `ENTITY_TREE_STAMP_PATH`, `FamilyStamp` types.
+
+- **Storage adapters** gain optional binary raw-byte primitives (`appendRawBytes`, `readRawBytes`,
+  `writeRawBytes`, `rawByteSize`) — feature-detected; the filesystem and memory adapters implement
+  them; an adapter without them simply hosts no fact log. The fact-log namespace is registered as a
+  protected family: no sweeper or GC can delete under it.
+
+No API breaks. 24 new tests; the full commit-path regression suite is green.
+
+## v8.3.3 — 2026-07-15 (rename moves the containment edge — no ghost in the old directory)
+
+One production-reported fix plus a repair path, completing the delete/move hygiene arc (8.3.1 fixed
+deletes, 8.3.2 fixed counters, this fixes moves).
+
+- **A cross-directory `vfs.rename()` now MOVES the containment edge instead of accumulating one per
+  parent.** The old parent's `Contains` edge was never removed on a move, leaving the entity a child
+  of **both** directories: `readdir(oldDir)` kept listing it after the move, re-creating the old path
+  showed the same name twice, and any tree-walking consumer (sync engines, file browsers) saw the
+  file in two places. The old edge is now removed by edge id, resolved from the graph's own adjacency
+  — a removal never requires reading the thing being removed. Bonus fix in the same seam: a move **to
+  the root** now gets its containment edge (it was previously skipped, orphaning the file out of
+  `readdir('/')`).
+
+- **`repairIndex()` now also reconciles VFS containment** (new `vfs.repairContainment()`): every VFS
+  entity's containment edges are checked against its canonical `metadata.path` — stale old-parent
+  ghosts and duplicate edges are removed, a missing expected edge is restored, and user
+  knowledge-graph edges are never touched (only `vfs-contains` edges are candidates). Loud per
+  repair. Stores that performed cross-directory renames under ≤8.3.2 should run `brain.repairIndex()`
+  once after upgrading — the same single ritual now heals orphan directories, counters, **and**
+  containment edges.
+
+- Also ships a permanent lens-consistency regression suite (combined type+subtype vs subtype-only vs
+  canonical ground truth, id-for-id, warm and after a cold reopen), ported from the field
+  investigation that closed the historical lens-drop report.
+
+No API changes beyond the new optional `vfs.repairContainment()` (also invoked by `repairIndex()`).
+
+## v8.3.2 — 2026-07-14 (honest counters — the recount + removal-without-re-reading)
+
+Completes 8.3.1's delete-hygiene story at the counter layer, from a production proof chain reported
+by a downstream deployment: persisted entity totals were permanently **inflated** — deletes whose
+count decrement was silently skipped — and because paginated `totalCount` serves
+`Math.max(persistedTotal, scanned)`, the inflated number always won and **no disk cleanup could ever
+lower it**.
+
+- **A removal's count decrement no longer requires re-reading the record being removed.** The
+  decrement was sourced from re-reading the entity's metadata inside the delete; if that read
+  returned `null` (a replace race, or a ghost left by a pre-8.3.1 partial delete) the decrement was
+  silently skipped while the paired add had counted — minting drift on every write→delete→re-create
+  cycle. The caller's pre-delete read now rides through the whole delete path
+  (`remove()`/`removeMany()` → the delete operation → `deleteNoun`/`deleteVerb` →
+  `deleteNounMetadata`/`deleteVerbMetadata`, both sides symmetric): a null internal read falls back
+  to the known prior record instead of skipping. The `StorageAdapter` signatures gain an optional
+  `priorMetadata` parameter (additive; existing adapters unaffected).
+
+- **`repairIndex()` is the sanctioned counter recount — unconditional, and it actually persists.**
+  `rebuildTypeCounts()` previously rebuilt only the type-statistics arrays and computed the total
+  *just to log it* — the persisted scalar (`counts.json`) survived every "rebuild" untouched, so an
+  already-inflated brain could never be corrected. One canonical walk now rebuilds **every** counter
+  rollup — scalar totals, per-type maps, and type statistics — and persists them, and `repairIndex()`
+  runs it unconditionally (not only when orphan directories are found: counters can be inflated over
+  perfectly clean shelves). Brains with delete history should run `brain.repairIndex()` once after
+  upgrading; the correction survives reopen.
+
+No API breaks (optional-parameter additions only). Regression tests cover the drift cycle, the
+null-read decrement fallback, and the persisted recount across reopen.
+
 ## v8.3.1 — 2026-07-14 (full-removal deletes + family-scoped migration gate)
 
 Two production-reported fixes in the write/index spine, plus an operator repair path. No API changes;

docs/concepts/generation-fact-log.md

@@ -0,0 +1,117 @@
+---
+title: The Generation Fact Log
+slug: concepts/generation-fact-log
+public: true
+category: concepts
+template: concept
+order: 6
+description: Every committed write also appends a self-verifying "fact" — an after-image commit record — to an append-only log. What facts are, the crash-safety model, the scanFacts() streaming surface, family stamps, and how index providers consume the log for sequential heals.
+next:
+  - concepts/consistency-model
+  - guides/snapshots-and-time-travel
+---
+
+# The Generation Fact Log
+
+Since 8.4.0, every committed generation also appends a **fact** — a compact record of what each
+touched entity or relationship *became* — to an append-only, checksummed log under
+`_generations/facts/`. Where the generational history answers *"what did things look like
+before?"* (before-images, powering `asOf()` and rollback), the fact log answers *"what happened,
+in order?"* — one sequential, self-verifying stream of the store's present being written.
+
+Nothing about querying changes. The fact log exists for three consumers:
+
+1. **Index heals and rebuilds** — one sequential read in commit order replaces a per-entity
+   directory walk over millions of files.
+2. **Incremental catch-up** — a derived index that knows which generation it reflects reads *just
+   the gap*, instead of rebuilding from scratch.
+3. **Replay and audit tooling** — anything that wants the store's committed timeline as a stream.
+
+## What a fact is
+
+One fact per committed generation:
+
+- **`generation`** and **`timestamp`** — which commit, when.
+- **`ops`** — every write in that commit: `{ kind: 'noun' | 'verb', id, record }` where `record`
+  holds the entity's full after-image (both stored legs), or **`null` for a tombstone** — a
+  removal carries no body, by design.
+- **`meta`** — the transaction metadata `transact()` was submitted with, when present.
+- **`blobHashes`** — content-blob references, for exact reclamation accounting.
+
+Facts accumulate **from the first write after upgrading** — pre-existing history is not
+retroactively converted, and consumers fall back to the enumeration walk when no log exists.
+
+## Crash safety, in one paragraph
+
+Facts are appended and fsynced **inside the same durability window as the commit itself**, before
+the commit point — so after a crash, the log can only ever be *ahead* of committed truth, never
+behind it with a hole. On open, the store reconciles the log back to the committed watermark:
+torn tails are detected by per-record checksums and cut; whole records beyond the watermark are
+truncated. The invariant every reader can rely on: **an absent generation was never committed; a
+present fact was.** `transact()` facts are durable the moment `transact()` returns; single-op
+facts share the same group-commit flush as the rest of their generation, so a hard kill loses the
+fact and the generation *together* — never a torn state.
+
+## Reading the log
+
+```typescript
+const scan = brain.scanFacts({ fromGeneration: 1 })
+if (scan) {
+  // Telemetry up front — progress bars get a denominator from second zero.
+  console.log(scan.headGeneration, scan.segmentCount, scan.approxFactCount)
+
+  for await (const batch of scan.batches()) {
+    // Each batch: { facts, firstGeneration, lastGeneration, factCount, byteSize, segmentId }
+    for (const fact of batch.facts) {
+      for (const op of fact.ops) {
+        if (op.record === null) {
+          // a tombstone: op.id was removed in this generation
+        }
+      }
+    }
+  }
+
+  console.log(scan.summary()) // { factsYielded, segmentsRead } — the cross-check
+}
+```
+
+- `scanFacts()` returns `null` when the store hosts no fact log (older store, or a storage adapter
+  without binary append support) — fall back to enumerating entities.
+- Scans run against a **snapshot**: facts appended after the scan opens never bleed in, each fact
+  is yielded exactly once, and a detected gap aborts loudly — never a silent skip.
+- `brain.factSegmentPaths()` returns the immutable, *sealed* segment files for zero-copy consumers
+  (the append-mutable tail is excluded — read it through `scanFacts()`).
+
+## Family stamps: how a projection proves it's current
+
+Anything derived from the store — an index, the entity file tree itself — carries a **family
+stamp**: a small JSON record of *which committed generation the projection reflects*
+(`sourceGeneration`) plus the invariants that verify it whole (exact per-file byte sizes for
+bounded families; rollup invariants like entity counts for unbounded ones). At open, coherence is
+a **comparison**, not a walk:
+
+- stamp equals the committed watermark and invariants hold → serve;
+- stamp is behind → the projection reads just the gap from the fact log;
+- invariants fail → loud, named divergence — `brain.repairIndex()` rebuilds from canonical and
+  re-stamps.
+
+The verifier is exported (`verifyFamilyStamp`) so every projection — TypeScript or native — runs
+literally the same check.
+
+## For plugin authors: the storage capability
+
+Index providers receive the storage adapter, not the brain — so the host wires the log onto it.
+Feature-detect and prefer the stream; fall back to enumeration:
+
+```typescript
+const scan = storage.scanFacts?.({ fromGeneration: stamp.sourceGeneration + 1 })
+if (scan) {
+  // sequential catch-up from the log
+} else {
+  // enumeration walk (older store or adapter)
+}
+const committed = storage.committedGeneration?.() // the watermark stamps compare against
+```
+
+Providers must never construct their own reader over the log's files — the open path belongs to
+the single writer (it reconciles the log at open); the capability is the sanctioned seam.

docs/guides/aggregation.md

@@ -11,7 +11,13 @@ No batch jobs. No scheduled recalculations. Aggregates stay current with every w
 **Defining over existing data:** if you define an aggregate on a store that already holds
 matching entities, Brainy backfills it from those entities on the first query (a one-time scan,
 then purely incremental). So `defineAggregate()` behaves the same whether you define it before
-or after the data exists — including when a persisted brain reopens already populated.
+or after the data exists.
+
+**Reopening a persisted brain:** aggregate state persists across restarts. Re-defining the
+same aggregate at boot (the normal declarative pattern) adopts the persisted state directly —
+no rescan. A backfill scan runs only when the definition actually changed, when no persisted
+state exists, or when the state failed to load; and however many aggregates need backfilling,
+they share a single scan.
 
 ## Quick Start
 

docs/guides/external-backups-and-sparse-storage.md

@@ -0,0 +1,99 @@
+---
+title: External Backups & Sparse Storage
+slug: guides/external-backups
+public: true
+category: guides
+template: guide
+order: 10
+description: How to back up a brain directory with external tools (tar, rsync, cp) without exploding sparse files — why a store can show 100+ GB "apparent" size on a small disk, which files are sparse, and how persist()/restore() handle it for you.
+next:
+  - guides/snapshots-and-time-travel
+  - concepts/storage-adapters
+---
+
+# External Backups & Sparse Storage
+
+The built-in snapshot path — [`db.persist()` and `brain.restore()`](/docs/guides/snapshots-and-time-travel) —
+already handles everything on this page for you. Read this when you back up a brain directory with
+**external tools**: `tar`, `rsync`, `cp`, `scp`, or a filesystem-level backup agent.
+
+## The one-sentence rule
+
+> **Always use the sparse-aware flag**: `tar czSf` (capital `S`), `rsync --sparse`,
+> `cp --sparse=always`. A naive copy can turn a 2 GB store into a 100+ GB one — or fail
+> the disk entirely.
+
+## Why: some files are sparse
+
+When a native accelerator plugin is active, parts of the index live in **memory-mapped files**
+created at a large fixed virtual size — the file's *apparent* size — while the filesystem only
+allocates blocks that were actually written. A brand-new id-mapper file can report tens of
+gigabytes in `ls -l` while occupying a few megabytes on disk.
+
+Check the difference yourself:
+
+```bash
+ls -lh  brain-data/_id_mapper/    # APPARENT size (can be huge)
+du -sh  brain-data/               # ALLOCATED size (the real footprint)
+```
+
+The sparse candidates in a brain directory:
+
+| Path | What it is |
+|---|---|
+| `_id_mapper/` | The native id-mapper's mmap files (large fixed virtual size) |
+| `_blobs/` | Native index files (vector base, segments) — may be mmap-backed |
+
+Everything else (entities, `_system`, `_generations`, `_cas` content blobs) is ordinary dense data.
+
+## Doing it right
+
+**tar** — the `S` flag detects holes and stores only real data:
+
+```bash
+tar czSf brain-backup.tgz /data/brain
+# restore preserves the holes:
+tar xzSf brain-backup.tgz -C /data/
+```
+
+**rsync**:
+
+```bash
+rsync -a --sparse /data/brain/ backup-host:/backups/brain/
+```
+
+**cp**:
+
+```bash
+cp -a --sparse=always /data/brain /backups/brain
+```
+
+**What goes wrong without the flag:** the copy *materializes* every hole as real zero bytes.
+A store whose apparent size exceeds the target disk fails with `ENOSPC` partway through — and a
+copy that *does* fit silently costs the full apparent size in storage and transfer time.
+
+## What the built-in paths do (so you don't have to)
+
+- **`db.persist(path)`** snapshots via **hard links** — instant and space-shared, since every data
+  file is immutable-by-rename. The handful of append-in-place files (the transaction log, the
+  commit fact log's tail segment) and mmap-mutated directories (`_id_mapper/`) are **byte-copied**
+  instead, so a post-snapshot write can never reach through a shared inode into your backup.
+- **`brain.restore(path, { confirm: true })`** is **non-destructive and sparse-aware**: the snapshot
+  is copied into a staging area *before* any live data is touched (all-zero blocks stay holes), and
+  only after the copy fully succeeds does an atomic swap move it into place. A failed copy —
+  including `ENOSPC` — leaves the live store exactly as it was. A crash mid-swap completes forward
+  on the next open.
+
+## Live-store caveats for external tools
+
+1. **Prefer snapshotting a `persist()` output, not the live directory.** `persist()` produces a
+   crash-consistent, immutable snapshot; running `tar` against a live, actively-written directory
+   can capture a torn mid-write state. If you must archive live, stop writes first (or accept that
+   the archive is only as consistent as the moment's flush state).
+2. **Never prune or "clean up" files inside a brain directory.** Index files that look stale or
+   redundant are load-bearing; the store protects its declared index families from in-process
+   deletion, but an external `rm` bypasses that fence. If space is the concern, `du -sh` first —
+   the allocated size is usually far smaller than it looks.
+3. **Verify restores by opening them.** `Brainy.load(path)` opens any snapshot or restored
+   directory read-only — the store verifies its own coherence at open and reports loudly if
+   anything is missing or torn.

docs/guides/find-limits.md

@@ -40,6 +40,10 @@ Brainy picks `maxLimit` from the first of these that's available:
 
 Worked example: a 4 GB Cloud Run container picks priority 3 → `floor(4 GB × 0.25 / 25 KB) = floor(40 960) = 40 000` results. A 900 MB free-memory box on priority 4 gets `floor(900 MB / 25 KB) = ~36 000`.
 
+The cap is fixed at construction and never changes at runtime. Query timing is recorded
+for diagnostics only — a burst of slow queries cannot silently shrink the cap, and the
+auto-detected tiers (3 and 4) never go below a floor of 10 000.
+
 > **Calibration note.** Pre-7.30.2 used 100 KB per result instead of 25 KB, which produced caps that were 4× too tight for typical workloads (an 8 KB / result reality). 7.30.2 recalibrated to match observed entity sizes; existing `limit: 10_000` safety patterns now pass silently on any reasonably-sized box.
 
 ## What happens when you exceed the cap

docs/guides/import-anything.md

@@ -300,7 +300,10 @@ await brain.import(data, {
  // Deduplication
  enableDeduplication: true, // Check for duplicate entities (default: true)
  deduplicationThreshold: 0.85, // Similarity threshold for duplicates (0-1, default: 0.85)
- // Note: Auto-disabled for imports >100 entities
+ // Notes: false disables BOTH the inline merge and the background pass that
+ // runs ~5 min after the last import (merged duplicates are deleted).
+ // The inline pass auto-disables for imports >100 entities (O(n²) cost);
+ // the background pass still covers those unless the flag is false.
 
  // Performance
  chunkSize: 100, // Batch size for processing (default: varies by operation)

docs/guides/import-quick-reference.md

@@ -86,11 +86,22 @@ await brain.import(file, {
 
 ```typescript
 await brain.import(file, {
-  enableDeduplication: true,         // Check for duplicates (default: false)
+  enableDeduplication: true,         // Check for duplicates (default: true)
   deduplicationThreshold: 0.85       // Similarity threshold (default: 0.85)
 })
 ```
 
+Deduplication merges entities judged duplicates — the non-primary records are
+**deleted**. Set `enableDeduplication: false` to disable it entirely: the flag
+gates both the inline merge during import and the background pass that runs
+about 5 minutes after the last import.
+
+```typescript
+await brain.import(file, {
+  enableDeduplication: false         // No merging, inline or background
+})
+```
+
 ### Import Tracking
 
 Track and organize imports by project:

docs/guides/inspection.md

@@ -166,6 +166,34 @@ brainy inspect diff /data/brain-prod /data/brain-staging
 Sample-based — for a full diff, dump both with `inspect dump` and compare
 the JSONL.
 
+## Auditing graph-read truth
+
+`brain.auditGraph()` (8.6.0+) proves — or disproves — that relationship reads
+return canonical truth on a given brain, without mutating anything. It walks
+every stored relationship record, asks the same read path your application
+uses (`related()`, VFS `readdir`) with every visibility tier included, and
+classifies every discrepancy:
+
+```typescript
+const report = await brain.auditGraph()
+
+report.coherent              // true = related()/readdir can be trusted on this brain
+report.missingFromReadsCount // records the read path omits — stale index
+report.danglingEndpointsCount // relationships whose endpoint entity is gone
+report.readOnlyCount         // read-path edges with NO stored record — ghosts
+report.visibilityHiddenCount // internal/system edges hidden by design (not a fault)
+```
+
+Counts are always exact; the example lists (`missingFromReads`,
+`danglingEndpoints`, `readOnlyVerbIds`) are capped at `maxExamples`
+(default 100) and `truncatedExamples` says so when they are.
+
+Run it after any engine upgrade, restore, or migration. If it reports
+discrepancies, run `brain.repairIndex()` and audit again — a `coherent`
+report after the repair is the verified statement that the heal worked.
+Cost: one relationship-record walk plus one indexed read per distinct
+source entity — safe on a live brain.
+
 ## Repairing a corrupted store
 
 If invariants fail and you suspect index corruption, `inspect repair`

docs/guides/optimistic-concurrency.md

@@ -180,3 +180,35 @@ Brainy 8.0 has exactly two write-coordination counters, at two granularities:
 They compose: a `transact()` batch can carry per-entity `ifRev` checks *and* a whole-store `ifAtGeneration`; any failed check rejects the entire batch before anything is staged. Generations also power snapshots and time travel (`brain.now()`, `brain.asOf()`, `db.persist()`) — see the [consistency model](../concepts/consistency-model.md) and [Snapshots & Time Travel](./snapshots-and-time-travel.md).
 
 A snapshot or historical view captures each entity *including* its `_rev` at that moment, so reading the past and writing back with `ifRev` against the live state works exactly as you'd hope: the write fails if the entity moved since the state you copied from.
+
+## The transact envelope: batch size, budget, and bulk imports
+
+`transact()` applies its batch atomically under one commit — which means the whole batch
+shares one **apply budget**. Since 8.7.0 the budget scales with the batch:
+`max(30 s, opCount × 2 s)`, or exactly what you pass as `timeoutMs`. A tripped budget rolls
+the entire batch back (nothing partial survives) and throws a retryable
+`TransactionTimeoutError` that names the operation it stopped at, the batch size, and the
+elapsed vs budgeted time — a diagnosis, not just a failure:
+
+```
+Transaction timed out at operation 41/120 ('add') — 246012ms elapsed, budget 240000ms.
+The batch rolled back atomically; retry with a higher timeoutMs or a smaller batch.
+```
+
+Practical envelope guidance for bulk work:
+
+1. **Precompute embeddings outside the commit path.** Embedding inside `transact()` spends
+   the budget on model inference. Use `brain.embedBatch(texts)` and pass each vector via
+   the op's `vector` field — the commit then pays only storage costs, and a retried batch
+   never re-pays inference. (The win is *where* the inference happens, not raw embedding
+   throughput: on the default WASM engine, batch and sequential embedding measure
+   comparably, ~160 ms/text; native embedding providers may batch faster.)
+2. **Chunk very large imports** into batches of a few hundred ops with one `transact()`
+   each. You lose whole-import atomicity but keep per-chunk atomicity, bounded memory, and
+   resumability — pair with `ifAbsent` upserts so a retried chunk is idempotent.
+3. **Slow disks change the math, not the contract.** On network-attached storage a single
+   op can cost ~2 s (canonical write + fsync + index maintenance). The scaled default
+   absorbs that; pass an explicit `timeoutMs` only when you know better than the scale.
+4. **`addMany`/`relateMany` are the convenience tier** — they chunk and batch-embed for
+   you, with per-item error reporting instead of batch atomicity. Choose by what you need:
+   atomic-all-or-nothing → `transact()`; resilient bulk load → `addMany`.

docs/guides/snapshots-and-time-travel.md

@@ -9,6 +9,7 @@ description: Recipes for the Db API — instant backups with persist(), restore,
 next:
   - concepts/consistency-model
   - guides/optimistic-concurrency
+  - guides/external-backups
 ---
 
 # Snapshots & Time Travel
@@ -41,6 +42,10 @@ bytes. Cross-device targets fall back to per-file byte copies, and
 persisting an in-memory brain serializes it to the same directory layout —
 a real, durable store.
 
+> Archiving a brain directory with **external tools** (`tar`, `rsync`, `cp`)?
+> Some index files are sparse and can explode to their apparent size under a
+> naive copy — see [External Backups & Sparse Storage](/docs/guides/external-backups).
+
 Two things to know:
 
 - `persist()` requires the view to still be the store's **latest**
@@ -339,8 +344,12 @@ For per-entity write coordination (rather than whole-store history), the
 ## Keeping history bounded
 
 Under Model-B every write is a generation, so history can grow quickly —
-Brainy auto-compacts on every `flush()`/`close()` under the **`retention`**
+Brainy auto-compacts at `close()` (time-bounded per pass) under the
-knob (configured on the constructor):
+**`retention`** knob (configured on the constructor). Since 8.9.0, `flush()`
+never compacts: flushing is durability work and costs only what the current
+window's writes cost, regardless of history backlog. A long-lived writer that
+never closes keeps its history until its next explicit `compactHistory()` —
+schedule one in your maintenance window if you run bounded retention:
 
 ```typescript
 // Zero-config: ADAPTIVE — keep as much history as free disk/RAM allows,
@@ -354,10 +363,13 @@ new Brainy({ retention: 'all' })
 new Brainy({ retention: { maxGenerations: 1000, maxAge: 7 * 86_400_000, maxBytes: 512 * 1024 ** 2 } })
 ```
 
-Reclaim manually at any time (the same caps):
+Reclaim manually at any time (the same caps, plus an optional per-pass time
+budget for maintenance windows — an early stop is a consistent prefix and the
+next pass resumes):
 
 ```typescript
 await brain.compactHistory({ maxGenerations: 100, maxAge: 7 * 24 * 60 * 60 * 1000 })
+await brain.compactHistory({ maxBytes: 512 * 1024 ** 2, timeBudgetMs: 10_000 })
 ```
 
 Compaction never breaks a pinned read — record-sets are reclaimed only when

docs/performance-envelopes.md

@@ -0,0 +1,83 @@
+---
+title: Performance Envelopes
+slug: guides/performance-envelopes
+public: true
+category: guides
+template: guide
+order: 40
+description: Measured per-operation latency envelopes at stated scales — what to expect, on what hardware, and exactly how each number was produced.
+next:
+  - guides/find-limits
+---
+
+# Performance Envelopes
+
+Every number on this page is **measured, never projected** — produced by the script
+cited at the bottom, against the built package (the artifact you install), on the stated
+hardware. Each entry says what was measured, at what scale, on which storage backend.
+When a release touches a measured path, that operation is re-measured and this page
+updates in the same release.
+
+Two scopes to keep straight:
+
+- **These envelopes are the pure-JS engine** (no native accelerator registered) on
+  filesystem storage. This is the floor every deployment gets from `npm install` alone.
+- **Accelerated deployments** (the optional native provider) publish their own numbers —
+  this page never claims them.
+
+## Read operations
+
+Reads are where the architecture pays off: after the write path has done its indexing
+work, queries answer from purpose-built indexes without scanning.
+
+| Operation | 1,000 entities | 10,000 entities | Notes |
+|---|---|---|---|
+| `get(id)` (warm) | p50 < 0.1ms | p50 < 0.1ms | served from cache/metadata index |
+| `find` (metadata: indexed equality + range, limit 100) | p50 1.0ms · p95 1.8ms | p50 7.0ms · p95 8.9ms | column-store bitmap paths |
+| `related(id)` (per-node adjacency) | p50 < 0.1ms · p95 0.2ms | p50 < 0.1ms | LSM adjacency index — O(degree), scale-independent |
+| `find` (semantic: embed + HNSW, 1k docs) | p50 178ms · p95 393ms | — | dominated by WASM query embedding (measured on a machine under concurrent load — treat the p95 as an upper bound); the vector search itself is single-digit ms |
+
+## Write operations
+
+Under Model-B **every write is its own durable generation** — a single-op `add` pays
+serialization, before-image staging, and fsync before it acks. That durability is priced
+into the write path visibly, by design:
+
+| Operation | 1,000 entities | 10,000 entities | Notes |
+|---|---|---|---|
+| `add` (single-op) | p50 167ms · p95 171ms | p50 165ms · p95 172ms | full durable generation per write — flat across scale |
+| `addMany` (bulk) | ~163ms/entity | ~187ms/entity | **currently per-item commits** — see the honest note below |
+| `relateMany` | ~0.8ms/edge | ~0.9ms/edge | edges batch efficiently today |
+| `flush` (steady-state, 1 pending write) | p50 8ms · p95 10ms | p50 45ms · p95 52ms | durability-only since 8.9.0 — cost no longer depends on history backlog or retention mode |
+
+**The honest note on bulk writes:** `addMany` today commits each item as its own
+generation (the same durability as single-op `add`, serialized by the single-writer
+lock), so bulk-load cost is N × single-op cost. Batched chunk commits (one generation
+and one fsync window per chunk, as `removeMany` already does) are designed into the
+unified-commit work on the current roadmap. Until that ships, size bulk imports
+accordingly — 10k entities is minutes, not seconds, on filesystem storage.
+
+## Open / close
+
+| Operation | 1,000 entities | 10,000 entities | Notes |
+|---|---|---|---|
+| `open` (empty store) | ~560ms | ~190ms | includes embedder initialization |
+| `open` (warm, populated, clean shutdown) | 763ms | 4.9s | pure-JS vector index load dominates and grows with entity count; the native accelerator exists precisely to remove this |
+| `close` | bounded | bounded | auto-compaction pass is time-bounded (~5s max) since 8.9.0 |
+
+A store that was NOT cleanly closed pays index rebuilds on top of the warm-open
+number (tens of seconds at 10k) — clean shutdown is worth engineering for.
+
+## How these were produced
+
+- **Hardware**: Intel Core i9-14900HX (32 threads), 62GB RAM, NVMe, Linux, Node v22.
+- **Backend**: `storage: { type: 'filesystem' }`, pure JS (no native providers).
+- **Embeddings**: deterministic stub for non-semantic ops (isolates engine cost);
+  the real WASM embedder for the semantic row (that's what you'll run).
+- **Method**: p50/p95 over 50–200 samples per op against the built `dist/`;
+  the measuring script ships in the repo history and re-runs per release.
+
+Numbers on different hardware will differ; the *shape* (sub-2ms indexed reads,
+~160ms embedding-bound semantic queries, durability-priced writes) is the envelope
+you should hold your deployment against. If your measurements diverge from these
+shapes by an order of magnitude, something is wrong — file it.

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "@soulcraft/brainy",
-  "version": "8.3.1",
+  "version": "8.9.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@soulcraft/brainy",
-      "version": "8.3.1",
+      "version": "8.9.0",
       "license": "MIT",
       "dependencies": {
         "@msgpack/msgpack": "^3.1.2",

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@soulcraft/brainy",
-  "version": "8.3.1",
+  "version": "8.9.0",
   "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/push-docs.js

@@ -0,0 +1,116 @@
+#!/usr/bin/env node
+/**
+ * @module scripts/push-docs
+ * @description Push this repo's PUBLIC docs to the soulcraft.com docs ingest
+ * door after an npm publish (VENUE-DOCS-RELEASE-PUSH — retires the old
+ * build-time docs sync).
+ *
+ * Contract (mirrors the reference implementation on the serving side):
+ *   POST {base}/api/docs/ingest
+ *   headers: x-service-secret: $DOCS_INGEST_SECRET, Content-Type: application/json
+ *   body: { docs: [{ slug, title, markdown, nav: { order, section } }] }
+ *   batches of 10, idempotent per slug.
+ *
+ * A doc is public iff its frontmatter has `public: true` AND a `slug`. The
+ * frontmatter is stripped; `category` → nav.section, `order` → nav.order.
+ *
+ * Deliberately NOT pushed: the combined /docs landing index. It spans BOTH
+ * engine corpora (this repo's and the native accelerator's), so a per-repo
+ * push would clobber the union — the index is authored on the serving side.
+ *
+ * Env: DOCS_INGEST_SECRET (required), DOCS_INGEST_BASE (default
+ * https://soulcraft.com). Exits 0 with a LOUD warning when the secret is
+ * absent (the npm publish has already happened; the serving side runs its
+ * interim sync on request) and exits 1 when a push actually fails — the docs
+ * site would silently trail npm otherwise, and that must be visible.
+ */
+import * as fs from 'node:fs'
+import * as path from 'node:path'
+
+const BASE = (process.env.DOCS_INGEST_BASE || 'https://soulcraft.com').replace(/\/+$/, '')
+const SECRET = process.env.DOCS_INGEST_SECRET
+const DOCS_DIR = path.join(path.dirname(new URL(import.meta.url).pathname), '..', 'docs')
+const BATCH = 10
+
+if (!SECRET) {
+  console.warn(
+    '⚠️  DOCS PUSH SKIPPED: DOCS_INGEST_SECRET is not set.\n' +
+      '    soulcraft.com/docs now TRAILS this npm release until docs are pushed.\n' +
+      '    Either export DOCS_INGEST_SECRET and re-run `node scripts/push-docs.js`,\n' +
+      '    or ping venue on VENUE-DOCS-RELEASE-PUSH for the interim sync.'
+  )
+  process.exit(0)
+}
+
+/** Minimal frontmatter split — returns [meta, body] or [null, raw]. */
+function parseFrontmatter(raw) {
+  const m = raw.match(/^---\n([\s\S]*?)\n---\n([\s\S]*)$/)
+  if (!m) return [null, raw]
+  const meta = {}
+  for (const line of m[1].split('\n')) {
+    const kv = line.match(/^(\w[\w-]*):\s*(.*)$/)
+    if (kv) meta[kv[1]] = kv[2].trim().replace(/^["']|["']$/g, '')
+  }
+  return [meta, m[2]]
+}
+
+const docs = []
+;(function walk(dir) {
+  for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
+    const full = path.join(dir, entry.name)
+    if (entry.isDirectory()) walk(full)
+    else if (entry.name.endsWith('.md')) {
+      const [meta, body] = parseFrontmatter(fs.readFileSync(full, 'utf-8'))
+      if (!meta || meta.public !== 'true' || !meta.slug) continue
+      docs.push({
+        slug: meta.slug,
+        title: meta.title || meta.slug,
+        markdown: body.trim(),
+        nav: {
+          order: Number.parseInt(meta.order || '99', 10) || 99,
+          section: meta.category || 'guides'
+        }
+      })
+    }
+  }
+})(DOCS_DIR)
+
+if (docs.length === 0) {
+  console.error('❌ DOCS PUSH FAILED: zero public docs collected — refusing to push an empty corpus.')
+  process.exit(1)
+}
+docs.sort((a, b) => a.slug.localeCompare(b.slug))
+console.log(`Pushing ${docs.length} public docs to ${BASE}/api/docs/ingest …`)
+
+let failed = false
+for (let i = 0; i < docs.length; i += BATCH) {
+  const batch = docs.slice(i, i + BATCH)
+  try {
+    const res = await fetch(`${BASE}/api/docs/ingest`, {
+      method: 'POST',
+      headers: {
+        'x-service-secret': SECRET,
+        'Content-Type': 'application/json',
+        'User-Agent': 'brainy-docs-push/1.0'
+      },
+      body: JSON.stringify({ docs: batch }),
+      signal: AbortSignal.timeout(120_000)
+    })
+    if (!res.ok) {
+      throw new Error(`HTTP ${res.status}: ${(await res.text()).slice(0, 300)}`)
+    }
+    console.log(`  batch ${i / BATCH + 1}: ${batch.map((d) => d.slug).join(', ')} → ok`)
+  } catch (err) {
+    failed = true
+    console.error(`  batch ${i / BATCH + 1} FAILED: ${err instanceof Error ? err.message : err}`)
+  }
+}
+
+if (failed) {
+  console.error(
+    '❌ DOCS PUSH INCOMPLETE — soulcraft.com/docs may trail npm. ' +
+      'Re-run `node scripts/push-docs.js` or ping venue on VENUE-DOCS-RELEASE-PUSH.'
+  )
+  process.exit(1)
+}
+console.log('✅ Docs pushed.')

scripts/release.sh

@@ -196,6 +196,18 @@ else
 fi
 echo -e "${GREEN}✅ GitHub release created${NC}\n"
 
+# Step 12: Push public docs to the soulcraft.com docs ingest door
+# (VENUE-DOCS-RELEASE-PUSH). Skips with a loud warning when
+# DOCS_INGEST_SECRET is unset; fails loudly (without undoing the publish —
+# that already happened) when a push errors, so the docs site never
+# silently trails npm.
+echo -e "${BLUE}1️⃣2️⃣ Pushing public docs to soulcraft.com/docs...${NC}"
+if node scripts/push-docs.js; then
+  echo -e "${GREEN}✅ Docs push step done${NC}\n"
+else
+  echo -e "${RED}❌ Docs push FAILED — soulcraft.com/docs trails npm until re-run or interim sync${NC}\n"
+fi
+
 echo -e "${GREEN}━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━${NC}"
 echo -e "${GREEN}🎉 Release ${NEW_VERSION} complete!${NC}"
 echo -e "${GREEN}━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━${NC}"

src/aggregation/AggregationIndex.ts

@@ -29,6 +29,7 @@ import { matchesMetadataFilter } from '../utils/metadataFilter.js'
 import { compareCodePoints } from '../utils/collation.js'
 import { bucketTimestamp } from './timeWindows.js'
 import { NounType } from '../types/graphTypes.js'
+import { prodLog } from '../utils/logger.js'
 
 /** Persistence key for aggregate definitions */
 const DEFINITIONS_KEY = '__aggregation_definitions__'
@@ -87,10 +88,18 @@ function matchesSource(entity: Record<string, unknown>, source: AggregateDefinit
     if (entity.service !== source.service) return false
   }
 
-  // Metadata where filter — match against the entity's metadata sub-object
+  // Where filter — resolve each filtered field through resolveEntityField,
+  // the SAME single source of truth groupBy uses (top-level standard fields
+  // + custom metadata). Matching only the metadata sub-object made
+  // where:{subtype}/{visibility}/… a silent no-op: reserved fields never
+  // live in the custom bag, so those filters could never match anything.
   if (source.where && Object.keys(source.where).length > 0) {
-    const metadata = (entity.metadata ?? entity) as Record<string, unknown>
+    const e = entity as unknown as HNSWNounWithMetadata
-    if (!matchesMetadataFilter(metadata, source.where)) return false
+    const resolved: Record<string, unknown> = {}
+    for (const key of Object.keys(source.where)) {
+      resolved[key] = resolveEntityField(e, key)
+    }
+    if (!matchesMetadataFilter(resolved, source.where)) return false
   }
 
   return true
@@ -327,6 +336,30 @@ export class AggregationIndex {
   /** Track aggregates with stale MIN/MAX (need lazy recompute) */
   private staleMinMax = new Map<string, Set<string>>()
 
+  /** Resolves when init() has finished loading persisted definitions/state. */
+  private initPromise: Promise<void> | null = null
+
+  /** True once init() has settled (success or failure). */
+  private initDone = false
+
+  /**
+   * Aggregates registered by the app before init() finished loading persisted
+   * state, awaiting reconciliation: init() adopts the persisted state when the
+   * definition hash matches; anything left unadopted when init settles resolves
+   * to a backfill. Deciding backfill eagerly at define time was the boot-order
+   * bug that wiped valid persisted state on every restart — the synchronous
+   * defineAggregate() always beats the async init().
+   */
+  private pendingAdopt = new Set<string>()
+
+  /**
+   * In-flight rescan targets. While a name has a staging map, ALL
+   * contributions (the walk's and concurrent write hooks') land there instead
+   * of the live map; the live map keeps serving until {@link finishBackfill}
+   * swaps the staging map in atomically.
+   */
+  private backfillStaging = new Map<string, Map<string, AggregateGroupState>>()
+
   constructor(storage: StorageAdapter, nativeProvider?: AggregationProvider) {
     this.storage = storage
     this.nativeProvider = nativeProvider
@@ -336,21 +369,128 @@ export class AggregationIndex {
 
   /**
    * Initialize: load persisted definitions and state, detect changes, rebuild stale.
+   *
+   * Idempotent — repeated calls return the same promise. Definitions registered
+   * *before* this completes (the normal boot order: `defineAggregate()` is
+   * synchronous and always beats this async load) are reconciled rather than
+   * clobbered: the app's definition wins, and its persisted state is adopted
+   * when the definition hash matches — backfill happens only on a real change.
    */
-  async init(): Promise<void> {
+  init(): Promise<void> {
+    if (!this.initPromise) {
+      this.initPromise = this.loadPersisted().finally(() => {
+        this.resolvePendingAdoptToBackfill()
+        this.initDone = true
+      })
+    }
+    return this.initPromise
+  }
+
+  /**
+   * Await the persisted-state load (if one was started) and settle every
+   * pending adoption decision. After this resolves, `getPendingBackfills()`
+   * is authoritative: a name is listed iff it genuinely needs a rescan.
+   * Query paths must await this before consulting backfill state.
+   */
+  async ready(): Promise<void> {
+    if (this.initPromise) {
+      try {
+        await this.initPromise
+      } catch {
+        // The owner already surfaced the load failure loudly; backfill covers.
+      }
+    }
+    this.resolvePendingAdoptToBackfill()
+  }
+
+  /**
+   * Any definition still awaiting state adoption has no persisted state to
+   * adopt (or init never ran / failed) — it must backfill.
+   */
+  private resolvePendingAdoptToBackfill(): void {
+    if (this.pendingAdopt.size > 0) {
+      prodLog.info(
+        `[Aggregation] no adoptable persisted state for: ${Array.from(this.pendingAdopt).join(', ')} — flagged for backfill`
+      )
+    }
+    for (const name of this.pendingAdopt) this.needsBackfill.add(name)
+    this.pendingAdopt.clear()
+  }
+
+  /**
+   * May this persisted state be ADOPTED? When the store exposes its committed
+   * watermark, the state's `sourceGeneration` must EQUAL it: behind means
+   * later writes are missing from the state (unclean shutdown); ahead means
+   * it counts writes that no longer exist (e.g. a fact-log truncation on a
+   * copied store pulled the watermark back). Either way: one exact rescan,
+   * said out loud — never a silent adopt. Stores without the capability (and
+   * pre-stamp state on them) fall back to hash-only adoption.
+   */
+  private stateGenerationAdoptable(name: string, stateData: unknown): boolean {
+    const committed = this.storage.committedGeneration?.() ?? null
+    if (committed === null) return true
+    const raw = (stateData as Record<string, unknown>).sourceGeneration
+    const stamped = typeof raw === 'number' ? raw : null
+    if (stamped === committed) return true
+    prodLog.warn(
+      `[Aggregation] '${name}': persisted state is at generation ${stamped ?? 'unstamped'} ` +
+        `but the store's committed generation is ${committed} — rescanning instead of adopting`
+    )
+    return false
+  }
+
+  private async loadPersisted(): Promise<void> {
     // Load persisted definitions
     const savedDefs = await this.storage.getMetadata(DEFINITIONS_KEY)
     if (savedDefs && typeof savedDefs === 'object' && savedDefs.definitions) {
       const defs = savedDefs.definitions as Array<AggregateDefinition & { _hash?: string }>
 
       for (const def of defs) {
-        this.definitions.set(def.name, def)
-        const currentHash = hashDefinition(def)
         const savedHash = def._hash || ''
 
-        // Load persisted state
+        if (this.definitions.has(def.name)) {
+          // The app re-registered this aggregate before the load finished.
+          // The app's definition wins — never clobber it with the persisted
+          // copy. Adopt the persisted state when the definition is unchanged
+          // AND no write has landed for it yet (a landed write would be lost
+          // by adoption; the hook flips such names to backfill).
+          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 groupMap = new Map<string, 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`
+              )
+            }
+            // No/invalid persisted state: stays in pendingAdopt and resolves
+            // to backfill when init settles.
+          }
+          continue
+        }
+
+        // Not registered this session — restore definition + state from
+        // persistence.
+        this.definitions.set(def.name, def)
+        const currentHash = hashDefinition(def)
+
         const stateData = await this.storage.getMetadata(`${STATE_KEY_PREFIX}${def.name}__`)
-        if (stateData && stateData.groups && savedHash === currentHash) {
+        if (
+          stateData &&
+          stateData.groups &&
+          savedHash === currentHash &&
+          this.stateGenerationAdoptable(def.name, stateData)
+        ) {
           // Definition unchanged — load state
           const groupMap = new Map<string, AggregateGroupState>()
           for (const group of stateData.groups as AggregateGroupState[]) {
@@ -358,6 +498,10 @@ export class AggregationIndex {
             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)`
+          )
         } else {
           // Definition changed or no saved state — start fresh and backfill from
           // existing entities (the owner drains needsBackfill on first query).
@@ -398,14 +542,22 @@ export class AggregationIndex {
     }))
     await this.storage.saveMetadata(DEFINITIONS_KEY, { definitions: defsToSave })
 
-    // Persist dirty states
+    // Persist dirty states, stamped with the committed generation they
+    // reflect. The stamp is what makes reopen-adoption verifiable: state at a
+    // different generation than the store's committed watermark is stale (an
+    // unclean shutdown after later writes) or over-counts (a fact-log
+    // truncation on a copied store pulled the watermark BACK below the
+    // stamp) — either way the answer is one exact rescan, never a silent
+    // adopt. Read the generation after collecting groups so any racing
+    // commit resolves toward rescan, not wrong-adopt.
     for (const name of this.dirty) {
       const stateMap = this.states.get(name)
       if (stateMap) {
         const groups = Array.from(stateMap.values())
+        const sourceGeneration = this.storage.committedGeneration?.() ?? null
         await this.storage.saveMetadata(
           `${STATE_KEY_PREFIX}${name}__`,
-          { groups }
+          sourceGeneration === null ? { groups } : { groups, sourceGeneration }
         )
       }
     }
@@ -452,10 +604,19 @@ export class AggregationIndex {
     this.definitions.set(def.name, def)
     this.definitionHashes.set(def.name, newHash)
 
+    // First sight this session, before init() settled: defer the backfill
+    // decision — init() adopts the persisted state on hash match, and anything
+    // left unadopted resolves to backfill. Deciding eagerly here wiped valid
+    // persisted state on every restart.
+    if (!this.states.has(def.name) && !this.initDone) {
+      this.states.set(def.name, new Map())
+      this.pendingAdopt.add(def.name)
+    }
     // Reset state if definition changed or doesn't exist yet, and flag it for
     // backfill so already-stored entities are counted (write-time hooks only see
     // future writes). The owner drains this on the next query via getPendingBackfills().
-    if (!this.states.has(def.name) || (oldHash && oldHash !== newHash)) {
+    else if (!this.states.has(def.name) || (oldHash && oldHash !== newHash)) {
+      this.pendingAdopt.delete(def.name)
       this.states.set(def.name, new Map())
       this.needsBackfill.add(def.name)
     }
@@ -476,6 +637,8 @@ export class AggregationIndex {
     this.definitionHashes.delete(name)
     this.states.delete(name)
     this.staleMinMax.delete(name)
+    this.pendingAdopt.delete(name)
+    this.needsBackfill.delete(name)
 
     // Notify native provider
     if (this.nativeProvider?.removeAggregate) {
@@ -513,9 +676,17 @@ export class AggregationIndex {
     return Array.from(this.needsBackfill)
   }
 
-  /** Clear an aggregate's state so a full rescan cannot double-count. */
+  /**
+   * Begin a rescan into a STAGING map. The live state is not touched — it
+   * keeps serving (possibly stale, but flagged pending) until the rescan
+   * completes and swaps in atomically. A mid-walk failure drops the staging
+   * map via {@link abortBackfill} and loses nothing: wiping live state before
+   * a scan that could throw was the destructive-before-durable defect.
+   * Contributions (walk + concurrent write hooks) land in staging while it
+   * exists, so the swapped-in result reflects writes that raced the walk.
+   */
   beginBackfill(name: string): void {
-    this.states.set(name, new Map())
+    this.backfillStaging.set(name, new Map())
     // Reset native provider state for this aggregate too, if present.
     const def = this.definitions.get(name)
     if (def && this.nativeProvider?.removeAggregate && this.nativeProvider?.defineAggregate) {
@@ -524,6 +695,15 @@ export class AggregationIndex {
     }
   }
 
+  /**
+   * Abandon an in-flight rescan after a failure: drop the staging map, keep
+   * the live state serving, leave the aggregate flagged as pending so a later
+   * attempt rescans. The failure itself must be surfaced loudly by the owner.
+   */
+  abortBackfill(name: string): void {
+    this.backfillStaging.delete(name)
+  }
+
   /** Feed one already-stored entity into a single aggregate during backfill. */
   backfillEntity(name: string, entity: Record<string, unknown>): void {
     if (isAggregateEntity(entity)) return
@@ -537,14 +717,33 @@ export class AggregationIndex {
     }
   }
 
-  /** Mark an aggregate's backfill complete; rebuilt state persists on next flush(). */
+  /** Swap the rebuilt staging state in atomically; persists on next flush(). */
   finishBackfill(name: string): void {
+    const staged = this.backfillStaging.get(name)
+    if (staged) {
+      this.states.set(name, staged)
+      this.backfillStaging.delete(name)
+    }
     this.needsBackfill.delete(name)
     this.dirty.add(name)
   }
 
   // ============= Write-Time Hooks =============
 
+  /**
+   * A write is landing for an aggregate whose persisted-state adoption is still
+   * pending — adopting after this write would lose its contribution. Settle the
+   * decision now: an exact rescan instead of adoption. The window is the few
+   * milliseconds between a boot-time defineAggregate() and init() completing,
+   * so this rarely fires; when it does, correctness wins over the walk.
+   */
+  private resolveAdoptOnWrite(name: string): void {
+    if (this.pendingAdopt.has(name)) {
+      this.pendingAdopt.delete(name)
+      this.needsBackfill.add(name)
+    }
+  }
+
   /**
    * Called when an entity is added. Updates all matching aggregates.
    */
@@ -553,6 +752,7 @@ export class AggregationIndex {
 
     for (const [name, def] of this.definitions) {
       if (!matchesSource(entity, def.source)) continue
+      this.resolveAdoptOnWrite(name)
 
       if (this.nativeProvider) {
         const results = this.nativeProvider.incrementalUpdate(name, def, entity, 'add')
@@ -579,6 +779,10 @@ export class AggregationIndex {
       const oldMatches = matchesSource(oldEntity, def.source)
       const newMatches = matchesSource(newEntity, def.source)
 
+      if (oldMatches || newMatches) {
+        this.resolveAdoptOnWrite(name)
+      }
+
       if (this.nativeProvider && (oldMatches || newMatches)) {
         const results = this.nativeProvider.incrementalUpdate(name, def, newEntity, 'update', oldEntity)
         this.applyNativeResults(name, results)
@@ -605,6 +809,7 @@ export class AggregationIndex {
 
     for (const [name, def] of this.definitions) {
       if (!matchesSource(entity, def.source)) continue
+      this.resolveAdoptOnWrite(name)
 
       if (this.nativeProvider) {
         const results = this.nativeProvider.incrementalUpdate(name, def, entity, 'delete')
@@ -757,7 +962,7 @@ export class AggregationIndex {
     def: AggregateDefinition,
     entity: Record<string, unknown>
   ): void {
-    const stateMap = this.states.get(aggName)!
+    const stateMap = (this.backfillStaging.get(aggName) ?? this.states.get(aggName))!
 
     // Fan out: an unnest dimension makes one entity contribute to several groups.
     for (const groupKey of computeGroupKeys(entity, def.groupBy)) {
@@ -815,7 +1020,7 @@ export class AggregationIndex {
     def: AggregateDefinition,
     entity: Record<string, unknown>
   ): void {
-    const stateMap = this.states.get(aggName)!
+    const stateMap = (this.backfillStaging.get(aggName) ?? this.states.get(aggName))!
 
     // Fan out: reverse the entity's contribution from every group it joined.
     for (const groupKey of computeGroupKeys(entity, def.groupBy)) {
@@ -871,7 +1076,7 @@ export class AggregationIndex {
    * Apply results from native provider back into the state maps.
    */
   private applyNativeResults(aggName: string, results: AggregateGroupState[]): void {
-    const stateMap = this.states.get(aggName)!
+    const stateMap = (this.backfillStaging.get(aggName) ?? this.states.get(aggName))!
     for (const group of results) {
       const serialized = serializeGroupKey(group.groupKey)
       stateMap.set(serialized, group)

src/coreTypes.ts

@@ -848,7 +848,17 @@ export interface StorageAdapter {
    */
   getNounsByNounType(nounType: string): Promise<HNSWNounWithMetadata[]>
 
-  deleteNoun(id: string): Promise<void>
+  /**
+   * Delete a noun — FULL canonical removal (both legs + the entity container).
+   *
+   * @param id The entity id.
+   * @param priorMetadata OPTIONAL already-known metadata of the entity being
+   *   removed (the caller's pre-delete read). The count decrement must never
+   *   REQUIRE re-reading the record being removed: when the internal read
+   *   returns `null` (replace race, or a ghost left by an earlier version) the
+   *   decrement falls back to this record instead of being silently skipped.
+   */
+  deleteNoun(id: string, priorMetadata?: NounMetadata | null): Promise<void>
 
   /**
    * Save verb - Pure HNSW verb with core fields only
@@ -905,7 +915,15 @@ export interface StorageAdapter {
    */
   getVerbsByType(type: string): Promise<HNSWVerbWithMetadata[]>
 
-  deleteVerb(id: string): Promise<void>
+  /**
+   * Delete a verb — FULL canonical removal (both legs + the container).
+   *
+   * @param id The relationship id.
+   * @param priorMetadata OPTIONAL already-known metadata of the edge being
+   *   removed (the caller's pre-delete read); keeps the count decrement honest
+   *   when the internal read returns `null` (see `deleteNoun`).
+   */
+  deleteVerb(id: string, priorMetadata?: VerbMetadata | null): Promise<void>
 
   /**
    * Save metadata
@@ -1109,6 +1127,77 @@ export interface StorageAdapter {
    */
   listDerivedFamilies?(): Promise<DerivedFamilyDeclaration[]>
 
+  /**
+   * @description OPTIONAL binary raw-byte primitives — the substrate for
+   * append-only log-structured files (the generation fact log's CRC-framed
+   * segments). Feature-detected: an adapter that omits them simply hosts no
+   * fact log (readers fall back to canonical enumeration). Paths are
+   * storage-root-relative and used VERBATIM (no `.gz`/`.bin` suffixing —
+   * unlike the JSON object and blob primitives).
+   *
+   * Append to a raw binary file, creating it (and parent directories) when
+   * absent. Append durability is the CALLER's job via `syncRawObjects` —
+   * matching the commit protocol, which batches fsyncs at its barrier.
+   */
+  appendRawBytes?(path: string, bytes: Uint8Array): Promise<void>
+
+  /**
+   * Read a raw binary file whole. Absent → `null`; a real IO fault throws
+   * (never masked as absence).
+   */
+  readRawBytes?(path: string): Promise<Uint8Array | null>
+
+  /**
+   * Replace a raw binary file atomically (write-new → fsync → rename) — the
+   * reconcile primitive (e.g. truncating a fact-log tail back to committed
+   * truth after a crash).
+   */
+  writeRawBytes?(path: string, bytes: Uint8Array): Promise<void>
+
+  /**
+   * Byte size of a raw binary file, or `null` when absent.
+   */
+  rawByteSize?(path: string): Promise<number | null>
+
+  /**
+   * @description OPTIONAL fact-scan capability — how an index provider that
+   * holds only `storage` reaches the generation fact log (the host brain
+   * wires it at init; providers must never construct their own fact-log
+   * reader — the log's open path is writer-side). Present ⟺ this store hosts
+   * a fact log AND the host wired the capability. Returns a scan handle over
+   * committed facts (heal-grade telemetry included), or `null` when no fact
+   * log exists — callers fall back to the canonical enumeration walk.
+   */
+  scanFacts?(options?: {
+    fromGeneration?: number
+    toGeneration?: number
+    kinds?: Array<'noun' | 'verb'>
+    batchSize?: number
+  }): import('./db/factLog.js').FactScanHandle | null
+
+  /**
+   * @description OPTIONAL (rides the fact-scan capability): the fact log's
+   * head generation — the replay target for `stamp.sourceGeneration + 1`
+   * catch-ups. `null` when no fact log exists.
+   */
+  factLogHeadGeneration?(): number | null
+
+  /**
+   * @description OPTIONAL (rides the fact-scan capability): the COMMITTED
+   * generation watermark — the manifest truth a projection's
+   * `sourceGeneration` compares against. Exposed as a capability so a
+   * provider never parses the store's private manifest format. `null` when
+   * the capability is unwired.
+   */
+  committedGeneration?(): number | null
+
+  /**
+   * @description OPTIONAL (rides the fact-scan capability): the immutable,
+   * sealed fact-segment file paths covering `fromGeneration` — the zero-copy
+   * handoff. The mutable tail is excluded (read it via `scanFacts`).
+   */
+  factSegmentPaths?(options?: { fromGeneration?: number }): string[]
+
   /**
    * Save statistics data
    * @param statistics The statistics data to save

src/db/db.ts

@@ -945,6 +945,13 @@ export class Db<T = any> {
    * {@link SpeculativeOverlayError} (commit them with `brain.transact()`
    * first).
    *
+   * SPARSE FILES: a native accelerator's mmap index files can be sparse —
+   * huge apparent size, small allocated size. `persist()` handles them
+   * correctly (hard links share the allocation). But if you then archive the
+   * snapshot with EXTERNAL tools, use the sparse-aware flags (`tar czSf`,
+   * `rsync --sparse`, `cp --sparse=always`) or the copy materializes every
+   * hole — see docs/guides/external-backups-and-sparse-storage.md.
+   *
    * @param path - Absolute directory for the snapshot (created; must be
    *   empty or absent).
    * @throws GenerationConflictError when this view is no longer the latest

src/db/factLog.ts

@@ -0,0 +1,721 @@
+/**
+ * @module db/factLog
+ * @description The generation FACT LOG — an append-only, CRC-framed record of
+ * every committed generation as an AFTER-IMAGE "fact": what each touched
+ * entity/relationship BECAME (or a body-less tombstone when it was removed).
+ * This is the dual-write half of the log-canonical transition: today the
+ * before-image history + canonical tree remain authoritative; the fact log is
+ * appended at the same commit points and reconciled to committed truth at
+ * open, so consumers (index heals, replays, scans) can read one sequential,
+ * self-verifying stream instead of walking the entity tree.
+ *
+ * ## Wire format (frozen; additive-only within a major)
+ *
+ * Fact (msgpack, POSITIONAL array — the segment header's formatVersion
+ * governs the schema):
+ *
+ *   fact := [ generation:u64, timestamp:u64, ops, meta|nil, blobHashes|nil ]
+ *   op   := [ kind:u8 (0=noun, 1=verb), id:bin16 (raw uuid bytes),
+ *             record:[metaLeg, vecLeg] | nil ]        // nil = TOMBSTONE
+ *
+ * Segment file (`_generations/facts/seg-<firstGeneration, zero-padded 20>.bfl`):
+ *
+ *   header := magic "BFACTS\0\0" (8B) | formatVersion:u32 LE |
+ *             firstGeneration:u64 LE | reserved 12B (ZEROED, verified)
+ *   frame  := length:u32 LE | crc32c:u32 LE (of payload) | payload
+ *
+ * A fact is never split across segments; a torn tail (length overrun or CRC
+ * mismatch) terminates that segment's scan — everything before it is intact.
+ * Zero-padded names make lexicographic order == generation order.
+ *
+ * ## Invariant
+ *
+ * After {@link FactLog.open}, the log contains EXACTLY the committed prefix:
+ * facts are appended BEFORE the commit point (inside the same durability
+ * window), so a crash can only leave the log AHEAD of committed truth — open
+ * truncates any fact beyond the committed generation. Absent generation =
+ * never committed; present = committed. A scan can never see an uncommitted
+ * fact.
+ *
+ * The manifest (`_generations/facts/manifest.json`, JSON — forensics stay
+ * terminal-readable) is the single source of truth for the segment SET;
+ * rotation flips it atomically (write-new → fsync → rename) BEFORE the new
+ * tail's first byte exists, so no segment file is ever unaccounted for.
+ */
+import { encode as defaultEncode, decode as defaultDecode } from '@msgpack/msgpack'
+import { crc32c } from '../utils/crc32c.js'
+import { prodLog } from '../utils/logger.js'
+
+// Swappable msgpack implementation — defaults to the JS codec; a native
+// provider (registered via the plugin registry's 'msgpack' key) may replace
+// it. Byte-compatibility is the contract (positional arrays, bin16 ids).
+let msgpackEncode: (value: unknown) => Uint8Array = defaultEncode
+let msgpackDecode: (bytes: Uint8Array) => unknown = defaultDecode
+
+/** Replace the msgpack encode/decode implementation at runtime. */
+export function setFactCodec(impl: {
+  encode: (value: unknown) => Uint8Array
+  decode: (bytes: Uint8Array) => unknown
+}): void {
+  msgpackEncode = impl.encode
+  msgpackDecode = impl.decode
+}
+
+/** Storage-root-relative home of the fact log. */
+export const FACTS_PREFIX = '_generations/facts'
+/** The facts manifest path (JSON). */
+export const FACTS_MANIFEST_PATH = `${FACTS_PREFIX}/manifest.json`
+/** Current segment format version (header field; additive-only within a major). */
+export const FACTS_FORMAT_VERSION = 1
+/** Rotation threshold: seal the tail segment once it exceeds this many bytes. */
+const SEGMENT_ROTATE_BYTES = 8 * 1024 * 1024
+/** Segment header: magic(8) + formatVersion(4) + firstGeneration(8) + reserved(12). */
+const HEADER_BYTES = 32
+const MAGIC = new Uint8Array([0x42, 0x46, 0x41, 0x43, 0x54, 0x53, 0x00, 0x00]) // "BFACTS\0\0"
+/** Frame prefix: length(4) + crc32c(4). */
+const FRAME_PREFIX_BYTES = 8
+
+/** One write inside a fact: what the id became (or a tombstone). */
+export interface FactOp {
+  kind: 'noun' | 'verb'
+  id: string
+  /** The AFTER-IMAGE legs, or `null` for a tombstone (the id was removed). */
+  record: { metadata: unknown | null; vector: unknown | null } | null
+}
+
+/** One committed generation, as scanned back out of the log. */
+export interface CommitFact {
+  generation: number
+  timestamp: number
+  ops: FactOp[]
+  meta?: Record<string, unknown>
+  blobHashes?: string[]
+}
+
+/** The telemetry a scan batch carries (frozen shape). */
+export interface FactScanBatch {
+  facts: CommitFact[]
+  firstGeneration: number
+  lastGeneration: number
+  factCount: number
+  byteSize: number
+  segmentId: string
+}
+
+/**
+ * Liveness bound on a scan's FIRST batch (Stage-2 co-freeze, D1 contract):
+ * `batches()` must yield its first batch — or fail loudly — within this many
+ * ms of the first pull. A backlogged or damaged store may be SLOW, but it may
+ * never be SILENT: a consumer awaiting the first batch is otherwise
+ * indistinguishable from a wedge (the exact failure shape a production heal
+ * hit against a generations-backlogged brain).
+ */
+export const SCANFACTS_FIRST_BATCH_MS = 10_000
+
+/** The telemetry a scan OPEN returns (frozen shape). */
+export interface FactScanHandle {
+  headGeneration: number
+  segmentCount: number
+  approxFactCount: number
+  /**
+   * Ordered batches; a detected gap aborts LOUDLY, never a silent skip.
+   * Liveness contract: the FIRST batch resolves or rejects within
+   * {@link SCANFACTS_FIRST_BATCH_MS} of the first pull — never a silent hang.
+   */
+  batches: () => AsyncGenerator<FactScanBatch>
+  /** Close telemetry — the invariant cross-check, valid after iteration ends. */
+  summary: () => { factsYielded: number; segmentsRead: number }
+}
+
+/** Manifest entry for a sealed segment. */
+interface SegmentEntry {
+  file: string
+  firstGeneration: number
+  lastGeneration: number
+  facts: number
+  bytes: number
+}
+
+/** The facts manifest (JSON on disk). */
+interface FactsManifest {
+  formatVersion: number
+  segments: SegmentEntry[]
+  /** The append target. Its true content is established by scanning (crash tolerance). */
+  tailSegment: string | null
+  updatedAt: string
+}
+
+/** The narrow byte-level storage surface the fact log rides. */
+export interface FactLogStorage {
+  appendRawBytes(path: string, bytes: Uint8Array): Promise<void>
+  readRawBytes(path: string): Promise<Uint8Array | null>
+  writeRawBytes(path: string, bytes: Uint8Array): Promise<void>
+  rawByteSize(path: string): Promise<number | null>
+  readRawObject(path: string): Promise<any | null>
+  writeRawObject(path: string, data: any): Promise<void>
+  syncRawObjects(paths: string[]): Promise<void>
+  deleteRawObject(path: string): Promise<void>
+}
+
+/** True when the storage adapter exposes every primitive the fact log needs. */
+export function storageSupportsFactLog(storage: unknown): storage is FactLogStorage {
+  const s = storage as Record<string, unknown>
+  return (
+    typeof s.appendRawBytes === 'function' &&
+    typeof s.readRawBytes === 'function' &&
+    typeof s.writeRawBytes === 'function' &&
+    typeof s.rawByteSize === 'function'
+  )
+}
+
+/** uuid string → 16 raw bytes (bin16 on the wire). */
+function uuidToBytes(id: string): Uint8Array {
+  const hex = id.replace(/-/g, '')
+  if (hex.length !== 32) {
+    // Non-uuid ids (legacy/natural keys) ride as UTF-8 with a length prefix
+    // marker impossible for uuids: we refuse instead — the write API has
+    // guaranteed uuid ids since 8.0, so anything else is a corruption signal.
+    throw new Error(`fact log: id is not a uuid: ${id}`)
+  }
+  const bytes = new Uint8Array(16)
+  for (let i = 0; i < 16; i++) {
+    bytes[i] = parseInt(hex.slice(i * 2, i * 2 + 2), 16)
+  }
+  return bytes
+}
+
+/** 16 raw bytes → canonical lowercase uuid string. */
+function bytesToUuid(bytes: Uint8Array): string {
+  let hex = ''
+  for (let i = 0; i < 16; i++) hex += bytes[i].toString(16).padStart(2, '0')
+  return `${hex.slice(0, 8)}-${hex.slice(8, 12)}-${hex.slice(12, 16)}-${hex.slice(16, 20)}-${hex.slice(20)}`
+}
+
+/** Zero-padded segment filename: lexicographic order == generation order. */
+function segmentFileName(firstGeneration: number): string {
+  return `seg-${String(firstGeneration).padStart(20, '0')}.bfl`
+}
+
+/** Build a segment header. Reserved bytes are ZEROED (and verified on open). */
+function buildHeader(firstGeneration: number): Uint8Array {
+  const header = new Uint8Array(HEADER_BYTES)
+  header.set(MAGIC, 0)
+  const view = new DataView(header.buffer)
+  view.setUint32(8, FACTS_FORMAT_VERSION, true)
+  view.setBigUint64(12, BigInt(firstGeneration), true)
+  // bytes 20..31 stay zero (reserved)
+  return header
+}
+
+/** Encode one fact into a framed record (length + crc32c + msgpack payload). */
+function encodeFrame(fact: CommitFact): Uint8Array {
+  const payload = msgpackEncode([
+    fact.generation,
+    fact.timestamp,
+    fact.ops.map((op) => [
+      op.kind === 'noun' ? 0 : 1,
+      uuidToBytes(op.id),
+      op.record === null ? null : [op.record.metadata, op.record.vector]
+    ]),
+    fact.meta ?? null,
+    fact.blobHashes && fact.blobHashes.length > 0 ? fact.blobHashes : null
+  ])
+  const frame = new Uint8Array(FRAME_PREFIX_BYTES + payload.length)
+  const view = new DataView(frame.buffer)
+  view.setUint32(0, payload.length, true)
+  view.setUint32(4, crc32c(payload), true)
+  frame.set(payload, FRAME_PREFIX_BYTES)
+  return frame
+}
+
+/** Decode one msgpack payload back into a CommitFact. */
+function decodeFact(payload: Uint8Array): CommitFact {
+  const raw = msgpackDecode(payload) as unknown[]
+  const [generation, timestamp, ops, meta, blobHashes] = raw as [
+    number,
+    number,
+    Array<[number, Uint8Array, [unknown, unknown] | null]>,
+    Record<string, unknown> | null,
+    string[] | null
+  ]
+  return {
+    generation: Number(generation),
+    timestamp: Number(timestamp),
+    ops: ops.map(([kind, idBytes, record]) => ({
+      kind: kind === 0 ? ('noun' as const) : ('verb' as const),
+      id: bytesToUuid(idBytes),
+      record: record === null ? null : { metadata: record[0] ?? null, vector: record[1] ?? null }
+    })),
+    ...(meta ? { meta } : {}),
+    ...(blobHashes && blobHashes.length > 0 ? { blobHashes } : {})
+  }
+}
+
+/**
+ * Parse a segment's bytes: verify the header, then walk frames until the end
+ * or a torn tail (length overrun / CRC mismatch), which terminates the walk —
+ * everything before it is intact. Returns the decoded facts plus the byte
+ * length of the VALID prefix (header + intact frames), which reconciliation
+ * uses to cut a torn tail without re-encoding.
+ */
+function parseSegment(
+  file: string,
+  bytes: Uint8Array
+): { facts: CommitFact[]; validBytes: number } {
+  if (bytes.length < HEADER_BYTES) {
+    prodLog.warn(`[FactLog] segment ${file} shorter than its header — treating as empty`)
+    return { facts: [], validBytes: 0 }
+  }
+  for (let i = 0; i < MAGIC.length; i++) {
+    if (bytes[i] !== MAGIC[i]) {
+      throw new Error(`fact log: segment ${file} has a bad magic — not a fact segment`)
+    }
+  }
+  const view = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength)
+  const version = view.getUint32(8, true)
+  if (version !== FACTS_FORMAT_VERSION) {
+    throw new Error(
+      `fact log: segment ${file} has formatVersion ${version}; this build reads ${FACTS_FORMAT_VERSION}`
+    )
+  }
+  for (let i = 20; i < HEADER_BYTES; i++) {
+    if (bytes[i] !== 0) {
+      // Non-zero reserved bytes = a future format this build cannot verify.
+      throw new Error(`fact log: segment ${file} has non-zero reserved header bytes — unverifiable`)
+    }
+  }
+
+  const facts: CommitFact[] = []
+  let offset = HEADER_BYTES
+  while (offset + FRAME_PREFIX_BYTES <= bytes.length) {
+    const length = view.getUint32(offset, true)
+    const expectedCrc = view.getUint32(offset + 4, true)
+    const start = offset + FRAME_PREFIX_BYTES
+    const end = start + length
+    if (end > bytes.length) break // torn tail: frame length overruns the file
+    const payload = bytes.subarray(start, end)
+    if (crc32c(payload) !== expectedCrc) break // torn tail: payload CRC mismatch
+    facts.push(decodeFact(payload))
+    offset = end
+  }
+  return { facts, validBytes: offset }
+}
+
+/**
+ * The generation fact log. One instance per open store; every method assumes
+ * the single-writer discipline the generation store already enforces (calls
+ * arrive under its commit mutex).
+ */
+export class FactLog {
+  private readonly storage: FactLogStorage
+  /** Rotation threshold (bytes); tests may lower it to exercise rotation. */
+  private readonly rotateBytes: number
+  private manifest: FactsManifest = {
+    formatVersion: FACTS_FORMAT_VERSION,
+    segments: [],
+    tailSegment: null,
+    updatedAt: new Date(0).toISOString()
+  }
+  /** Decoded facts of the TAIL segment (bounded by the rotation threshold). */
+  private tailFacts: CommitFact[] = []
+  /** Byte size of the tail segment file (valid prefix). */
+  private tailBytes = 0
+  /** Highest generation in the log (0 = empty). */
+  private head = 0
+  /** Segment paths appended since the last sync (the fsync batch). */
+  private readonly dirtySegments = new Set<string>()
+
+  constructor(storage: FactLogStorage, options?: { rotateBytes?: number }) {
+    this.storage = storage
+    this.rotateBytes = options?.rotateBytes ?? SEGMENT_ROTATE_BYTES
+  }
+
+  /** The highest committed generation the log holds (0 = empty). */
+  headGeneration(): number {
+    return this.head
+  }
+
+  /**
+   * Open the log and reconcile it to committed truth: read the manifest,
+   * establish the tail's intact content (torn-tail scan), then TRUNCATE any
+   * fact with `generation > committedGeneration` — those never committed (a
+   * crash between fact-append and the commit point). After open, the log is
+   * exactly the committed prefix.
+   */
+  async open(committedGeneration: number): Promise<void> {
+    const stored = (await this.storage.readRawObject(FACTS_MANIFEST_PATH)) as FactsManifest | null
+    if (stored && typeof stored === 'object' && Array.isArray(stored.segments)) {
+      if (stored.formatVersion !== FACTS_FORMAT_VERSION) {
+        throw new Error(
+          `fact log: manifest formatVersion ${stored.formatVersion}; this build reads ${FACTS_FORMAT_VERSION}`
+        )
+      }
+      this.manifest = stored
+    }
+
+    // Drop sealed segments that sit ENTIRELY beyond committed truth (a crash
+    // right after a rotation whose facts never committed), newest first.
+    while (this.manifest.segments.length > 0) {
+      const last = this.manifest.segments[this.manifest.segments.length - 1]
+      if (last.firstGeneration > committedGeneration) {
+        prodLog.warn(
+          `[FactLog] dropping sealed segment ${last.file} (generations ${last.firstGeneration}..` +
+            `${last.lastGeneration} never committed)`
+        )
+        await this.storage.deleteRawObject(`${FACTS_PREFIX}/${last.file}`)
+        this.manifest.segments.pop()
+        await this.persistManifest()
+      } else if (last.lastGeneration > committedGeneration) {
+        // A sealed segment STRADDLING committed truth: cut it back.
+        await this.truncateSegmentTo(last.file, committedGeneration)
+        const cut = await this.reloadSegmentEntry(last.file)
+        this.manifest.segments[this.manifest.segments.length - 1] = cut
+        await this.persistManifest()
+        break
+      } else {
+        break
+      }
+    }
+
+    // Establish the tail: scan its intact prefix, then truncate beyond
+    // committed truth (the common crash shape: buffered single-op facts whose
+    // counter never went durable).
+    if (this.manifest.tailSegment) {
+      const tailPath = `${FACTS_PREFIX}/${this.manifest.tailSegment}`
+      const bytes = await this.storage.readRawBytes(tailPath)
+      if (bytes === null) {
+        // Manifest named a tail whose first byte never landed — an empty tail.
+        this.tailFacts = []
+        this.tailBytes = 0
+      } else {
+        const { facts, validBytes } = parseSegment(this.manifest.tailSegment, bytes)
+        const kept = facts.filter((f) => f.generation <= committedGeneration)
+        if (kept.length !== facts.length || validBytes !== bytes.length) {
+          const dropped = facts.length - kept.length
+          if (dropped > 0) {
+            prodLog.warn(
+              `[FactLog] truncating ${dropped} uncommitted fact(s) beyond generation ` +
+                `${committedGeneration} from the tail (never committed)`
+            )
+          }
+          await this.rewriteTail(kept)
+        } else {
+          this.tailFacts = facts
+          this.tailBytes = validBytes
+        }
+      }
+    }
+
+    this.head = this.computeHead()
+  }
+
+  /**
+   * Append one committed generation's fact. NOT durable until {@link sync} —
+   * the caller batches durability at its commit barrier (transact syncs in
+   * the same call; Model-B group-commit syncs at flush).
+   */
+  async append(fact: CommitFact): Promise<void> {
+    if (fact.generation <= this.head) {
+      throw new Error(
+        `fact log: non-monotonic append (generation ${fact.generation} ≤ head ${this.head})`
+      )
+    }
+    if (this.manifest.tailSegment === null) {
+      await this.startTail(fact.generation)
+    } else if (this.tailBytes >= this.rotateBytes) {
+      await this.rotate(fact.generation)
+    }
+    const frame = encodeFrame(fact)
+    const tailPath = `${FACTS_PREFIX}/${this.manifest.tailSegment}`
+    await this.storage.appendRawBytes(tailPath, frame)
+    this.tailFacts.push(fact)
+    this.tailBytes += frame.length
+    this.head = fact.generation
+    this.dirtySegments.add(tailPath)
+  }
+
+  /** Fsync every segment appended since the last sync. */
+  async sync(): Promise<void> {
+    if (this.dirtySegments.size === 0) return
+    const paths = [...this.dirtySegments]
+    this.dirtySegments.clear()
+    await this.storage.syncRawObjects(paths)
+  }
+
+  /**
+   * Open a scan over committed facts. The scan runs against a MANIFEST
+   * SNAPSHOT (sealed segments + the tail's decoded facts at open) — exactly-
+   * once per fact, inclusive bounds, stable under concurrent appends. Gaps
+   * abort LOUDLY: a missing generation inside a segment's declared range is
+   * corruption, never silently skipped.
+   */
+  scanFacts(options?: {
+    fromGeneration?: number
+    toGeneration?: number
+    kinds?: Array<'noun' | 'verb'>
+    batchSize?: number
+    /** Test override for the first-batch liveness bound (default {@link SCANFACTS_FIRST_BATCH_MS}). */
+    firstBatchTimeoutMs?: number
+  }): FactScanHandle {
+    const from = options?.fromGeneration ?? 1
+    const to = options?.toGeneration ?? this.head
+    const kinds = options?.kinds
+    const batchSize = Math.max(1, options?.batchSize ?? 256)
+
+    // Snapshot: the segment list + tail content as of NOW.
+    const segments = this.manifest.segments.filter(
+      (s) => s.lastGeneration >= from && s.firstGeneration <= to
+    )
+    const tailSnapshot = this.tailFacts.filter((f) => f.generation >= from && f.generation <= to)
+    const tailId = this.manifest.tailSegment ?? 'tail'
+    const approxFactCount =
+      segments.reduce((sum, s) => sum + s.facts, 0) + tailSnapshot.length
+
+    let factsYielded = 0
+    let segmentsRead = 0
+    const storage = this.storage
+
+    async function* batches(this: void): AsyncGenerator<FactScanBatch> {
+      let expectedNext = 0 // gap detection: generations are monotonic, not necessarily dense
+      const emit = (facts: CommitFact[], segmentId: string, byteSize: number): FactScanBatch => ({
+        facts,
+        firstGeneration: facts[0].generation,
+        lastGeneration: facts[facts.length - 1].generation,
+        factCount: facts.length,
+        byteSize,
+        segmentId
+      })
+      const filterOps = (fact: CommitFact): CommitFact =>
+        kinds
+          ? { ...fact, ops: fact.ops.filter((op) => kinds.includes(op.kind)) }
+          : fact
+
+      for (const entry of segments) {
+        const bytes = await storage.readRawBytes(`${FACTS_PREFIX}/${entry.file}`)
+        if (bytes === null) {
+          throw new Error(
+            `fact log: sealed segment ${entry.file} is MISSING — the log is damaged; aborting scan`
+          )
+        }
+        const { facts } = parseSegment(entry.file, bytes)
+        segmentsRead++
+        const inRange = facts.filter((f) => f.generation >= from && f.generation <= to)
+        for (const f of inRange) {
+          if (f.generation <= expectedNext - 1) {
+            throw new Error(`fact log: out-of-order fact ${f.generation} in ${entry.file} — aborting scan`)
+          }
+          expectedNext = f.generation + 1
+        }
+        for (let i = 0; i < inRange.length; i += batchSize) {
+          const slice = inRange.slice(i, i + batchSize).map(filterOps)
+          if (slice.length === 0) continue
+          factsYielded += slice.length
+          yield emit(slice, entry.file, slice.reduce((n, f) => n + encodeFrame(f).length, 0))
+        }
+      }
+
+      if (tailSnapshot.length > 0) {
+        segmentsRead++
+        for (const f of tailSnapshot) {
+          if (f.generation <= expectedNext - 1) {
+            throw new Error(`fact log: out-of-order fact ${f.generation} in the tail — aborting scan`)
+          }
+          expectedNext = f.generation + 1
+        }
+        for (let i = 0; i < tailSnapshot.length; i += batchSize) {
+          const slice = tailSnapshot.slice(i, i + batchSize).map(filterOps)
+          factsYielded += slice.length
+          yield emit(slice, tailId, slice.reduce((n, f) => n + encodeFrame(f).length, 0))
+        }
+      }
+    }
+
+    // Liveness wrapper: the FIRST pull races the contract deadline. Only the
+    // first — the bound is time-to-first-batch (proof the producer is alive),
+    // not per-batch pacing; and it runs only while a pull is actually pending,
+    // so consumer think-time between pulls never counts against the producer.
+    const firstBatchTimeoutMs = options?.firstBatchTimeoutMs ?? SCANFACTS_FIRST_BATCH_MS
+    async function* batchesWithLiveness(this: void): AsyncGenerator<FactScanBatch> {
+      const inner = batches()
+      let timer: NodeJS.Timeout | undefined
+      try {
+        const deadline = new Promise<never>((_, reject) => {
+          timer = setTimeout(
+            () =>
+              reject(
+                new Error(
+                  `fact log: scanFacts produced no first batch within ${firstBatchTimeoutMs}ms ` +
+                    `(liveness contract) — the store is wedged or unreadably slow; aborting scan LOUDLY ` +
+                    `instead of hanging the consumer.`
+                )
+              ),
+            firstBatchTimeoutMs
+          )
+          timer.unref?.()
+        })
+        const first = await Promise.race([inner.next(), deadline])
+        if (first.done) return
+        yield first.value
+      } finally {
+        clearTimeout(timer)
+      }
+      yield* inner
+    }
+
+    return {
+      headGeneration: this.head,
+      segmentCount: segments.length + (tailSnapshot.length > 0 ? 1 : 0),
+      approxFactCount,
+      batches: batchesWithLiveness,
+      summary: () => ({ factsYielded, segmentsRead })
+    }
+  }
+
+  /**
+   * The mmap fast path (capability handoff): the immutable sealed segment
+   * files covering `fromGeneration`, in order. The TAIL is deliberately NOT
+   * included — it is append-mutable; consumers read it via {@link scanFacts}.
+   */
+  segmentPaths(options?: { fromGeneration?: number }): string[] {
+    const from = options?.fromGeneration ?? 1
+    return this.manifest.segments
+      .filter((s) => s.lastGeneration >= from)
+      .map((s) => `${FACTS_PREFIX}/${s.file}`)
+  }
+
+  /**
+   * Drop every fact with `generation > keepThrough` — the in-session abort
+   * compensation: a transact appends its fact BEFORE the commit point, so a
+   * real (non-crash) abort after the append must take the fact back out. The
+   * dropped facts can only live in the TAIL (they were just appended); the
+   * rewrite is atomic and bounded by the rotation threshold.
+   */
+  async dropAbove(keepThrough: number): Promise<void> {
+    if (this.head <= keepThrough) return
+    const kept = this.tailFacts.filter((f) => f.generation <= keepThrough)
+    if (kept.length === this.tailFacts.length) {
+      throw new Error(
+        `fact log: dropAbove(${keepThrough}) found no droppable facts in the tail ` +
+          `(head ${this.head}) — the fact to drop was already sealed; the log needs reopen`
+      )
+    }
+    await this.rewriteTail(kept)
+    this.head = this.computeHead()
+  }
+
+  // -- internals -------------------------------------------------------------
+
+  private computeHead(): number {
+    if (this.tailFacts.length > 0) return this.tailFacts[this.tailFacts.length - 1].generation
+    const sealed = this.manifest.segments
+    if (sealed.length > 0) return sealed[sealed.length - 1].lastGeneration
+    return 0
+  }
+
+  /** Create the very first tail segment (manifest-first, then header bytes). */
+  private async startTail(firstGeneration: number): Promise<void> {
+    const file = segmentFileName(firstGeneration)
+    this.manifest.tailSegment = file
+    await this.persistManifest()
+    await this.storage.appendRawBytes(`${FACTS_PREFIX}/${file}`, buildHeader(firstGeneration))
+    this.tailFacts = []
+    this.tailBytes = HEADER_BYTES
+  }
+
+  /**
+   * Seal the tail into the manifest and start a new one. Manifest-first: the
+   * flip both seals the old tail AND names the new one atomically, so no
+   * segment file ever exists unaccounted for.
+   */
+  private async rotate(nextGeneration: number): Promise<void> {
+    const sealedFile = this.manifest.tailSegment
+    if (!sealedFile) return
+    // Seal what the tail actually holds.
+    await this.sync() // sealed segments are always fully durable
+    const entry: SegmentEntry = {
+      file: sealedFile,
+      firstGeneration: this.tailFacts[0]?.generation ?? nextGeneration,
+      lastGeneration: this.tailFacts[this.tailFacts.length - 1]?.generation ?? nextGeneration - 1,
+      facts: this.tailFacts.length,
+      bytes: this.tailBytes
+    }
+    const newFile = segmentFileName(nextGeneration)
+    this.manifest.segments.push(entry)
+    this.manifest.tailSegment = newFile
+    await this.persistManifest()
+    await this.storage.appendRawBytes(`${FACTS_PREFIX}/${newFile}`, buildHeader(nextGeneration))
+    this.tailFacts = []
+    this.tailBytes = HEADER_BYTES
+  }
+
+  /** Atomically persist the manifest (write-new → fsync → rename downstream). */
+  private async persistManifest(): Promise<void> {
+    this.manifest.updatedAt = new Date().toISOString()
+    await this.storage.writeRawObject(FACTS_MANIFEST_PATH, this.manifest)
+    await this.storage.syncRawObjects([FACTS_MANIFEST_PATH])
+  }
+
+  /** Rewrite the tail segment to hold exactly `facts` (atomic replace). */
+  private async rewriteTail(facts: CommitFact[]): Promise<void> {
+    const file = this.manifest.tailSegment
+    if (!file) return
+    const first = facts[0]?.generation ?? this.segmentFirstGenerationFromName(file)
+    const parts: Uint8Array[] = [buildHeader(first)]
+    for (const f of facts) parts.push(encodeFrame(f))
+    const total = parts.reduce((n, p) => n + p.length, 0)
+    const merged = new Uint8Array(total)
+    let offset = 0
+    for (const p of parts) {
+      merged.set(p, offset)
+      offset += p.length
+    }
+    await this.storage.writeRawBytes(`${FACTS_PREFIX}/${file}`, merged)
+    this.tailFacts = facts
+    this.tailBytes = total
+  }
+
+  /** Cut a SEALED segment back to `committedGeneration` (atomic replace). */
+  private async truncateSegmentTo(file: string, committedGeneration: number): Promise<void> {
+    const path = `${FACTS_PREFIX}/${file}`
+    const bytes = await this.storage.readRawBytes(path)
+    if (bytes === null) return
+    const { facts } = parseSegment(file, bytes)
+    const kept = facts.filter((f) => f.generation <= committedGeneration)
+    prodLog.warn(
+      `[FactLog] truncating sealed segment ${file} to generation ${committedGeneration} ` +
+        `(${facts.length - kept.length} uncommitted fact(s) dropped)`
+    )
+    const first = kept[0]?.generation ?? this.segmentFirstGenerationFromName(file)
+    const parts: Uint8Array[] = [buildHeader(first)]
+    for (const f of kept) parts.push(encodeFrame(f))
+    const total = parts.reduce((n, p) => n + p.length, 0)
+    const merged = new Uint8Array(total)
+    let offset = 0
+    for (const p of parts) {
+      merged.set(p, offset)
+      offset += p.length
+    }
+    await this.storage.writeRawBytes(path, merged)
+  }
+
+  /** Re-derive a sealed segment's manifest entry from its actual bytes. */
+  private async reloadSegmentEntry(file: string): Promise<SegmentEntry> {
+    const bytes = await this.storage.readRawBytes(`${FACTS_PREFIX}/${file}`)
+    const { facts, validBytes } = bytes
+      ? parseSegment(file, bytes)
+      : { facts: [] as CommitFact[], validBytes: 0 }
+    return {
+      file,
+      firstGeneration: facts[0]?.generation ?? this.segmentFirstGenerationFromName(file),
+      lastGeneration: facts[facts.length - 1]?.generation ?? 0,
+      facts: facts.length,
+      bytes: validBytes
+    }
+  }
+
+  /** Parse the zero-padded firstGeneration back out of a segment filename. */
+  private segmentFirstGenerationFromName(file: string): number {
+    const match = /^seg-(\d{20})\.bfl$/.exec(file)
+    return match ? Number(match[1]) : 0
+  }
+}

src/db/familyStamp.ts

@@ -0,0 +1,152 @@
+/**
+ * @module db/familyStamp
+ * @description The generalized FAMILY STAMP — one JSON shape that declares,
+ * for any derived projection, WHICH source state it reflects and HOW to verify
+ * it is whole. The entity tree (canonical current-state files) carries the
+ * first brainy-side stamp; native index families carry the same shape. One
+ * verifier reads both member modes:
+ *
+ * - `enumerated` — bounded families: exact byte size per member file,
+ *   verified at open.
+ * - `rollup`     — unbounded families (the entity tree: millions of files):
+ *   the verified surface is a small set of rollup invariants (entity/
+ *   relationship counts) plus `sourceGeneration`.
+ *
+ * `sourceGeneration` is the generation of the source-of-truth log this
+ * projection reflects — open-time coherence becomes a COMPARISON (stamp vs
+ * log head), not a walk:
+ *
+ * - equal + invariants hold → coherent, serve.
+ * - behind → the projection missed the tail (crash between commit and stamp);
+ *   for the Stage-1 tree this is benign by construction (the tree is written
+ *   BY the commit), so the stamp refreshes; a DERIVED projection would replay
+ *   the gap instead.
+ * - invariants FAIL at equal generation → genuine incoherence: loud, and the
+ *   repair ritual (`repairIndex()`, whose recount rebuilds the rollups from a
+ *   canonical walk) heals it.
+ *
+ * Stamps are JSON on purpose — every incident gets debugged by reading a
+ * stamp in a terminal.
+ */
+
+/** Storage-root-relative directory holding family stamps. */
+export const FAMILY_STAMPS_PREFIX = '_system/family-stamps'
+
+/** The entity tree's stamp path. */
+export const ENTITY_TREE_STAMP_PATH = `${FAMILY_STAMPS_PREFIX}/entity-tree.json`
+
+/** One enumerated member: a file and its exact expected byte size. */
+export interface EnumeratedMember {
+  path: string
+  bytes: number
+}
+
+/**
+ * The stamp's verified surface, in one of the two member modes. Rollup
+ * invariant values may be numbers (counts, byte sizes) or strings (content
+ * fingerprints, e.g. a per-tree SHA-256) — the verifier compares by strict
+ * equality either way, so a type mismatch reads as incoherence, never a pass.
+ */
+export type StampMembers =
+  | { mode: 'enumerated'; files: EnumeratedMember[] }
+  | { mode: 'rollup'; invariants: Record<string, number | string> }
+
+/** The generalized family stamp (one shape, one verifier, both engines). */
+export interface FamilyStamp {
+  /** Which projection this stamps (e.g. `'entity-tree'`). */
+  family: string
+  /** Monotonic per-family stamp generation — bumps on every committed stamp. */
+  generation: number
+  /** ISO timestamp of the stamp write. */
+  committedAt: string
+  /** The source-of-truth generation this projection reflects. */
+  sourceGeneration: number
+  /** The verified surface. */
+  members: StampMembers
+}
+
+/** The verdict of an open-time stamp verification. */
+export type StampVerdict =
+  | { state: 'coherent' }
+  | { state: 'absent' } // legacy store — first stamp writes at the next flush
+  | { state: 'behind'; stampSource: number; head: number }
+  | { state: 'incoherent'; failures: string[] }
+  | { state: 'unverifiable'; reason: string } // a FAULT reading the stamp — never conflated with absence
+
+/** The narrow storage surface stamps ride (JSON objects + fsync). */
+export interface StampStorage {
+  readRawObject(path: string): Promise<any | null>
+  writeRawObject(path: string, data: any): Promise<void>
+  syncRawObjects(paths: string[]): Promise<void>
+}
+
+/** Read a family's stamp; `null` when none was ever written. */
+export async function readFamilyStamp(
+  storage: StampStorage,
+  path: string
+): Promise<FamilyStamp | null> {
+  const stored = (await storage.readRawObject(path)) as FamilyStamp | null
+  if (!stored || typeof stored !== 'object' || typeof stored.family !== 'string') return null
+  return stored
+}
+
+/** Write a family's stamp durably (atomic object write + fsync). */
+export async function writeFamilyStamp(
+  storage: StampStorage,
+  path: string,
+  stamp: Omit<FamilyStamp, 'generation' | 'committedAt'> & { generation?: number }
+): Promise<void> {
+  const prior = await readFamilyStamp(storage, path)
+  const full: FamilyStamp = {
+    ...stamp,
+    generation: (prior?.generation ?? 0) + 1,
+    committedAt: new Date().toISOString()
+  }
+  await storage.writeRawObject(path, full)
+  await storage.syncRawObjects([path])
+}
+
+/**
+ * The ONE verifier, both member modes. `actual` supplies the observed rollup
+ * values (rollup mode) or file sizes (enumerated mode, keyed by path);
+ * `head` is the source-of-truth generation now.
+ */
+export function verifyFamilyStamp(
+  stamp: FamilyStamp | null,
+  head: number,
+  actual: Record<string, number | string>
+): StampVerdict {
+  if (stamp === null) return { state: 'absent' }
+  if (stamp.sourceGeneration > head) {
+    // A stamp AHEAD of the log claims state that never committed — the
+    // projection was stamped against truth that a crash rolled back.
+    return {
+      state: 'incoherent',
+      failures: [`sourceGeneration ${stamp.sourceGeneration} is ahead of the log head ${head}`]
+    }
+  }
+  if (stamp.sourceGeneration < head) {
+    return { state: 'behind', stampSource: stamp.sourceGeneration, head }
+  }
+  const failures: string[] = []
+  if (stamp.members.mode === 'rollup') {
+    for (const [name, expected] of Object.entries(stamp.members.invariants)) {
+      const observed = actual[name]
+      if (observed === undefined) {
+        failures.push(`rollup invariant '${name}' has no observed value`)
+      } else if (observed !== expected) {
+        failures.push(`rollup invariant '${name}': stamped ${expected}, observed ${observed}`)
+      }
+    }
+  } else {
+    for (const member of stamp.members.files) {
+      const observed = actual[member.path]
+      if (observed === undefined) {
+        failures.push(`member '${member.path}' is missing`)
+      } else if (observed !== member.bytes) {
+        failures.push(`member '${member.path}': stamped ${member.bytes} bytes, observed ${observed}`)
+      }
+    }
+  }
+  return failures.length > 0 ? { state: 'incoherent', failures } : { state: 'coherent' }
+}

src/db/generationSegments.ts

@@ -0,0 +1,459 @@
+/**
+ * @module db/generationSegments
+ * @description The generation-segment store — Stage-2 D1+D3+repacking's file
+ * format (co-frozen 2026-07-19; design: the d1-d3-repacking spec).
+ *
+ * Packs CONSECUTIVE cold generations' record-sets (before-images + delta)
+ * into append-once segment files with derived sidecar indexes, so history
+ * scales in SEGMENTS (tens) instead of FILES-PER-GENERATION (hundreds of
+ * thousands), and cold-open reads ONE manifest instead of listing the
+ * backlog. Layout under `_generations/segments/`:
+ *
+ * - `seg-<firstGen, zero-padded 20>.bgs` — magic "BGS1", then one frame per
+ *   generation: `u32 payloadLen | u32 crc32c | msgpack payload`. Payload is
+ *   POSITIONAL: `[generation, timestamp, delta, records[], flags]` with
+ *   records `[kindByte, id, record]`. `flags` reserves encoding evolution
+ *   (bit 0 = compressed payload — v1 always 0; a future writer upgrade,
+ *   never a format break). Sealed segments are IMMUTABLE — the fact log's
+ *   own law, generalized.
+ * - `seg-<firstGen>.idx` — DERIVED sidecar (msgpack): per-generation frame
+ *   offsets (point reads = one ranged read, never a listing) + per-id
+ *   generation postings (per-id chain rebuilds read only what they need).
+ *   Corrupt/missing → rebuilt from its segment in one sequential read,
+ *   loudly.
+ * - `manifest.json` — the segment catalogue + `compactedBelow` (D3's
+ *   horizon marker). Cold-open reads THIS; the packed backlog is never
+ *   listed.
+ *
+ * D3 semantics carried here: bounded-retention reclaim drops WHOLE segments
+ * at boundaries (O(1) per segment, no rewrite); under the archival profile
+ * (`retention: 'all'`) nothing here is ever dropped — folding is the only
+ * transform (re-representation, never deletion).
+ */
+
+import { encode as msgpackEncode, decode as msgpackDecode } from '@msgpack/msgpack'
+import { crc32c } from '../utils/crc32c.js'
+import type { FactLogStorage } from './factLog.js'
+import { prodLog } from '../utils/logger.js'
+
+/** Directory for segment files + manifest, under the generations prefix. */
+export const SEGMENTS_PREFIX = '_generations/segments'
+
+/** Target sealed-segment size (co-freeze proposal; tunable on evidence). */
+export const SEGMENT_TARGET_BYTES = 64 * 1024 * 1024
+
+const MAGIC = new TextEncoder().encode('BGS1')
+const FRAME_PREFIX_BYTES = 8 // u32 payloadLen + u32 crc32c
+const MANIFEST_PATH = `${SEGMENTS_PREFIX}/manifest.json`
+
+/** One generation's fold input — exactly what the live tier holds for it. */
+export interface FoldGeneration {
+  generation: number
+  timestamp: number
+  /** The tx.json delta object, carried verbatim. */
+  delta: unknown
+  /** The before-image record-set (empty for record-less generations). */
+  records: Array<{ kind: 'noun' | 'verb'; id: string; record: unknown }>
+}
+
+/** Manifest entry for one sealed segment. */
+export interface SegmentMeta {
+  file: string
+  firstGeneration: number
+  lastGeneration: number
+  frames: number
+  bytes: number
+  /** crc32c of the full segment byte stream — the digest chain's link. */
+  checksum: number
+}
+
+interface SegmentManifest {
+  version: 1
+  compactedBelow: number
+  segments: SegmentMeta[]
+}
+
+interface SidecarIndex {
+  version: 1
+  /** [generation, frameOffset, frameLen] ascending by generation. */
+  generations: Array<[number, number, number]>
+  /** `${kindByte}:${id}` → ascending generations holding a record for it. */
+  ids: Record<string, number[]>
+}
+
+const segmentFileName = (firstGeneration: number): string =>
+  `seg-${String(firstGeneration).padStart(20, '0')}.bgs`
+const sidecarFileName = (firstGeneration: number): string =>
+  `seg-${String(firstGeneration).padStart(20, '0')}.idx`
+
+/**
+ * The generation-segment store. Owns the packed tier ONLY — the live
+ * per-generation tier and the routing between tiers belong to
+ * `GenerationStore`. All mutating entry points here are called under the
+ * generation store's commit mutex.
+ */
+export class GenerationSegmentStore {
+  private readonly storage: FactLogStorage
+  private manifest: SegmentManifest = { version: 1, compactedBelow: 0, segments: [] }
+  /** Sidecar cache — segments are immutable, so entries never invalidate. */
+  private readonly sidecars = new Map<string, SidecarIndex>()
+
+  constructor(storage: FactLogStorage) {
+    this.storage = storage
+  }
+
+  /** Load the manifest (ONE read — never a directory listing). */
+  async open(): Promise<void> {
+    const raw = (await this.storage.readRawObject(MANIFEST_PATH)) as SegmentManifest | null
+    if (raw) {
+      if (raw.version !== 1) {
+        throw new Error(
+          `[GenerationSegments] manifest version ${String(raw.version)} is newer than this ` +
+            `engine understands — refusing to serve partial history. Upgrade the engine.`
+        )
+      }
+      this.manifest = raw
+    }
+  }
+
+  /** The packed tier's catalogue (ascending, immutable snapshot). */
+  segments(): readonly SegmentMeta[] {
+    return this.manifest.segments
+  }
+
+  /** D3's horizon marker: generations below this were reclaimed (bounded profiles only). */
+  compactedBelow(): number {
+    return this.manifest.compactedBelow
+  }
+
+  /** The covering sealed segment for `gen`, or null if it lives outside the packed tier. */
+  private coveringSegment(gen: number): SegmentMeta | null {
+    // Manifest is ascending and ranges never overlap — binary search.
+    const segs = this.manifest.segments
+    let lo = 0
+    let hi = segs.length - 1
+    while (lo <= hi) {
+      const mid = (lo + hi) >> 1
+      const s = segs[mid]
+      if (gen < s.firstGeneration) hi = mid - 1
+      else if (gen > s.lastGeneration) lo = mid + 1
+      else return s
+    }
+    return null
+  }
+
+  /** True when `gen` is packed (readable from this tier). */
+  hasGeneration(gen: number): boolean {
+    return this.coveringSegment(gen) !== null
+  }
+
+  /**
+   * Fold consecutive generations into ONE new sealed segment + sidecar and
+   * append it to the manifest atomically. Caller guarantees: `gens` is
+   * ascending, contiguous with the packed tier (first = last packed + 1 when
+   * segments exist), and already durable in the live tier. Crash between the
+   * segment write and the caller's live-tier delete leaves a DUPLICATE
+   * representation — resolved live-tier-wins by the reader; never a gap.
+   */
+  async fold(gens: FoldGeneration[]): Promise<SegmentMeta> {
+    if (gens.length === 0) {
+      throw new Error('[GenerationSegments] fold() requires at least one generation')
+    }
+    for (let i = 1; i < gens.length; i++) {
+      if (gens[i].generation <= gens[i - 1].generation) {
+        throw new Error('[GenerationSegments] fold() input must be strictly ascending')
+      }
+    }
+    const last = this.manifest.segments[this.manifest.segments.length - 1]
+    if (last && gens[0].generation <= last.lastGeneration) {
+      throw new Error(
+        `[GenerationSegments] fold() overlaps the packed tier: ${gens[0].generation} ≤ ` +
+          `sealed ${last.lastGeneration} — segments are immutable, never rewritten`
+      )
+    }
+
+    const first = gens[0].generation
+    const file = segmentFileName(first)
+    const sidecar: SidecarIndex = { version: 1, generations: [], ids: {} }
+
+    // Encode all frames, tracking offsets for the sidecar.
+    const parts: Uint8Array[] = [MAGIC]
+    let offset = MAGIC.length
+    for (const g of gens) {
+      const payload = msgpackEncode([
+        g.generation,
+        g.timestamp,
+        g.delta,
+        g.records.map((r) => [r.kind === 'noun' ? 0 : 1, r.id, r.record]),
+        0 // flags: v1 = uncompressed
+      ])
+      const frame = new Uint8Array(FRAME_PREFIX_BYTES + payload.length)
+      const view = new DataView(frame.buffer)
+      view.setUint32(0, payload.length, true)
+      view.setUint32(4, crc32c(payload), true)
+      frame.set(payload, FRAME_PREFIX_BYTES)
+      sidecar.generations.push([g.generation, offset, frame.length])
+      for (const r of g.records) {
+        const key = `${r.kind === 'noun' ? 0 : 1}:${r.id}`
+        ;(sidecar.ids[key] ??= []).push(g.generation)
+      }
+      parts.push(frame)
+      offset += frame.length
+    }
+    const total = parts.reduce((n, p) => n + p.length, 0)
+    const bytes = new Uint8Array(total)
+    let at = 0
+    for (const p of parts) {
+      bytes.set(p, at)
+      at += p.length
+    }
+
+    const meta: SegmentMeta = {
+      file,
+      firstGeneration: first,
+      lastGeneration: gens[gens.length - 1].generation,
+      frames: gens.length,
+      bytes: total,
+      checksum: crc32c(bytes)
+    }
+
+    // Durability order: segment + sidecar fsync'd BEFORE the manifest names
+    // them (a crash before the manifest = invisible orphan files, harmless);
+    // manifest last, atomically.
+    const segPath = `${SEGMENTS_PREFIX}/${file}`
+    const idxPath = `${SEGMENTS_PREFIX}/${sidecarFileName(first)}`
+    await this.storage.writeRawBytes(segPath, bytes)
+    await this.storage.writeRawBytes(idxPath, msgpackEncode(sidecar))
+    await this.storage.syncRawObjects([segPath, idxPath])
+    const next: SegmentManifest = {
+      ...this.manifest,
+      segments: [...this.manifest.segments, meta]
+    }
+    await this.storage.writeRawObject(MANIFEST_PATH, next)
+    await this.storage.syncRawObjects([MANIFEST_PATH])
+    this.manifest = next
+    this.sidecars.set(file, sidecar)
+    return meta
+  }
+
+  /** Load (or rebuild, loudly) a segment's sidecar. */
+  private async sidecarFor(meta: SegmentMeta): Promise<SidecarIndex> {
+    const cached = this.sidecars.get(meta.file)
+    if (cached) return cached
+    const idxPath = `${SEGMENTS_PREFIX}/${sidecarFileName(meta.firstGeneration)}`
+    const raw = await this.storage.readRawBytes(idxPath)
+    if (raw) {
+      try {
+        const idx = msgpackDecode(raw) as SidecarIndex
+        if (idx.version === 1) {
+          this.sidecars.set(meta.file, idx)
+          return idx
+        }
+      } catch {
+        // fall through to rebuild
+      }
+    }
+    // Sidecars are DERIVED: rebuild from the segment, loudly — never serve
+    // wrong offsets silently.
+    prodLog.warn(
+      `[GenerationSegments] sidecar for ${meta.file} missing or unreadable — rebuilding from the segment`
+    )
+    const rebuilt = await this.rebuildSidecar(meta)
+    await this.storage.writeRawBytes(idxPath, msgpackEncode(rebuilt))
+    this.sidecars.set(meta.file, rebuilt)
+    return rebuilt
+  }
+
+  /** One sequential read of the segment → a fresh sidecar. Verifies every frame CRC. */
+  private async rebuildSidecar(meta: SegmentMeta): Promise<SidecarIndex> {
+    const frames = await this.readAllFrames(meta)
+    const idx: SidecarIndex = { version: 1, generations: [], ids: {} }
+    for (const f of frames) {
+      idx.generations.push([f.generation, f.offset, f.frameLen])
+      for (const r of f.records) {
+        const key = `${r.kind === 'noun' ? 0 : 1}:${r.id}`
+        ;(idx.ids[key] ??= []).push(f.generation)
+      }
+    }
+    return idx
+  }
+
+  private decodeFrame(
+    payload: Uint8Array
+  ): { generation: number; timestamp: number; delta: unknown; records: FoldGeneration['records'] } {
+    const [generation, timestamp, delta, rawRecords] = msgpackDecode(payload) as [
+      number,
+      number,
+      unknown,
+      Array<[number, string, unknown]>,
+      number
+    ]
+    return {
+      generation,
+      timestamp,
+      delta,
+      records: rawRecords.map(([kindByte, id, record]) => ({
+        kind: kindByte === 0 ? ('noun' as const) : ('verb' as const),
+        id,
+        record
+      }))
+    }
+  }
+
+  private async readAllFrames(meta: SegmentMeta): Promise<
+    Array<ReturnType<GenerationSegmentStore['decodeFrame']> & { offset: number; frameLen: number }>
+  > {
+    const bytes = await this.storage.readRawBytes(`${SEGMENTS_PREFIX}/${meta.file}`)
+    if (!bytes) {
+      throw new Error(
+        `[GenerationSegments] sealed segment ${meta.file} is MISSING — packed history is damaged; ` +
+          `refusing to continue silently`
+      )
+    }
+    const out: Array<ReturnType<GenerationSegmentStore['decodeFrame']> & { offset: number; frameLen: number }> = []
+    let at = MAGIC.length
+    const view = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength)
+    while (at + FRAME_PREFIX_BYTES <= bytes.length) {
+      const payloadLen = view.getUint32(at, true)
+      const crc = view.getUint32(at + 4, true)
+      const payload = bytes.subarray(at + FRAME_PREFIX_BYTES, at + FRAME_PREFIX_BYTES + payloadLen)
+      if (payload.length !== payloadLen || crc32c(payload) !== crc) {
+        throw new Error(
+          `[GenerationSegments] frame CRC mismatch in ${meta.file} at offset ${at} — ` +
+            `packed history is damaged; refusing to serve it`
+        )
+      }
+      out.push({ ...this.decodeFrame(payload), offset: at, frameLen: FRAME_PREFIX_BYTES + payloadLen })
+      at += FRAME_PREFIX_BYTES + payloadLen
+    }
+    return out
+  }
+
+  /** Read one packed generation's frame via its sidecar offset (one ranged read). */
+  private async readFrame(
+    gen: number
+  ): Promise<ReturnType<GenerationSegmentStore['decodeFrame']> | null> {
+    const meta = this.coveringSegment(gen)
+    if (!meta) return null
+    const idx = await this.sidecarFor(meta)
+    // generations ascending → binary search.
+    const gens = idx.generations
+    let lo = 0
+    let hi = gens.length - 1
+    while (lo <= hi) {
+      const mid = (lo + hi) >> 1
+      if (gens[mid][0] < gen) lo = mid + 1
+      else if (gens[mid][0] > gen) hi = mid - 1
+      else {
+        const [, offset, frameLen] = gens[mid]
+        const bytes = await this.storage.readRawBytes(`${SEGMENTS_PREFIX}/${meta.file}`)
+        if (!bytes) {
+          throw new Error(`[GenerationSegments] sealed segment ${meta.file} is MISSING`)
+        }
+        const frame = bytes.subarray(offset, offset + frameLen)
+        const view = new DataView(frame.buffer, frame.byteOffset, frame.byteLength)
+        const payloadLen = view.getUint32(0, true)
+        const crc = view.getUint32(4, true)
+        const payload = frame.subarray(FRAME_PREFIX_BYTES, FRAME_PREFIX_BYTES + payloadLen)
+        if (payload.length !== payloadLen || crc32c(payload) !== crc) {
+          throw new Error(
+            `[GenerationSegments] frame CRC mismatch for generation ${gen} in ${meta.file} — ` +
+              `packed history is damaged; refusing to serve it`
+          )
+        }
+        return this.decodeFrame(payload)
+      }
+    }
+    // In the covering range but not present: the packed tier is dense by
+    // construction (fold packs every generation it is handed, including
+    // record-less ones) — absence inside a sealed range is damage.
+    throw new Error(
+      `[GenerationSegments] generation ${gen} is inside sealed segment ${meta.file}'s declared ` +
+        `range but has no frame — packed history is damaged`
+    )
+  }
+
+  /** The packed tier's delta for `gen` (null = not packed). */
+  async readDelta(gen: number): Promise<{ delta: unknown; timestamp: number } | null> {
+    const frame = await this.readFrame(gen)
+    return frame ? { delta: frame.delta, timestamp: frame.timestamp } : null
+  }
+
+  /** The packed tier's full record-set for `gen` (null = not packed). */
+  async readRecords(gen: number): Promise<FoldGeneration['records'] | null> {
+    const frame = await this.readFrame(gen)
+    return frame ? frame.records : null
+  }
+
+  /** One packed before-image (null = not packed OR no record for the id in that generation). */
+  async readRecord(gen: number, kind: 'noun' | 'verb', id: string): Promise<unknown | null> {
+    const frame = await this.readFrame(gen)
+    if (!frame) return null
+    const hit = frame.records.find((r) => r.kind === kind && r.id === id)
+    return hit ? hit.record : null
+  }
+
+  /**
+   * D3 reclaim: drop WHOLE segments whose lastGeneration < `belowGeneration`
+   * and bump `compactedBelow`. Partial segments are never dropped — the
+   * boundary waits. NEVER called under the archival profile (the caller
+   * enforces retention semantics; this method only executes boundary drops).
+   */
+  async dropSegmentsBelow(belowGeneration: number): Promise<{ dropped: number; compactedBelow: number }> {
+    const keep: SegmentMeta[] = []
+    const drop: SegmentMeta[] = []
+    for (const s of this.manifest.segments) {
+      ;(s.lastGeneration < belowGeneration ? drop : keep).push(s)
+    }
+    if (drop.length === 0) {
+      return { dropped: 0, compactedBelow: this.manifest.compactedBelow }
+    }
+    const compactedBelow = Math.max(
+      this.manifest.compactedBelow,
+      drop[drop.length - 1].lastGeneration + 1
+    )
+    // Manifest first (the drop is authoritative once named), then bytes —
+    // a crash between leaves orphan segment files invisible to the manifest,
+    // harmless and re-collectable.
+    const next: SegmentManifest = { ...this.manifest, compactedBelow, segments: keep }
+    await this.storage.writeRawObject(MANIFEST_PATH, next)
+    await this.storage.syncRawObjects([MANIFEST_PATH])
+    this.manifest = next
+    for (const s of drop) {
+      await this.storage.deleteRawObject(`${SEGMENTS_PREFIX}/${s.file}`)
+      await this.storage.deleteRawObject(`${SEGMENTS_PREFIX}/${sidecarFileName(s.firstGeneration)}`)
+      this.sidecars.delete(s.file)
+    }
+    return { dropped: drop.length, compactedBelow }
+  }
+
+  /**
+   * D8 rider — the packed portion of `generationDigest(g)`: a deterministic
+   * crc32c chain over sealed-segment checksums fully below `g`, plus the
+   * frame CRC of `g`'s own frame when `g` is mid-segment. O(segments), not
+   * O(generations); identical history ⇒ identical digest on any machine.
+   * The live-tier portion is composed by the caller.
+   */
+  async digestThroughPacked(g: number): Promise<number | null> {
+    let digest = 0
+    let covered = false
+    for (const s of this.manifest.segments) {
+      if (s.lastGeneration <= g) {
+        digest = crc32c(new TextEncoder().encode(`${digest}:${s.checksum}`))
+        if (s.lastGeneration === g) covered = true
+      } else if (s.firstGeneration <= g) {
+        // g is mid-segment: chain the partial prefix via g's frame CRC.
+        const frame = await this.readFrame(g)
+        if (frame === null) return null
+        const idx = await this.sidecarFor(s)
+        const upTo = idx.generations.filter(([gen]) => gen <= g)
+        for (const [gen, offset, frameLen] of upTo) {
+          digest = crc32c(new TextEncoder().encode(`${digest}:${gen}:${offset}:${frameLen}`))
+        }
+        covered = true
+        break
+      }
+    }
+    return covered || this.manifest.segments.length > 0 ? digest : null
+  }
+}

src/db/generationStore.ts

@@ -45,6 +45,9 @@ import type {
   GenerationStorage,
   TxLogEntry
 } from './types.js'
+import { FactLog, storageSupportsFactLog, type CommitFact, type FactOp } from './factLog.js'
+import { GenerationSegmentStore, type FoldGeneration } from './generationSegments.js'
+import { crc32c } from '../utils/crc32c.js'
 
 /**
  * The byte-identical before-images of every id a commit touches, read UNDER
@@ -121,6 +124,16 @@ export interface GenerationStoreOpenResult {
 export class GenerationStore {
   private readonly storage: GenerationStorage
 
+  /**
+   * The generation FACT LOG (dual-write transition) — an append-only,
+   * CRC-framed record of every committed generation as an AFTER-IMAGE fact.
+   * `null` when the storage layer lacks the binary raw-byte primitives.
+   * Appends ride the same commit protocol: a fact-append failure FAILS the
+   * write (loud — a silent fact gap would make the log a lie that a later
+   * replay discovers), and open() reconciles the log to committed truth.
+   */
+  private factLog: FactLog | null = null
+
   /** Latest reserved/observed generation (≥ {@link committed}). */
   private counter = 0
   /** Committed-transaction watermark (manifest generation). */
@@ -246,6 +259,30 @@ export class GenerationStore {
    */
   private deltaCacheMax = 4096
 
+  /**
+   * Running total of on-disk history bytes across committed generations —
+   * `null` until {@link historyBytes} pays its one seeding walk. Maintained
+   * incrementally at commit/reclaim so the adaptive retention check on every
+   * flush() is O(1), never a tail re-walk. Never updated by cache re-reads
+   * ({@link setDelta} inserts are cache population, not new history).
+   */
+  private historyBytesTotal: number | null = null
+
+  /**
+   * The packed tier (D1+D3): sealed segments holding folded cold
+   * generations. Null until {@link open} wires it (and on storage adapters
+   * without raw-byte primitives — the live tier then carries everything,
+   * exactly as before the packed tier existed).
+   */
+  private segments: GenerationSegmentStore | null = null
+
+  /**
+   * Live-tier window: generations newer than `committed - REPACK_LIVE_WINDOW`
+   * are never folded — the hot tail stays in the per-generation layout the
+   * write path owns. Matches the resident chain window's scale.
+   */
+  static readonly REPACK_LIVE_WINDOW = 1024
+
   /**
    * Model-B per-write group-commit — the in-memory PENDING tier.
    *
@@ -400,6 +437,46 @@ export class GenerationStore {
 
     this.opened = true
 
+    // Generation FACT LOG (dual-write transition): when the storage layer
+    // exposes the binary raw-byte primitives, open the after-image fact log
+    // and reconcile it to committed truth — facts are appended BEFORE the
+    // commit point, so a crash can only leave the log AHEAD; open truncates
+    // any fact beyond `committed`. Storage without the primitives simply
+    // hosts no fact log (readers fall back to canonical enumeration).
+    if (storageSupportsFactLog(this.storage)) {
+      this.factLog = new FactLog(this.storage)
+      await this.factLog.open(this.committed)
+    } else {
+      this.factLog = null
+    }
+
+    // PACKED TIER (D1+D3): same capability gate as the fact log. Opening
+    // reads ONE manifest — never a listing of the packed backlog — and seeds
+    // committedRanges with the sealed ranges so packed generations resolve
+    // exactly like live ones.
+    if (storageSupportsFactLog(this.storage)) {
+      this.segments = new GenerationSegmentStore(this.storage)
+      await this.segments.open()
+      const packedRanges = this.segments
+        .segments()
+        .map((s): [number, number] => [s.firstGeneration, Math.min(s.lastGeneration, this.committed)])
+        .filter(([lo, hi]) => lo <= hi)
+      if (packedRanges.length > 0) {
+        // Merge packed (older) + live (newer) interval sets — both ascending;
+        // coalesce adjacency so range arithmetic stays interval-exact.
+        const merged: Array<[number, number]> = []
+        for (const r of [...packedRanges, ...this.committedRanges].sort((a, b) => a[0] - b[0])) {
+          const last = merged[merged.length - 1]
+          if (last && r[0] <= last[1] + 1) last[1] = Math.max(last[1], r[1])
+          else merged.push([r[0], r[1]])
+        }
+        this.committedRanges = merged
+      }
+      this.horizonGen = Math.max(this.horizonGen, this.segments.compactedBelow() - 1)
+    } else {
+      this.segments = null
+    }
+
     // Hook single-op write batches so generation() is always meaningful.
     // Suppressed while a transact batch executes (the batch is ONE generation).
     if (!options?.readOnly) {
@@ -459,6 +536,85 @@ export class GenerationStore {
     return this.horizonGen
   }
 
+  /**
+   * @description Read-only history footprint for fleet audits: how much
+   * generational history this store holds on disk. `bytes` pays (and seeds)
+   * the one-time {@link historyBytes} walk on first call — subsequent calls
+   * are O(1). The oldest/newest timestamps come from those generations'
+   * deltas (cache-bounded reads).
+   * @returns Counts, bytes, generation range, and the compaction horizon.
+   */
+  /**
+   * @description D8 (gate-to-generation provenance): a deterministic content
+   * digest of the generation log THROUGH `g` — identical history ⇒ identical
+   * digest on any machine; any divergence (different records, different
+   * order, reclaimed range) ⇒ different digest. Composed from the packed
+   * tier's sealed-segment checksum chain (O(segments)) plus the live tier's
+   * per-generation delta digests (O(live window at most)). Release gates pin
+   * {generation, digest} and verify both at execution time.
+   * @param g - The generation to digest through (≤ committed).
+   * @returns A hex digest string, stable across reopen and repacking states
+   *   ONLY for fully-packed prefixes — repacking changes representation, so
+   *   the composed digest is defined over CONTENT: live-tier gens hash their
+   *   delta + record ids, packed gens hash via frame CRCs. A gate should pin
+   *   after a repack pass for long-term stability, or re-pin on repack.
+   */
+  async generationDigest(g: number): Promise<string> {
+    if (!Number.isInteger(g) || g < 1 || g > this.committed) {
+      throw new RangeError(
+        `generationDigest(): generation ${g} is out of range [1, ${this.committed}]`
+      )
+    }
+    if (g <= this.horizonGen) {
+      throw new GenerationCompactedError(g, this.horizonGen)
+    }
+    let digest = 0
+    const enc = new TextEncoder()
+    if (this.segments) {
+      const packed = await this.segments.digestThroughPacked(g)
+      if (packed !== null) digest = packed
+    }
+    // Live-tier composition: every committed gen ≤ g not covered by a sealed
+    // segment hashes its delta content in ascending order.
+    for (const gen of this.committedGensAsc()) {
+      if (gen > g) break
+      if (this.segments?.hasGeneration(gen)) continue
+      const delta = await this.getDelta(gen)
+      digest = crc32c(
+        enc.encode(
+          `${digest}:${gen}:${delta.timestamp}:${[...delta.nouns].sort().join(',')}:${[...delta.verbs].sort().join(',')}`
+        )
+      )
+    }
+    return digest.toString(16).padStart(8, '0')
+  }
+
+  async historyStats(): Promise<{
+    generations: number
+    bytes: number
+    oldestGeneration: number | null
+    newestGeneration: number | null
+    oldestTimestamp: number | null
+    newestTimestamp: number | null
+    horizon: number
+  }> {
+    let oldest: number | null = null
+    let newest: number | null = null
+    for (const gen of this.committedGensAsc()) {
+      if (oldest === null) oldest = gen
+      newest = gen
+    }
+    return {
+      generations: this.committedCount(),
+      bytes: await this.historyBytes(),
+      oldestGeneration: oldest,
+      newestGeneration: newest,
+      oldestTimestamp: oldest !== null ? (await this.getDelta(oldest)).timestamp : null,
+      newestTimestamp: newest !== null ? (await this.getDelta(newest)).timestamp : null,
+      horizon: this.horizonGen
+    }
+  }
+
   /**
    * @description Read one generation's persisted before-image records — the
    * compaction fallback for generations written before deltas carried
@@ -471,14 +627,17 @@ export class GenerationStore {
     try {
       paths = await this.storage.listRawObjects(`${GENERATIONS_PREFIX}/${gen}/prev`)
     } catch {
-      return []
+      paths = []
     }
     const records: GenerationRecord[] = []
     for (const p of paths) {
       const record = (await this.storage.readRawObject(p)) as GenerationRecord | null
       if (record) records.push(record)
     }
-    return records
+    if (records.length > 0) return records
+    // Two-tier: folded generations serve their record-set from the segment.
+    const packed = await this.segments?.readRecords(gen)
+    return packed ? (packed.map((r) => r.record) as GenerationRecord[]) : []
   }
 
   /**
@@ -600,6 +759,58 @@ export class GenerationStore {
    * @returns The committed generation and its commit timestamp.
    * @throws GenerationConflictError when the CAS expectation fails.
    */
+  /**
+   * The generation fact log, or `null` when the storage layer cannot host one.
+   * Consumers scan committed facts through it (`scanFacts` / `segmentPaths`).
+   */
+  getFactLog(): FactLog | null {
+    return this.factLog
+  }
+
+  /**
+   * @description Build one commit's AFTER-IMAGE fact by reading canonical
+   * state back for every touched id — under the commit mutex, immediately
+   * after the operations applied, so canonical IS the after-image (and the
+   * reads are page-cache-warm: the operations just wrote these files). An
+   * absent id (both legs null) becomes a body-less TOMBSTONE — the delete
+   * fact needs no body, so removal never requires reading the removed thing.
+   * The fact's blobHashes are extracted from the AFTER records (the content
+   * this generation's state references), unlike the history path's
+   * before-image hashes.
+   */
+  private async buildCommitFact(args: {
+    generation: number
+    timestamp: number
+    nouns: string[]
+    verbs: string[]
+    meta?: Record<string, unknown>
+  }): Promise<CommitFact> {
+    const ops: FactOp[] = []
+    const afterRecords: GenerationRecord[] = []
+    for (const id of args.nouns) {
+      const after = await this.storage.readNounRaw(id)
+      const absent = after.metadata === null && after.vector === null
+      ops.push({ kind: 'noun', id, record: absent ? null : after })
+      if (!absent) afterRecords.push({ kind: 'noun', metadata: after.metadata, vector: after.vector })
+    }
+    for (const id of args.verbs) {
+      const after = await this.storage.readVerbRaw(id)
+      const absent = after.metadata === null && after.vector === null
+      ops.push({ kind: 'verb', id, record: absent ? null : after })
+      if (!absent) afterRecords.push({ kind: 'verb', metadata: after.metadata, vector: after.vector })
+    }
+    const blobHashes = this.storage.extractBlobHashesFromRecords
+      ? this.storage.extractBlobHashesFromRecords(afterRecords)
+      : []
+    return {
+      generation: args.generation,
+      timestamp: args.timestamp,
+      ops,
+      ...(args.meta ? { meta: args.meta } : {}),
+      ...(blobHashes.length > 0 ? { blobHashes } : {})
+    }
+  }
+
   async commitTransaction(args: {
     touched: TouchedIds
     meta?: Record<string, unknown>
@@ -733,6 +944,24 @@ export class GenerationStore {
         await this.storage.flushWriteBarrier?.()
         faultPoint('after-execute')
 
+        // Fact log (dual-write): append + fsync this generation's AFTER-IMAGE
+        // fact BEFORE the commit point, inside the same durability window —
+        // so a crash can only leave the log AHEAD (open truncates), never a
+        // committed generation without its fact. A real abort below this point
+        // compensates via dropAbove in the catch. An append failure fails the
+        // write, loudly — a silent fact gap would be a lie a replay discovers.
+        if (this.factLog) {
+          const fact = await this.buildCommitFact({
+            generation: gen,
+            timestamp,
+            nouns,
+            verbs,
+            ...(args.meta ? { meta: args.meta } : {})
+          })
+          await this.factLog.append(fact)
+          await this.factLog.sync()
+        }
+
         // -- 5. Counter + manifest rename (COMMIT POINT) ----------------------
         await this.persistCounterUnlocked()
         faultPoint('before-manifest-rename')
@@ -755,6 +984,9 @@ export class GenerationStore {
           timestamp,
           bytes: delta.bytes ?? 0
         })
+        if (this.historyBytesTotal !== null) {
+          this.historyBytesTotal += delta.bytes ?? 0
+        }
         this.extendChains(gen, nouns, verbs)
         const logEntry: TxLogEntry = { generation: gen, timestamp, ...(args.meta && { meta: args.meta }) }
         await this.storage.appendTxLogLine(JSON.stringify(logEntry))
@@ -800,6 +1032,13 @@ export class GenerationStore {
             // over-count-safe; the scrub restores exactness
           }
         }
+        // Fact-log compensation: a real (non-crash) abort after the fact was
+        // appended must take the fact back out — the generation never
+        // committed. A crash instead reaches open(), whose truncation does the
+        // same reconcile from disk.
+        if (this.factLog && this.factLog.headGeneration() >= gen) {
+          await this.factLog.dropAbove(gen - 1)
+        }
         // Return the reservation when no concurrent bump consumed a later
         // number, so a failed transaction leaves generation() unchanged.
         if (this.counter === gen) this.counter = gen - 1
@@ -991,6 +1230,14 @@ export class GenerationStore {
             this.pendingBuffer.set(gen, { nouns: nounBefore, verbs: verbBefore, timestamp })
             this.pendingGens.push(gen)
             this.extendChains(gen, nouns, verbs)
+            // The adopted generation is committed — it gets its fact like any
+            // other (durability rides the group-commit flush, same as the
+            // buffered history).
+            if (this.factLog) {
+              await this.factLog.append(
+                await this.buildCommitFact({ generation: gen, timestamp, nouns, verbs })
+              )
+            }
             prodLog.warn(
               `[GenerationStore] Recovered a failed rollback FORWARD: single-op write ` +
                 `committed as generation ${gen} because its canonical undo could not be ` +
@@ -1020,6 +1267,17 @@ export class GenerationStore {
       this.pendingBuffer.set(gen, { nouns: nounBefore, verbs: verbBefore, timestamp })
       this.pendingGens.push(gen)
       this.extendChains(gen, nouns, verbs)
+      // 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.
+      if (this.factLog) {
+        await this.factLog.append(
+          await this.buildCommitFact({ generation: gen, timestamp, nouns, verbs })
+        )
+      }
       this.schedulePendingFlush()
       return { generation: gen, timestamp }
     })
@@ -1141,6 +1399,12 @@ export class GenerationStore {
       // ONE fsync for the whole window — the durability-batching win.
       await this.storage.syncRawObjects(stagedPaths)
 
+      // Fact log (dual-write): make the window's buffered facts durable in the
+      // same batch, BEFORE the commit point below — so a crash can only leave
+      // the log AHEAD of the counter (open truncates), never a committed
+      // generation without its durable fact.
+      await this.factLog?.sync()
+
       // 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
@@ -1176,6 +1440,9 @@ export class GenerationStore {
           timestamp: buf.timestamp,
           bytes: genBytes.get(gen) ?? 0
         })
+        if (this.historyBytesTotal !== null) {
+          this.historyBytesTotal += genBytes.get(gen) ?? 0
+        }
         this.pendingBuffer.delete(gen)
       }
       this.pendingGens = []
@@ -1608,9 +1875,15 @@ export class GenerationStore {
     if (pending) {
       return (kind === 'noun' ? pending.nouns : pending.verbs).get(id) ?? null
     }
-    return (await this.storage.readRawObject(
+    const live = (await this.storage.readRawObject(
       `${GENERATIONS_PREFIX}/${gen}/prev/${id}.json`
     )) as GenerationRecord | null
+    if (live) return live
+    // Two-tier: the packed tier serves folded generations (live-tier-wins).
+    if (this.segments?.hasGeneration(gen)) {
+      return (await this.segments.readRecord(gen, kind, id)) as GenerationRecord | null
+    }
+    return null
   }
 
   /**
@@ -1957,6 +2230,21 @@ export class GenerationStore {
       `${GENERATIONS_PREFIX}/${gen}/tx.json`
     )) as GenerationDelta | null
     if (delta === null) {
+      // Two-tier read (D1+D3): not in the live tier → the packed tier.
+      // Live-tier-wins ordering (a crash mid-fold leaves a duplicate, never
+      // a gap), so the segment lookup runs only after the live miss.
+      const packed = await this.segments?.readDelta(gen)
+      if (packed) {
+        const d = packed.delta as GenerationDelta
+        const entry = {
+          nouns: new Set(d.nouns),
+          verbs: new Set(d.verbs),
+          timestamp: packed.timestamp,
+          bytes: d.bytes ?? 0
+        }
+        this.setDelta(gen, entry)
+        return entry
+      }
       throw new Error(
         `Generation delta missing: ${GENERATIONS_PREFIX}/${gen}/tx.json ` +
           `(store corrupted or records removed outside compactHistory())`
@@ -1996,17 +2284,26 @@ export class GenerationStore {
   /**
    * @description Total serialized bytes of the ON-DISK generational history —
    * the sum of every committed generation's recorded `bytes`. Backs the
-   * `maxBytes` and adaptive retention caps. Reads each committed generation's
+   * `maxBytes` and adaptive retention caps. O(1) after the first call: the
-   * delta (cached; a re-read only for cache-evicted ones) — O(committed
+   * total is computed by ONE walk over committed deltas, then maintained
-   * generations), bounded by retention itself and invoked only at compaction
+   * incrementally at every commit (+bytes) and reclaim (−bytes) and dropped on
-   * time. Pending (un-flushed) generations are excluded (they are not on disk).
+   * a wholesale state replacement (restore). Without the running total, the
+   * adaptive auto-compaction on every flush() re-walked the ENTIRE history —
+   * O(committed generations) file reads per flush past the delta-cache bound —
+   * which is how a 70k-generation production brain turned every write into a
+   * full-tail scan (SELF-GENERATIONS-GROWTH). Pending (un-flushed) generations
+   * are excluded (they are not on disk).
    * @returns The total on-disk history byte count.
    */
   async historyBytes(): Promise<number> {
+    if (this.historyBytesTotal !== null) {
+      return this.historyBytesTotal
+    }
     let total = 0
     for (const gen of this.committedGensAsc()) {
       total += (await this.getDelta(gen)).bytes
     }
+    this.historyBytesTotal = total
     return total
   }
 
@@ -2029,6 +2326,94 @@ export class GenerationStore {
    * @param options - Retention caps (see {@link CompactHistoryOptions}).
    * @returns Count of removed record-sets and the new horizon.
    */
+  /**
+   * @description The REPACKER (D1+D3+repacking): fold cold live-tier
+   * generations into sealed segments — re-representation, never deletion.
+   * Every record and delta stays readable (asOf/chains unchanged); the
+   * per-generation directories are deleted only AFTER their segment is
+   * durable (crash between = duplicate representation, resolved
+   * live-tier-wins by every reader; never a gap). This is the transform that
+   * takes a 70k-file history to tens of segment files, and the ONLY history
+   * transform permitted under the archival profile.
+   *
+   * Folds oldest-first, contiguous from the packed boundary, in batches, and
+   * stops at the live window ({@link GenerationStore.REPACK_LIVE_WINDOW})
+   * or when `timeBudgetMs` is spent — an early stop is a consistent prefix;
+   * the next pass resumes.
+   */
+  async repackHistory(options?: { timeBudgetMs?: number; batchGenerations?: number }): Promise<{
+    foldedGenerations: number
+    segmentsCreated: number
+  }> {
+    if (!this.segments) return { foldedGenerations: 0, segmentsCreated: 0 }
+    const segments = this.segments
+    return this.withMutex(async () => {
+      const deadline =
+        options?.timeBudgetMs !== undefined ? Date.now() + options.timeBudgetMs : undefined
+      const batchSize = options?.batchGenerations ?? 512
+      const coldCeiling = this.committed - GenerationStore.REPACK_LIVE_WINDOW
+      const packedThrough =
+        segments.segments().length > 0
+          ? segments.segments()[segments.segments().length - 1].lastGeneration
+          : 0
+
+      // Cold, unpacked, committed generations — ascending, contiguous scan.
+      const eligible: number[] = []
+      for (const gen of this.committedGensAsc()) {
+        if (gen > coldCeiling) break
+        if (gen <= packedThrough) continue // already packed (dup fold barred)
+        if (this.pendingBuffer.has(gen)) continue // un-flushed = live by definition
+        eligible.push(gen)
+      }
+
+      let folded = 0
+      let segmentsCreated = 0
+      for (let i = 0; i < eligible.length; i += batchSize) {
+        if (deadline !== undefined && Date.now() >= deadline) break
+        const batch = eligible.slice(i, i + batchSize)
+        const foldInput: FoldGeneration[] = []
+        for (const gen of batch) {
+          const delta = (await this.storage.readRawObject(
+            `${GENERATIONS_PREFIX}/${gen}/tx.json`
+          )) as GenerationDelta | null
+          if (delta === null) {
+            // Already folded by a prior crashed pass whose dirs were removed,
+            // or damage — getDelta's two-tier read decides which, loudly,
+            // when someone asks. Skip; never fold a generation we cannot read.
+            continue
+          }
+          const records: FoldGeneration['records'] = []
+          for (const [kind, ids] of [
+            ['noun', delta.nouns] as const,
+            ['verb', delta.verbs] as const
+          ]) {
+            for (const id of ids) {
+              const record = await this.storage.readRawObject(
+                `${GENERATIONS_PREFIX}/${gen}/prev/${id}.json`
+              )
+              if (record) records.push({ kind, id, record })
+            }
+          }
+          foldInput.push({ generation: gen, timestamp: delta.timestamp, delta, records })
+        }
+        if (foldInput.length === 0) continue
+        await segments.fold(foldInput)
+        segmentsCreated++
+        // Segment + manifest durable → the live copies retire.
+        for (const g of foldInput) {
+          await this.storage.removeRawPrefix(`${GENERATIONS_PREFIX}/${g.generation}`)
+        }
+        folded += foldInput.length
+      }
+      if (folded > 0) {
+        prodLog.info(
+          `[GenerationStore] repacked ${folded} cold generation(s) into ${segmentsCreated} segment(s) — history preserved, file count reduced`
+        )
+      }
+      return { foldedGenerations: folded, segmentsCreated }
+    })
+  }
+
   async compact(options?: CompactHistoryOptions): Promise<CompactHistoryResult> {
     return this.withMutex(async () => {
       const minPinned = this.minPinnedGeneration()
@@ -2036,6 +2421,11 @@ export class GenerationStore {
       const maxAge = options?.maxAge
       const maxBytes = options?.maxBytes
       const ageCutoff = maxAge !== undefined ? Date.now() - maxAge : undefined
+      // Bounded maintenance pass (8.9.0): stop reclaiming once the budget is
+      // spent. Safe mid-loop — reclamation is oldest-first, so an early stop
+      // leaves a consistent contiguous prefix and the next pass resumes.
+      const deadline =
+        options?.timeBudgetMs !== undefined ? Date.now() + options.timeBudgetMs : undefined
       const noCaps =
         maxGenerations === undefined && maxAge === undefined && maxBytes === undefined
 
@@ -2049,6 +2439,7 @@ export class GenerationStore {
       for (const gen of [...this.committedGensAsc()]) {
         // Pins are always exempt: never reclaim a generation a live pin needs.
         if (gen > minPinned) break // committedGensAsc ascending → nothing newer is eligible either
+        if (deadline !== undefined && Date.now() >= deadline) break // budget spent — resume next pass
         const delta = await this.getDelta(gen)
         if (!noCaps) {
           const violatesCount = maxGenerations !== undefined && remainingCount > maxGenerations
@@ -2080,6 +2471,9 @@ export class GenerationStore {
 
         await this.storage.removeRawPrefix(`${GENERATIONS_PREFIX}/${gen}`)
         this.deltaCache.delete(gen)
+        if (this.historyBytesTotal !== null) {
+          this.historyBytesTotal -= delta.bytes
+        }
 
         // AFTER the record-set is gone (over-count-only crash ordering):
         // release its history references and reclaim any blob left with zero
@@ -2111,6 +2505,16 @@ export class GenerationStore {
         // Reclaimed generations leave the per-id chains stale → rebuild on next read.
         this.invalidateChains()
         this.horizonGen = Math.max(this.horizonGen, highestRemoved)
+        // Packed-tier reclaim (D3): a packed generation's bytes live in a
+        // sealed segment — removeRawPrefix above was a no-op for it. Drop
+        // WHOLE segments now fully below the horizon; a partially-reclaimed
+        // segment keeps its bytes until the boundary passes it (the frozen
+        // partial-segments-wait rule; logical reclamation above still holds —
+        // the generations left committedRanges and asOf below the horizon
+        // throws regardless).
+        if (this.segments) {
+          await this.segments.dropSegmentsBelow(this.horizonGen + 1)
+        }
         const manifest: GenerationManifest = {
           version: 1,
           generation: this.committed,
@@ -2140,6 +2544,9 @@ export class GenerationStore {
   async reopenAfterRestore(floorGeneration: number): Promise<void> {
     await this.withMutex(async () => {
       this.deltaCache.clear()
+      // The running history-byte total describes the REPLACED store — drop it;
+      // the next historyBytes() re-seeds with one walk over the new state.
+      this.historyBytesTotal = null
       // A wholesale state replacement invalidates any buffered single-op
       // history — discard the pending tier (its live writes are gone with the
       // replaced store).

src/db/types.ts

@@ -116,6 +116,16 @@ export interface TransactOptions {
    * record is staged.
    */
   ifAtGeneration?: number
+  /**
+   * Budget (ms) for the atomic apply phase. When omitted, the budget SCALES
+   * with the batch: `max(30 000, opCount × 2 000)` — production imports on
+   * network-attached disks measure ~2 s per operation, so a flat 30 s budget
+   * silently capped honest bulk work at ~15 operations. A tripped budget
+   * rolls the whole batch back and throws a retryable
+   * `TransactionTimeoutError` naming the operation it stopped at, the batch
+   * size, and the elapsed/budget times.
+   */
+  timeoutMs?: number
 }
 
 /**
@@ -166,6 +176,15 @@ export interface CompactHistoryOptions {
    * of each surviving generation's serialized record set (`GenerationDelta.bytes`).
    */
   maxBytes?: number
+  /**
+   * Stop reclaiming after this many milliseconds even if caps are still
+   * exceeded (8.9.0). Compaction is maintenance — a bounded pass keeps
+   * `close()` (and any explicit maintenance window) from stalling on a large
+   * backlog; the next pass resumes where this one stopped (reclamation is
+   * oldest-first, so an early stop is always a consistent prefix). Unset =
+   * run to completion.
+   */
+  timeBudgetMs?: number
 }
 
 /**
@@ -183,6 +202,36 @@ export interface CompactHistoryResult {
   horizon: number
 }
 
+/**
+ * @description Result of `brain.historyStats()` — the read-only generational
+ * history footprint, for fleet audits and ops doors. A pool operator runs this
+ * per brain to size retention exposure (how much MVCC history each brain
+ * carries and under which policy) without touching any data.
+ */
+export interface HistoryStats {
+  /** Committed generation record-sets currently on disk. */
+  generations: number
+  /** Total on-disk history bytes across those record-sets. */
+  bytes: number
+  /** Oldest committed generation still on disk (null when history is empty). */
+  oldestGeneration: number | null
+  /** Newest committed generation (null when history is empty). */
+  newestGeneration: number | null
+  /** Commit timestamp (ms) of the oldest on-disk generation. */
+  oldestTimestamp: number | null
+  /** Commit timestamp (ms) of the newest on-disk generation. */
+  newestTimestamp: number | null
+  /** Compaction horizon — generations below it were reclaimed. */
+  horizon: number
+  /** The effective retention mode this brain runs under. */
+  retentionMode: 'all' | 'adaptive' | 'explicit'
+  /**
+   * The adaptive byte budget in force (coordinator-driven or the local
+   * free-memory probe); null under 'all' or explicit caps.
+   */
+  effectiveBudgetBytes: number | null
+}
+
 // ============================================================================
 // Db surfaces
 // ============================================================================
@@ -423,6 +472,22 @@ export interface GenerationStorage {
   /** Read all lines of `_system/tx-log.jsonl` (empty array if absent). */
   readTxLogLines(): Promise<string[]>
 
+  /**
+   * OPTIONAL binary raw-byte primitives — the substrate for the generation
+   * fact log's append-only CRC-framed segments. Feature-detected: a storage
+   * layer that omits them hosts no fact log (dual-write is skipped; readers
+   * fall back to canonical enumeration). Paths are used VERBATIM (no
+   * suffixing). Append durability rides `syncRawObjects` at the commit
+   * barrier, exactly like the staged history files.
+   */
+  appendRawBytes?(path: string, bytes: Uint8Array): Promise<void>
+  /** Read a raw binary file whole; absent → null; a real fault throws. */
+  readRawBytes?(path: string): Promise<Uint8Array | null>
+  /** Replace a raw binary file atomically (tmp → fsync → rename). */
+  writeRawBytes?(path: string, bytes: Uint8Array): Promise<void>
+  /** Byte size of a raw binary file, or null when absent. */
+  rawByteSize?(path: string): Promise<number | null>
+
   /**
    * OPTIONAL temporal-blob contract (implemented by blob-aware storage; the
    * generation store treats the hashes as opaque strings). Extract the

src/graph/graphAdjacencyIndex.ts

@@ -282,6 +282,16 @@ export class GraphAdjacencyIndex implements GraphIndexProvider {
       }
 
       hasMore = result.hasMore
+      if (hasMore && (!result.nextCursor || result.nextCursor === cursor)) {
+        // A stalled cursor with hasMore=true would re-read the same page
+        // forever — a silent full-CPU loop at cold open. Abort loudly; a
+        // graph read failing beats a process that spins without a log line.
+        throw new Error(
+          `GraphAdjacencyIndex: verb walk stalled after ${count} verbs — storage returned ` +
+            `hasMore=true with ${result.nextCursor ? 'a non-advancing' : 'no'} cursor. ` +
+            `Aborting the cold-load; run brain.repairIndex() if this persists.`
+        )
+      }
       cursor = result.nextCursor
     }
 

src/graph/graphAudit.ts

@@ -0,0 +1,214 @@
+/**
+ * @module graph/graphAudit
+ * @description Read-only graph-truth audit — the graph sibling of `repairIndex()`'s
+ * diagnosis half. Verifies three layers against each other without mutating anything:
+ *
+ *   1. CANONICAL verb records (the storage walk — the source of truth)
+ *   2. the RELATIONSHIP READ PATH (`related()` with all visibility tiers — exactly
+ *      what application reads like a VFS `readdir` consult)
+ *   3. ENTITY ENDPOINTS (does each verb's source/target still exist?)
+ *
+ * and classifies every discrepancy into the three failure families production
+ * incidents have shown:
+ *
+ *   - `missingFromReads` — a canonical verb record the read path does NOT return
+ *     for its source: PRESENT BUT INVISIBLE (adjacency/membership staleness).
+ *   - `danglingEndpoints` — a canonical verb whose endpoint entity is gone:
+ *     the SCAR class (write-path loss / partial delete).
+ *   - `readOnlyVerbIds` — the read path returns an edge with NO canonical
+ *     record: GHOST edges (stale index entries).
+ *
+ * `visibilityHiddenCount` is reported separately: an internal/system edge that is
+ * indexed and present but hidden from DEFAULT reads is working as designed — the
+ * audit reads with all tiers included so design-hiding is never misclassified as
+ * index loss.
+ *
+ * Full counts are always exact; only the example LISTS are capped (`maxExamples`)
+ * — a capped report says so via `truncatedExamples`, never silently.
+ */
+
+import { prodLog } from '../utils/logger.js'
+
+/** One discrepant relationship, identified fully enough to inspect by hand. */
+export interface GraphAuditDiscrepancy {
+  verbId: string
+  from: string
+  to: string
+  type: string
+}
+
+export interface GraphAuditReport {
+  /** True iff every discrepancy count is zero — `related()` returns canonical truth. */
+  coherent: boolean
+  verbsInCanonical: number
+  entitiesInCanonical: number
+  /** Distinct source entities whose read path was actually consulted (coverage honesty). */
+  sourcesChecked: number
+
+  /** PRESENT BUT INVISIBLE: canonical records the read path omits. */
+  missingFromReadsCount: number
+  missingFromReads: GraphAuditDiscrepancy[]
+
+  /** SCAR CLASS: canonical verbs with a missing endpoint entity. */
+  danglingEndpointsCount: number
+  danglingEndpoints: Array<GraphAuditDiscrepancy & { missingEnd: 'from' | 'to' | 'both' }>
+
+  /** GHOST EDGES: read-path verb ids with no canonical record. */
+  readOnlyCount: number
+  readOnlyVerbIds: string[]
+
+  /** Canonical verbs hidden from DEFAULT reads by design (internal/system visibility). */
+  visibilityHiddenCount: number
+
+  /** Example lists above were capped at maxExamples; counts remain exact. */
+  truncatedExamples: boolean
+  durationMs: number
+}
+
+/** A canonical verb record, as the audit needs it. */
+export interface AuditVerbRecord {
+  id: string
+  type: string
+  sourceId: string
+  targetId: string
+  visibility?: string
+}
+
+/** The seams the audit runs over — injected so the walk is testable in isolation. */
+export interface GraphAuditDeps {
+  /** Stream every canonical entity id (id-only; no per-entity reads needed). */
+  eachNounId(consume: (id: string) => void): Promise<void>
+  /** Stream every canonical verb record. */
+  eachVerb(consume: (verb: AuditVerbRecord) => void): Promise<void>
+  /**
+   * The END-TO-END relationship read for one source, ALL visibility tiers
+   * included — must be the same path application reads consult.
+   */
+  readRelationsFrom(sourceId: string): Promise<Array<{ id: string }>>
+}
+
+export interface GraphAuditOptions {
+  /** Cap on entries per example list (counts stay exact). Default 100. */
+  maxExamples?: number
+}
+
+export async function runGraphAudit(
+  deps: GraphAuditDeps,
+  options: GraphAuditOptions = {}
+): Promise<GraphAuditReport> {
+  const maxExamples = options.maxExamples ?? 100
+  const started = Date.now()
+
+  // 1. Canonical entity ids — endpoint existence oracle.
+  const entityIds = new Set<string>()
+  await deps.eachNounId((id) => entityIds.add(id))
+
+  // 2. Canonical verb walk: group by source, check endpoints, note visibility.
+  const canonicalVerbIds = new Set<string>()
+  const bySource = new Map<string, AuditVerbRecord[]>()
+  let verbsInCanonical = 0
+  let visibilityHiddenCount = 0
+  let danglingEndpointsCount = 0
+  const danglingEndpoints: GraphAuditReport['danglingEndpoints'] = []
+
+  await deps.eachVerb((verb) => {
+    verbsInCanonical++
+    canonicalVerbIds.add(verb.id)
+    const list = bySource.get(verb.sourceId)
+    if (list) list.push(verb)
+    else bySource.set(verb.sourceId, [verb])
+
+    if (verb.visibility === 'internal' || verb.visibility === 'system') {
+      visibilityHiddenCount++
+    }
+
+    const fromMissing = !entityIds.has(verb.sourceId)
+    const toMissing = !entityIds.has(verb.targetId)
+    if (fromMissing || toMissing) {
+      danglingEndpointsCount++
+      if (danglingEndpoints.length < maxExamples) {
+        danglingEndpoints.push({
+          verbId: verb.id,
+          from: verb.sourceId,
+          to: verb.targetId,
+          type: verb.type,
+          missingEnd: fromMissing && toMissing ? 'both' : fromMissing ? 'from' : 'to'
+        })
+      }
+    }
+  })
+
+  // 3. Per-source read-path comparison. A verb must be returned by the read
+  //    path of ITS OWN source — the exact consult a readdir/traversal makes.
+  let missingFromReadsCount = 0
+  const missingFromReads: GraphAuditDiscrepancy[] = []
+  let readOnlyCount = 0
+  const readOnlyVerbIds: string[] = []
+  const readOnlySeen = new Set<string>()
+
+  for (const [sourceId, verbs] of bySource) {
+    const readIds = new Set((await deps.readRelationsFrom(sourceId)).map((r) => r.id))
+
+    for (const verb of verbs) {
+      if (!readIds.has(verb.id)) {
+        missingFromReadsCount++
+        if (missingFromReads.length < maxExamples) {
+          missingFromReads.push({
+            verbId: verb.id,
+            from: verb.sourceId,
+            to: verb.targetId,
+            type: verb.type
+          })
+        }
+      }
+    }
+
+    for (const readId of readIds) {
+      if (!canonicalVerbIds.has(readId) && !readOnlySeen.has(readId)) {
+        readOnlySeen.add(readId)
+        readOnlyCount++
+        if (readOnlyVerbIds.length < maxExamples) {
+          readOnlyVerbIds.push(readId)
+        }
+      }
+    }
+  }
+
+  const coherent =
+    missingFromReadsCount === 0 && danglingEndpointsCount === 0 && readOnlyCount === 0
+
+  const report: GraphAuditReport = {
+    coherent,
+    verbsInCanonical,
+    entitiesInCanonical: entityIds.size,
+    sourcesChecked: bySource.size,
+    missingFromReadsCount,
+    missingFromReads,
+    danglingEndpointsCount,
+    danglingEndpoints,
+    readOnlyCount,
+    readOnlyVerbIds,
+    visibilityHiddenCount,
+    truncatedExamples:
+      missingFromReadsCount > missingFromReads.length ||
+      danglingEndpointsCount > danglingEndpoints.length ||
+      readOnlyCount > readOnlyVerbIds.length,
+    durationMs: Date.now() - started
+  }
+
+  if (coherent) {
+    prodLog.info(
+      `[GraphAudit] coherent: ${verbsInCanonical} verbs across ${bySource.size} sources — ` +
+        `the read path returns canonical truth (${report.durationMs}ms)`
+    )
+  } else {
+    prodLog.warn(
+      `[GraphAudit] INCOHERENT: ${missingFromReadsCount} present-but-invisible, ` +
+        `${danglingEndpointsCount} dangling-endpoint, ${readOnlyCount} ghost ` +
+        `(of ${verbsInCanonical} canonical verbs, ${bySource.size} sources, ` +
+        `${visibilityHiddenCount} visibility-hidden by design) — ${report.durationMs}ms`
+    )
+  }
+
+  return report
+}

src/import/BackgroundDeduplicator.ts

@@ -41,6 +41,14 @@ export interface DeduplicationStats {
  * - Import-scoped deduplication (no cross-contamination)
  * - 3-tier strategy (ID → Name → Similarity)
  * - Uses existing indexes (EntityIdMapper, MetadataIndexManager, TypeAware HNSW)
+ *
+ * Lifecycle: ONE instance per brain, owned by Brainy (getBackgroundDeduplicator)
+ * so the debounce genuinely spans imports and brain.close() cancels pending
+ * work via cancelPending() — this pass merge-DELETES duplicate entities, so it
+ * must never fire against a closed brain. The enableDeduplication gate lives
+ * at the scheduling call site (ImportCoordinator); scheduleDedup itself is
+ * unconditional. The timer is unref'd — a pending pass never holds the
+ * process open.
  */
 export class BackgroundDeduplicator {
   private brain: Brainy
@@ -67,12 +75,15 @@ export class BackgroundDeduplicator {
       clearTimeout(this.debounceTimer)
     }
 
-    // Schedule for 5 minutes from now
+    // Schedule for 5 minutes from now. unref'd: a pending dedup pass must
+    // never hold the process open (exit-hang class) — if the process exits
+    // first, the pass simply never runs; imports are already durable.
     this.debounceTimer = setTimeout(() => {
       this.runBatchDedup().catch(error => {
         prodLog.error('[BackgroundDedup] Batch dedup failed:', error)
       })
     }, 5 * 60 * 1000)
+    this.debounceTimer.unref?.()
   }
 
   /**

src/import/ImportCoordinator.ts

@@ -13,7 +13,6 @@
 import { Brainy } from '../brainy.js'
 import { FormatDetector, SupportedFormat } from './FormatDetector.js'
 import { ImportHistory, type ImportHistoryEntry } from './ImportHistory.js'
-import { BackgroundDeduplicator } from './BackgroundDeduplicator.js'
 import { SmartExcelImporter } from '../importers/SmartExcelImporter.js'
 import { SmartPDFImporter } from '../importers/SmartPDFImporter.js'
 import { SmartCSVImporter } from '../importers/SmartCSVImporter.js'
@@ -112,7 +111,12 @@ export interface ValidImportOptions {
   /** Confidence threshold for entities */
   confidenceThreshold?: number
 
-  /** Enable entity deduplication across imports */
+  /**
+   * Enable entity deduplication (default: true). Gates BOTH passes: the
+   * inline merge during import AND the debounced background pass that runs
+   * ~5 minutes after the last import (which merge-DELETES duplicate entities).
+   * Set false for deployments that must never auto-remove records.
+   */
   enableDeduplication?: boolean
 
   /** Similarity threshold for deduplication (0-1) */
@@ -286,7 +290,6 @@ export class ImportCoordinator {
   private brain: Brainy
   private detector: FormatDetector
   private history: ImportHistory
-  private backgroundDedup: BackgroundDeduplicator
   private excelImporter: SmartExcelImporter
   private pdfImporter: SmartPDFImporter
   private csvImporter: SmartCSVImporter
@@ -300,7 +303,6 @@ export class ImportCoordinator {
     this.brain = brain
     this.detector = new FormatDetector()
     this.history = new ImportHistory(brain)
-    this.backgroundDedup = new BackgroundDeduplicator(brain)
     this.excelImporter = new SmartExcelImporter(brain)
     this.pdfImporter = new SmartPDFImporter(brain)
     this.csvImporter = new SmartCSVImporter(brain)
@@ -1459,9 +1461,16 @@ export class ImportCoordinator {
       }
     }
 
-    // Schedule background deduplication (debounced 5 minutes)
+    // Schedule background deduplication (debounced 5 minutes, brain-owned so
-    if (trackingContext && trackingContext.importId) {
+    // close() can cancel it). Honors the same enableDeduplication gate as the
-      this.backgroundDedup.scheduleDedup(trackingContext.importId)
+    // inline pass — false means NO dedup, inline or background.
+    if (
+      trackingContext &&
+      trackingContext.importId &&
+      options.enableDeduplication !== false
+    ) {
+      const backgroundDedup = await this.brain.getBackgroundDeduplicator()
+      backgroundDedup.scheduleDedup(trackingContext.importId)
     }
 
     return {

src/index.ts

@@ -28,6 +28,16 @@ export type { FileVersion } from './vfs/types.js'
 
 // Export diagnostics result type
 export type { DiagnosticsResult } from './brainy.js'
+export type {
+  GraphAuditReport,
+  GraphAuditDiscrepancy
+} from './graph/graphAudit.js'
+export {
+  checkOsLimits,
+  NOFILE_POOL_FLOOR,
+  MAX_MAP_COUNT_POOL_FLOOR
+} from './utils/osLimits.js'
+export type { OsLimitsReport } from './utils/osLimits.js'
 
 // Export Brainy configuration and types
 export type {
@@ -191,11 +201,26 @@ export type {
   TxLogEntry,
   CompactHistoryOptions,
   CompactHistoryResult,
+  HistoryStats,
   ChangedIds,
   DiffResult,
   HistoryVersion,
   EntityHistory
 } from './db/types.js'
+// The generation fact log — sequential after-image scan surface
+// (brain.scanFacts / brain.factSegmentPaths) for index heals and replays.
+export type {
+  CommitFact,
+  FactOp,
+  FactScanBatch,
+  SCANFACTS_FIRST_BATCH_MS,
+  FactScanHandle
+} from './db/factLog.js'
+// The generalized family stamp — which source generation a projection
+// reflects + the surface that verifies it whole; one verifier, both member
+// modes (enumerated byte-exact / rollup invariants).
+export { readFamilyStamp, verifyFamilyStamp, ENTITY_TREE_STAMP_PATH } from './db/familyStamp.js'
+export type { FamilyStamp, StampMembers, StampVerdict } from './db/familyStamp.js'
 // Optional provider capability for generation-aware native indexes
 export { isVersionedIndexProvider } from './plugin.js'
 export type { VersionedIndexProvider } from './plugin.js'

src/internals.ts

@@ -19,3 +19,29 @@ export type { MemoryInfo, CacheAllocationStrategy } from './utils/memoryDetectio
 // HNSWNounWithMetadata. First-party plugins (Cor) use this to stay in
 // lockstep with the entity shape contract.
 export { resolveEntityField, STANDARD_ENTITY_FIELDS } from './coreTypes.js'
+
+// The generalized family stamp — ONE verifier, both member modes, shared
+// verbatim with native providers so stamp verification is literally one
+// function, never two synchronized copies. Providers write the same shape
+// (their set-swap rewrites stamps, so adoption is migration-free).
+export {
+  readFamilyStamp,
+  writeFamilyStamp,
+  verifyFamilyStamp,
+  FAMILY_STAMPS_PREFIX,
+  ENTITY_TREE_STAMP_PATH
+} from './db/familyStamp.js'
+export type {
+  FamilyStamp,
+  StampMembers,
+  StampVerdict,
+  EnumeratedMember,
+  StampStorage
+} from './db/familyStamp.js'
+
+// Generation fact-log types — the scan surface a provider reaches through the
+// storage capability (`storage.scanFacts` / `storage.factLogHeadGeneration` /
+// `storage.factSegmentPaths`, wired by the host brain at init). Providers
+// never construct a FactLog themselves: open() is writer-side (it reconciles
+// by truncating/rewriting) and there is exactly one writer.
+export type { CommitFact, FactOp, FactScanBatch, FactScanHandle } from './db/factLog.js'

src/storage/adapters/fileSystemStorage.ts

@@ -96,6 +96,14 @@ export class FileSystemStorage extends BaseStorage {
   private static readonly WRITER_STALE_THRESHOLD_MS = 60_000
   private writerLockHeartbeat?: NodeJS.Timeout
   private writerLockInfo?: WriterLockInfo
+  /**
+   * The currently-executing heartbeat refresh, if any. `releaseWriterLock()`
+   * awaits it before unlinking: clearInterval() stops FUTURE ticks but not a
+   * tick already in flight, and a straggler landing after the unlink would
+   * RE-CREATE the lock file — a phantom lock blocking the next writer until
+   * the stale TTL expires (the pool-eviction reopen case).
+   */
+  private writerHeartbeatInFlight?: Promise<void>
 
   // Flush-request RPC state. The writer polls `locks/_flush_requests/` for
   // new `.req` files and emits `.ack` files in `locks/_flush_responses/` after
@@ -693,6 +701,17 @@ export class FileSystemStorage extends BaseStorage {
    */
   private static readonly SNAPSHOT_BYTE_COPY_DIRS = new Set<string>(['_id_mapper'])
 
+  /**
+   * Nested path PREFIXES whose files are byte-copied into snapshots, not
+   * hard-linked — for append-in-place files below the top level. The
+   * generation fact log's tail segment is appended in place between rotations;
+   * a hard-linked tail would let post-snapshot appends reach through into the
+   * snapshot. (Sealed segments are immutable and would be link-safe, but the
+   * prefix rule keeps the discipline simple; segments are bounded by the
+   * rotation threshold, so the copy cost is small.)
+   */
+  private static readonly SNAPSHOT_BYTE_COPY_PREFIXES: string[] = ['_generations/facts/']
+
   /**
    * Top-level directories excluded from snapshots: process-local lock state
    * (writer lock, flush-request RPC files) must never travel with the data, and
@@ -870,6 +889,75 @@ export class FileSystemStorage extends BaseStorage {
     }
   }
 
+  // ==========================================================================
+  // Binary raw-byte primitives — the substrate for append-only log-structured
+  // files (the generation fact log's CRC-framed segments). Paths are used
+  // VERBATIM (no .gz/.bin suffixing). Append durability rides syncRawObjects
+  // at the commit barrier, like every other staged write.
+  // ==========================================================================
+
+  /**
+   * Append bytes to a raw binary file, creating it (and parent directories)
+   * when absent. NOT fsync'd here — the caller batches durability via
+   * `syncRawObjects` at its commit barrier.
+   */
+  public async appendRawBytes(rawPath: string, bytes: Uint8Array): Promise<void> {
+    await this.ensureInitialized()
+    const fullPath = path.join(this.rootDir, rawPath)
+    await fs.promises.mkdir(path.dirname(fullPath), { recursive: true })
+    await fs.promises.appendFile(fullPath, bytes)
+  }
+
+  /**
+   * Read a raw binary file whole. Absent → `null`; a real IO fault throws —
+   * a present-but-unreadable log segment must never read as "no facts".
+   */
+  public async readRawBytes(rawPath: string): Promise<Uint8Array | null> {
+    await this.ensureInitialized()
+    try {
+      const buf: Buffer = await fs.promises.readFile(path.join(this.rootDir, rawPath))
+      return new Uint8Array(buf.buffer, buf.byteOffset, buf.byteLength)
+    } catch (error: any) {
+      if (isAbsentError(error)) return null
+      throw error
+    }
+  }
+
+  /**
+   * Replace a raw binary file atomically: write-new → fsync → rename. The
+   * reconcile primitive (e.g. truncating a fact-log tail back to committed
+   * truth after a crash) — a crash mid-replace leaves either the old file or
+   * the new one, never a mix.
+   */
+  public async writeRawBytes(rawPath: string, bytes: Uint8Array): Promise<void> {
+    await this.ensureInitialized()
+    const fullPath = path.join(this.rootDir, rawPath)
+    await fs.promises.mkdir(path.dirname(fullPath), { recursive: true })
+    const tmpPath = `${fullPath}.tmp.${Date.now()}.${Math.random().toString(36).slice(2)}`
+    const handle = await fs.promises.open(tmpPath, 'w')
+    try {
+      await handle.writeFile(bytes)
+      await handle.sync()
+    } finally {
+      await handle.close()
+    }
+    await fs.promises.rename(tmpPath, fullPath)
+  }
+
+  /**
+   * Byte size of a raw binary file, or `null` when absent.
+   */
+  public async rawByteSize(rawPath: string): Promise<number | null> {
+    await this.ensureInitialized()
+    try {
+      const stat = await fs.promises.stat(path.join(this.rootDir, rawPath))
+      return stat.size
+    } catch (error: any) {
+      if (isAbsentError(error)) return null
+      throw error
+    }
+  }
+
   /**
    * Snapshot the entire store into `targetPath` as a hard-link farm
    * (Cassandra-style: instant, space-shared). Safe because every data file
@@ -919,7 +1007,8 @@ export class FileSystemStorage extends BaseStorage {
       // msync/truncate reach through into the snapshot.
       if (
         FileSystemStorage.SNAPSHOT_BYTE_COPY_PATHS.has(normalized) ||
-        FileSystemStorage.SNAPSHOT_BYTE_COPY_DIRS.has(normalized.split('/')[0])
+        FileSystemStorage.SNAPSHOT_BYTE_COPY_DIRS.has(normalized.split('/')[0]) ||
+        FileSystemStorage.SNAPSHOT_BYTE_COPY_PREFIXES.some((p) => normalized.startsWith(p))
       ) {
         await fs.promises.copyFile(sourceFile, targetFile)
         continue
@@ -1683,79 +1772,158 @@ export class FileSystemStorage extends BaseStorage {
     const lockFile = path.join(this.lockDir, FileSystemStorage.WRITER_LOCK_FILE)
     const os = await import('node:os')
     const hostname = os.hostname()
-    const now = new Date().toISOString()
+    const myPid = typeof process !== 'undefined' && process.pid ? process.pid : 0
 
-    const existing = await this.readWriterLock()
+    // Bounded acquire loop. The CLAIM itself is an atomic create-exclusive
-    if (existing && !options?.force) {
+    // write (O_EXCL) — two processes racing an ABSENT lock can never both
-      // Same-process re-open: a second Brainy instance in this Node process
+    // succeed, which closes the read-then-write window where the loser used
-      // (e.g. test "simulate server restart" patterns, or a consumer that
+    // to keep running unlocked, silently. An EEXIST loser loops, re-reads,
-      // explicitly re-instantiates without closing first). This isn't the
+    // and handles whatever it finds honestly (fresh foreign lock → loud
-      // dangerous cross-process case the lock exists to prevent — the two
+    // throw; stale/forced → verified takeover).
-      // instances share a memory space and can't silently diverge from each
+    const MAX_ATTEMPTS = 3
-      // other beyond what their callers already see. Warn and take over the lock.
+    for (let attempt = 0; attempt < MAX_ATTEMPTS; attempt++) {
-      if (existing.pid === (typeof process !== 'undefined' ? process.pid : 0) &&
+      const now = new Date().toISOString()
-          existing.hostname === hostname) {
+      const existing = await this.readWriterLock()
-        console.warn(
+
-          `[brainy] Re-acquiring writer lock for ${this.rootDir} held by the same process (PID ${existing.pid}). ` +
+      if (existing) {
-          `If you intended to keep the previous Brainy instance alive, this is a bug — close it first.`
+        // Same-process re-open: a second Brainy instance in this Node process
-        )
+        // (e.g. test "simulate server restart" patterns, or a consumer that
-      } else {
+        // explicitly re-instantiates without closing first). This isn't the
-        const stale = await this.isWriterLockStale(existing)
+        // dangerous cross-process case the lock exists to prevent — the two
-        if (!stale) {
+        // instances share a memory space and can't silently diverge from each
+        // other beyond what their callers already see. Warn and take over.
+        if (existing.pid === myPid && existing.hostname === hostname && !options?.force) {
+          console.warn(
+            `[brainy] Re-acquiring writer lock for ${this.rootDir} held by the same process (PID ${existing.pid}). ` +
+            `If you intended to keep the previous Brainy instance alive, this is a bug — close it first.`
+          )
+          const info: WriterLockInfo = {
+            pid: myPid,
+            hostname,
+            startedAt: now,
+            lastHeartbeat: now,
+            version: getBrainyVersion(),
+            rootDir: this.rootDir
+          }
+          await this.writeFileAtomic(lockFile, JSON.stringify(info, null, 2))
+          this.installWriterLock(info)
+          return info
+        }
+
+        const stale = !options?.force && (await this.isWriterLockStale(existing))
+        if (!options?.force && !stale) {
           // Consumer-facing error contract: callers detect this case via
           // err.code and read the holder's details from err.lockInfo.
-          const err = new Error(
+          throw this.writerLockedError(existing)
-            `Another writer holds this Brainy directory.\n` +
-            `  PID:        ${existing.pid} on host ${existing.hostname}\n` +
-            `  Started:    ${existing.startedAt}\n` +
-            `  Heartbeat:  ${existing.lastHeartbeat}\n` +
-            `  Version:    ${existing.version}\n` +
-            `  Directory:  ${this.rootDir}\n\n` +
-            `For diagnostic queries against this live store, use:\n` +
-            `  const reader = await Brainy.openReadOnly({ storage: { type: 'filesystem', path: '${this.rootDir}' } })\n\n` +
-            `If you have verified the existing lock is stale (e.g. a crashed writer on a different host that PID liveness cannot reach), pass { force: true }.`
-          ) as Error & { code: string; lockInfo: WriterLockInfo }
-          err.code = 'BRAINY_WRITER_LOCKED'
-          err.lockInfo = existing
-          throw err
         }
+
         console.warn(
-          `[brainy] Overwriting stale writer lock for ${this.rootDir} ` +
+          options?.force
-          `(PID ${existing.pid} on ${existing.hostname} appears dead).`
+            ? `[brainy] Force-overwriting writer lock for ${this.rootDir} ` +
+              `(was held by PID ${existing.pid} on ${existing.hostname}).`
+            : `[brainy] Overwriting stale writer lock for ${this.rootDir} ` +
+              `(PID ${existing.pid} on ${existing.hostname} appears dead).`
         )
+        // Takeover: verify the file still holds the lock we judged (a live
+        // successor may have claimed meanwhile), then remove it and fall
+        // through to the atomic claim below. A racing claimer who beats us to
+        // the create simply wins — our next loop iteration reads their fresh
+        // lock and throws honestly. (Advisory file locking has no
+        // compare-and-delete; staleness requiring a 60s-old heartbeat keeps
+        // the residual verify-to-unlink window practically unreachable.)
+        const recheck = await this.readWriterLock()
+        if (
+          recheck &&
+          (recheck.pid !== existing.pid ||
+            recheck.startedAt !== existing.startedAt ||
+            recheck.lastHeartbeat !== existing.lastHeartbeat)
+        ) {
+          continue // the lock changed hands while we deliberated — re-evaluate
+        }
+        try {
+          await fs.promises.unlink(lockFile)
+        } catch (err: any) {
+          if (err.code !== 'ENOENT') throw err
+        }
       }
-    } else if (existing && options?.force) {
+
-      console.warn(
+      const info: WriterLockInfo = {
-        `[brainy] Force-overwriting writer lock for ${this.rootDir} ` +
+        pid: myPid,
-        `(was held by PID ${existing.pid} on ${existing.hostname}).`
+        hostname,
-      )
+        startedAt: existing && options?.force ? existing.startedAt : now,
+        lastHeartbeat: now,
+        version: getBrainyVersion(),
+        rootDir: this.rootDir
+      }
+
+      // The atomic claim: create-exclusive, so exactly ONE racer wins.
+      try {
+        await fs.promises.writeFile(lockFile, JSON.stringify(info, null, 2), { flag: 'wx' })
+      } catch (err: any) {
+        if (err.code === 'EEXIST') {
+          continue // someone else claimed between our read and create — re-evaluate
+        }
+        throw err
+      }
+
+      this.installWriterLock(info)
+      return info
     }
 
-    const info: WriterLockInfo = {
+    // Attempts exhausted: something is claiming this directory faster than we
-      pid: typeof process !== 'undefined' && process.pid ? process.pid : 0,
+    // can evaluate it. Read whoever holds it now and fail loudly with their
-      hostname,
+    // details rather than degrading into a lockless open.
-      startedAt: existing && options?.force ? existing.startedAt : now,
+    const holder = await this.readWriterLock()
-      lastHeartbeat: now,
+    if (holder) throw this.writerLockedError(holder)
-      version: getBrainyVersion(),
+    throw new Error(
-      rootDir: this.rootDir
+      `Failed to acquire the writer lock for ${this.rootDir} after ${MAX_ATTEMPTS} attempts — ` +
-    }
+      `the lock file is being contended. Retry, or inspect ${lockFile}.`
+    )
+  }
 
-    await this.writeFileAtomic(lockFile, JSON.stringify(info, null, 2))
+  /** Record lock ownership + start the unref'd heartbeat. */
+  private installWriterLock(info: WriterLockInfo): void {
     this.writerLockInfo = info
 
     // Heartbeat — rewrite lastHeartbeat every WRITER_HEARTBEAT_MS so other
     // processes can tell a live writer from one that crashed without releasing.
     this.writerLockHeartbeat = setInterval(() => {
-      this.refreshWriterLockHeartbeat().catch((err) => {
+      const tick = this.refreshWriterLockHeartbeat().catch((err) => {
-        console.warn('[brainy] Failed to refresh writer lock heartbeat:', err)
+        // ENOENT = the lock (or its directory) vanished mid-refresh — the
+        // store was released or removed under us; the next acquire recreates
+        // it. Benign by construction; anything else stays loud.
+        if ((err as NodeJS.ErrnoException)?.code !== 'ENOENT') {
+          console.warn('[brainy] Failed to refresh writer lock heartbeat:', err)
+        }
+      })
+      this.writerHeartbeatInFlight = tick.finally(() => {
+        if (this.writerHeartbeatInFlight === tick) {
+          this.writerHeartbeatInFlight = undefined
+        }
       })
     }, FileSystemStorage.WRITER_HEARTBEAT_MS)
     if (typeof this.writerLockHeartbeat.unref === 'function') {
       // Don't keep the event loop alive just for the heartbeat.
       this.writerLockHeartbeat.unref()
     }
+  }
 
-    return info
+  /** The consumer-facing BRAINY_WRITER_LOCKED error, holder details attached. */
+  private writerLockedError(existing: WriterLockInfo): Error {
+    const err = new Error(
+      `Another writer holds this Brainy directory.\n` +
+      `  PID:        ${existing.pid} on host ${existing.hostname}\n` +
+      `  Started:    ${existing.startedAt}\n` +
+      `  Heartbeat:  ${existing.lastHeartbeat}\n` +
+      `  Version:    ${existing.version}\n` +
+      `  Directory:  ${this.rootDir}\n\n` +
+      `For diagnostic queries against this live store, use:\n` +
+      `  const reader = await Brainy.openReadOnly({ storage: { type: 'filesystem', path: '${this.rootDir}' } })\n\n` +
+      `If you have verified the existing lock is stale (e.g. a crashed writer on a different host that PID liveness cannot reach), pass { force: true }.`
+    ) as Error & { code: string; lockInfo: WriterLockInfo }
+    err.code = 'BRAINY_WRITER_LOCKED'
+    err.lockInfo = existing
+    return err
   }
 
   public override async releaseWriterLock(): Promise<void> {
@@ -1763,6 +1931,15 @@ export class FileSystemStorage extends BaseStorage {
       clearInterval(this.writerLockHeartbeat)
       this.writerLockHeartbeat = undefined
     }
+    // Drain an in-flight heartbeat tick BEFORE unlinking: clearInterval stops
+    // future ticks only, and a straggler write landing after the unlink would
+    // re-create the lock as a phantom (blocking the next writer until the
+    // stale TTL). After the drain, any refresh is either fully landed (we
+    // unlink its output below) or not started (it sees writerLockInfo
+    // undefined and returns).
+    if (this.writerHeartbeatInFlight) {
+      await this.writerHeartbeatInFlight
+    }
     if (!this.writerLockInfo) {
       return
     }

src/storage/adapters/memoryStorage.ts

@@ -133,6 +133,11 @@ export class MemoryStorage extends BaseStorage {
    */
   protected async deleteObjectFromPath(path: string): Promise<void> {
     this.objectStore.delete(path)
+    // Filesystem parity: on disk, objects and raw BYTE files are both just
+    // files — unlink removes whichever exists. Without this, deleteRawObject
+    // on a raw-bytes path (fact-log/generation segments) silently no-ops on
+    // memory storage: the delete "succeeds" and the bytes remain.
+    this.rawBytesStore.delete(path)
   }
 
   /**
@@ -222,6 +227,45 @@ export class MemoryStorage extends BaseStorage {
     return [...this.txLogLines]
   }
 
+  // ===========================================================================
+  // Binary raw-byte primitives — in-memory mirror of the filesystem adapter's
+  // append-only substrate (the generation fact log's segments), so memory
+  // brains dual-write facts too and the compat suite runs on both adapters.
+  // ===========================================================================
+
+  /** Raw binary files, keyed by verbatim path. */
+  private rawBytesStore: Map<string, Uint8Array> = new Map()
+
+  /** Append bytes to a raw binary file, creating it when absent. */
+  public async appendRawBytes(rawPath: string, bytes: Uint8Array): Promise<void> {
+    const existing = this.rawBytesStore.get(rawPath)
+    if (!existing) {
+      this.rawBytesStore.set(rawPath, bytes.slice())
+      return
+    }
+    const merged = new Uint8Array(existing.length + bytes.length)
+    merged.set(existing, 0)
+    merged.set(bytes, existing.length)
+    this.rawBytesStore.set(rawPath, merged)
+  }
+
+  /** Read a raw binary file whole (a copy); absent → null. */
+  public async readRawBytes(rawPath: string): Promise<Uint8Array | null> {
+    const bytes = this.rawBytesStore.get(rawPath)
+    return bytes ? bytes.slice() : null
+  }
+
+  /** Replace a raw binary file (atomic by construction in memory). */
+  public async writeRawBytes(rawPath: string, bytes: Uint8Array): Promise<void> {
+    this.rawBytesStore.set(rawPath, bytes.slice())
+  }
+
+  /** Byte size of a raw binary file, or null when absent. */
+  public async rawByteSize(rawPath: string): Promise<number | null> {
+    const bytes = this.rawBytesStore.get(rawPath)
+    return bytes ? bytes.length : null
+  }
+
   /**
    * Serialize the entire in-memory store to a directory in the exact layout
    * the filesystem adapter uses (uncompressed JSON objects, `_blobs/*.bin`
@@ -354,6 +398,7 @@ export class MemoryStorage extends BaseStorage {
   public async clear(): Promise<void> {
     this.objectStore.clear()
     this.blobStore.clear()
+    this.rawBytesStore.clear()
     this.txLogLines = []
     this.statistics = null
 

src/storage/baseStorage.ts

@@ -377,7 +377,14 @@ export abstract class BaseStorage extends BaseStorageAdapter {
       id.startsWith('statistics_') ||
       id === 'statistics' ||
       id.startsWith('__chunk__') ||      // Metadata index chunks (roaring bitmap data)
-      id.startsWith('__sparse_index__')  // Metadata sparse indices (zone maps + bloom filters)
+      id.startsWith('__sparse_index__') || // Metadata sparse indices (zone maps + bloom filters)
+      id.startsWith('__aggregation_') || // Aggregation engine definitions + state (routing is
+                                         // identical to the unknown-key fallback these keys hit
+                                         // before being listed here — this only kills the
+                                         // per-boot "Unknown key format" warning)
+      isSingletonSystemKey(id)           // Known singletons (e.g. brainy:entityIdMapper) hit the
+                                         // same warn-then-route fallback without this — the
+                                         // routing below already handles them identically
 
     if (isSystemKey) {
       if (isSingletonSystemKey(id)) {
@@ -842,6 +849,64 @@ export abstract class BaseStorage extends BaseStorageAdapter {
     return this.deleteObjectFromPath(path)
   }
 
+  // ==========================================================================
+  // Fact-scan capability — the seam through which an index provider holding
+  // only `storage` reaches the generation fact log. The HOST brain wires the
+  // source at init (a closure over its live fact log, so restore/reopen stays
+  // transparent); providers call storage.scanFacts?.(...) and fall back to the
+  // enumeration walk when it returns null. Providers never construct a
+  // fact-log reader themselves — the log's open path is writer-side.
+  // ==========================================================================
+
+  /** The host-wired fact-scan source (closures over the live generation state). */
+  private _factScanSource: {
+    factLog: () => import('../db/factLog.js').FactLog | null
+    committedGeneration: () => number
+  } | null = null
+
+  /** HOST-ONLY: wire (or clear) the fact-scan capability's source. */
+  public setFactScanSource(
+    source: {
+      factLog: () => import('../db/factLog.js').FactLog | null
+      committedGeneration: () => number
+    } | null
+  ): void {
+    this._factScanSource = source
+  }
+
+  /** Open a scan over committed facts, or `null` when no fact log exists. */
+  public scanFacts(options?: {
+    fromGeneration?: number
+    toGeneration?: number
+    kinds?: Array<'noun' | 'verb'>
+    batchSize?: number
+  }): import('../db/factLog.js').FactScanHandle | null {
+    const log = this._factScanSource?.factLog()
+    return log ? log.scanFacts(options) : null
+  }
+
+  /** The fact log's head generation, or `null` when no fact log exists. */
+  public factLogHeadGeneration(): number | null {
+    const log = this._factScanSource?.factLog()
+    return log ? log.headGeneration() : null
+  }
+
+  /**
+   * The COMMITTED generation watermark (the manifest truth) — the value a
+   * projection's `sourceGeneration` compares against. Exposed here so a
+   * provider never parses the store's private manifest format. `null` when
+   * the capability is unwired (no host, or a bare adapter).
+   */
+  public committedGeneration(): number | null {
+    return this._factScanSource ? this._factScanSource.committedGeneration() : null
+  }
+
+  /** Sealed fact-segment paths (zero-copy handoff); empty when none. */
+  public factSegmentPaths(options?: { fromGeneration?: number }): string[] {
+    const log = this._factScanSource?.factLog()
+    return log ? log.segmentPaths(options) : []
+  }
+
   /**
    * @description Remove the container that held a canonical entity's leg files,
    * called after both legs are deleted so a delete leaves NOTHING behind — no
@@ -1616,7 +1681,7 @@ export abstract class BaseStorage extends BaseStorageAdapter {
   /**
    * Delete a noun from storage
    */
-  public async deleteNoun(id: string): Promise<void> {
+  public async deleteNoun(id: string, priorMetadata?: NounMetadata | null): Promise<void> {
     await this.ensureInitialized()
 
     // FULL removal (live-HEAD hygiene): remove BOTH canonical legs AND the
@@ -1631,7 +1696,9 @@ export abstract class BaseStorage extends BaseStorageAdapter {
     // success); a REAL fault must surface loudly (loud errors, never quiet
     // losses) and must never silently skip the count decrement — so this is NO
     // LONGER wrapped in a blind catch that masked faults as "file didn't exist".
-    await this.deleteNounMetadata(id)
+    // `priorMetadata` (the caller's pre-delete read) keeps the decrement honest
+    // even when the canonical read inside returns null (replace race / ghost).
+    await this.deleteNounMetadata(id, priorMetadata)
 
     // Remove the now-empty entity container (a no-op for key/prefix stores).
     await this.removeCanonicalContainer(getNounVectorPath(id))
@@ -2001,11 +2068,20 @@ export abstract class BaseStorage extends BaseStorageAdapter {
     // Cursor (8.0): resume token carrying the (shard, nounId) of the last returned
     // noun — the noun mirror of getVerbsWithPagination. When present it supersedes
     // `offset` and resumes the shard walk immediately AFTER that position, so a full
-    // walk is O(N) instead of the O(N²) of offset paging. Malformed/foreign tokens
+    // walk is O(N) instead of the O(N²) of offset paging. (Previously the cursor was
-    // decode to null → offset fallback. (Previously the cursor was ignored, which
+    // ignored, which was latent — the only multi-page consumer used a single big
-    // was latent — the only multi-page consumer used a single big page — until small
+    // page — until small chunk sizes needed page 2 and an offset-0-on-every-call
-    // chunk sizes needed page 2 and an offset-0-on-every-call walk never terminated.)
+    // walk never terminated.)
     const cursor = this.decodeNounWalkCursor(options.cursor)
+    if (options.cursor && cursor === null) {
+      // A supplied-but-undecodable resume token must FAIL, not silently restart
+      // at offset 0 — to a while(hasMore) caller the silent fallback re-serves
+      // page 1 forever: an unbounded CPU loop wearing pagination's clothes.
+      throw BrainyError.storage(
+        `getNouns: invalid pagination cursor '${options.cursor}' — cannot resume this walk. ` +
+          `Restart it without a cursor.`
+      )
+    }
     const collected: Array<{ noun: HNSWNounWithMetadata; shard: number }> = []
 
     // Peek one past the window so `hasMore` is decidable. Cursor mode collects one
@@ -2154,6 +2230,14 @@ export abstract class BaseStorage extends BaseStorageAdapter {
 
     const { limit, offset = 0, filter } = options
     const cursor = this.decodeNounWalkCursor(options.cursor)
+    if (options.cursor && cursor === null) {
+      // Same law as getNouns/getVerbs: an undecodable resume token FAILS
+      // instead of silently restarting the walk at offset 0.
+      throw BrainyError.storage(
+        `getNounIds: invalid pagination cursor '${options.cursor}' — cannot resume this walk. ` +
+          `Restart it without a cursor.`
+      )
+    }
     const collected: Array<{ id: string; shard: number }> = []
     const peekCount = cursor ? limit + 1 : offset + limit + 1
     const startShard = cursor ? cursor.shard : 0
@@ -2299,8 +2383,17 @@ export abstract class BaseStorage extends BaseStorageAdapter {
     // (shard, verbId) of the last returned verb. When present it SUPERSEDES `offset`
     // and resumes the shard walk immediately AFTER that position, so a full walk is
     // O(N) total instead of the O(N²) of offset paging (which re-scans from shard 0
-    // every page). Malformed / foreign tokens decode to null → offset fallback.
+    // every page).
     const cursor = this.decodeVerbWalkCursor(options.cursor)
+    if (options.cursor && cursor === null) {
+      // A supplied-but-undecodable resume token must FAIL, not silently restart
+      // at offset 0 — to a while(hasMore) caller the silent fallback re-serves
+      // page 1 forever: an unbounded CPU loop wearing pagination's clothes.
+      throw BrainyError.storage(
+        `getVerbs: invalid pagination cursor '${options.cursor}' — cannot resume this walk. ` +
+          `Restart it without a cursor.`
+      )
+    }
 
     // Each collected entry remembers its shard so nextCursor can point at the exact
     // (shard, id) resume position.
@@ -2936,14 +3029,15 @@ export abstract class BaseStorage extends BaseStorageAdapter {
   /**
    * Delete a verb from storage
    */
-  public async deleteVerb(id: string): Promise<void> {
+  public async deleteVerb(id: string, priorMetadata?: VerbMetadata | null): Promise<void> {
     await this.ensureInitialized()
 
     // FULL removal (see deleteNoun): both canonical legs + the verb container.
     // The blind catch that masked real faults as "no metadata file" is gone — a
     // genuine absence is already a no-op downstream; a real fault surfaces loudly.
+    // `priorMetadata` keeps the count decrement honest on a null internal read.
     await this.deleteVerb_internal(id) // vectors.json leg
-    await this.deleteVerbMetadata(id)  // metadata leg + count decrement
+    await this.deleteVerbMetadata(id, priorMetadata) // metadata leg + count decrement
     await this.removeCanonicalContainer(getVerbVectorPath(id))
   }
   /**
@@ -3596,19 +3690,32 @@ export abstract class BaseStorage extends BaseStorageAdapter {
   }
 
   /**
-   * Delete noun metadata from storage (ID-first, O(1) delete)
+   * Delete noun metadata from storage (ID-first, O(1) delete).
+   *
+   * @param id - The entity id.
+   * @param priorRecord - OPTIONAL already-known metadata of the entity being
+   *   removed (e.g. the pre-delete read `remove()` performs, or a captured
+   *   before-image). The count decrement must never REQUIRE re-reading the
+   *   thing being removed: when the canonical read here returns `null` (a
+   *   replace race, or a partial-delete ghost from an earlier version) the
+   *   decrement falls back to this record instead of being silently skipped —
+   *   the skip permanently inflated the persisted totals (adds counted, paired
+   *   removals not decremented), and `Math.max(totalNounCount, scanned)` made
+   *   the inflation unfixable by any disk cleanup.
    */
-  public async deleteNounMetadata(id: string): Promise<void> {
+  public async deleteNounMetadata(id: string, priorRecord?: NounMetadata | null): Promise<void> {
     await this.ensureInitialized()
 
     // Direct O(1) delete with ID-first path. Read the canonical record BEFORE
     // removing it: the per-type and subtype decrements are sourced from the
     // entity's own metadata (`noun` type, `subtype`, `visibility`) rather than an
     // id-keyed cache, keeping type-statistics honest across deletes — symmetric
-    // with the increments in `saveNounMetadata_internal()`.
+    // with the increments in `saveNounMetadata_internal()`. A null read falls
+    // back to the caller-provided prior record (see @param priorRecord).
     const path = getNounMetadataPath(id)
-    const record = await this.readCanonicalObject(path)
+    const read = await this.readCanonicalObject(path)
     await this.deleteCanonicalObject(path)
+    const record = read ?? priorRecord
 
     const priorType = record?.noun as NounType | undefined
     // 8.0 visibility: an internal/system entity was never added to `nounCountsByType`
@@ -3782,16 +3889,20 @@ export abstract class BaseStorage extends BaseStorageAdapter {
   /**
    * Delete verb metadata from storage (ID-first, O(1) delete)
    */
-  public async deleteVerbMetadata(id: string): Promise<void> {
+  public async deleteVerbMetadata(id: string, priorRecord?: VerbMetadata | null): Promise<void> {
     await this.ensureInitialized()
 
     // Direct O(1) delete with ID-first path. Read the canonical record BEFORE
     // removing it so every decrement is sourced from the edge's own metadata
     // (`verb` type, `subtype`, `visibility`) rather than an id-keyed cache —
-    // symmetric with the increments in `saveVerbMetadata_internal()`.
+    // symmetric with the increments in `saveVerbMetadata_internal()`. A null
+    // read falls back to the caller-provided prior record: the decrement must
+    // never REQUIRE re-reading the thing being removed (a silent skip minted
+    // permanent counter inflation — see deleteNounMetadata).
     const path = getVerbMetadataPath(id)
-    const record = await this.readCanonicalObject(path)
+    const read = await this.readCanonicalObject(path)
     await this.deleteCanonicalObject(path)
+    const record = read ?? priorRecord
 
     const priorVerb = record?.verb as VerbType | undefined
     // Symmetric count decrement (previously OMITTED — verb deletes touched neither the
@@ -4228,6 +4339,17 @@ export abstract class BaseStorage extends BaseStorageAdapter {
     this.nounCountsByType = new Uint32Array(NOUN_TYPE_COUNT)
     this.verbCountsByType = new Uint32Array(VERB_TYPE_COUNT)
 
+    // The SAME walk also rebuilds the user-facing scalar totals + per-type maps
+    // persisted in counts.json (totalNounCount / totalVerbCount / entityCounts /
+    // verbCounts). Previously only the type-statistics arrays were rebuilt and
+    // the total was computed just to LOG it — so a drifted persisted scalar
+    // (deletes whose decrement was skipped) survived every "rebuild" forever,
+    // and Math.max(totalNounCount, scanned) made the inflation unfixable by any
+    // disk cleanup. This method is now the SANCTIONED RECOUNT: one canonical
+    // walk, every counter rollup rebuilt and persisted from it.
+    const countedNouns = new Map<string, number>()
+    const countedVerbs = new Map<string, number>()
+
     // Scan noun shards
     for (let shard = 0; shard < 256; shard++) {
       const shardHex = shard.toString(16).padStart(2, '0')
@@ -4248,6 +4370,7 @@ export abstract class BaseStorage extends BaseStorageAdapter {
                 if (typeIndex >= 0 && typeIndex < NOUN_TYPE_COUNT) {
                   this.nounCountsByType[typeIndex]++
                 }
+                countedNouns.set(metadata.noun, (countedNouns.get(metadata.noun) || 0) + 1)
               }
             }
           } catch (error) {
@@ -4279,6 +4402,7 @@ export abstract class BaseStorage extends BaseStorageAdapter {
                 if (typeIndex >= 0 && typeIndex < VERB_TYPE_COUNT) {
                   this.verbCountsByType[typeIndex]++
                 }
+                countedVerbs.set(metadata.verb, (countedVerbs.get(metadata.verb) || 0) + 1)
               }
             }
           } catch (error) {
@@ -4295,7 +4419,19 @@ export abstract class BaseStorage extends BaseStorageAdapter {
 
     const totalVerbs = this.verbCountsByType.reduce((sum, count) => sum + count, 0)
     const totalNouns = this.nounCountsByType.reduce((sum, count) => sum + count, 0)
-    prodLog.info(`[BaseStorage] Rebuilt counts: ${totalNouns} nouns, ${totalVerbs} verbs`)
+
+    // The sanctioned recount half: replace the user-facing scalar totals + the
+    // per-type maps with the walk's truth and PERSIST them (counts.json), so an
+    // inflated persisted counter is actually corrected — not merely out-voted
+    // in memory until the next reopen rehydrates the stale file.
+    this.entityCounts = countedNouns
+    this.verbCounts = countedVerbs
+    this.totalNounCount = totalNouns
+    this.totalVerbCount = totalVerbs
+    this.countCache.clear()
+    await this.persistCounts()
+
+    prodLog.info(`[BaseStorage] Rebuilt counts: ${totalNouns} nouns, ${totalVerbs} verbs (scalar + per-type persisted)`)
   }
 
   /**

src/transaction/Transaction.ts

@@ -37,6 +37,24 @@ const DEFAULT_OPTIONS: Required<TransactionOptions> = {
   maxRollbackRetries: 3
 }
 
+/**
+ * The apply-phase budget for a batch of `opCount` operations.
+ *
+ * An explicit override wins untouched. Otherwise the budget SCALES with the
+ * batch: `max(30 000 ms, opCount × 2 000 ms)`. The per-op term is calibrated
+ * from field data — bulk imports on network-attached disks measure ~2 s per
+ * operation (each op pays canonical writes + fsync + index maintenance) — so
+ * a flat 30 s budget silently capped honest work at ~15 operations while
+ * looking generous for small batches. Scaling keeps small transacts
+ * fast-failing and gives bulk ones a budget proportional to the work they
+ * actually asked for; a trip still rolls back atomically and throws a
+ * retryable, fully-labeled TransactionTimeoutError.
+ */
+export function transactTimeoutBudget(opCount: number, override?: number): number {
+  if (override !== undefined) return override
+  return Math.max(30_000, opCount * 2_000)
+}
+
 /**
  * Transaction class
  */
@@ -114,7 +132,11 @@ export class Transaction implements TransactionContext {
         // into the catch below and rolls back like any other failure — it must
         // never bypass rollback.
         if (Date.now() - this.startTime > this.options.timeout) {
-          throw new TransactionTimeoutError(this.options.timeout, i)
+          throw new TransactionTimeoutError(this.options.timeout, i, {
+            elapsedMs: Date.now() - this.startTime,
+            totalOperations: this.operations.length,
+            operationName: this.operations[i]?.name
+          })
         }
 
         const operation = this.operations[i]

src/transaction/errors.ts

@@ -77,11 +77,24 @@ export class InvalidTransactionStateError extends TransactionError {
 export class TransactionTimeoutError extends TransactionError {
   constructor(
     timeoutMs: number,
-    operationIndex: number
+    operationIndex: number,
+    telemetry?: {
+      elapsedMs?: number
+      totalOperations?: number
+      operationName?: string
+    }
   ) {
+    const progress =
+      telemetry?.totalOperations !== undefined
+        ? `${operationIndex}/${telemetry.totalOperations}`
+        : String(operationIndex)
+    const name = telemetry?.operationName ? ` ('${telemetry.operationName}')` : ''
+    const elapsed =
+      telemetry?.elapsedMs !== undefined ? `${telemetry.elapsedMs}ms elapsed, ` : ''
     super(
-      `Transaction timed out after ${timeoutMs}ms at operation ${operationIndex}`,
+      `Transaction timed out at operation ${progress}${name} — ${elapsed}budget ${timeoutMs}ms. ` +
-      { timeoutMs, operationIndex }
+        `The batch rolled back atomically; retry with a higher timeoutMs or a smaller batch.`,
+      { timeoutMs, operationIndex, ...telemetry }
     )
     this.name = 'TransactionTimeoutError'
   }

src/transaction/operations/StorageOperations.ts

@@ -127,22 +127,33 @@ export class DeleteNounMetadataOperation implements Operation {
 
   constructor(
     private readonly storage: StorageAdapter,
-    private readonly id: string
+    private readonly id: string,
+    /**
+     * OPTIONAL already-known metadata of the entity being removed (the caller's
+     * pre-delete read). Removal must never REQUIRE re-reading the thing being
+     * removed: if the reads here return null (replace race, or a ghost left by
+     * an earlier version), the count decrement downstream falls back to this
+     * record instead of being silently skipped — the skip minted permanent
+     * counter inflation (adds counted, paired removals not decremented).
+     */
+    private readonly priorMetadata?: NounMetadata | null
   ) {}
 
   async execute(): Promise<RollbackAction> {
     // 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)
+    const previousMetadata = (await this.storage.getNounMetadata(this.id)) ?? this.priorMetadata ?? null
 
     if (!previousNoun && !previousMetadata) {
       // Nothing to delete - no rollback needed
       return async () => {}
     }
 
-    // Full removal: both canonical legs + the entity container + count decrement.
+    // Full removal: both canonical legs + the entity container + count decrement
-    await this.storage.deleteNoun(this.id)
+    // (the prior record keeps the decrement honest on a null canonical read).
+    await this.storage.deleteNoun(this.id, previousMetadata)
 
     // Return rollback action
     return async () => {
@@ -268,9 +279,9 @@ export class DeleteVerbMetadataOperation implements Operation {
       return async () => {}
     }
 
-    // Delete verb (metadata + vector)
+    // Delete verb (metadata + vector). The pre-read rides along so the count
-    // Note: StorageAdapter has deleteVerb but not deleteVerbMetadata
+    // decrement never depends on re-reading the record being removed.
-    await this.storage.deleteVerb(this.id)
+    await this.storage.deleteVerb(this.id, previousMetadata)
 
     // Return rollback action
     return async () => {

src/types/brainy.types.ts

@@ -1737,7 +1737,10 @@ export interface BrainyConfig {
    * Under Model-B EVERY write (`transact()` AND single-op `add`/`update`/
    * `remove`/`relate`) produces an immutable generation record-set serving
    * historical reads (`asOf()`, pinned `Db` values). Without compaction those
-   * accumulate, so Brainy **auto-compacts on every `flush()` and `close()`**.
+   * accumulate, so Brainy **auto-compacts at `close()`** (time-bounded per
+   * pass; 8.9.0 removed compaction from `flush()` — flush is durability work
+   * and never pays maintenance costs). A long-lived writer that never closes
+   * accumulates history until its next explicit `compactHistory()` call.
    * Live `Db` pins are ALWAYS exempt from reclamation, in every mode.
    *
    * Modes:
@@ -1754,7 +1757,7 @@ export interface BrainyConfig {
    *   the oldest unpinned generations while ANY supplied cap is exceeded
    *   (predictable ops). `maxAge` in ms; `maxBytes` total history bytes.
    *
-   * `autoCompact: false` disables the automatic flush/close compaction (manage
+   * `autoCompact: false` disables the automatic close() compaction (manage
    * manually via `brain.compactHistory()`). `budgetBytes` is the settable
    * adaptive byte budget a coordinator drives (also via `brain.setRetentionBudget()`).
    * Long-term archives belong in `db.persist(path)` snapshots, which compaction
@@ -1772,7 +1775,7 @@ export interface BrainyConfig {
         maxBytes?: number
         /** Adaptive byte budget for this brain, driven by a coordinator (e.g. cor). */
         budgetBytes?: number
-        /** Run compaction automatically on flush()/close() (default: true). */
+        /** Run compaction automatically at close() (default: true; 8.9.0 — flush() never compacts). */
         autoCompact?: boolean
       }
 

src/utils/crc32c.ts

@@ -0,0 +1,43 @@
+/**
+ * @module utils/crc32c
+ * @description CRC-32C (Castagnoli, polynomial 0x1EDC6F41, reflected 0x82F63B78)
+ * — the storage-industry frame checksum (ext4, iSCSI, SCTP, LSM segment files).
+ * Used to frame generation-fact segments: every appended record carries the
+ * CRC-32C of its payload, so a torn tail (crash mid-append) or bit rot is
+ * DETECTED at scan time and never silently read as data.
+ *
+ * Table-driven, dependency-free reference implementation. Native providers may
+ * substitute a hardware-accelerated (SSE4.2 / ARMv8 CRC) implementation — the
+ * polynomial is the contract, byte-identical results required.
+ */
+
+/** The 256-entry lookup table for the reflected CRC-32C polynomial. */
+const TABLE: Uint32Array = (() => {
+  const table = new Uint32Array(256)
+  for (let n = 0; n < 256; n++) {
+    let c = n
+    for (let k = 0; k < 8; k++) {
+      c = c & 1 ? 0x82f63b78 ^ (c >>> 1) : c >>> 1
+    }
+    table[n] = c >>> 0
+  }
+  return table
+})()
+
+/**
+ * Compute the CRC-32C checksum of a byte buffer.
+ *
+ * Known-answer vectors (RFC 3720 appendix / the standard test suite):
+ * - ASCII "123456789" → 0xE3069283
+ * - 32 zero bytes → 0x8A9136AA
+ *
+ * @param bytes - The payload to checksum.
+ * @returns The CRC-32C as an unsigned 32-bit integer.
+ */
+export function crc32c(bytes: Uint8Array): number {
+  let crc = 0xffffffff
+  for (let i = 0; i < bytes.length; i++) {
+    crc = TABLE[(crc ^ bytes[i]) & 0xff] ^ (crc >>> 8)
+  }
+  return (crc ^ 0xffffffff) >>> 0
+}

src/utils/metadataIndex.ts

@@ -1867,9 +1867,26 @@ export class MetadataIndexManager implements MetadataIndexProvider {
     // not once per AND-clause inside it.
     const unindexedFields: string[] = []
 
-    for (const [field, condition] of Object.entries(filter)) {
+    for (const [rawField, condition] of Object.entries(filter)) {
       // Skip logical operators
-      if (field === 'allOf' || field === 'anyOf' || field === 'not') continue
+      if (rawField === 'allOf' || rawField === 'anyOf' || rawField === 'not') continue
+
+      // Metadata is FLATTENED at index time (metadata.entry.title indexes as
+      // entry.title), so a `metadata.`-prefixed where key is almost always
+      // the caller spelling the STORAGE shape rather than the index shape.
+      // Accept both spellings: when the key as spelled is unindexed but its
+      // stripped spelling is, query the stripped one. A literal nested
+      // custom key named `metadata` still wins when indexed as spelled
+      // (checked first), so that rare shape keeps working.
+      let field = rawField
+      if (
+        rawField.startsWith('metadata.') &&
+        this.columnStore &&
+        !this.columnStore.hasField(rawField) &&
+        this.columnStore.hasField(rawField.slice('metadata.'.length))
+      ) {
+        field = rawField.slice('metadata.'.length)
+      }
 
       let fieldResults: string[] = []
 

src/utils/osLimits.ts

@@ -0,0 +1,141 @@
+/**
+ * @module utils/osLimits
+ * @description Detect-and-warn for OS resource limits that bite at POOL scale.
+ *
+ * A single brain rarely notices them, but a pool of brains — especially with a
+ * native accelerator memory-mapping many index files per brain — consumes file
+ * descriptors and memory mappings multiplicatively. On stock Linux defaults
+ * (RLIMIT_NOFILE soft 1024, vm.max_map_count 65530) the failure arrives as
+ * EMFILE or a failed mmap deep inside an index open, long after the real cause
+ * (the limit) stopped being visible. This module reads the limits at open and
+ * WARNS ONCE per process with the exact raise commands, so the operator learns
+ * the fix before the incident instead of from it.
+ *
+ * Read-only and Linux-only by construction: both sources are `/proc` files.
+ * On platforms where they are absent the check reports nulls and stays silent —
+ * no limit read means no claim made, never a guessed warning.
+ */
+
+import * as fs from 'node:fs'
+import { prodLog } from './logger.js'
+
+/** Soft-NOFILE floor below which pool-scale use is at EMFILE risk. */
+export const NOFILE_POOL_FLOOR = 65536
+
+/** vm.max_map_count floor below which mmap-heavy native indexes are at risk. */
+export const MAX_MAP_COUNT_POOL_FLOOR = 262144
+
+export interface OsLimitsReport {
+  /** RLIMIT_NOFILE soft limit (null when unreadable; Infinity for 'unlimited'). */
+  nofileSoft: number | null
+  /** RLIMIT_NOFILE hard limit (null when unreadable; Infinity for 'unlimited'). */
+  nofileHard: number | null
+  /** vm.max_map_count (null when unreadable). */
+  maxMapCount: number | null
+  /** Human-actionable warnings for limits below the pool floors. Empty = fine. */
+  warnings: string[]
+}
+
+/**
+ * Parse the `Max open files` row of a `/proc/<pid>/limits` document into
+ * soft/hard values. Returns nulls when the row is absent or malformed.
+ */
+export function parseProcLimits(content: string): { soft: number | null; hard: number | null } {
+  const line = content.split('\n').find((l) => l.startsWith('Max open files'))
+  if (!line) return { soft: null, hard: null }
+  const m = line.match(/^Max open files\s+(\S+)\s+(\S+)/)
+  if (!m) return { soft: null, hard: null }
+  const parse = (v: string): number | null => {
+    if (v === 'unlimited') return Infinity
+    const n = Number.parseInt(v, 10)
+    return Number.isNaN(n) ? null : n
+  }
+  return { soft: parse(m[1]), hard: parse(m[2]) }
+}
+
+/**
+ * Assess readable limits against the pool floors. Pure — feed it any values.
+ * A null (unreadable) limit produces NO warning: no measurement, no claim.
+ */
+export function assessOsLimits(limits: {
+  nofileSoft: number | null
+  nofileHard: number | null
+  maxMapCount: number | null
+}): string[] {
+  const warnings: string[] = []
+
+  if (limits.nofileSoft !== null && limits.nofileSoft < NOFILE_POOL_FLOOR) {
+    const hardNote =
+      limits.nofileHard !== null && limits.nofileHard >= NOFILE_POOL_FLOOR
+        ? ` (the hard limit ${limits.nofileHard === Infinity ? 'unlimited' : limits.nofileHard} already allows it — raise the soft limit only)`
+        : ''
+    warnings.push(
+      `RLIMIT_NOFILE soft limit is ${limits.nofileSoft} — below the ${NOFILE_POOL_FLOOR} recommended ` +
+        `for pool-scale use (a pool of brains with a native accelerator opens many index files per brain; ` +
+        `the failure mode is EMFILE deep inside an index open). Raise with \`ulimit -n ${NOFILE_POOL_FLOOR}\` ` +
+        `or LimitNOFILE=${NOFILE_POOL_FLOOR} in the service unit${hardNote}.`
+    )
+  }
+
+  if (limits.maxMapCount !== null && limits.maxMapCount < MAX_MAP_COUNT_POOL_FLOOR) {
+    warnings.push(
+      `vm.max_map_count is ${limits.maxMapCount} — below the ${MAX_MAP_COUNT_POOL_FLOOR} recommended ` +
+        `for mmap-heavy native indexes at pool scale (each mapped index segment consumes map entries; ` +
+        `the failure mode is a failed mmap mid-heal). Raise with ` +
+        `\`sysctl -w vm.max_map_count=${MAX_MAP_COUNT_POOL_FLOOR}\` (persist in /etc/sysctl.d/).`
+    )
+  }
+
+  return warnings
+}
+
+/**
+ * Read the limits from /proc and assess them. `readFile` is injectable for
+ * tests; absent/unreadable sources yield nulls (and therefore no warnings).
+ */
+export async function checkOsLimits(
+  readFile: (path: string) => Promise<string> = async (p) => fs.promises.readFile(p, 'utf-8')
+): Promise<OsLimitsReport> {
+  let nofileSoft: number | null = null
+  let nofileHard: number | null = null
+  let maxMapCount: number | null = null
+
+  try {
+    const parsed = parseProcLimits(await readFile('/proc/self/limits'))
+    nofileSoft = parsed.soft
+    nofileHard = parsed.hard
+  } catch {
+    // Not Linux (or /proc unavailable) — no measurement, no claim.
+  }
+
+  try {
+    const raw = (await readFile('/proc/sys/vm/max_map_count')).trim()
+    const n = Number.parseInt(raw, 10)
+    maxMapCount = Number.isNaN(n) ? null : n
+  } catch {
+    // Not Linux — same rule.
+  }
+
+  const warnings = assessOsLimits({ nofileSoft, nofileHard, maxMapCount })
+  return { nofileSoft, nofileHard, maxMapCount, warnings }
+}
+
+/** Once-per-process latch so a brain pool warns once, not once per brain. */
+let osLimitsWarned = false
+
+/**
+ * Run the check and warn (once per process) about limits below the pool
+ * floors. Called from brain open; safe everywhere (silent off-Linux).
+ */
+export async function warnOnLowOsLimits(): Promise<void> {
+  if (osLimitsWarned) return
+  osLimitsWarned = true
+  try {
+    const report = await checkOsLimits()
+    for (const warning of report.warnings) {
+      prodLog.warn(`[Brainy] OS limit check: ${warning}`)
+    }
+  } catch {
+    // The check must never affect open — measurement-only.
+  }
+}

src/utils/paramValidation.ts

@@ -209,8 +209,10 @@ export interface ValidationConfigOptions {
 }
 
 /**
- * Auto-configured limits based on system resources
+ * Auto-configured limits based on system resources.
- * These adapt to available memory and observed performance
+ * Derived from memory (explicit overrides > reserved memory > container limit >
+ * free memory). Query timing is recorded for diagnostics only — it never
+ * changes the cap (see `recordQuery`).
  */
 export class ValidationConfig {
   private static instance: ValidationConfig | null = null
@@ -323,24 +325,23 @@ export class ValidationConfig {
   }
 
   /**
-   * Learn from actual usage to adjust limits
+   * Record query timing for diagnostics. Telemetry ONLY — never mutates the cap.
+   *
+   * `maxLimit` is a MEMORY-protection bound; query duration says nothing about
+   * memory-per-result, so duration must never drive it. An earlier version
+   * "learned" here: while the lifetime-average query time exceeded 1s it shrank
+   * `maxLimit` by 20% per recorded query down to a floor of 1000 — below the
+   * documented `MIN_AUTO_QUERY_LIMIT` (10 000) and with no recovery once slow
+   * samples poisoned the cumulative average. On a production host a burst of
+   * slow aggregate queries silently strangled every consumer's `find()` to
+   * 1000 while the error message blamed "available free memory" — exactly the
+   * silent throttling this module's own contract forbids. The cap now comes
+   * from its construction-time basis (or explicit overrides) alone.
    */
   recordQuery(duration: number, resultCount: number) {
+    void resultCount
     this.queryCount++
     this.avgQueryTime = (this.avgQueryTime * (this.queryCount - 1) + duration) / this.queryCount
-
-    // Only auto-adjust if not using explicit overrides
-    if (this.limitBasis !== 'override') {
-      // If queries are consistently fast with large results, increase limits
-      if (this.avgQueryTime < 100 && resultCount > this.maxLimit * 0.8) {
-        this.maxLimit = Math.min(this.maxLimit * 1.5, 100000)
-      }
-
-      // If queries are slow, reduce limits
-      if (this.avgQueryTime > 1000) {
-        this.maxLimit = Math.max(this.maxLimit * 0.8, 1000)
-      }
-    }
   }
 }
 

src/vfs/VirtualFileSystem.ts

@@ -1954,15 +1954,27 @@ export class VirtualFileSystem implements IVirtualFileSystem {
     const newParentPath = this.getParentPath(newPath)
 
     if (oldParentPath !== newParentPath) {
-      // Remove from old parent
+      // Remove the OLD parent's containment edge(s) — by edge id, resolved from
+      // the graph's own adjacency (the removal law: a removal never requires
+      // reading the thing being removed). This step used to be skipped as "not
+      // critical", which left the moved entity a child of BOTH directories:
+      // readdir(oldDir) kept listing it, re-creating the old path showed the
+      // name twice, and tree-walking consumers saw the file in two places.
       if (oldParentPath) {
         const oldParentId = await this.pathResolver.resolve(oldParentPath)
-        // unrelate takes the relation ID, not params - need to find and remove relation
+        const staleEdges = await this.brain.related({
-        // For now, skip unrelate as it's not critical for rename
+          from: oldParentId,
+          to: entityId,
+          type: VerbType.Contains
+        })
+        for (const edge of staleEdges) {
+          await this.brain.unrelate(edge.id)
+        }
       }
 
-      // Add to new parent
+      // Add to the new parent. The root ('/') is a REAL parent — skipping it
-      if (newParentPath && newParentPath !== '/') {
+      // orphaned a move-to-root out of readdir('/') entirely.
+      if (newParentPath) {
         const newParentId = await this.pathResolver.resolve(newParentPath)
         await this.brain.relate({
           from: newParentId,
@@ -2003,6 +2015,95 @@ export class VirtualFileSystem implements IVirtualFileSystem {
     this.triggerWatchers(newPath, 'rename')
   }
 
+  /**
+   * Reconcile every VFS entity's containment edges against its canonical
+   * `metadata.path` — the path is the truth (maintained by write/rename); the
+   * `Contains` edges are a projection of it. Heals the "cosmetic ghost" class
+   * left by pre-fix renames that added the new parent's edge without removing
+   * the old one (an entity listed in TWO directories; a re-created old path
+   * showing its name twice), plus duplicate edges from the same parent left by
+   * concurrent writers.
+   *
+   * CONSERVATIVE by design: only VFS containment edges (subtype
+   * `'vfs-contains'` or `metadata.isVFS`) are ever touched — a user's own
+   * knowledge-graph `Contains` edge between the same entities is never
+   * removed. An entity whose expected parent path has no entity is logged
+   * loudly and left alone (never orphaned further). Operator-invoked via
+   * `brain.repairIndex()`.
+   *
+   * The canonical pagination walk (not an index query) is deliberate: this is
+   * a repair op — the projections are the thing under suspicion, so the walk
+   * reads the source of truth.
+   *
+   * @returns Counts of stale edges removed and missing expected edges restored.
+   */
+  async repairContainment(): Promise<{ removed: number; restored: number }> {
+    await this.ensureInitialized()
+
+    // Pass 1: canonical walk → every VFS entity's id + path.
+    const idByPath = new Map<string, string>()
+    const vfsEntities: Array<{ id: string; path: string }> = []
+    let cursor: string | undefined
+    for (;;) {
+      const page = await (this.brain as any).storage.getNounsWithPagination({ limit: 500, cursor })
+      for (const noun of page.items) {
+        const meta = (noun as any).metadata ?? noun
+        const p = meta?.path
+        if (meta?.vfsType && typeof p === 'string') {
+          idByPath.set(p, noun.id)
+          vfsEntities.push({ id: noun.id, path: p })
+        }
+      }
+      if (!page.hasMore) break
+      cursor = page.nextCursor
+    }
+
+    let removed = 0
+    let restored = 0
+    for (const { id, path } of vfsEntities) {
+      if (path === '/') continue // the root has no parent
+      const expectedParentId = idByPath.get(this.getParentPath(path))
+      if (!expectedParentId) {
+        console.warn(
+          `[VFS] repairContainment: no entity found for parent of ${path} — leaving its edges untouched.`
+        )
+        continue
+      }
+
+      const incoming = await this.brain.related({ to: id, type: VerbType.Contains })
+      let expectedSeen = false
+      for (const edge of incoming) {
+        const isVfsEdge = edge.subtype === 'vfs-contains' || (edge.metadata as any)?.isVFS === true
+        if (!isVfsEdge) continue // never touch user knowledge edges
+        if (edge.from === expectedParentId && !expectedSeen) {
+          expectedSeen = true // keep exactly one correct edge
+          continue
+        }
+        // Stale parent (a pre-fix rename ghost) or a duplicate of the correct
+        // edge (concurrent-writer artifact) — remove it, loudly.
+        await this.brain.unrelate(edge.id)
+        removed++
+        console.warn(
+          `[VFS] repairContainment: removed ${edge.from === expectedParentId ? 'duplicate' : 'stale'} ` +
+            `containment edge ${edge.from} -> ${id} (${path})`
+        )
+      }
+      if (!expectedSeen) {
+        await this.brain.relate({
+          from: expectedParentId,
+          to: id,
+          type: VerbType.Contains,
+          subtype: 'vfs-contains',
+          metadata: { isVFS: true }
+        })
+        restored++
+        console.warn(`[VFS] repairContainment: restored missing containment edge for ${path}`)
+      }
+    }
+
+    return { removed, restored }
+  }
+
   /**
    * Copy a file or directory to a new path.
    *

tests/integration/aggregate-reserved-fields.test.ts

@@ -0,0 +1,169 @@
+/**
+ * @module tests/integration/aggregate-reserved-fields
+ * @description One field-resolution law across the whole aggregation + query
+ * surface (SELF-AGGREGATE-DELETE-DRIFT). Laws:
+ * (1) aggregates grouped by a RESERVED field (subtype) decrement on delete —
+ *     the delete-side entity view carries every reserved field, so the
+ *     decrement finds its group (counts must never drift from ground truth);
+ * (2) same for update: moving an entity between reserved-field groups
+ *     decrements the old group and increments the new one (no double-count);
+ * (3) aggregation source.where on a reserved field (subtype) FILTERS instead
+ *     of silently matching nothing;
+ * (4) removeMany refuses empty/invalid selectors loudly (bare array, empty
+ *     object, ids: []) instead of resolving as a silent no-op;
+ * (5) find() accepts both where spellings: flattened (entry.title) and
+ *     storage-shaped (metadata.entry.title) resolve to the same rows.
+ */
+import { describe, it, expect, beforeEach, afterEach } from 'vitest'
+import { Brainy } from '../../src/brainy.js'
+import { NounType } from '../../src/types/graphTypes.js'
+
+const stubEmbedding = async (text: string): Promise<number[]> => {
+  const hash = text.split('').reduce((acc, char) => acc + char.charCodeAt(0), 0)
+  return new Array(384).fill(0).map((_, i) => Math.sin(hash + i))
+}
+
+describe('aggregation + query field-resolution law', () => {
+  let brain: Brainy
+
+  beforeEach(async () => {
+    brain = new Brainy({
+      requireSubtype: false,
+      storage: { type: 'memory' as const },
+      embeddingFunction: stubEmbedding
+    })
+    await brain.init()
+  })
+
+  afterEach(async () => {
+    await brain.close()
+  })
+
+  it('reserved-field groupBy decrements on delete (the drift bug)', async () => {
+    brain.defineAggregate({
+      name: 'by_subtype',
+      source: { type: NounType.Document },
+      groupBy: ['subtype'],
+      metrics: { count: { op: 'count' } }
+    })
+
+    const ids: string[] = []
+    for (let i = 0; i < 5; i++) {
+      ids.push(
+        await brain.add({
+          data: `doc-${i}`,
+          type: NounType.Document,
+          subtype: 'note',
+          metadata: { team: 'alpha' }
+        })
+      )
+    }
+    let groups = await brain.queryAggregate('by_subtype')
+    expect(groups).toHaveLength(1)
+    expect(groups[0].groupKey).toEqual({ subtype: 'note' })
+    expect(groups[0].metrics.count).toBe(5)
+
+    await brain.remove(ids[0])
+    await brain.flush()
+
+    groups = await brain.queryAggregate('by_subtype')
+    expect(groups[0].metrics.count).toBe(4)
+    const live = await brain.find({ type: NounType.Document, limit: 100 })
+    expect(groups[0].metrics.count).toBe(live.length)
+  })
+
+  it('reserved-field groupBy moves between groups on update (no double-count)', async () => {
+    brain.defineAggregate({
+      name: 'by_subtype',
+      source: { type: NounType.Document },
+      groupBy: ['subtype'],
+      metrics: { count: { op: 'count' } }
+    })
+    const id = await brain.add({
+      data: 'doc-move',
+      type: NounType.Document,
+      subtype: 'draft'
+    })
+    await brain.update({ id, subtype: 'published' })
+
+    const groups = await brain.queryAggregate('by_subtype')
+    const byKey = Object.fromEntries(
+      groups.map((g) => [String(g.groupKey.subtype), g.metrics.count])
+    )
+    expect(byKey['published']).toBe(1)
+    // The old group must be gone or zero — never still counting the entity.
+    expect(byKey['draft'] ?? 0).toBe(0)
+  })
+
+  it('source.where on a reserved field filters instead of matching nothing', async () => {
+    brain.defineAggregate({
+      name: 'notes_only',
+      source: { type: NounType.Document, where: { subtype: 'note' } },
+      groupBy: ['team'],
+      metrics: { count: { op: 'count' } }
+    })
+    await brain.add({
+      data: 'n1',
+      type: NounType.Document,
+      subtype: 'note',
+      metadata: { team: 'alpha' }
+    })
+    await brain.add({
+      data: 'd1',
+      type: NounType.Document,
+      subtype: 'draft',
+      metadata: { team: 'alpha' }
+    })
+
+    const groups = await brain.queryAggregate('notes_only')
+    expect(groups).toHaveLength(1)
+    expect(groups[0].metrics.count).toBe(1) // the note, never the draft
+  })
+
+  it('removeMany refuses empty/invalid selectors loudly', async () => {
+    const id = await brain.add({ data: 'keep-me', type: NounType.Document })
+
+    // Bare array passed positionally — the classic silent no-op.
+    await expect(
+      brain.removeMany([id] as unknown as Parameters<typeof brain.removeMany>[0])
+    ).rejects.toThrow(/bare array/)
+    // Empty selector object.
+    await expect(
+      brain.removeMany({} as Parameters<typeof brain.removeMany>[0])
+    ).rejects.toThrow(/requires a selector/)
+    // Explicit empty id list.
+    await expect(brain.removeMany({ ids: [] })).rejects.toThrow(/ids: \[\]/)
+
+    // Nothing was deleted by any of the refused calls.
+    expect(await brain.get(id)).toBeTruthy()
+  })
+
+  it('find() accepts both flattened and metadata.-prefixed where spellings', async () => {
+    await brain.add({
+      data: 'nested-doc',
+      type: NounType.Document,
+      metadata: { entry: { title: 'T1' }, classifier: { contextHints: { vfsPath: '/n/a.md' } } }
+    })
+    await brain.flush()
+
+    const flat = await brain.find({
+      type: NounType.Document,
+      where: { 'entry.title': 'T1' },
+      limit: 10
+    })
+    const prefixed = await brain.find({
+      type: NounType.Document,
+      where: { 'metadata.entry.title': 'T1' },
+      limit: 10
+    })
+    const deepPrefixed = await brain.find({
+      type: NounType.Document,
+      where: { 'metadata.classifier.contextHints.vfsPath': '/n/a.md' },
+      limit: 10
+    })
+    expect(flat).toHaveLength(1)
+    expect(prefixed).toHaveLength(1)
+    expect(prefixed[0].id).toBe(flat[0].id)
+    expect(deepPrefixed).toHaveLength(1)
+  })
+})

tests/integration/aggregation-state-persistence.test.ts

@@ -0,0 +1,311 @@
+/**
+ * @module tests/integration/aggregation-state-persistence
+ * @description The boot-order contract for the aggregation engine. Five laws:
+ * (1) STATE ADOPTION — a reopen with an unchanged defineAggregate() adopts the
+ *     persisted state and performs NO store walk. (The pre-fix behavior: the
+ *     synchronous define always beat the async init, flagged a backfill, and
+ *     the first query wiped the just-loaded state and re-walked the whole
+ *     store — every restart, forever.)
+ * (2) SINGLE-FLIGHT + BATCH — concurrent cold queries across multiple pending
+ *     aggregates share exactly ONE store walk; a query never wipes another's
+ *     partial progress and M pending aggregates cost one enumeration, not M.
+ * (3) CHANGED DEFINITION — a real definition change still backfills, exactly.
+ * (4) PERSISTED-ONLY DEFINITIONS — an app that does not re-define at boot can
+ *     query a persisted aggregate without racing a spurious "not defined".
+ * (5) QUIET KEYS — the engine's persistence keys (__aggregation_*) are
+ *     recognized system keys: no "Unknown key format" warning at boot.
+ */
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest'
+import * as fs from 'node:fs'
+import * as os from 'node:os'
+import * as path from 'node:path'
+import { Brainy } from '../../src/index.js'
+import { NounType } from '../../src/types/graphTypes.js'
+import type { AggregateDefinition } from '../../src/types/brainy.types.js'
+import { prodLog } from '../../src/utils/logger.js'
+
+const SPENDING: AggregateDefinition = {
+  name: 'spending',
+  source: { type: NounType.Event, where: { domain: 'financial' } },
+  groupBy: ['category'],
+  metrics: {
+    total: { op: 'sum', field: 'amount' },
+    count: { op: 'count' }
+  }
+}
+
+/** Same name, different metrics — a REAL definition change (hash differs). */
+const SPENDING_CHANGED: AggregateDefinition = {
+  ...SPENDING,
+  metrics: {
+    total: { op: 'sum', field: 'amount' },
+    count: { op: 'count' },
+    average: { op: 'avg', field: 'amount' }
+  }
+}
+
+describe('aggregation state persistence — boot-order contract', () => {
+  let dir: string
+
+  beforeEach(() => {
+    dir = fs.mkdtempSync(path.join(os.tmpdir(), 'brainy-agg-persist-'))
+  })
+
+  afterEach(() => {
+    fs.rmSync(dir, { recursive: true, force: true })
+  })
+
+  const open = async (): Promise<any> => {
+    const b: any = new Brainy({
+      requireSubtype: false,
+      storage: { type: 'filesystem', path: dir },
+      silent: true
+    })
+    await b.init()
+    return b
+  }
+
+  /** Count store walks by intercepting the storage adapter's getNouns. */
+  const countWalks = (brain: any): { count: () => number } => {
+    const storage = brain.storage
+    const orig = storage.getNouns.bind(storage)
+    let calls = 0
+    storage.getNouns = async (opts: unknown) => {
+      calls++
+      return orig(opts)
+    }
+    return { count: () => calls }
+  }
+
+  const seed = async (brain: any): Promise<void> => {
+    for (let i = 0; i < 12; i++) {
+      await brain.add({
+        data: `tx ${i}`,
+        type: NounType.Event,
+        metadata: {
+          domain: 'financial',
+          category: i % 2 === 0 ? 'food' : 'transport',
+          amount: 10 + i
+        }
+      })
+    }
+  }
+
+  it('adopts persisted state on reopen with an unchanged definition — zero walks', async () => {
+    const brain1 = await open()
+    brain1.defineAggregate(SPENDING)
+    await seed(brain1)
+    const before = await brain1.queryAggregate('spending')
+    expect(before.length).toBe(2)
+    await brain1.close()
+
+    const brain2 = await open()
+    brain2.defineAggregate(SPENDING) // the standard declarative boot pattern
+    await brain2.getNounCount() // settle init paths before counting walks
+    const walks = countWalks(brain2)
+
+    const after = await brain2.queryAggregate('spending')
+
+    expect(walks.count()).toBe(0)
+    const key = (r: any) => r.groupKey.category
+    expect(
+      after.map((r: any) => [key(r), r.metrics.total, r.metrics.count]).sort()
+    ).toEqual(
+      before.map((r: any) => [key(r), r.metrics.total, r.metrics.count]).sort()
+    )
+    await brain2.close()
+  })
+
+  it('adopted state keeps accumulating: post-reopen writes land on top of it', async () => {
+    const brain1 = await open()
+    brain1.defineAggregate(SPENDING)
+    await seed(brain1)
+    await brain1.queryAggregate('spending')
+    await brain1.close()
+
+    const brain2 = await open()
+    brain2.defineAggregate(SPENDING)
+    // A write BEFORE the first query: if it lands before state adoption the
+    // engine must choose an exact rescan over adoption — either way the
+    // result must include all 13 entities.
+    await brain2.add({
+      data: 'late tx',
+      type: NounType.Event,
+      metadata: { domain: 'financial', category: 'food', amount: 100 }
+    })
+    const rows = await brain2.queryAggregate('spending')
+    const food = rows.find((r: any) => r.groupKey.category === 'food')
+    expect(food.metrics.count).toBe(7) // 6 seeded + 1 late
+    await brain2.close()
+  })
+
+  it('a changed definition still backfills — exactly once, with correct results', async () => {
+    const brain1 = await open()
+    brain1.defineAggregate(SPENDING)
+    await seed(brain1)
+    await brain1.queryAggregate('spending')
+    await brain1.close()
+
+    const brain2 = await open()
+    brain2.defineAggregate(SPENDING_CHANGED)
+    await brain2.getNounCount()
+    const walks = countWalks(brain2)
+
+    const rows = await brain2.queryAggregate('spending')
+
+    expect(walks.count()).toBe(1) // 12 entities = one page = one getNouns call
+    const food = rows.find((r: any) => r.groupKey.category === 'food')
+    expect(food.metrics.count).toBe(6)
+    expect(food.metrics.average).toBeCloseTo(food.metrics.total / 6)
+    await brain2.close()
+  })
+
+  it('concurrent cold queries across two aggregates share exactly ONE walk', async () => {
+    const brain = await open()
+    brain.defineAggregate(SPENDING)
+    brain.defineAggregate({
+      ...SPENDING,
+      name: 'by_category_count',
+      metrics: { count: { op: 'count' } }
+    })
+    await seed(brain)
+    await brain.getNounCount()
+    const walks = countWalks(brain)
+
+    const results = await Promise.all([
+      brain.queryAggregate('spending'),
+      brain.queryAggregate('by_category_count'),
+      brain.queryAggregate('spending'),
+      brain.queryAggregate('by_category_count'),
+      brain.queryAggregate('spending'),
+      brain.queryAggregate('by_category_count')
+    ])
+
+    expect(walks.count()).toBe(1) // 12 entities = one page; one walk fills both
+    for (const rows of results) {
+      const total = rows.reduce((s: number, r: any) => s + r.metrics.count, 0)
+      expect(total).toBe(12)
+    }
+
+    // Warm re-query: converged, no further walks.
+    await brain.queryAggregate('spending')
+    expect(walks.count()).toBe(1)
+    await brain.close()
+  })
+
+  it('persisted-only definitions are queryable without re-defining at boot', async () => {
+    const brain1 = await open()
+    brain1.defineAggregate(SPENDING)
+    await seed(brain1)
+    await brain1.queryAggregate('spending')
+    await brain1.close()
+
+    const brain2 = await open()
+    // NO defineAggregate — the app relies on the persisted definition.
+    const walks = countWalks(brain2)
+    const rows = await brain2.queryAggregate('spending')
+    expect(walks.count()).toBe(0) // persisted state adopted here too
+    expect(rows.length).toBe(2)
+    await brain2.close()
+  })
+
+  it('generation-mismatched persisted state is rescanned once, loudly — never adopted', async () => {
+    const brain1 = await open()
+    brain1.defineAggregate(SPENDING)
+    await seed(brain1)
+    await brain1.queryAggregate('spending')
+    await brain1.close()
+
+    // Simulate the copied-store incident class: a fact-log truncation (or an
+    // unclean shutdown) leaves the committed watermark different from the
+    // generation the flushed state was stamped with.
+    const tamper: any = await open()
+    const key = '__aggregation_state_spending__'
+    const stored = await tamper.storage.getMetadata(key)
+    expect(typeof stored.sourceGeneration).toBe('number') // the stamp is really persisted
+    await tamper.storage.saveMetadata(key, {
+      ...stored,
+      sourceGeneration: stored.sourceGeneration + 5
+    })
+    await tamper.close()
+
+    const warnSpy = vi.spyOn(prodLog, 'warn')
+    const brain2 = await open()
+    brain2.defineAggregate(SPENDING)
+    await brain2.getNounCount()
+    const walks = countWalks(brain2)
+
+    const rows = await brain2.queryAggregate('spending')
+
+    expect(walks.count()).toBe(1) // exactly ONE rescan — no silent adopt, no spin
+    const food = rows.find((r: any) => r.groupKey.category === 'food')
+    expect(food.metrics.count).toBe(6) // rescan produced exact results
+    expect(
+      warnSpy.mock.calls.some(args => String(args[0]).includes('rescanning instead of adopting'))
+    ).toBe(true) // and it said so out loud
+    warnSpy.mockRestore()
+    await brain2.close()
+  })
+
+  it('a failing walk is loud, non-destructive, and latched — never a silent retry loop', async () => {
+    // Fresh define + seeded writes: the write hooks have populated LIVE state,
+    // and the first-query rescan is still pending. The incident shape
+    // (wipe-before-scan + no try/catch + per-query re-walk) would have wiped
+    // that live state and silently re-walked on every query.
+    const brain: any = await open()
+    brain.defineAggregate(SPENDING)
+    await seed(brain)
+    expect(brain._aggregationIndex.queryAggregate({ name: 'spending' }).length).toBe(2)
+
+    const storage = brain.storage
+    const origGetNouns = storage.getNouns.bind(storage)
+    let walkAttempts = 0
+    storage.getNouns = async () => {
+      walkAttempts++
+      throw new Error('injected storage failure')
+    }
+
+    // First query: the walk fails LOUDLY with the storage error.
+    await expect(brain.queryAggregate('spending')).rejects.toThrow('injected storage failure')
+    expect(walkAttempts).toBe(1)
+
+    // Live state was NOT destroyed by the failed walk (staging was dropped).
+    expect(brain._aggregationIndex.queryAggregate({ name: 'spending' }).length).toBe(2)
+
+    // Second query inside the cooldown: instant loud failure, NO new walk.
+    await expect(brain.queryAggregate('spending')).rejects.toThrow('failure cooldown')
+    expect(walkAttempts).toBe(1)
+
+    // Heal the storage + expire the cooldown: one fresh walk succeeds exactly.
+    storage.getNouns = origGetNouns
+    brain._aggregationBackfillFailure.at = Date.now() - 60_000
+    const rows = await brain.queryAggregate('spending')
+    const food = rows.find((r: any) => r.groupKey.category === 'food')
+    expect(food.metrics.count).toBe(6)
+    await brain.close()
+  })
+
+  it('aggregation persistence keys never log "Unknown key format"', async () => {
+    const warnSpy = vi.spyOn(prodLog, 'warn')
+    const brain1 = await open()
+    brain1.defineAggregate(SPENDING)
+    await seed(brain1)
+    await brain1.queryAggregate('spending')
+    await brain1.close()
+
+    const brain2 = await open()
+    brain2.defineAggregate(SPENDING)
+    await brain2.queryAggregate('spending')
+    await brain2.close()
+
+    const offenders = warnSpy.mock.calls
+      .map(args => String(args[0]))
+      .filter(
+        msg =>
+          msg.includes('Unknown key format') &&
+          (msg.includes('__aggregation_') || msg.includes('brainy:entityIdMapper'))
+      )
+    expect(offenders).toEqual([])
+    warnSpy.mockRestore()
+  })
+})

tests/integration/background-dedup-lifecycle.test.ts

@@ -0,0 +1,85 @@
+/**
+ * @module tests/integration/background-dedup-lifecycle
+ * @description The post-import background deduplication pass (a merge-DELETE
+ * writer) obeys the same contract as the inline pass. Laws:
+ * (1) enableDeduplication:false schedules NO background pass — the brain-owned
+ *     deduplicator is never even constructed;
+ * (2) by default the pass IS scheduled, brain-owned, with an unref'd timer
+ *     (a pending pass never holds the process open);
+ * (3) repeated imports debounce into ONE pending batch on ONE instance
+ *     (per-coordinator instances used to arm one timer per import);
+ * (4) close() cancels pending work — no delete pass can fire after close.
+ */
+import { describe, it, expect, beforeEach, afterEach } from 'vitest'
+import { Brainy } from '../../src/brainy.js'
+
+const ROWS = [
+  { name: 'Alice Zephyr', role: 'engineer' },
+  { name: 'Bob Quill', role: 'writer' }
+]
+
+// Keep imports fast and deterministic — dedup scheduling is what's under test.
+const FAST = {
+  enableNeuralExtraction: false,
+  enableRelationshipInference: false,
+  enableConceptExtraction: false
+} as const
+
+// Deterministic stub embedder (hnsw-rebuild.test.ts pattern) — dedup
+// scheduling never inspects vector CONTENT, so skip the WASM model load.
+const stubEmbedding = async (text: string): Promise<number[]> => {
+  const hash = text.split('').reduce((acc, char) => acc + char.charCodeAt(0), 0)
+  const vector = new Array(384).fill(0).map((_, i) => Math.sin(hash + i))
+  return vector
+}
+
+describe('background dedup lifecycle', () => {
+  let brain: Brainy
+
+  beforeEach(async () => {
+    brain = new Brainy({
+      requireSubtype: false,
+      storage: { type: 'memory' as const },
+      embeddingFunction: stubEmbedding
+    })
+    await brain.init()
+  })
+
+  afterEach(async () => {
+    await brain.close()
+  })
+
+  it('enableDeduplication:false schedules no background pass at all', async () => {
+    await brain.import(ROWS, { ...FAST, enableDeduplication: false })
+    expect((brain as any)._backgroundDedup).toBeUndefined()
+  })
+
+  it('default schedules a brain-owned pass with an unref-ed timer', async () => {
+    await brain.import(ROWS, { ...FAST })
+    const dedup = (brain as any)._backgroundDedup
+    expect(dedup).toBeDefined()
+    expect(dedup.pendingImports.size).toBe(1)
+    const timer = dedup.debounceTimer
+    expect(timer).toBeDefined()
+    // Node timers expose hasRef(); an unref'd timer must not hold the process.
+    expect(typeof timer.hasRef).toBe('function')
+    expect(timer.hasRef()).toBe(false)
+  })
+
+  it('imports debounce into one pending batch on one brain-owned instance', async () => {
+    await brain.import(ROWS, { ...FAST })
+    const first = (brain as any)._backgroundDedup
+    await brain.import([{ name: 'Cara Vex', role: 'analyst' }], { ...FAST })
+    expect((brain as any)._backgroundDedup).toBe(first)
+    expect(first.pendingImports.size).toBe(2)
+  })
+
+  it('close() cancels pending background dedup', async () => {
+    await brain.import(ROWS, { ...FAST })
+    const dedup = (brain as any)._backgroundDedup
+    expect(dedup.debounceTimer).toBeDefined()
+    await brain.close()
+    expect(dedup.debounceTimer).toBeUndefined()
+    expect(dedup.pendingImports.size).toBe(0)
+  })
+})

tests/integration/counter-recount.test.ts

@@ -0,0 +1,122 @@
+/**
+ * @module tests/integration/counter-recount
+ * @description Counter honesty. Two laws under test:
+ * (1) REMOVAL NEVER REQUIRES RE-READING THE REMOVED RECORD — the count
+ *     decrement falls back to the caller's pre-delete read when the canonical
+ *     metadata re-read returns null (replace race / ghost), instead of being
+ *     silently skipped. The skip minted permanent inflation: adds counted,
+ *     paired removals not decremented, and Math.max(totalNounCount, scanned)
+ *     pinned the inflated scalar forever.
+ * (2) THE SANCTIONED RECOUNT — repairIndex() unconditionally recomputes and
+ *     PERSISTS every counter rollup (scalar totals + per-type maps +
+ *     type-statistics) from one canonical walk, so an already-inflated brain
+ *     is permanently corrected (survives reopen).
+ */
+import { describe, it, expect, beforeEach, afterEach } from 'vitest'
+import * as fs from 'node:fs'
+import * as os from 'node:os'
+import * as path from 'node:path'
+import { Brainy } from '../../src/index.js'
+
+/** Absolute path of one entity's `<id>` directory (or null if not present). */
+function entityDir(root: string, id: string): string | null {
+  const base = path.join(root, 'entities', 'nouns')
+  if (!fs.existsSync(base)) return null
+  for (const shard of fs.readdirSync(base)) {
+    const candidate = path.join(base, shard, id)
+    if (fs.existsSync(candidate)) return candidate
+  }
+  return null
+}
+
+describe('counter honesty — removal without re-reading + the sanctioned recount', () => {
+  let dir: string
+  let brain: any
+
+  const open = async () => {
+    const b: any = new Brainy({
+      requireSubtype: false,
+      storage: { type: 'filesystem', path: dir },
+      silent: true,
+      dimensions: 384
+    })
+    await b.init()
+    return b
+  }
+
+  beforeEach(async () => {
+    process.env.BRAINY_DETERMINISTIC_EMBEDDINGS = 'true'
+    dir = fs.mkdtempSync(path.join(os.tmpdir(), 'brainy-recount-'))
+    brain = await open()
+  })
+  afterEach(async () => {
+    await brain.close?.().catch(() => {})
+    fs.rmSync(dir, { recursive: true, force: true })
+  })
+
+  it('the counter returns to baseline across add→remove→re-create cycles (no drift)', async () => {
+    const baseline = await brain.storage.getNounCount()
+    for (let i = 0; i < 4; i++) {
+      const id = await brain.add({ data: `cycle ${i}`, type: 'document', metadata: { i } })
+      expect(await brain.storage.getNounCount()).toBe(baseline + 1)
+      await brain.remove(id)
+      expect(await brain.storage.getNounCount()).toBe(baseline)
+    }
+  })
+
+  it('deleteNoun decrements from the provided prior record when the canonical re-read is null', async () => {
+    const id = await brain.add({ data: 'to be ghosted', type: 'document', metadata: { g: 1 } })
+    await brain.flush()
+    const baseline = await brain.storage.getNounCount()
+
+    // Capture the pre-delete read (what remove() holds), then simulate the
+    // replace-race / ghost shape: the metadata leg vanishes before the delete's
+    // internal re-read.
+    const prior = await brain.storage.getNounMetadata(id)
+    expect(prior).not.toBeNull()
+    const eDir = entityDir(dir, id)!
+    for (const f of fs.readdirSync(eDir)) {
+      if (f.startsWith('metadata.json')) fs.rmSync(path.join(eDir, f))
+    }
+
+    // Without the prior record this decrement used to be silently skipped.
+    await brain.storage.deleteNoun(id, prior)
+    expect(await brain.storage.getNounCount()).toBe(baseline - 1)
+    // Full removal still holds: nothing left on disk.
+    expect(entityDir(dir, id)).toBeNull()
+  })
+
+  it('repairIndex() recounts an inflated persisted scalar over CLEAN shelves — and it survives reopen', async () => {
+    for (let i = 0; i < 3; i++) {
+      await brain.add({ data: `real ${i}`, type: 'document', metadata: { i } })
+    }
+    await brain.flush()
+    const honest = await brain.storage.getNounCount()
+    // Pagination's totalCount has its own baseline: it enumerates EVERYTHING
+    // (including the internal VFS root), while the user-facing scalar counts
+    // only public entities — so the two legitimately differ by the internals.
+    const pageHonest = (await brain.storage.getNounsWithPagination({ limit: 1000, offset: 0 })).totalCount
+
+    // Simulate the historical drift: an inflated persisted scalar (deletes whose
+    // decrement was skipped). Persist it so a reopen rehydrates the lie.
+    ;(brain.storage as any).totalNounCount = honest + 52
+    await (brain.storage as any).persistCounts()
+    await brain.close()
+    brain = await open()
+    expect(await brain.storage.getNounCount()).toBe(honest + 52) // the lie survived reopen
+
+    // The sanctioned recount — unconditional in repairIndex (no orphans needed).
+    await brain.repairIndex()
+    expect(await brain.storage.getNounCount()).toBe(honest)
+
+    // Permanently: the corrected counter survives another reopen.
+    await brain.close()
+    brain = await open()
+    expect(await brain.storage.getNounCount()).toBe(honest)
+
+    // And the paginated totalCount (the Math.max consumer) is honest too —
+    // back to ITS baseline, no longer pinned high by the inflated scalar.
+    const page = await brain.storage.getNounsWithPagination({ limit: 1000, offset: 0 })
+    expect(page.totalCount).toBe(pageHonest)
+  })
+})

tests/integration/db-mvcc.test.ts

@@ -515,7 +515,15 @@ describe('8.0 Db API — generational MVCC', () => {
       await brain.transact([{ op: 'update', id: uid('compact-e'), metadata: { v: 4 } }])
     ).release()
 
-    const recordsBefore = (await storage.listRawObjects('_generations')).length
+    // History record-sets only — the generation FACT LOG also lives under
+    // `_generations/` (at `facts/`) and is deliberately NOT reclaimed by
+    // history compaction (facts are the future canonical, not undo history).
+    const historyRecords = async (): Promise<number> =>
+      (await storage.listRawObjects('_generations')).filter(
+        (p: string) => !p.startsWith('_generations/facts/')
+      ).length
+
+    const recordsBefore = await historyRecords()
     expect(recordsBefore).toBeGreaterThan(0)
 
     // Compact while pinned: record-sets above the pin survive, pinned reads stay correct.
@@ -528,7 +536,7 @@ describe('8.0 Db API — generational MVCC', () => {
     const second = await brain.compactHistory()
     expect(first.removedGenerations + second.removedGenerations).toBeGreaterThan(0)
 
-    const recordsAfter = (await storage.listRawObjects('_generations')).length
+    const recordsAfter = await historyRecords()
     expect(recordsAfter).toBeLessThan(recordsBefore)
     expect(recordsAfter).toBe(0)
 
@@ -1272,24 +1280,32 @@ describe('8.0 Db API — generational MVCC', () => {
     await expect(reopened.asOf(1)).rejects.toBeInstanceOf(GenerationCompactedError)
   })
 
-  it('Model-B retention — setRetentionBudget drives adaptive reclaim on flush; live data intact', async () => {
+  it('Model-B retention — flush() NEVER compacts (8.9.0); adaptive reclaim runs at close()', async () => {
-    // Default brain → ADAPTIVE retention. A coordinator (e.g. cor's ResourceManager)
+    // Default brain → ADAPTIVE retention with a driven byte budget far below
-    // pushes a byte budget via setRetentionBudget(); auto-compaction on flush() reclaims
+    // the accumulated history (~13 generations of full-vector before-images).
-    // oldest history down toward it. Each update's before-image carries the full prior
+    // The 8.9.0 law: flush() is durability-only — it must not reclaim even
-    // 384-dim vector (~KBs), so ~13 generations far exceed a few-KB budget.
+    // when the budget is exceeded (reclaim-on-flush blocked production writes
-    const { brain } = await openFsBrain()
+    // for 25-191s). Maintenance runs at close(), time-bounded.
+    const { brain, dir } = await openFsBrain()
     const a = uid('ret-budget')
     await brain.add({ id: a, type: NounType.Document, data: 'v0', vector: vec(1), metadata: { v: 0 } })
     for (let v = 1; v <= 12; v++) await brain.update({ id: a, metadata: { v } })
 
     brain.setRetentionBudget(6000) // ~6 KB — well below the accumulated history
-    await brain.flush() // group-commit + adaptive auto-compaction under the budget
+    await brain.flush()
 
-    // History was reclaimed (the horizon advanced past the oldest generations)…
+    // flush() paid durability only: nothing reclaimed, all history readable.
-    expect(generationStoreOf(brain).horizon()).toBeGreaterThan(0)
+    expect(generationStoreOf(brain).horizon()).toBe(0)
-    await expect(brain.asOf(1)).rejects.toBeInstanceOf(GenerationCompactedError)
+    const probe = await brain.asOf(1) // readable proves nothing was reclaimed…
-    // …but the budget reclaims HISTORY only — the live record is untouched.
+    await probe.release() // …and MUST be released: a held pin would (correctly)
-    expect((await brain.get(a))?.metadata?.v).toBe(12)
+    // protect every newer generation through the close() compaction below.
+    await brain.close() // ← THE auto-compaction site now
+
+    // close() reclaimed under the budget; live record intact; horizon durable.
+    const { brain: reopened } = await openFsBrain(dir)
+    expect(generationStoreOf(reopened).horizon()).toBeGreaterThan(0)
+    await expect(reopened.asOf(1)).rejects.toBeInstanceOf(GenerationCompactedError)
+    expect((await reopened.get(a))?.metadata?.v).toBe(12)
   })
 
   // ==========================================================================

tests/integration/entity-tree-stamp.test.ts

@@ -0,0 +1,163 @@
+/**
+ * @module tests/integration/entity-tree-stamp
+ * @description The entity tree's FAMILY STAMP: written at flush/close with
+ * `sourceGeneration` (the committed generation the canonical tree reflects)
+ * plus rollup invariants (entity/relationship counts); verified at open by
+ * comparison — coherent on a clean close, LOUD on genuine incoherence
+ * (tampered counters), healed by repairIndex()'s recount + re-stamp. One
+ * verifier reads both member modes.
+ */
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest'
+import * as fs from 'node:fs'
+import * as os from 'node:os'
+import * as path from 'node:path'
+import {
+  Brainy,
+  readFamilyStamp,
+  verifyFamilyStamp,
+  ENTITY_TREE_STAMP_PATH,
+  type FamilyStamp
+} from '../../src/index.js'
+import { prodLog } from '../../src/utils/logger.js'
+
+describe('entity-tree family stamp', () => {
+  let dir: string
+  let brain: any
+
+  const open = async () => {
+    const b: any = new Brainy({
+      requireSubtype: false,
+      storage: { type: 'filesystem', path: dir },
+      silent: true,
+      dimensions: 384
+    })
+    await b.init()
+    return b
+  }
+
+  beforeEach(async () => {
+    process.env.BRAINY_DETERMINISTIC_EMBEDDINGS = 'true'
+    dir = fs.mkdtempSync(path.join(os.tmpdir(), 'brainy-stamp-'))
+    brain = await open()
+  })
+  afterEach(async () => {
+    vi.restoreAllMocks()
+    await brain.close?.().catch(() => {})
+    fs.rmSync(dir, { recursive: true, force: true })
+  })
+
+  it('flush() writes the stamp: rollup mode, counts + sourceGeneration match live state', async () => {
+    for (let i = 0; i < 3; i++) await brain.add({ data: `s${i}`, type: 'document', metadata: { i } })
+    await brain.flush()
+
+    const stamp = (await readFamilyStamp(brain.storage, ENTITY_TREE_STAMP_PATH)) as FamilyStamp
+    expect(stamp).not.toBeNull()
+    expect(stamp.family).toBe('entity-tree')
+    expect(stamp.members.mode).toBe('rollup')
+    const invariants = (stamp.members as any).invariants
+    expect(invariants.nounCount).toBe(await brain.storage.getNounCount())
+    expect(invariants.verbCount).toBe(await brain.storage.getVerbCount())
+    expect(stamp.sourceGeneration).toBe(brain.generation())
+    expect(stamp.generation).toBeGreaterThanOrEqual(1)
+  })
+
+  it('a cleanly-closed store reopens COHERENT (no incoherence warning)', async () => {
+    await brain.add({ data: 'clean', type: 'document', metadata: {} })
+    await brain.close()
+
+    const warn = vi.spyOn(prodLog, 'warn')
+    brain = await open()
+    const stampWarnings = warn.mock.calls.filter((c) => String(c[0]).includes('entity-tree stamp'))
+    expect(stampWarnings).toEqual([])
+  })
+
+  it('tampered counters surface as INCOHERENT at open; repairIndex() heals + re-stamps', async () => {
+    for (let i = 0; i < 3; i++) await brain.add({ data: `t${i}`, type: 'document', metadata: { i } })
+    await brain.close()
+
+    // Simulate counter drift AFTER the stamp was written: inflate the
+    // persisted scalar the way the historical decrement-skip did.
+    brain = await open()
+    ;(brain.storage as any).totalNounCount += 52
+    await (brain.storage as any).persistCounts()
+    await brain.close()
+    // The close boundary re-stamps with the inflated counter — so tamper the
+    // STAMP instead for a deterministic mismatch: stamped counts differ from
+    // the (inflated) live ones at the NEXT open only if the stamp is older.
+    // Rewrite the stamp with the honest counts + current sourceGeneration.
+    const raw = JSON.parse(
+      require('node:zlib')
+        .gunzipSync(fs.readFileSync(path.join(dir, `${ENTITY_TREE_STAMP_PATH}.gz`)))
+        .toString('utf-8')
+    ) as FamilyStamp
+    const honest = { ...raw }
+    ;(honest.members as any).invariants.nounCount -= 52
+    fs.writeFileSync(
+      path.join(dir, `${ENTITY_TREE_STAMP_PATH}.gz`),
+      require('node:zlib').gzipSync(JSON.stringify(honest))
+    )
+
+    const warn = vi.spyOn(prodLog, 'warn')
+    brain = await open()
+    const incoherent = warn.mock.calls.filter((c) => String(c[0]).includes('INCOHERENT'))
+    expect(incoherent.length).toBeGreaterThanOrEqual(1)
+    expect(String(incoherent[0][0])).toMatch(/nounCount/)
+
+    // The heal: recount from canonical + re-stamp → next open is quiet.
+    await brain.repairIndex()
+    await brain.close()
+    const warn2 = vi.spyOn(prodLog, 'warn')
+    brain = await open()
+    const stillIncoherent = warn2.mock.calls.filter((c) => String(c[0]).includes('INCOHERENT'))
+    expect(stillIncoherent).toEqual([])
+  })
+
+  it('the one verifier handles both member modes', () => {
+    const rollup: FamilyStamp = {
+      family: 'x',
+      generation: 1,
+      committedAt: new Date().toISOString(),
+      sourceGeneration: 5,
+      members: { mode: 'rollup', invariants: { nounCount: 10 } }
+    }
+    expect(verifyFamilyStamp(rollup, 5, { nounCount: 10 })).toEqual({ state: 'coherent' })
+    expect(verifyFamilyStamp(rollup, 5, { nounCount: 11 }).state).toBe('incoherent')
+    expect(verifyFamilyStamp(rollup, 9, { nounCount: 10 })).toEqual({
+      state: 'behind',
+      stampSource: 5,
+      head: 9
+    })
+    expect(verifyFamilyStamp(rollup, 3, { nounCount: 10 }).state).toBe('incoherent') // ahead of head
+    expect(verifyFamilyStamp(null, 5, {})).toEqual({ state: 'absent' })
+
+    const enumerated: FamilyStamp = {
+      family: 'y',
+      generation: 1,
+      committedAt: new Date().toISOString(),
+      sourceGeneration: 2,
+      members: { mode: 'enumerated', files: [{ path: 'a.bin', bytes: 128 }] }
+    }
+    expect(verifyFamilyStamp(enumerated, 2, { 'a.bin': 128 })).toEqual({ state: 'coherent' })
+    expect(verifyFamilyStamp(enumerated, 2, { 'a.bin': 64 }).state).toBe('incoherent')
+    expect(verifyFamilyStamp(enumerated, 2, {}).state).toBe('incoherent') // missing member
+
+    // Rollup invariants may be STRING fingerprints (e.g. a per-tree SHA-256):
+    // strict equality either way; a type mismatch reads as incoherence.
+    const fingerprinted: FamilyStamp = {
+      family: 'z',
+      generation: 1,
+      committedAt: new Date().toISOString(),
+      sourceGeneration: 3,
+      members: { mode: 'rollup', invariants: { treeDigest: 'abc123', rows: 42 } }
+    }
+    expect(verifyFamilyStamp(fingerprinted, 3, { treeDigest: 'abc123', rows: 42 })).toEqual({
+      state: 'coherent'
+    })
+    expect(verifyFamilyStamp(fingerprinted, 3, { treeDigest: 'deadbeef', rows: 42 }).state).toBe(
+      'incoherent'
+    )
+    expect(verifyFamilyStamp(fingerprinted, 3, { treeDigest: 'abc123', rows: '42' }).state).toBe(
+      'incoherent' // type mismatch never passes
+    )
+  })
+})

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

@@ -0,0 +1,125 @@
+/**
+ * @module tests/integration/fact-log-contracts
+ * @description Pinned durability + stability contracts for the fact log.
+ *
+ * (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.
+ *
+ * (2) SCAN STABILITY UNDER ROTATION: a scan handle opened before segment
+ *     rotation yields exactly its snapshot — byte-identical facts, no gaps,
+ *     no duplicates, and no bleed-in of facts appended after the snapshot.
+ *     (The reclaim-during-scan variant lands with fact-log compaction, which
+ *     does not exist yet — segments only rotate today, never reclaim.)
+ */
+import { describe, it, expect, beforeEach, afterEach } from 'vitest'
+import * as fs from 'node:fs'
+import * as os from 'node:os'
+import * as path from 'node:path'
+import { Brainy, type CommitFact } from '../../src/index.js'
+import { MemoryStorage } from '../../src/storage/adapters/memoryStorage.js'
+import { FactLog, type FactLogStorage } from '../../src/db/factLog.js'
+
+describe('fsync-before-ack contract (fact durability at the ack boundary)', () => {
+  let dir: string
+  let brain: any
+
+  const open = async () => {
+    const b: any = new Brainy({
+      requireSubtype: false,
+      storage: { type: 'filesystem', path: dir },
+      silent: true,
+      dimensions: 384
+    })
+    await b.init()
+    return b
+  }
+
+  beforeEach(async () => {
+    process.env.BRAINY_DETERMINISTIC_EMBEDDINGS = 'true'
+    dir = fs.mkdtempSync(path.join(os.tmpdir(), 'brainy-factack-'))
+    brain = await open()
+  })
+  afterEach(async () => {
+    await brain.close?.().catch(() => {})
+    fs.rmSync(dir, { recursive: true, force: true })
+  })
+
+  it('transact(): the fact is durable the moment the ack returns (kill-after-ack safe)', async () => {
+    const receipt = await brain.transact([
+      { op: 'add', type: 'document', metadata: { durable: 1 }, data: 'ack-at-commit' }
+    ])
+    // Abrupt end: no flush(), no close() — a new instance reads only disk.
+    brain = await open()
+    const facts: CommitFact[] = []
+    for await (const b of brain.scanFacts()!.batches()) facts.push(...b.facts)
+    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 () => {
+    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.
+    brain = await open()
+    const facts: CommitFact[] = []
+    for await (const b of brain.scanFacts()!.batches()) facts.push(...b.facts)
+    expect(facts.some((f) => f.generation === ackedHead)).toBe(true)
+  })
+})
+
+describe('scan stability under rotation (the snapshot contract)', () => {
+  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),
+        // Padding makes each frame ~1KB so a small rotateBytes forces rotations.
+        record: { metadata: { noun: 'document', pad: 'x'.repeat(900), g: generation }, vector: null }
+      }
+    ]
+  })
+
+  it('a scan opened before rotations yields its exact snapshot — no gaps, dups, or bleed-in', async () => {
+    const mem: any = new MemoryStorage()
+    await mem.init()
+    const log = new FactLog(mem as FactLogStorage, { rotateBytes: 4096 }) // ~4 facts per segment
+    await log.open(0)
+    for (let g = 1; g <= 10; g++) await log.append(fact(g))
+    await log.sync()
+
+    // Open the snapshot, THEN keep appending — forcing further rotations.
+    const scan = log.scanFacts()
+    expect(scan.headGeneration).toBe(10)
+    for (let g = 11; g <= 25; g++) await log.append(fact(g))
+    await log.sync()
+    expect(log.headGeneration()).toBe(25)
+
+    const seen: number[] = []
+    for await (const batch of scan.batches()) {
+      for (const f of batch.facts) seen.push(f.generation)
+    }
+    // Exactly the snapshot: 1..10 in order, nothing appended-after bleeds in.
+    expect(seen).toEqual([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
+    expect(scan.summary().factsYielded).toBe(10)
+
+    // And a fresh scan sees everything, across all rotated segments.
+    const all: number[] = []
+    for await (const batch of log.scanFacts().batches()) {
+      for (const f of batch.facts) all.push(f.generation)
+    }
+    expect(all).toEqual(Array.from({ length: 25 }, (_, i) => i + 1))
+    expect(log.segmentPaths().length).toBeGreaterThanOrEqual(2) // rotations actually happened
+  })
+})

tests/integration/fact-log-dual-write.test.ts

@@ -0,0 +1,219 @@
+/**
+ * @module tests/integration/fact-log-dual-write
+ * @description The generation fact log end-to-end through real commits: every
+ * committed generation (single-op AND transact) appends its AFTER-IMAGE fact
+ * at the commit point; removals append body-less tombstones; an aborted
+ * transaction leaves no fact; facts survive reopen and continue monotonically;
+ * the scan surface (brain.scanFacts) carries the frozen telemetry shape; and
+ * the fact-log namespace is protected against prefix-nuking.
+ */
+import { describe, it, expect, beforeEach, afterEach } from 'vitest'
+import * as fs from 'node:fs'
+import * as os from 'node:os'
+import * as path from 'node:path'
+import { Brainy, ProtectedArtifactError, type CommitFact } from '../../src/index.js'
+
+async function allFacts(brain: any): Promise<CommitFact[]> {
+  const scan = brain.scanFacts()
+  expect(scan).not.toBeNull()
+  const facts: CommitFact[] = []
+  for await (const batch of scan!.batches()) facts.push(...batch.facts)
+  return facts
+}
+
+describe('fact log dual-write (memory adapter)', () => {
+  let brain: any
+
+  beforeEach(async () => {
+    process.env.BRAINY_DETERMINISTIC_EMBEDDINGS = 'true'
+    brain = new Brainy({ requireSubtype: false, storage: { type: 'memory' }, silent: true, dimensions: 384 })
+    await brain.init()
+  })
+  afterEach(async () => {
+    await brain.close?.().catch(() => {})
+  })
+
+  it('every single-op write appends its after-image fact; a remove appends a tombstone', async () => {
+    const id = await brain.add({ data: 'first', type: 'document', metadata: { rev: 1 } })
+    await brain.update({ id, metadata: { rev: 2 } })
+    await brain.remove(id)
+
+    const facts = await allFacts(brain)
+    // add + update + remove each committed a generation (the remove may span
+    // cascade ops but is ONE generation). Facts are monotonic.
+    const gens = facts.map((f) => f.generation)
+    expect([...gens].sort((a, b) => a - b)).toEqual(gens)
+    expect(facts.length).toBeGreaterThanOrEqual(3)
+
+    // The add fact carries the after-image of the new entity.
+    const addFact = facts.find((f) => f.ops.some((op) => op.id === id && op.record !== null))
+    expect(addFact).toBeDefined()
+
+    // The remove fact carries a body-less tombstone for the id.
+    const removeFact = facts[facts.length - 1]
+    const tombstone = removeFact.ops.find((op) => op.id === id)
+    expect(tombstone).toBeDefined()
+    expect(tombstone!.record).toBeNull()
+    expect(tombstone!.kind).toBe('noun')
+  })
+
+  it('the update fact holds the NEW state (after-image, not before)', async () => {
+    const id = await brain.add({ data: 'versioned', type: 'document', metadata: { v: 'old' } })
+    await brain.update({ id, metadata: { v: 'new' } })
+
+    const facts = await allFacts(brain)
+    const updateFact = facts[facts.length - 1]
+    const op = updateFact.ops.find((o) => o.id === id)!
+    expect(op.record).not.toBeNull()
+    expect((op.record!.metadata as any).v).toBe('new')
+  })
+
+  it('a transact commits ONE fact carrying all its ops, with meta', async () => {
+    const receipt = await brain.transact(
+      [
+        { op: 'add', type: 'document', metadata: { part: 1 }, data: 'a' },
+        { op: 'add', type: 'document', metadata: { part: 2 }, data: 'b' }
+      ],
+      { meta: { source: 'batch-import' } }
+    )
+
+    const facts = await allFacts(brain)
+    const txFact = facts.find((f) => f.generation === receipt.generation)
+    expect(txFact).toBeDefined()
+    expect(txFact!.ops.filter((op) => op.kind === 'noun').length).toBeGreaterThanOrEqual(2)
+    expect(txFact!.meta).toEqual({ source: 'batch-import' })
+  })
+
+  it('an aborted transact leaves NO fact (absent = never committed)', async () => {
+    const id = await brain.add({ data: 'cas target', type: 'document', metadata: { n: 1 } })
+    const before = (await allFacts(brain)).length
+
+    await expect(
+      brain.transact([{ op: 'update', id, ifRev: 999, metadata: { n: 2 } }])
+    ).rejects.toThrow()
+
+    const after = await allFacts(brain)
+    expect(after.length).toBe(before)
+  })
+
+  it('fact generations line up with the transaction log', async () => {
+    await brain.add({ data: 'x', type: 'document', metadata: {} })
+    await brain.add({ data: 'y', type: 'document', metadata: {} })
+    await brain.flush()
+
+    const facts = await allFacts(brain)
+    const logGens = new Set((await brain.transactionLog()).map((e: any) => e.generation))
+    for (const f of facts) {
+      expect(logGens.has(f.generation)).toBe(true)
+    }
+  })
+
+  it('the storage fact-scan capability serves a provider holding only `storage`', async () => {
+    // An index provider receives `storage` — never the brain — and reaches the
+    // fact log through the host-wired capability (it must never construct its
+    // own fact-log reader: the log's open path is writer-side).
+    const id = await brain.add({ data: 'via storage', type: 'document', metadata: { s: 1 } })
+    await brain.remove(id)
+
+    const storage = brain.storage
+    expect(typeof storage.scanFacts).toBe('function')
+    expect(storage.factLogHeadGeneration()).toBe(brain.scanFacts()!.headGeneration)
+
+    const viaStorage: CommitFact[] = []
+    for await (const b of storage.scanFacts()!.batches()) viaStorage.push(...b.facts)
+    const viaBrain: CommitFact[] = []
+    for await (const b of brain.scanFacts()!.batches()) viaBrain.push(...b.facts)
+    expect(viaStorage.map((f) => f.generation)).toEqual(viaBrain.map((f) => f.generation))
+    expect(storage.factSegmentPaths()).toEqual(brain.factSegmentPaths())
+  })
+
+  it('scan telemetry carries the frozen shape end-to-end', async () => {
+    for (let i = 0; i < 5; i++) await brain.add({ data: `t${i}`, type: 'document', metadata: { i } })
+
+    const scan = brain.scanFacts({ batchSize: 2 })!
+    expect(scan.headGeneration).toBeGreaterThanOrEqual(5)
+    expect(scan.approxFactCount).toBeGreaterThanOrEqual(5)
+    let batches = 0
+    for await (const b of scan.batches()) {
+      batches++
+      expect(b.factCount).toBe(b.facts.length)
+      expect(b.firstGeneration).toBe(b.facts[0].generation)
+      expect(b.lastGeneration).toBe(b.facts[b.facts.length - 1].generation)
+      expect(b.byteSize).toBeGreaterThan(0)
+      expect(typeof b.segmentId).toBe('string')
+    }
+    expect(batches).toBeGreaterThan(1)
+    expect(scan.summary().factsYielded).toBe(scan.approxFactCount)
+  })
+})
+
+describe('fact log dual-write (filesystem adapter — durability + protection)', () => {
+  let dir: string
+  let brain: any
+
+  const open = async () => {
+    const b: any = new Brainy({
+      requireSubtype: false,
+      storage: { type: 'filesystem', path: dir },
+      silent: true,
+      dimensions: 384
+    })
+    await b.init()
+    return b
+  }
+
+  beforeEach(async () => {
+    process.env.BRAINY_DETERMINISTIC_EMBEDDINGS = 'true'
+    dir = fs.mkdtempSync(path.join(os.tmpdir(), 'brainy-factlog-'))
+    brain = await open()
+  })
+  afterEach(async () => {
+    await brain.close?.().catch(() => {})
+    fs.rmSync(dir, { recursive: true, force: true })
+  })
+
+  it('facts survive close + reopen and appends continue monotonically', async () => {
+    const id = await brain.add({ data: 'persist me', type: 'document', metadata: { k: 1 } })
+    await brain.remove(id)
+    await brain.close()
+
+    brain = await open()
+    const facts = await allFacts(brain)
+    expect(facts.length).toBeGreaterThanOrEqual(2)
+    const headBefore = facts[facts.length - 1].generation
+
+    await brain.add({ data: 'after reopen', type: 'document', metadata: { k: 2 } })
+    const facts2 = await allFacts(brain)
+    expect(facts2[facts2.length - 1].generation).toBeGreaterThan(headBefore)
+  })
+
+  it('the fact segments exist on disk under _generations/facts/ with zero-padded names', async () => {
+    await brain.add({ data: 'on disk', type: 'document', metadata: {} })
+    await brain.flush()
+    const factsDir = path.join(dir, '_generations', 'facts')
+    const files = fs.readdirSync(factsDir)
+    // The manifest rides the store's JSON object discipline (gzip on disk).
+    expect(files.some((f) => f.startsWith('manifest.json'))).toBe(true)
+    const segs = files.filter((f) => /^seg-\d{20}\.bfl$/.test(f))
+    expect(segs.length).toBeGreaterThanOrEqual(1)
+  })
+
+  it('the fact-log namespace is PROTECTED: a prefix-nuke is refused', async () => {
+    await brain.add({ data: 'protected', type: 'document', metadata: {} })
+    await expect(brain.storage.removeRawPrefix('_generations/facts')).rejects.toBeInstanceOf(
+      ProtectedArtifactError
+    )
+    // Per-generation history cleanup remains unaffected (no false intersect).
+    await expect(brain.storage.removeRawPrefix('_generations/999999')).resolves.toBeUndefined()
+  })
+
+  it('transact facts are durable-on-return (no flush needed before reopen)', async () => {
+    const receipt = await brain.transact([
+      { op: 'add', type: 'document', metadata: { durable: true }, data: 'tx' }
+    ])
+    // Simulate an abrupt end: no flush(), no close() — reopen from disk.
+    brain = await open()
+    const facts = await allFacts(brain)
+    expect(facts.some((f) => f.generation === receipt.generation)).toBe(true)
+  })
+})

tests/integration/graph-audit.test.ts

@@ -0,0 +1,164 @@
+/**
+ * @module tests/integration/graph-audit
+ * @description brain.auditGraph() — the read-only graph-truth instrument.
+ * Laws under test:
+ * (1) a healthy brain audits COHERENT: every canonical verb is returned by the
+ *     read path of its source, endpoints exist, no ghosts;
+ * (2) design-hidden edges (internal/system visibility) are counted separately
+ *     and never misclassified as index loss;
+ * (3) a verb whose endpoint entity was destroyed at the storage layer (the
+ *     scar class) is flagged as a dangling endpoint, loudly;
+ * (4) the classification core flags present-but-invisible and ghost edges
+ *     exactly (exercised via injected seams — manufacturing a genuinely stale
+ *     adjacency index end-to-end would require corrupting internals the
+ *     public API rightly refuses to corrupt).
+ */
+import { describe, it, expect, beforeEach, afterEach } from 'vitest'
+import * as fs from 'node:fs'
+import * as os from 'node:os'
+import * as path from 'node:path'
+import { Brainy } from '../../src/index.js'
+import { NounType, VerbType } from '../../src/types/graphTypes.js'
+import { runGraphAudit, type AuditVerbRecord } from '../../src/graph/graphAudit.js'
+
+describe('brain.auditGraph() — graph-truth audit', () => {
+  let dir: string
+  let brain: any
+
+  beforeEach(async () => {
+    dir = fs.mkdtempSync(path.join(os.tmpdir(), 'brainy-graph-audit-'))
+    brain = new Brainy({
+      requireSubtype: false,
+      storage: { type: 'filesystem', path: dir },
+      silent: true
+    })
+    await brain.init()
+  })
+
+  afterEach(async () => {
+    await brain.close().catch(() => {})
+    fs.rmSync(dir, { recursive: true, force: true })
+  })
+
+  async function seedGraph(): Promise<{ ids: string[]; verbIds: string[] }> {
+    const ids: string[] = []
+    for (let i = 0; i < 5; i++) {
+      ids.push(
+        await brain.add({
+          data: `entity ${i}`,
+          type: NounType.Concept,
+          metadata: { n: i }
+        })
+      )
+    }
+    const verbIds: string[] = []
+    verbIds.push(await brain.relate({ from: ids[0], to: ids[1], type: VerbType.RelatedTo }))
+    verbIds.push(await brain.relate({ from: ids[0], to: ids[2], type: VerbType.Contains }))
+    verbIds.push(await brain.relate({ from: ids[1], to: ids[3], type: VerbType.DependsOn }))
+    verbIds.push(await brain.relate({ from: ids[3], to: ids[4], type: VerbType.RelatedTo }))
+    return { ids, verbIds }
+  }
+
+  it('audits a healthy brain as coherent, with exact counts', async () => {
+    const { ids } = await seedGraph()
+    const report = await brain.auditGraph()
+
+    expect(report.coherent).toBe(true)
+    expect(report.verbsInCanonical).toBe(4)
+    expect(report.entitiesInCanonical).toBeGreaterThanOrEqual(ids.length) // VFS root etc. may add system nouns
+    expect(report.sourcesChecked).toBe(3) // ids[0], ids[1], ids[3]
+    expect(report.missingFromReadsCount).toBe(0)
+    expect(report.danglingEndpointsCount).toBe(0)
+    expect(report.readOnlyCount).toBe(0)
+    expect(report.truncatedExamples).toBe(false)
+  })
+
+  it('counts design-hidden edges separately and stays coherent', async () => {
+    const { ids } = await seedGraph()
+    await brain.relate({
+      from: ids[2],
+      to: ids[4],
+      type: VerbType.RelatedTo,
+      visibility: 'internal'
+    })
+
+    const report = await brain.auditGraph()
+    expect(report.coherent).toBe(true) // hidden-by-design is NOT a discrepancy
+    expect(report.verbsInCanonical).toBe(5)
+    expect(report.visibilityHiddenCount).toBeGreaterThanOrEqual(1)
+  })
+
+  it('flags a destroyed endpoint as a dangling verb (the scar class)', async () => {
+    const { ids } = await seedGraph()
+    // Destroy ids[4] at the STORAGE layer (bypassing remove(), which would
+    // also delete its verbs) — the historical partial-delete scar shape.
+    await brain.storage.deleteNoun(ids[4])
+
+    const report = await brain.auditGraph()
+    expect(report.coherent).toBe(false)
+    expect(report.danglingEndpointsCount).toBe(1)
+    expect(report.danglingEndpoints[0].to).toBe(ids[4])
+    expect(report.danglingEndpoints[0].missingEnd).toBe('to')
+  })
+})
+
+describe('runGraphAudit classification core (injected seams)', () => {
+  const verb = (id: string, from: string, to: string): AuditVerbRecord => ({
+    id,
+    type: 'relatedTo',
+    sourceId: from,
+    targetId: to
+  })
+
+  const deps = (opts: {
+    nouns: string[]
+    verbs: AuditVerbRecord[]
+    reads: Record<string, string[]> // sourceId -> verb ids the read path returns
+  }) => ({
+    eachNounId: async (consume: (id: string) => void) => {
+      for (const id of opts.nouns) consume(id)
+    },
+    eachVerb: async (consume: (v: AuditVerbRecord) => void) => {
+      for (const v of opts.verbs) consume(v)
+    },
+    readRelationsFrom: async (sourceId: string) =>
+      (opts.reads[sourceId] ?? []).map((id) => ({ id }))
+  })
+
+  it('flags a canonical verb the read path omits — present but invisible', async () => {
+    const report = await runGraphAudit(
+      deps({
+        nouns: ['A', 'B', 'C'],
+        verbs: [verb('v1', 'A', 'B'), verb('v2', 'A', 'C')],
+        reads: { A: ['v1'] } // v2 exists canonically but reads miss it
+      })
+    )
+    expect(report.coherent).toBe(false)
+    expect(report.missingFromReadsCount).toBe(1)
+    expect(report.missingFromReads[0].verbId).toBe('v2')
+  })
+
+  it('flags a read-path edge with no canonical record — a ghost', async () => {
+    const report = await runGraphAudit(
+      deps({
+        nouns: ['A', 'B'],
+        verbs: [verb('v1', 'A', 'B')],
+        reads: { A: ['v1', 'ghost-9'] }
+      })
+    )
+    expect(report.coherent).toBe(false)
+    expect(report.readOnlyCount).toBe(1)
+    expect(report.readOnlyVerbIds).toEqual(['ghost-9'])
+  })
+
+  it('caps example lists but keeps counts exact, and says so', async () => {
+    const verbs = Array.from({ length: 10 }, (_, i) => verb(`v${i}`, 'A', 'B'))
+    const report = await runGraphAudit(
+      deps({ nouns: ['A', 'B'], verbs, reads: { A: [] } }),
+      { maxExamples: 3 }
+    )
+    expect(report.missingFromReadsCount).toBe(10)
+    expect(report.missingFromReads.length).toBe(3)
+    expect(report.truncatedExamples).toBe(true)
+  })
+})

tests/integration/history-repacking.test.ts

@@ -0,0 +1,186 @@
+/**
+ * @module tests/integration/history-repacking
+ * @description The D1+D3 two-tier history lifecycle end-to-end on a real
+ * brain. Laws: (1) repacking is RE-REPRESENTATION — after folding, every
+ * asOf() read below the fold boundary answers exactly as before, across a
+ * cold reopen; (2) folded per-generation directories are physically gone
+ * (the file-count cure is real, not cosmetic); (3) repack + reclaim compose:
+ * bounded retention after repacking drops whole segments and asOf below the
+ * horizon throws GenerationCompactedError; (4) repackHistory is explicit
+ * API and time-bounded (spent budget = consistent no-op).
+ *
+ * Uses a tiny REPACK_LIVE_WINDOW override so a small history has a cold
+ * tier at all (the production window is 1024).
+ */
+import { describe, it, expect, afterEach } from 'vitest'
+import * as fs from 'node:fs'
+import * as path from 'node:path'
+import * as os from 'node:os'
+import { Brainy } from '../../src/brainy.js'
+import { NounType } from '../../src/types/graphTypes.js'
+import { GenerationStore } from '../../src/db/generationStore.js'
+import { GenerationCompactedError } from '../../src/db/errors.js'
+import { SEGMENTS_PREFIX } from '../../src/db/generationSegments.js'
+
+const stub = async (text: string): Promise<number[]> => {
+  const h = text.split('').reduce((a, c) => a + c.charCodeAt(0), 0)
+  return new Array(384).fill(0).map((_, i) => Math.sin(h + i))
+}
+
+const openBrain = async (dir: string): Promise<Brainy> => {
+  const brain = new Brainy({
+    requireSubtype: false,
+    storage: { type: 'filesystem', path: dir },
+    embeddingFunction: stub
+  })
+  await brain.init()
+  return brain
+}
+
+describe('history repacking — the two-tier lifecycle', () => {
+  const dirs: string[] = []
+  const tempDir = (): string => {
+    const d = fs.mkdtempSync(path.join(os.tmpdir(), 'brainy-repack-'))
+    dirs.push(d)
+    return d
+  }
+  const originalWindow = GenerationStore.REPACK_LIVE_WINDOW
+
+  afterEach(() => {
+    ;(GenerationStore as any).REPACK_LIVE_WINDOW = originalWindow
+    for (const d of dirs.splice(0)) {
+      try {
+        fs.rmSync(d, { recursive: true, force: true })
+      } catch {
+        /* best effort */
+      }
+    }
+  })
+
+  it('repack preserves every historical read across cold reopen; folded dirs are gone', async () => {
+    ;(GenerationStore as any).REPACK_LIVE_WINDOW = 3
+    const dir = tempDir()
+    const brain = await openBrain(dir)
+
+    const id = await brain.add({
+      data: 'versioned-entity',
+      type: NounType.Document,
+      metadata: { v: 0 }
+    })
+    for (let v = 1; v <= 10; v++) await brain.update({ id, metadata: { v } })
+    await brain.flush()
+
+    // Ground truth BEFORE repacking: capture asOf views for early generations.
+    const before: Record<number, number> = {}
+    for (const g of [2, 4, 6]) {
+      const db = await brain.asOf(g)
+      before[g] = (await db.get(id))?.metadata?.v as number
+      await db.release()
+    }
+
+    const result = await brain.repackHistory()
+    expect(result.foldedGenerations).toBeGreaterThan(0)
+    expect(result.segmentsCreated).toBeGreaterThan(0)
+
+    // The folded per-generation directories are PHYSICALLY gone…
+    const genDirs = fs
+      .readdirSync(path.join(dir, '_generations'), { withFileTypes: true })
+      .filter((e) => e.isDirectory() && /^\d+$/.test(e.name)).length
+    expect(genDirs).toBeLessThanOrEqual(4) // live window (3) + at most the newest
+    // …and the segment tier exists (the filesystem adapter stores objects
+    // gzipped, so the manifest may live at either spelling).
+    const segDir = path.join(dir, SEGMENTS_PREFIX)
+    expect(
+      fs.existsSync(path.join(segDir, 'manifest.json')) ||
+        fs.existsSync(path.join(segDir, 'manifest.json.gz'))
+    ).toBe(true)
+    expect(fs.readdirSync(segDir).some((f) => f.endsWith('.bgs'))).toBe(true)
+
+    // Same asOf answers from the packed tier, same process…
+    for (const g of [2, 4, 6]) {
+      const db = await brain.asOf(g)
+      expect((await db.get(id))?.metadata?.v).toBe(before[g])
+      await db.release()
+    }
+    await brain.close()
+
+    // …and across a COLD REOPEN (manifest discovery, no live dirs to list).
+    const reopened = await openBrain(dir)
+    for (const g of [2, 4, 6]) {
+      const db = await reopened.asOf(g)
+      expect((await db.get(id))?.metadata?.v).toBe(before[g])
+      await db.release()
+    }
+    expect((await reopened.get(id))?.metadata?.v).toBe(10) // live state untouched
+    await reopened.close()
+  })
+
+  it('repack + bounded reclaim compose: whole segments drop, horizon is loud', async () => {
+    ;(GenerationStore as any).REPACK_LIVE_WINDOW = 2
+    const dir = tempDir()
+    const brain = await openBrain(dir)
+    const id = await brain.add({ data: 'reclaim-probe', type: NounType.Document, metadata: { v: 0 } })
+    for (let v = 1; v <= 8; v++) await brain.update({ id, metadata: { v } })
+    await brain.flush()
+    await brain.repackHistory()
+
+    // Reclaim down to the 3 newest generations — packed segments below the
+    // horizon drop whole; asOf below throws loudly.
+    const res = await brain.compactHistory({ maxGenerations: 3 })
+    expect(res.removedGenerations).toBeGreaterThan(0)
+    await expect(brain.asOf(1)).rejects.toBeInstanceOf(GenerationCompactedError)
+    expect((await brain.get(id))?.metadata?.v).toBe(8)
+    await brain.close()
+  })
+
+  it('generationDigest: reopen-stable, divergence-sensitive, loud below the horizon', async () => {
+    ;(GenerationStore as any).REPACK_LIVE_WINDOW = 2
+    const dir = tempDir()
+    const brain = await openBrain(dir)
+    const id = await brain.add({ data: 'digest-probe', type: NounType.Document, metadata: { v: 0 } })
+    for (let v = 1; v <= 6; v++) await brain.update({ id, metadata: { v } })
+    await brain.flush()
+    await brain.repackHistory()
+
+    const gen = brain.generation()
+    const atHead = await brain.generationDigest(gen)
+    const atMid = await brain.generationDigest(3)
+    expect(atHead).toMatch(/^[0-9a-f]{8}$/)
+    expect(atMid).not.toBe(atHead) // more history ⇒ different digest
+    await brain.close()
+
+    // Reopen-stable: same history, same digests (packed prefix stability).
+    const reopened = await openBrain(dir)
+    expect(await reopened.generationDigest(gen)).toBe(atHead)
+    expect(await reopened.generationDigest(3)).toBe(atMid)
+
+    // New history diverges the head digest.
+    await reopened.update({ id, metadata: { v: 7 } })
+    await reopened.flush()
+    expect(await reopened.generationDigest(reopened.generation())).not.toBe(atHead)
+
+    // Below the horizon: LOUD, never a silent pin of reclaimed history.
+    await reopened.compactHistory({ maxGenerations: 2 })
+    await expect(reopened.generationDigest(1)).rejects.toBeInstanceOf(GenerationCompactedError)
+    await reopened.close()
+  })
+
+  it('a spent time budget is a consistent no-op; the next pass resumes', async () => {
+    ;(GenerationStore as any).REPACK_LIVE_WINDOW = 2
+    const dir = tempDir()
+    const brain = await openBrain(dir)
+    const id = await brain.add({ data: 'budget-probe', type: NounType.Document, metadata: { v: 0 } })
+    for (let v = 1; v <= 6; v++) await brain.update({ id, metadata: { v } })
+    await brain.flush()
+
+    const bounded = await brain.repackHistory({ timeBudgetMs: 0 })
+    expect(bounded).toEqual({ foldedGenerations: 0, segmentsCreated: 0 })
+
+    const resumed = await brain.repackHistory()
+    expect(resumed.foldedGenerations).toBeGreaterThan(0)
+    const db = await brain.asOf(3)
+    expect((await db.get(id))?.metadata?.v).toBeDefined()
+    await db.release()
+    await brain.close()
+  })
+})

tests/integration/lens-consistency.test.ts

@@ -0,0 +1,138 @@
+/**
+ * @module tests/integration/lens-consistency
+ * @description The three metadata "lenses" over one corpus must agree with
+ * canonical ground truth id-for-id, warm AND after a cold reopen:
+ *   - combined:      find({ type: T, where: { subtype: S } })
+ *   - subtype-only:  find({ where: { subtype: S } })
+ *   - type-only:     find({ type: T })
+ * Ported from the fresh-brain probe that closed the type+subtype lens-drop
+ * investigation (a restored pre-8.2.2 torn capture had entities visible to the
+ * subtype-only lens but dropped by the combined lens — "0 of 2 migrated, all
+ * gates green"). The corpus is seeded through the REAL write API — never
+ * restored bytes — which is what made the original datapoint decisive. The
+ * invariants: every lens matches an unfiltered canonical scan exactly (no
+ * missing ids, no extras) and combined ⊆ subtype-only always holds.
+ */
+import { describe, it, expect, beforeAll, afterAll } from 'vitest'
+import * as fs from 'node:fs'
+import * as os from 'node:os'
+import * as path from 'node:path'
+import { Brainy } from '../../src/index.js'
+
+/** The corpus: 7 (type, subtype) pairs, uneven counts, incl. the incident's 2-of-a-pair shape. */
+const CORPUS: Array<{ type: string; subtype: string; count: number }> = [
+  { type: 'proposition', subtype: 'decision', count: 2 }, // the incident shape: "0 of 2"
+  { type: 'concept', subtype: 'decision', count: 3 },
+  { type: 'task', subtype: 'decision', count: 2 },
+  { type: 'concept', subtype: 'action', count: 4 },
+  { type: 'message', subtype: 'note', count: 5 },
+  { type: 'message', subtype: 'ship', count: 3 },
+  { type: 'document', subtype: 'guide', count: 4 }
+]
+
+/** Canonical ground truth: unfiltered enumeration, post-filtered IN THE TEST. */
+async function groundTruth(
+  brain: any,
+  match: { type?: string; subtype?: string }
+): Promise<Set<string>> {
+  const ids = new Set<string>()
+  let cursor: string | undefined
+  for (;;) {
+    const page = await brain.storage.getNounsWithPagination({ limit: 500, cursor })
+    for (const noun of page.items) {
+      // Hydrated shape: `type`/`subtype` are TOP-LEVEL; `metadata` holds only
+      // custom user fields (vfsType is one — the VFS plumbing marker).
+      const n = noun as any
+      if (n.metadata?.vfsType) continue // VFS plumbing is not corpus
+      if (!n.type || !n.subtype) continue
+      if (match.type && n.type !== match.type) continue
+      if (match.subtype && n.subtype !== match.subtype) continue
+      ids.add(n.id)
+    }
+    if (!page.hasMore) break
+    cursor = page.nextCursor
+  }
+  return ids
+}
+
+const idSet = (results: Array<{ id: string }>): Set<string> => new Set(results.map((r) => r.id))
+
+/** Every lens vs ground truth, id-for-id, for every pair in the corpus. */
+async function assertAllLenses(brain: any): Promise<void> {
+  const types = [...new Set(CORPUS.map((c) => c.type))]
+  const subtypes = [...new Set(CORPUS.map((c) => c.subtype))]
+
+  for (const { type, subtype } of CORPUS) {
+    const combined = idSet(await brain.find({ type, where: { subtype }, limit: 1000 }))
+    const subtypeOnly = idSet(await brain.find({ where: { subtype }, limit: 1000 }))
+    const truthPair = await groundTruth(brain, { type, subtype })
+    const truthSubtype = await groundTruth(brain, { subtype })
+
+    expect([...combined].sort()).toEqual([...truthPair].sort()) // no drops, no extras
+    expect([...subtypeOnly].sort()).toEqual([...truthSubtype].sort())
+    for (const id of combined) expect(subtypeOnly.has(id)).toBe(true) // combined ⊆ subtype-only
+  }
+
+  for (const type of types) {
+    const typeOnly = idSet(await brain.find({ type, limit: 1000 }))
+    const truthType = await groundTruth(brain, { type })
+    expect([...typeOnly].sort()).toEqual([...truthType].sort())
+  }
+
+  // Count cross-check against the corpus definition itself.
+  for (const subtype of subtypes) {
+    const expected = CORPUS.filter((c) => c.subtype === subtype).reduce((s, c) => s + c.count, 0)
+    const got = (await brain.find({ where: { subtype }, limit: 1000 })).length
+    expect(got).toBe(expected)
+  }
+}
+
+describe('lens consistency — combined vs subtype-only vs canonical ground truth', () => {
+  let dir: string
+  let brain: any
+
+  beforeAll(async () => {
+    process.env.BRAINY_DETERMINISTIC_EMBEDDINGS = 'true'
+    dir = fs.mkdtempSync(path.join(os.tmpdir(), 'brainy-lens-'))
+    brain = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir }, silent: true, dimensions: 384 })
+    await brain.init()
+    // Seed through the REAL write API — never restored bytes.
+    let i = 0
+    for (const { type, subtype, count } of CORPUS) {
+      for (let k = 0; k < count; k++) {
+        await brain.add({ data: `${type} ${subtype} ${i++}`, type, subtype, metadata: { k } })
+      }
+    }
+    await brain.flush()
+  })
+  afterAll(async () => {
+    await brain.close?.().catch(() => {})
+    fs.rmSync(dir, { recursive: true, force: true })
+  })
+
+  it('WARM: all lenses agree with ground truth id-for-id', async () => {
+    await assertAllLenses(brain)
+  })
+
+  it('COLD REOPEN: all lenses still agree after close + reopen from disk', async () => {
+    await brain.close()
+    brain = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir }, silent: true, dimensions: 384 })
+    await brain.init()
+    await assertAllLenses(brain)
+  })
+
+  it('after an update() flips type AND subtype, every lens tracks the move exactly', async () => {
+    // The historical cross-bucket-staleness path: change (concept, action) -> (task, review).
+    const victims = await brain.find({ type: 'concept', where: { subtype: 'action' }, limit: 1 })
+    expect(victims.length).toBe(1)
+    const id = victims[0].id
+    await brain.update({ id, type: 'task', subtype: 'review' })
+
+    const oldCombined = idSet(await brain.find({ type: 'concept', where: { subtype: 'action' }, limit: 1000 }))
+    expect(oldCombined.has(id)).toBe(false) // unposted from the old buckets
+    const newCombined = idSet(await brain.find({ type: 'task', where: { subtype: 'review' }, limit: 1000 }))
+    expect(newCombined.has(id)).toBe(true) // posted to the new buckets
+    const subtypeOnly = idSet(await brain.find({ where: { subtype: 'review' }, limit: 1000 }))
+    expect(subtypeOnly.has(id)).toBe(true)
+  })
+})

tests/integration/multi-process-safety.test.ts

@@ -110,6 +110,89 @@ describe('Multi-process safety + read-only mode', () => {
       // Don't track `blocked` for afterEach cleanup since init failed.
     })
 
+    it('takes over a STALE foreign lock (dead PID + old heartbeat) and claims atomically', async () => {
+      const { mkdirSync, writeFileSync, readFileSync } = await import('node:fs')
+      const { join } = await import('node:path')
+      const os = await import('node:os')
+      mkdirSync(join(dir, 'locks'), { recursive: true })
+      const tenMinutesAgo = new Date(Date.now() - 10 * 60 * 1000).toISOString()
+      writeFileSync(join(dir, 'locks', '_writer.lock'), JSON.stringify({
+        pid: 999999999, // no such process — provably dead
+        hostname: os.hostname(),
+        startedAt: tenMinutesAgo,
+        lastHeartbeat: tenMinutesAgo,
+        version: '8.0.0',
+        rootDir: dir
+      }))
+
+      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
+      await writer.init() // stale takeover must succeed
+
+      const lock = JSON.parse(readFileSync(join(dir, 'locks', '_writer.lock'), 'utf-8'))
+      expect(lock.pid).toBe(process.pid) // the atomic wx claim installed OUR lock
+    })
+
+    it('the writer-locked error carries the machine-readable contract (code + lockInfo)', async () => {
+      const { mkdirSync, writeFileSync } = await import('node:fs')
+      const { join } = await import('node:path')
+      const os = await import('node:os')
+      mkdirSync(join(dir, 'locks'), { recursive: true })
+      const otherPid = (process as any).ppid || 1
+      writeFileSync(join(dir, 'locks', '_writer.lock'), JSON.stringify({
+        pid: otherPid,
+        hostname: os.hostname(),
+        startedAt: new Date().toISOString(),
+        lastHeartbeat: new Date().toISOString(),
+        version: '8.7.0',
+        rootDir: dir
+      }))
+
+      const blocked = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
+      const err: any = await blocked.init().catch((e) => e)
+      expect(err.code).toBe('BRAINY_WRITER_LOCKED')
+      expect(err.lockInfo?.pid).toBe(otherPid)
+    })
+
+    it('release drains an in-flight heartbeat — no phantom lock re-created after unlink', async () => {
+      // The race (8.9.0): clearInterval stops FUTURE heartbeat ticks, but a
+      // tick already in flight could land its lock rewrite AFTER release's
+      // unlink — re-creating the lock as a phantom that blocks the next
+      // writer until the stale TTL. Simulate the in-flight tick explicitly
+      // and prove release waits for it.
+      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
+      await writer.init()
+      const storage: any = (writer as any).storage
+
+      // An in-flight refresh that is ALREADY PAST its ownership guards
+      // (captured the lock info before release ran) and lands its atomic
+      // rewrite slowly — the exact straggler shape; absent the drain it
+      // writes after the unlink.
+      const { join: joinPath } = await import('node:path')
+      const capturedInfo = { ...storage.writerLockInfo }
+      const lockPath = joinPath(dir, 'locks', '_writer.lock')
+      const slowTick = (async () => {
+        await new Promise((r) => setTimeout(r, 100))
+        await storage.writeFileAtomic(
+          lockPath,
+          JSON.stringify({ ...capturedInfo, lastHeartbeat: new Date().toISOString() })
+        )
+      })()
+      storage.writerHeartbeatInFlight = slowTick.catch(() => {})
+
+      await writer.close() // → releaseWriterLock must drain slowTick first
+      await slowTick.catch(() => {}) // both paths fully settled either way
+      writer = null
+
+      const { existsSync } = await import('node:fs')
+      const { join } = await import('node:path')
+      expect(existsSync(join(dir, 'locks', '_writer.lock'))).toBe(false)
+
+      // And the directory is immediately claimable — no stale-TTL wait.
+      const next = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
+      await expect(next.init()).resolves.toBeUndefined()
+      await next.close()
+    })
+
     it('allows a second in-process writer with a warning (same PID)', async () => {
       // Two Brainy instances in the same Node process: not the dangerous
       // cross-process case. Should succeed (with a console warning).

tests/integration/vfs-rename-containment.test.ts

@@ -0,0 +1,157 @@
+/**
+ * @module tests/integration/vfs-rename-containment
+ * @description A cross-directory rename must MOVE the containment edge, not
+ * accumulate one per parent. The pre-fix rename added the new parent's
+ * Contains edge but skipped removing the old one ("not critical") — leaving
+ * the entity a child of BOTH directories: readdir(oldDir) kept listing it,
+ * re-creating the old path showed the name twice (the duplicate-readdir /
+ * "cosmetic ghost" field report), and tree-walking consumers saw the file in
+ * two places. Also covers the repair sweep (repairIndex → vfs.repairContainment)
+ * that heals ghosts left by earlier versions, and move-to-root (whose edge
+ * used to be skipped entirely).
+ */
+import { describe, it, expect, beforeEach, afterEach } from 'vitest'
+import { Brainy, VerbType } from '../../src/index.js'
+
+describe('VFS rename moves the containment edge (no ghost in the old directory)', () => {
+  let brain: any
+
+  beforeEach(async () => {
+    process.env.BRAINY_DETERMINISTIC_EMBEDDINGS = 'true'
+    brain = new Brainy({ requireSubtype: false, storage: { type: 'memory' }, silent: true, dimensions: 384 })
+    await brain.init()
+    await brain.vfs.mkdir('/a', { recursive: true })
+    await brain.vfs.mkdir('/b', { recursive: true })
+  })
+  afterEach(async () => {
+    await brain.close?.().catch(() => {})
+  })
+
+  it('cross-directory move: old dir stops listing it, new dir lists it exactly once', async () => {
+    await brain.vfs.writeFile('/a/x.txt', 'v1')
+    await brain.vfs.rename('/a/x.txt', '/b/x.txt')
+
+    expect(await brain.vfs.readdir('/a')).toEqual([])
+    expect(await brain.vfs.readdir('/b')).toEqual(['x.txt'])
+    expect(String(await brain.vfs.readFile('/b/x.txt'))).toBe('v1')
+  })
+
+  it('re-creating the old path lists each name exactly once in each directory', async () => {
+    await brain.vfs.writeFile('/a/x.txt', 'moved away')
+    await brain.vfs.rename('/a/x.txt', '/b/x.txt')
+    await brain.vfs.writeFile('/a/x.txt', 'new file at old path')
+
+    const a = (await brain.vfs.readdir('/a')) as string[]
+    const b = (await brain.vfs.readdir('/b')) as string[]
+    expect(a).toEqual(['x.txt']) // exactly once — the pre-fix ghost made this list the moved entity too
+    expect(b).toEqual(['x.txt'])
+    expect(String(await brain.vfs.readFile('/a/x.txt'))).toBe('new file at old path')
+    expect(String(await brain.vfs.readFile('/b/x.txt'))).toBe('moved away')
+  })
+
+  it('repeated moves never accumulate containment edges', async () => {
+    await brain.vfs.writeFile('/a/f.txt', 'wanderer')
+    for (let i = 0; i < 3; i++) {
+      await brain.vfs.rename('/a/f.txt', '/b/f.txt')
+      await brain.vfs.rename('/b/f.txt', '/a/f.txt')
+    }
+    expect(await brain.vfs.readdir('/a')).toEqual(['f.txt'])
+    expect(await brain.vfs.readdir('/b')).toEqual([])
+
+    // Exactly ONE containment edge exists on the entity.
+    const stat = await brain.vfs.stat('/a/f.txt')
+    const edges = await brain.related({ to: stat.entityId, type: VerbType.Contains })
+    expect(edges).toHaveLength(1)
+  })
+
+  it('move to the root gets a containment edge (used to be skipped → orphan)', async () => {
+    await brain.vfs.writeFile('/a/up.txt', 'to the top')
+    await brain.vfs.rename('/a/up.txt', '/up.txt')
+
+    const rootListing = (await brain.vfs.readdir('/')) as string[]
+    expect(rootListing).toContain('up.txt')
+    expect(await brain.vfs.readdir('/a')).toEqual([])
+    expect(String(await brain.vfs.readFile('/up.txt'))).toBe('to the top')
+  })
+})
+
+describe('repairIndex() heals pre-fix containment ghosts (vfs.repairContainment)', () => {
+  let brain: any
+
+  beforeEach(async () => {
+    process.env.BRAINY_DETERMINISTIC_EMBEDDINGS = 'true'
+    brain = new Brainy({ requireSubtype: false, storage: { type: 'memory' }, silent: true, dimensions: 384 })
+    await brain.init()
+    await brain.vfs.mkdir('/a', { recursive: true })
+    await brain.vfs.mkdir('/b', { recursive: true })
+  })
+  afterEach(async () => {
+    await brain.close?.().catch(() => {})
+  })
+
+  /** Reproduce the PRE-FIX defect state: file lives at /b/g.txt but a stale
+   *  vfs-contains edge from /a lingers (what old renames left behind). */
+  const synthesizeGhost = async () => {
+    await brain.vfs.writeFile('/b/g.txt', 'ghost target')
+    const fileId = (await brain.vfs.stat('/b/g.txt')).entityId
+    const aId = (await brain.vfs.stat('/a')).entityId
+    await brain.relate({
+      from: aId,
+      to: fileId,
+      type: VerbType.Contains,
+      subtype: 'vfs-contains',
+      metadata: { isVFS: true }
+    })
+    return { fileId, aId }
+  }
+
+  it('a stale old-parent edge is removed; listings become honest', async () => {
+    const { fileId } = await synthesizeGhost()
+    // The defect state is visible: /a lists a file whose path says /b.
+    expect((await brain.vfs.readdir('/a')) as string[]).toContain('g.txt')
+
+    await brain.repairIndex()
+
+    expect(await brain.vfs.readdir('/a')).toEqual([])
+    expect(await brain.vfs.readdir('/b')).toEqual(['g.txt'])
+    const edges = await brain.related({ to: fileId, type: VerbType.Contains })
+    expect(edges).toHaveLength(1)
+  })
+
+  it("a user's own knowledge Contains edge onto the file survives the repair", async () => {
+    const { fileId } = await synthesizeGhost()
+    // A knowledge-graph containment from a NON-directory entity (a collection
+    // curating the file) — same verb TYPE, not a vfs-contains edge. The repair
+    // must remove only VFS containment ghosts, never user knowledge edges.
+    // (Edges dedupe by (from,to,type), so the user edge needs its own source.)
+    const collectionId = await brain.add({
+      data: 'reading list',
+      type: 'collection',
+      metadata: { kind: 'curation' }
+    })
+    await brain.relate({ from: collectionId, to: fileId, type: VerbType.Contains, subtype: 'curates' })
+
+    await brain.repairIndex()
+
+    const edges = await brain.related({ to: fileId, type: VerbType.Contains })
+    const subtypes = edges.map((e: any) => e.subtype).sort()
+    // The stale vfs ghost edge is gone; the correct vfs edge + the user's
+    // curation edge remain.
+    expect(subtypes).toEqual(['curates', 'vfs-contains'])
+    expect(edges.find((e: any) => e.subtype === 'curates')?.from).toBe(collectionId)
+  })
+
+  it('a missing expected edge is restored (entity unreachable from its own directory)', async () => {
+    await brain.vfs.writeFile('/b/lost.txt', 'find me')
+    const fileId = (await brain.vfs.stat('/b/lost.txt')).entityId
+    // Simulate total edge loss (an older damage shape).
+    for (const e of await brain.related({ to: fileId, type: VerbType.Contains })) {
+      await brain.unrelate(e.id)
+    }
+    expect((await brain.vfs.readdir('/b')) as string[]).not.toContain('lost.txt')
+
+    await brain.repairIndex()
+
+    expect((await brain.vfs.readdir('/b')) as string[]).toContain('lost.txt')
+  })
+})

tests/regression/metadata-index-cleanup.unit.test.ts

@@ -205,10 +205,10 @@ describe('Metadata index cleanup after remove / removeMany', () => {
       }
     })
 
-    it('handles empty ids array gracefully', async () => {
+    it('refuses an empty ids array loudly (a silent no-op is not "graceful")', async () => {
-      const result = await brain.removeMany({ ids: [] })
+      // 8.8.2: an empty selector used to resolve successfully having deleted
-      expect(result.successful).toHaveLength(0)
+      // NOTHING — the caller believed the delete happened. Now it throws.
-      expect(result.failed).toHaveLength(0)
+      await expect(brain.removeMany({ ids: [] })).rejects.toThrow(/ids: \[\]/)
     })
 
     it('handles large batch (> 1 chunk) without leaving stale index entries', async () => {

tests/transaction/TransactionManager.unit.test.ts

@@ -10,6 +10,7 @@
 
 import { describe, it, expect, beforeEach } from 'vitest'
 import { TransactionManager } from '../../src/transaction/TransactionManager.js'
+import { transactTimeoutBudget } from '../../src/transaction/Transaction.js'
 import { TransactionError } from '../../src/transaction/errors.js'
 
 describe('TransactionManager', () => {
@@ -105,14 +106,17 @@ describe('TransactionManager', () => {
       const result = await manager.executeTransactionWithResult(async (tx) => {
         tx.addOperation({
           execute: async () => {
-            await new Promise(resolve => setTimeout(resolve, 10))
+            await new Promise(resolve => setTimeout(resolve, 25))
             return async () => {}
           }
         })
         return 'done'
       })
 
-      expect(result.executionTimeMs).toBeGreaterThanOrEqual(10)
+      // Timer coalescing can fire a setTimeout up to a few ms EARLY under
+      // load, so assert well below the sleep — this tests that time is
+      // MEASURED, not the OS timer's precision.
+      expect(result.executionTimeMs).toBeGreaterThanOrEqual(20)
     })
   })
 
@@ -325,4 +329,45 @@ describe('TransactionManager', () => {
       expect(stats1).toEqual(stats2) // Same values
     })
   })
+
+  describe('Timeout budget + telemetry', () => {
+    it('transactTimeoutBudget: explicit override wins; default scales with batch size', () => {
+      expect(transactTimeoutBudget(1)).toBe(30_000) // small batches keep the 30s floor
+      expect(transactTimeoutBudget(15)).toBe(30_000) // the old flat cap's break-even point
+      expect(transactTimeoutBudget(100)).toBe(200_000) // 100 ops × 2s — bulk gets an honest budget
+      expect(transactTimeoutBudget(1000, 5_000)).toBe(5_000) // caller override is untouched
+    })
+
+    it('a tripped budget rolls back and names the operation, progress, and budget', async () => {
+      const rolledBack: string[] = []
+
+      const failing = manager.executeTransaction(
+        async (tx) => {
+          tx.addOperation({
+            name: 'slow-first-op',
+            execute: async () => {
+              await new Promise((r) => setTimeout(r, 30))
+              return async () => {
+                rolledBack.push('slow-first-op')
+              }
+            }
+          })
+          tx.addOperation({
+            name: 'never-reached',
+            execute: async () => undefined
+          })
+        },
+        { timeout: 5 } // the first op's 30ms sleep guarantees the pre-op-2 check trips
+      )
+
+      await expect(failing).rejects.toThrow(TransactionError)
+      const err = await failing.catch((e) => e)
+      expect(err.name).toBe('TransactionTimeoutError')
+      expect(err.message).toContain('operation 1/2') // which op, of how many
+      expect(err.message).toContain("('never-reached')") // its name
+      expect(err.message).toContain('budget 5ms') // the budget that tripped
+      expect(err.message).toContain('rolled back') // the retryability statement
+      expect(rolledBack).toEqual(['slow-first-op']) // the applied op was undone
+    })
+  })
 })

tests/unit/aggregation/AggregationIndex.test.ts

@@ -675,4 +675,104 @@ describe('AggregationIndex', () => {
       await reloaded.close()
     })
   })
+
+  // ============= Boot-order reconciliation =============
+  //
+  // The production boot pattern: defineAggregate() is synchronous and always
+  // beats the async init() that loads persisted state. The old code flagged a
+  // backfill at define time and init never cleared it — so the loaded state
+  // was wiped and the whole store re-walked on EVERY restart.
+
+  describe('boot-order reconciliation (define-before-init)', () => {
+    const DEF: AggregateDefinition = {
+      name: 'boot_agg',
+      source: { type: NounType.Event },
+      groupBy: ['category'],
+      metrics: { count: { op: 'count' } }
+    }
+
+    const entity = (id: string, category: string): Record<string, unknown> => ({
+      id,
+      noun: NounType.Event,
+      metadata: { category },
+      createdAt: Date.now(),
+      updatedAt: Date.now()
+    })
+
+    /** Simulate the previous session: define, contribute, flush. */
+    async function seedAndFlush(store: MemoryStorage): Promise<void> {
+      const first = new AggregationIndex(store)
+      await first.init()
+      first.defineAggregate(DEF)
+      first.onEntityAdded('e1', entity('e1', 'food'))
+      first.onEntityAdded('e2', entity('e2', 'food'))
+      first.onEntityAdded('e3', entity('e3', 'transport'))
+      await first.flush()
+    }
+
+    it('adopts persisted state when define beats init with an unchanged definition', async () => {
+      const store = new MemoryStorage()
+      await store.init()
+      await seedAndFlush(store)
+
+      const second = new AggregationIndex(store)
+      second.defineAggregate(DEF) // synchronous define FIRST — the real boot order
+      await second.init()
+      await second.ready()
+
+      expect(second.getPendingBackfills()).toEqual([])
+      const rows = second.queryAggregate({ name: 'boot_agg' })
+      const food = rows.find(r => r.groupKey.category === 'food')!
+      expect(food.metrics.count).toBe(2)
+    })
+
+    it('a write landing before adoption forces an exact rescan instead', async () => {
+      const store = new MemoryStorage()
+      await store.init()
+      await seedAndFlush(store)
+
+      const second = new AggregationIndex(store)
+      second.defineAggregate(DEF)
+      second.onEntityAdded('e4', entity('e4', 'food')) // lands before init settles
+      await second.init()
+      await second.ready()
+
+      // Adoption would lose e4's contribution — the engine must rescan.
+      expect(second.getPendingBackfills()).toEqual(['boot_agg'])
+    })
+
+    it('init never clobbers a changed app definition registered before it', async () => {
+      const store = new MemoryStorage()
+      await store.init()
+      await seedAndFlush(store)
+
+      const CHANGED: AggregateDefinition = {
+        ...DEF,
+        metrics: { count: { op: 'count' }, total: { op: 'sum', field: 'amount' } }
+      }
+      const second = new AggregationIndex(store)
+      second.defineAggregate(CHANGED)
+      await second.init()
+      await second.ready()
+
+      const def = second.getDefinitions().find(d => d.name === 'boot_agg')!
+      expect(Object.keys(def.metrics).sort()).toEqual(['count', 'total'])
+      expect(second.getPendingBackfills()).toEqual(['boot_agg'])
+    })
+
+    it('init alone restores persisted definitions with adopted state, no backfill', async () => {
+      const store = new MemoryStorage()
+      await store.init()
+      await seedAndFlush(store)
+
+      const second = new AggregationIndex(store)
+      await second.init()
+      await second.ready()
+
+      expect(second.hasAggregate('boot_agg')).toBe(true)
+      expect(second.getPendingBackfills()).toEqual([])
+      const rows = second.queryAggregate({ name: 'boot_agg' })
+      expect(rows.reduce((s, r) => s + (r.metrics.count as number), 0)).toBe(3)
+    })
+  })
 })

tests/unit/brainy/batch-operations.test.ts

@@ -533,8 +533,10 @@ describe('Brainy Batch Operations', () => {
       expect(result.successful).toHaveLength(0)
       
       await brain.updateMany({ items: [] })
-      await brain.removeMany({ ids: [] })
+      // removeMany is the exception (8.8.2): an empty id list is a refused
-      // Should not throw
+      // selector, not an empty batch — deleting "nothing" silently was the
+      // bug class (a positional/bare-array call looked identical).
+      await expect(brain.removeMany({ ids: [] })).rejects.toThrow(/ids: \[\]/)
     })
     
     it('should validate batch size limits', async () => {

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

@@ -0,0 +1,237 @@
+/**
+ * @module tests/unit/db/fact-log
+ * @description The generation fact log in isolation: wire-format round-trip
+ * (positional msgpack facts, bin16 uuids, body-less tombstones), crc32c
+ * framing with torn-tail detection, open-time truncation to committed truth
+ * (the log can only ever be AHEAD after a crash; open cuts it back), rotation
+ * with a manifest-first flip, exactly-once scans with the frozen telemetry
+ * shape, and the mmap segment handoff excluding the mutable tail.
+ */
+import { describe, it, expect, beforeEach } from 'vitest'
+import { MemoryStorage } from '../../../src/storage/adapters/memoryStorage.js'
+import {
+  FactLog,
+  FACTS_PREFIX,
+  type CommitFact,
+  type FactLogStorage,
+  storageSupportsFactLog
+} from '../../../src/db/factLog.js'
+import { crc32c } from '../../../src/utils/crc32c.js'
+
+const UUID = (n: number): string =>
+  `00000000-0000-4000-8000-${String(n).padStart(12, '0')}`
+
+const fact = (generation: number, overrides?: Partial<CommitFact>): 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] } }
+    }
+  ],
+  ...overrides
+})
+
+describe('crc32c known-answer vectors', () => {
+  it('matches the RFC 3720 test vectors', () => {
+    expect(crc32c(new TextEncoder().encode('123456789'))).toBe(0xe3069283)
+    expect(crc32c(new Uint8Array(32))).toBe(0x8a9136aa)
+  })
+})
+
+describe('fact log — round-trip, framing, reconcile, rotation, scan', () => {
+  let storage: FactLogStorage
+  let log: FactLog
+
+  beforeEach(async () => {
+    const mem: any = new MemoryStorage()
+    await mem.init()
+    expect(storageSupportsFactLog(mem)).toBe(true)
+    storage = mem
+    log = new FactLog(storage)
+    await log.open(0)
+  })
+
+  it('facts round-trip byte-exactly: ops, tombstones, meta, blobHashes', async () => {
+    await log.append(fact(1))
+    await log.append(
+      fact(2, {
+        ops: [
+          { kind: 'verb', id: UUID(21), record: { metadata: { verb: 'contains' }, vector: null } },
+          { kind: 'noun', id: UUID(22), record: null } // TOMBSTONE
+        ],
+        meta: { source: 'test' },
+        blobHashes: ['abc123', 'abc123'] // multiset — duplicates preserved
+      })
+    )
+    await log.sync()
+
+    const scan = log.scanFacts()
+    expect(scan.headGeneration).toBe(2)
+    const all: CommitFact[] = []
+    for await (const batch of scan.batches()) all.push(...batch.facts)
+
+    expect(all).toHaveLength(2)
+    expect(all[0].generation).toBe(1)
+    expect(all[0].ops[0].id).toBe(UUID(1))
+    expect(all[0].ops[0].record?.metadata).toEqual({ noun: 'document', title: 'doc 1' })
+    expect(all[1].ops[0].kind).toBe('verb')
+    expect(all[1].ops[1].record).toBeNull() // the tombstone is body-less
+    expect(all[1].meta).toEqual({ source: 'test' })
+    expect(all[1].blobHashes).toEqual(['abc123', 'abc123'])
+    expect(scan.summary().factsYielded).toBe(2)
+  })
+
+  it('appends are monotonic — a replayed/duplicate generation throws', async () => {
+    await log.append(fact(5))
+    await expect(log.append(fact(5))).rejects.toThrow(/non-monotonic/)
+    await expect(log.append(fact(3))).rejects.toThrow(/non-monotonic/)
+    await expect(log.append(fact(6))).resolves.toBeUndefined() // gaps are fine (aborted reservations)
+  })
+
+  it('a torn tail (partial frame) is detected and ignored — intact prefix survives', async () => {
+    await log.append(fact(1))
+    await log.append(fact(2))
+    await log.sync()
+
+    // Simulate a crash mid-append: chop bytes off the tail file.
+    const tailPath = `${FACTS_PREFIX}/seg-${'1'.padStart(20, '0')}.bfl`
+    const bytes = (await storage.readRawBytes(tailPath))!
+    await storage.writeRawBytes(tailPath, bytes.subarray(0, bytes.length - 7))
+
+    const reopened = new FactLog(storage)
+    await reopened.open(2)
+    expect(reopened.headGeneration()).toBe(1) // fact 2's frame was torn → gone
+
+    const all: CommitFact[] = []
+    for await (const b of reopened.scanFacts().batches()) all.push(...b.facts)
+    expect(all.map((f) => f.generation)).toEqual([1])
+  })
+
+  it('open() truncates facts beyond committed truth (the crash-ahead shape)', async () => {
+    await log.append(fact(1))
+    await log.append(fact(2))
+    await log.append(fact(3))
+    await log.sync()
+
+    // The store's committed generation is 1 — facts 2..3 never committed.
+    const reopened = new FactLog(storage)
+    await reopened.open(1)
+    expect(reopened.headGeneration()).toBe(1)
+
+    const all: CommitFact[] = []
+    for await (const b of reopened.scanFacts().batches()) all.push(...b.facts)
+    expect(all.map((f) => f.generation)).toEqual([1])
+
+    // And appends continue cleanly from the truncated head.
+    await reopened.append(fact(2))
+    expect(reopened.headGeneration()).toBe(2)
+  })
+
+  it('a cleared store (committed=0) truncates everything', async () => {
+    await log.append(fact(1))
+    await log.append(fact(2))
+    await log.sync()
+    const reopened = new FactLog(storage)
+    await reopened.open(0)
+    expect(reopened.headGeneration()).toBe(0)
+  })
+
+  it('scan honors fromGeneration/toGeneration inclusively and filters kinds', async () => {
+    for (let g = 1; g <= 6; g++) await log.append(fact(g))
+    await log.sync()
+
+    const scan = log.scanFacts({ fromGeneration: 2, toGeneration: 4 })
+    const all: CommitFact[] = []
+    for await (const b of scan.batches()) all.push(...b.facts)
+    expect(all.map((f) => f.generation)).toEqual([2, 3, 4])
+
+    const verbsOnly = log.scanFacts({ kinds: ['verb'] })
+    for await (const b of verbsOnly.batches()) {
+      for (const f of b.facts) expect(f.ops.every((op) => op.kind === 'verb')).toBe(true)
+    }
+  })
+
+  it('batch telemetry carries the frozen shape', async () => {
+    for (let g = 1; g <= 5; g++) await log.append(fact(g))
+    await log.sync()
+
+    const scan = log.scanFacts({ batchSize: 2 })
+    expect(scan.approxFactCount).toBe(5)
+    const batches = []
+    for await (const b of scan.batches()) batches.push(b)
+    expect(batches.length).toBe(3)
+    expect(batches[0]).toMatchObject({ firstGeneration: 1, lastGeneration: 2, factCount: 2 })
+    expect(batches[0].byteSize).toBeGreaterThan(0)
+    expect(typeof batches[0].segmentId).toBe('string')
+    expect(scan.summary()).toEqual({ factsYielded: 5, segmentsRead: 1 })
+  })
+
+  it('survives reopen: head and content come back from disk', async () => {
+    for (let g = 1; g <= 3; g++) await log.append(fact(g))
+    await log.sync()
+
+    const reopened = new FactLog(storage)
+    await reopened.open(3)
+    expect(reopened.headGeneration()).toBe(3)
+    const all: CommitFact[] = []
+    for await (const b of reopened.scanFacts().batches()) all.push(...b.facts)
+    expect(all.map((f) => f.generation)).toEqual([1, 2, 3])
+  })
+
+  it('segmentPaths excludes the mutable tail (mmap handoff = sealed only)', async () => {
+    await log.append(fact(1))
+    await log.sync()
+    expect(log.segmentPaths()).toEqual([]) // only a tail exists — nothing sealed
+  })
+
+  describe('scanFacts liveness contract (Stage-2 D1)', () => {
+    it('a wedged store fails LOUDLY within the first-batch bound — never a silent hang', async () => {
+      // Force a sealed segment (tiny rotateBytes) so the scan must READ from
+      // storage, then wedge that read: the exact production shape (a
+      // backlogged brain whose segment read never returned).
+      const mem: any = new MemoryStorage()
+      await mem.init()
+      const wedgeable = new FactLog(mem, { rotateBytes: 1 })
+      await wedgeable.open(0)
+      await wedgeable.append(fact(1))
+      await wedgeable.append(fact(2)) // second append rotates → seg 1 sealed
+      await wedgeable.sync()
+
+      const realRead = mem.readRawBytes.bind(mem)
+      mem.readRawBytes = (p: string) =>
+        p.includes('facts/seg-') ? new Promise(() => {}) : realRead(p) // hangs forever
+
+      const scan = wedgeable.scanFacts({ firstBatchTimeoutMs: 200 })
+      const started = Date.now()
+      await expect(scan.batches().next()).rejects.toThrow(/no first batch within 200ms/)
+      expect(Date.now() - started).toBeLessThan(5_000) // bound held, not a hang
+    })
+
+    it('a healthy scan is unaffected — first batch well inside the bound, all facts delivered', async () => {
+      for (let g = 1; g <= 5; g++) await log.append(fact(g))
+      await log.sync()
+      const scan = log.scanFacts({ batchSize: 2 })
+      const all: CommitFact[] = []
+      for await (const b of scan.batches()) all.push(...b.facts)
+      expect(all.map((f) => f.generation)).toEqual([1, 2, 3, 4, 5])
+      expect(scan.summary().factsYielded).toBe(5)
+    })
+
+    it('consumer think-time between pulls never counts against the producer', async () => {
+      for (let g = 1; g <= 4; g++) await log.append(fact(g))
+      await log.sync()
+      // Bound tighter than the consumer's pause: only the FIRST pull is
+      // raced, so a slow consumer after batch 1 must not trip the deadline.
+      const gen = log.scanFacts({ batchSize: 2, firstBatchTimeoutMs: 150 }).batches()
+      const first = await gen.next()
+      expect(first.done).toBe(false)
+      await new Promise((r) => setTimeout(r, 400)) // dawdle past the bound
+      const second = await gen.next()
+      expect(second.done).toBe(false)
+      expect((await gen.next()).done).toBe(true)
+    })
+  })
+})

tests/unit/db/generation-segments.test.ts

@@ -0,0 +1,150 @@
+/**
+ * @module tests/unit/db/generation-segments
+ * @description The generation-segment store (Stage-2 D1+D3 file format).
+ * Laws: (1) fold → read round-trips deltas and records byte-faithfully via
+ * sidecar point-reads; (2) the manifest is the ONLY discovery path — reopen
+ * reads one file, never a listing; (3) a lost/corrupt sidecar rebuilds from
+ * its segment loudly, a damaged SEGMENT fails loudly (never silent wrong
+ * data); (4) D3 reclaim drops whole segments only and bumps compactedBelow;
+ * (5) the packed digest is deterministic across reopen; (6) immutability —
+ * fold refuses overlap with sealed ranges.
+ */
+import { describe, it, expect, beforeEach } from 'vitest'
+import { MemoryStorage } from '../../../src/storage/adapters/memoryStorage.js'
+import {
+  GenerationSegmentStore,
+  SEGMENTS_PREFIX,
+  type FoldGeneration
+} from '../../../src/db/generationSegments.js'
+
+const UUID = (n: number): string => `00000000-0000-4000-8000-${String(n).padStart(12, '0')}`
+
+const gen = (g: number, recordCount = 2): FoldGeneration => ({
+  generation: g,
+  timestamp: 1_700_000_000_000 + g,
+  delta: { generation: g, nouns: [UUID(g)], verbs: [], bytes: 123 + g },
+  records: Array.from({ length: recordCount }, (_, i) => ({
+    kind: (i % 2 === 0 ? 'noun' : 'verb') as 'noun' | 'verb',
+    id: UUID(g * 100 + i),
+    record: { metadata: { noun: 'document', v: g }, vector: { v: [g, i] } }
+  }))
+})
+
+describe('db/GenerationSegmentStore — the D1+D3 packed tier', () => {
+  let storage: MemoryStorage
+  let store: GenerationSegmentStore
+
+  beforeEach(async () => {
+    storage = new MemoryStorage()
+    await storage.init()
+    store = new GenerationSegmentStore(storage as any)
+    await store.open()
+  })
+
+  it('fold → read round-trips deltas and records via sidecar point-reads', async () => {
+    const meta = await store.fold([gen(1), gen(2), gen(3)])
+    expect(meta).toMatchObject({ firstGeneration: 1, lastGeneration: 3, frames: 3 })
+    expect(meta.checksum).toBeGreaterThan(0)
+
+    expect(store.hasGeneration(2)).toBe(true)
+    expect(store.hasGeneration(4)).toBe(false)
+
+    const d2 = await store.readDelta(2)
+    expect(d2?.delta).toEqual({ generation: 2, nouns: [UUID(2)], verbs: [], bytes: 125 })
+    expect(d2?.timestamp).toBe(1_700_000_000_002)
+
+    const records = await store.readRecords(3)
+    expect(records).toHaveLength(2)
+    expect(records![0]).toEqual({
+      kind: 'noun',
+      id: UUID(300),
+      record: { metadata: { noun: 'document', v: 3 }, vector: { v: [3, 0] } }
+    })
+    // Point read by id, both kinds.
+    expect(await store.readRecord(3, 'verb', UUID(301))).toEqual({
+      metadata: { noun: 'document', v: 3 },
+      vector: { v: [3, 1] }
+    })
+    expect(await store.readRecord(3, 'noun', UUID(999))).toBeNull()
+  })
+
+  it('reopen discovers everything from the manifest alone — no listing', async () => {
+    await store.fold([gen(1), gen(2)])
+    await store.fold([gen(3), gen(4)])
+
+    const reopened = new GenerationSegmentStore(storage as any)
+    await reopened.open()
+    expect(reopened.segments()).toHaveLength(2)
+    expect(reopened.hasGeneration(4)).toBe(true)
+    expect((await reopened.readDelta(1))?.timestamp).toBe(1_700_000_000_001)
+  })
+
+  it('a lost sidecar rebuilds from its segment; a damaged segment fails LOUDLY', async () => {
+    const meta = await store.fold([gen(1), gen(2)])
+    const idxPath = `${SEGMENTS_PREFIX}/seg-${String(1).padStart(20, '0')}.idx`
+    await storage.deleteRawObject(idxPath)
+
+    const reopened = new GenerationSegmentStore(storage as any)
+    await reopened.open()
+    // Rebuild path: still serves correct data.
+    expect((await reopened.readRecords(2))!).toHaveLength(2)
+
+    // Now damage the SEGMENT itself: flip a payload byte → CRC mismatch, loud.
+    const segPath = `${SEGMENTS_PREFIX}/${meta.file}`
+    const bytes = (await storage.readRawBytes(segPath))!
+    bytes[bytes.length - 3] ^= 0xff
+    await storage.writeRawBytes(segPath, bytes)
+    const damaged = new GenerationSegmentStore(storage as any)
+    await damaged.open()
+    ;(damaged as any).sidecars.clear()
+    await storage.deleteRawObject(idxPath) // force the sequential rebuild over damaged bytes
+    await expect(damaged.readRecords(2)).rejects.toThrow(/CRC mismatch|damaged/)
+  })
+
+  it('D3 reclaim drops whole segments only and bumps compactedBelow', async () => {
+    await store.fold([gen(1), gen(2)])
+    await store.fold([gen(3), gen(4)])
+    await store.fold([gen(5), gen(6)])
+
+    // Horizon mid-segment-2 (below 4): only segment 1 is FULLY below → drops.
+    const r1 = await store.dropSegmentsBelow(4)
+    expect(r1).toEqual({ dropped: 1, compactedBelow: 3 })
+    expect(store.hasGeneration(1)).toBe(false)
+    expect(store.hasGeneration(3)).toBe(true) // partial segment survives whole
+
+    // Bytes actually gone.
+    expect(await storage.readRawBytes(`${SEGMENTS_PREFIX}/seg-${String(1).padStart(20, '0')}.bgs`)).toBeNull()
+
+    // Horizon past everything: the rest drop; compactedBelow is durable.
+    const r2 = await store.dropSegmentsBelow(7)
+    expect(r2.dropped).toBe(2)
+    const reopened = new GenerationSegmentStore(storage as any)
+    await reopened.open()
+    expect(reopened.compactedBelow()).toBe(7)
+    expect(reopened.segments()).toHaveLength(0)
+  })
+
+  it('the packed digest is deterministic across reopen and changes with history', async () => {
+    await store.fold([gen(1), gen(2), gen(3)])
+    const atSeal = await store.digestThroughPacked(3)
+    const midSegment = await store.digestThroughPacked(2)
+    expect(atSeal).not.toBeNull()
+    expect(midSegment).not.toBeNull()
+    expect(midSegment).not.toBe(atSeal)
+
+    const reopened = new GenerationSegmentStore(storage as any)
+    await reopened.open()
+    expect(await reopened.digestThroughPacked(3)).toBe(atSeal)
+    expect(await reopened.digestThroughPacked(2)).toBe(midSegment)
+
+    await reopened.fold([gen(4)])
+    expect(await reopened.digestThroughPacked(4)).not.toBe(atSeal)
+  })
+
+  it('sealed segments are immutable — fold refuses overlap, requires ascending input', async () => {
+    await store.fold([gen(1), gen(2)])
+    await expect(store.fold([gen(2), gen(3)])).rejects.toThrow(/overlaps the packed tier/)
+    await expect(store.fold([gen(4), gen(4)])).rejects.toThrow(/strictly ascending/)
+    await expect(store.fold([])).rejects.toThrow(/at least one generation/)
+  })
+})

tests/unit/db/generationStore.test.ts

@@ -249,7 +249,11 @@ describe('db/GenerationStore', () => {
       store.release(pinned)
       const result = await store.compact()
       expect(result.removedGenerations).toBeGreaterThan(0)
-      const remaining = await storage.listRawObjects(GENERATIONS_PREFIX)
+      // History record-sets only — the fact log (at `_generations/facts/`) is
+      // deliberately NOT reclaimed by history compaction.
+      const remaining = (await storage.listRawObjects(GENERATIONS_PREFIX)).filter(
+        (p: string) => !p.startsWith(`${GENERATIONS_PREFIX}/facts/`)
+      )
       expect(remaining).toEqual([])
     })
 
@@ -484,5 +488,95 @@ describe('db/GenerationStore', () => {
       expect(result.removedGenerations).toBe(2)
       store.release(2)
     })
+
+    it('timeBudgetMs bounds a pass; the next pass resumes the same prefix', async () => {
+      await manyGens(4)
+      // A spent budget (0ms) stops before reclaiming anything — an early stop
+      // is a consistent prefix, never a partial generation.
+      const bounded = await store.compact({ timeBudgetMs: 0 })
+      expect(bounded.removedGenerations).toBe(0)
+      expect(bounded.horizon).toBe(0)
+      // The next (unbounded) pass picks up exactly where the bounded one
+      // stopped and completes the same work.
+      const resumed = await store.compact()
+      expect(resumed.removedGenerations).toBe(4)
+      expect(resumed.horizon).toBe(4)
+    })
+  })
+
+  // ==========================================================================
+  describe('history-bytes running total (the O(1) retention check)', () => {
+    /** A fresh walk with the cache dropped — ground truth for the invariant. */
+    async function groundTruthBytes(): Promise<number> {
+      ;(store as any).historyBytesTotal = null
+      return store.historyBytes()
+    }
+
+    it('is seeded once, then maintained through commits WITHOUT re-walks', async () => {
+      await commitWrite(ID_A, 1)
+      await commitWrite(ID_A, 2)
+      const seeded = await store.historyBytes()
+      expect(seeded).toBe(await groundTruthBytes())
+
+      // From here every read must come from the running total, not a walk:
+      // getDelta re-reads are the walk's cost — commits must not trigger any.
+      const getDeltaSpy = vi.spyOn(store as any, 'getDelta')
+      await commitWrite(ID_B, 1)
+      const afterCommit = await store.historyBytes()
+      expect(getDeltaSpy).not.toHaveBeenCalled()
+      getDeltaSpy.mockRestore()
+      expect(afterCommit).toBe(await groundTruthBytes())
+    })
+
+    it('stays exact through single-op group commits and compaction', async () => {
+      await commitWrite(ID_A, 1)
+      await store.historyBytes() // seed
+      // Single-op path: buffered generations flushed as one group commit.
+      await store.commitSingleOp({
+        touched: { nouns: [ID_B] },
+        execute: async () => {
+          await storage.saveNounMetadata(ID_B, metadataFixture(1))
+        }
+      })
+      await store.flushPendingSingleOps()
+      expect(await store.historyBytes()).toBe(await groundTruthBytes())
+
+      await store.historyBytes() // re-seed after ground-truth reset
+      await store.compact({ maxGenerations: 1 })
+      expect(await store.historyBytes()).toBe(await groundTruthBytes())
+    })
+
+    it('historyStats reports counts, bytes, range, and horizon read-only', async () => {
+      await commitWrite(ID_A, 1)
+      await commitWrite(ID_B, 1)
+      const stats = await store.historyStats()
+      expect(stats.generations).toBe(2)
+      expect(stats.bytes).toBe(await store.historyBytes())
+      expect(stats.oldestGeneration).toBe(1)
+      expect(stats.newestGeneration).toBe(2)
+      expect(stats.oldestTimestamp).toBeLessThanOrEqual(stats.newestTimestamp!)
+      expect(stats.horizon).toBe(0)
+      // Read-only: nothing was reclaimed by asking.
+      expect(store.committedGeneration()).toBe(2)
+
+      await store.compact({ maxGenerations: 1 })
+      const after = await store.historyStats()
+      expect(after.generations).toBe(1)
+      expect(after.oldestGeneration).toBe(2)
+      expect(after.horizon).toBe(1)
+    })
+
+    it('empty history reports null range and zero bytes', async () => {
+      const stats = await store.historyStats()
+      expect(stats).toMatchObject({
+        generations: 0,
+        bytes: 0,
+        oldestGeneration: null,
+        newestGeneration: null,
+        oldestTimestamp: null,
+        newestTimestamp: null,
+        horizon: 0
+      })
+    })
   })
 })

tests/unit/storage/verb-cursor-pagination.test.ts

@@ -95,9 +95,15 @@ describe('verb cursor pagination (graph-perf #2)', () => {
     expect(new Set(cursorSeen)).toEqual(new Set(offsetSeen))
   })
 
-  it('a foreign/malformed cursor falls back gracefully (no throw, starts from the beginning)', async () => {
+  it('a foreign/malformed cursor FAILS LOUDLY — never a silent restart from page 1', async () => {
-    const page = await storage.getVerbs({ pagination: { limit: 5, cursor: 'not-a-cv1-token' } })
+    // The old behavior (decode-null → silent offset-0 fallback) re-served page 1
-    expect(page.items.length).toBe(5)
+    // forever to any while(hasMore) walker: an unbounded CPU loop with no log
-    expect(page.hasMore).toBe(true)
+    // line. An undecodable resume token now refuses the walk instead.
+    await expect(
+      storage.getVerbs({ pagination: { limit: 5, cursor: 'not-a-cv1-token' } })
+    ).rejects.toThrow('invalid pagination cursor')
+    await expect(
+      storage.getNouns({ pagination: { limit: 5, cursor: 'not-a-cv1-token' } })
+    ).rejects.toThrow('invalid pagination cursor')
   })
 })

tests/unit/utils/osLimits.test.ts

@@ -0,0 +1,76 @@
+/**
+ * @module tests/unit/utils/osLimits
+ * @description OS-limit detection for pool-scale use. Laws:
+ * (1) the /proc/self/limits parser reads soft/hard NOFILE exactly, including
+ *     'unlimited'; (2) assessment warns ONLY below the pool floors and NEVER
+ *     on an unreadable (null) limit — no measurement, no claim; (3) the full
+ *     check composes both sources and survives unreadable /proc silently.
+ */
+import { describe, it, expect } from 'vitest'
+import {
+  parseProcLimits,
+  assessOsLimits,
+  checkOsLimits,
+  NOFILE_POOL_FLOOR,
+  MAX_MAP_COUNT_POOL_FLOOR
+} from '../../../src/utils/osLimits.js'
+
+const SAMPLE_LIMITS = [
+  'Limit                     Soft Limit           Hard Limit           Units',
+  'Max cpu time              unlimited            unlimited            seconds',
+  'Max open files            1024                 1048576              files',
+  'Max locked memory         8388608              8388608              bytes'
+].join('\n')
+
+describe('osLimits — detect + warn at pool scale', () => {
+  it('parses soft/hard NOFILE from /proc/self/limits, including unlimited', () => {
+    expect(parseProcLimits(SAMPLE_LIMITS)).toEqual({ soft: 1024, hard: 1048576 })
+    expect(
+      parseProcLimits('Max open files            unlimited            unlimited            files')
+    ).toEqual({ soft: Infinity, hard: Infinity })
+    expect(parseProcLimits('no such row here')).toEqual({ soft: null, hard: null })
+  })
+
+  it('warns below the floors, stays quiet at or above them', () => {
+    const low = assessOsLimits({ nofileSoft: 1024, nofileHard: 1048576, maxMapCount: 65530 })
+    expect(low).toHaveLength(2)
+    expect(low[0]).toContain('RLIMIT_NOFILE soft limit is 1024')
+    expect(low[0]).toContain(`ulimit -n ${NOFILE_POOL_FLOOR}`)
+    expect(low[0]).toContain('raise the soft limit only') // hard already allows it
+    expect(low[1]).toContain('vm.max_map_count is 65530')
+    expect(low[1]).toContain(`vm.max_map_count=${MAX_MAP_COUNT_POOL_FLOOR}`)
+
+    expect(
+      assessOsLimits({
+        nofileSoft: NOFILE_POOL_FLOOR,
+        nofileHard: Infinity,
+        maxMapCount: MAX_MAP_COUNT_POOL_FLOOR
+      })
+    ).toEqual([])
+  })
+
+  it('an unreadable limit makes NO claim — nulls never warn', () => {
+    expect(assessOsLimits({ nofileSoft: null, nofileHard: null, maxMapCount: null })).toEqual([])
+  })
+
+  it('checkOsLimits composes both sources and survives unreadable /proc silently', async () => {
+    const report = await checkOsLimits(async (p) => {
+      if (p === '/proc/self/limits') return SAMPLE_LIMITS
+      if (p === '/proc/sys/vm/max_map_count') return '65530\n'
+      throw new Error('unexpected path')
+    })
+    expect(report.nofileSoft).toBe(1024)
+    expect(report.maxMapCount).toBe(65530)
+    expect(report.warnings).toHaveLength(2)
+
+    const offLinux = await checkOsLimits(async () => {
+      throw Object.assign(new Error('ENOENT'), { code: 'ENOENT' })
+    })
+    expect(offLinux).toEqual({
+      nofileSoft: null,
+      nofileHard: null,
+      maxMapCount: null,
+      warnings: []
+    })
+  })
+})

tests/unit/utils/paramValidation.test.ts

@@ -270,27 +270,24 @@ describe('Zero-Config Parameter Validation', () => {
       expect(config.availableMemory).toBeGreaterThan(0)
     })
     
-    it('should adapt limits based on query performance', () => {
+    it('never mutates the cap from query timing (telemetry only)', () => {
-      const initialConfig = getValidationConfig()
+      const initialLimit = getValidationConfig().maxLimit
-      const initialLimit = initialConfig.maxLimit
 
-      // Simulate fast queries with large results
+      // Fast queries with large results: no silent growth.
       for (let i = 0; i < 10; i++) {
         recordQueryPerformance(50, initialLimit * 0.9)
       }
+      expect(getValidationConfig().maxLimit).toBe(initialLimit)
 
-      const updatedConfig = getValidationConfig()
+      // A burst of catastrophically slow queries must not strangle the cap.
-      // Limit might increase if performance is good
+      // The removed "learning" ratchet shrank it 20% per recorded query down
-      expect(updatedConfig.maxLimit).toBeGreaterThanOrEqual(initialLimit)
+      // to a floor of 1000 — below the documented MIN_AUTO_QUERY_LIMIT — and
-      
+      // the error message blamed "available free memory" (a production
-      // Simulate slow queries
+      // incident: every find({ limit: 5000 }) failed on an idle 23GB-free box).
-      for (let i = 0; i < 10; i++) {
+      for (let i = 0; i < 50; i++) {
-        recordQueryPerformance(2000, 100)
+        recordQueryPerformance(90_000, 100)
       }
-      
+      expect(getValidationConfig().maxLimit).toBe(initialLimit)
-      const finalConfig = getValidationConfig()
-      // Limit should decrease if performance is poor
-      expect(finalConfig.maxLimit).toBeLessThanOrEqual(updatedConfig.maxLimit)
     })
   })
 })