The temporal model had a hole exactly where files were concerned: every
entity write is an immutable generation with before-images, but VFS content
BYTES lived under an eager refCount GC left over from the pre-8.0 design —
unlink could physically destroy bytes that in-window history still
referenced, and overwrite never released the old hash at all (an unbounded
silent leak whose accidental byproduct was the only thing "preserving"
history). Reading the past could therefore return a stale field, a dangling
hash, or nothing, depending on luck.
Fix: blob reclamation becomes a HISTORY decision instead of a LIVENESS
decision. Each blob's metadata now carries historyRefCount alongside the
live refCount:
- The commit seam counts one history reference per persisted before-image
record carrying a content hash (commitTransaction staging and the
group-commit flush), recorded BEFORE the record-set persists and carried
in the generation delta (blobHashes — always present on new deltas, so
compaction only falls back to reading records for pre-contract
generations). An aborted transaction compensates best-effort.
- unlink/rmdir/overwrite drop ONLY the live reference (BlobStorage.delete →
release; overwrite finally releases the superseded hash — cancelling the
dedup increment on same-content rewrites and closing the leak), and only
AFTER the canonical mutation commits, so a failed delete can never leave a
live file whose bytes compaction might reclaim.
- History compaction is the ONE reclamation point: after deleting a
generation's record-set it releases that set's references and physically
reclaims any hash at zero live AND zero history references. Pins are
exempt automatically. Crash ordering is over-count-only in every path
(record before persist, release after delete), so a crash can leak until
the scrub recounts but can never reclaim bytes a retained generation
needs. scrubBlobHistoryRefCounts() restores exactness; existing stores get
a one-time marker-gated backfill on open, failing into leak-safe mode
(reclamation disabled) rather than guessing.
On top of the protected history, the temporal API the generational model
always implied:
- vfs.readFile(path, { asOf }) — the exact bytes as of a generation or Date,
materialized from the history (pinned view released so compaction is
never blocked by a read).
- vfs.history(path) — FileVersion[] ascending ({ generation, timestamp,
hash, size, mimeType? }), the newest entry being the live state.
- Overwrites now refresh the file entity's data/embedding text — semantic
search and the data field previously served the FIRST version's text
forever (the stale-field defect a consumer's incident recovery depended
on by luck).
Integration suite (temporal-vfs.test.ts): per-version exact reads +
history listing, leak-fix + history protection on overwrite, rm keeps bytes
readable, compaction reclaims past-window bytes and preserves in-window
(including the cross-file dedup case where an old file's history and a
newer file's removal share one hash), data freshness, and scrub exactness.
Subscribe once and receive one post-commit event per affected record for
EVERY canonical write, regardless of origin: direct calls, batch methods,
transact(), imports, and Virtual Filesystem writes all funnel through the
same commit points the feed is emitted from. This is the authoritative
in-process signal for live UIs, cache invalidation, and realtime sync layers
that forward it over their own transports.
Architecture — the post-commit dual of the ifRev precommit hook: mutation
methods hand lightweight event descriptors to the commit seam
(persistSingleOp / transact's plan), which stamps the committed
{generation, timestamp}, enriches entity deletes with the record's LAST
committed state from the commit's own before-images (free — Model B reads
them anyway; removeMany's id-only deletes gain full payloads this way), and
emits only after the commit succeeds — a losing CAS or rejected batch never
announces anything. Dispatch is a microtask FIFO after the mutex releases:
commit-ordered, a slow listener never delays a write, a throwing listener is
logged and isolated, and with no subscribers the write path constructs no
events at all. Single-point emission was chosen over per-method hooks
because the aggregation-hook pattern demonstrably drifted (relation ops and
removeMany were silently missing from it).
Coverage: add/update/remove (+ cascade unrelate per deleted relationship),
relate (both edges when bidirectional)/unrelate/updateRelation, per-item
events for addMany/updateMany/relateMany/removeMany, per-item events sharing
one generation for transact(), and transitively imports + VFS. clear() and
restore() — wholesale raw-state operations outside the per-record commit
path — emit a single store-level event meaning "refetch everything".
brain.close() drops all listeners.
New module src/events/changeFeed.ts (BrainyChangeEvent + ChangeFeed,
exported from the package root); guide docs/guides/reacting-to-changes.md.
Integration suite pins the contract: per-op payload fidelity, delete
last-state payloads, batch per-item emission, one-generation transact
batches, VFS-origin events, CAS-loser silence, ordering, listener isolation,
unsubscribe, and store-level events.
