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.
David Snelling
fd5edb5a13