An internal cross-engine fault-injection run (frozen-platter power-loss
capture) surfaced three release-gating findings; each cured in its owning
layer, each pinned:
1. WHOLE-LOG REPLAY ON UNCLEAN OPEN (the big one): log-authority replay
only covered facts ABOVE the manifest — but live canonical entity
writes are tmp+rename without per-file fsync, and the group-commit
flush syncs staging + manifest, never the live tree. Power loss could
therefore vaporize acked canonical bytes BELOW the manifest while the
log held every fact scan-clean (measured: 299 of 301 acks lost).
Now: a clean close stamps a clean-shutdown marker (fsynced, written
last); every open consumes it; an UNCLEAN open under log authority
folds the ENTIRE log into canonical — whole-entity after-images make
the re-apply idempotent and byte-safe. Zero cost on the happy path;
crash recovery pays one narrated fold. Recovery is replay: a crash is
just bigger lag.
2. TORN WRITER LOCK: power loss legally leaves the lock file present but
empty; the parse failure read as 'no holder' while the O_EXCL claim
EEXISTed forever — a PERMANENT lockout no staleness check could clear.
An unparseable lock is stale by definition (no live holder has one):
unlink loudly and re-loop; a racer rewriting a valid lock first wins.
3. PAIR GUARD: flush() called metadataIndex.stampWatermark unguarded;
a replacement metadata provider without the method killed the pair at
first flush. All three stamp calls are optional-chained — a missing
stamp is a verdict-side rescan, never a flush crash.
Pins: whole-log fold restores rows vanished below the manifest ·
clean-shutdown marker lifecycle (stamp/consume/re-stamp) · torn-lock
recovery with a fresh write after · stampless-provider flush.
Gates: unit 2055/2055 · integration 824 · kill-matrix 15/15.
David Snelling
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