fix(tracking): close append/compaction TOCTOU lost-write - #92
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…pend lock) The journal append path used a bare appendFileSync (O_APPEND) with no mutual exclusion against the compactor. Compaction is rename -> fold -> unlink on a fresh inode; an append could straddle open->write between compaction's rename and unlink, landing its write in the renamed inode that then got unlinked -- a silent lost write, never surfaced by the per-line HMAC (fail-closed per line has nothing to reject: the write simply never reached the surviving file). Fix: appendEvent now serialises on withTrackLockSyncBlocking, the same track.lock the compaction takes, spinning (1ms step, stale-lock TTL as the only anti-deadlock guard) until acquired -- never skipped, unlike the existing non-blocking withTrackLockSync used elsewhere. An append can no longer race compaction's rename/fold/unlink window. Probe (test/track-journal-toctou.test.ts) is deterministic and proven non-vacant independently: (A) a child process blocked on a manually held track.lock must NOT complete its append until the lock is released -- red without the fix (bare appendFileSync ignores the lock), green with it. (B) a real appendEvent loop running during a real maybeCompactJournal must serialise behind the compaction with zero event loss -- red without the fix (loop finishes inside the compaction window), green with it. Verified non-flaky 5/5, full suite 900/0.
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Summary
appendEventnow serialises on a blocking twin of the existing track lock (withTrackLockSyncBlocking), never skipped, so an append can no longer race compaction's rename/unlink window.test/track-journal-toctou.test.ts): a manual-lock block test and a real append-loop-vs-real-compaction race test asserting zero event loss.package.jsonto 0.1.83 (PATCH) and updatesCHANGELOG.md.Test plan
bunx tsc --noEmitcleanbun test— 900 pass / 1 skip / 0 failgrep -rEn "bun:|Bun\.|from ['"'"'bun['"'"']" src/tracking— no runtime hits20f72154e8876e02180ba7f8dd8a018005968cb5)