Copilot review round 5. Both comments upheld; the first is a real hole in
round 4's own fix.
**The ownership guard was in the wrong place, and overclaimed.**
Round 4 checked ownership and then called `release()`. Two problems:
- Check-then-act. The `stat` and the `rmdir` were separate async steps, so a
waiter could replace the directory in between and we deleted the winner's
fresh lock anyway — the very thing the check was added to prevent.
- Skipping `release()` on a mismatch left proper-lockfile's record registered
in its `locks` map, and its `signal-exit` handler `rmdirSync`s every
registered lock with **no ownership check of its own**. An exit during that
window deleted the winner too.
The guard now lives in `options.fs`, which is the single seam *both* removal
paths route through — `removeLock` on release, and the exit handler. It
refuses to remove a directory whose inode and birth time are not the ones
recorded at acquire, and reports the refusal as success so the library's
bookkeeping forgets the lock either way (leaving it registered is what hands
the exit handler a record pointing at the winner's directory).
The check is a `statSync` immediately followed by an `rmdirSync`, with no
`await` between them, so nothing in this process can interleave. **It still
does not close the race** — it is check-then-act across processes, which needs
the compare-and-swap Node does not expose — and saying it "closes the
destructive half outright" was wrong. file-lock.ts, README.md,
specification/v2_servers_file.md and AGENTS.md now all say it narrows the
window rather than closing it. AGENTS.md carries the negative instruction
alongside round 4's, since this is the third round spent on an overclaim.
**"It expires on its own after 10s" is false for the ENOTEMPTY case** the new
test exercises. Stale takeover reclaims through the same `rmdir`, which also
cannot remove a non-empty directory — so nothing clears it, and every later
save fails ELOCKED against it. `releaseAdvice` now branches: by-hand removal
for ENOTEMPTY, expiry for everything else.
Tests: a real child process demonstrates the exit handler removing a
replacement lock (with an **empty** directory — a non-empty one makes
`rmdirSync` fail ENOTEMPTY, which is how the first draft of this test passed
for the wrong reason). The release-failure test now asserts the message says
"by hand" and does not promise expiry. The shim's `rmdirSync` arm carries a
justified `v8 ignore`: it is reachable only from a real process exit, and its
logic is `removeIfMine`, covered through the async arm.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JTHVxSu8AUgHRLvo1ntZ8H
Signed-off-by: cliffhall <cliff@futurescale.com>
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