`writeBridgeAtomic` wrote to a fixed `${target}.tmp` path before
calling `renameSync`. When two processes write to the same session
bridge concurrently (e.g. PostToolUse `ecc-metrics-bridge` + the
background `ecc-statusline`, both calling `writeBridgeAtomic(sessionId, ...)`),
the canonical atomic-rename race fires:
1. Process A: writeFileSync(target.tmp, JSON_A) — tmp file exists.
2. Process B: writeFileSync(target.tmp, JSON_B) — tmp file overwritten.
3. Process A: renameSync(target.tmp, target) — succeeds; target = JSON_B
(A's payload silently corrupted en-route).
4. Process B: renameSync(target.tmp, target) — throws ENOENT (the
rename consumed the file).
Every caller in the repo wraps `writeBridgeAtomic` in `try {} catch {}`,
so the ENOENT exception is swallowed and the user-visible symptom is
just "the bridge file occasionally contains the wrong process's
payload" with no diagnostic.
Reproduced before this commit:
$ # two concurrent writers, each calling writeBridgeAtomic 500 times
$ # against the same session ID
[A] errors=244 # 244 ENOENT exceptions swallowed
[B] errors=248 # ditto
After this commit the same workload reports 0 errors in both
subprocesses: tmp paths no longer collide.
Fix: change `${target}.tmp` to
`${target}.${process.pid}.${crypto.randomBytes(4).toString('hex')}.tmp`,
matching the pattern already used by `writeCostWarningIfChanged` in
`scripts/hooks/ecc-metrics-bridge.js` (commit 9b1d8918). The pid +
4-byte nonce gives each writer process a distinct tmp path, so step 2
above no longer overwrites step 1's payload and step 4 no longer
races step 3.
Also added: on `renameSync` failure, attempt `fs.unlinkSync(tmp)` so
a writer that fails (disk full, permission, parent dir gone) does
not leak its tmp file. The cleanup is best-effort and the original
error is still re-thrown.
**Scope clarification.** This commit closes the atomic-rename
primitive's race only. The *read-modify-write* race in callers —
two writers each read the same bridge state, increment, and write
back, the second clobbering the first — is a separate concern that
needs locking or per-writer logs, and is intentionally out of scope
for this PR. The cost-tracker / metrics-bridge callers tolerate
last-writer-wins on their cumulative aggregates today and this
commit does not change that contract.
The companion `writeWarnState` in `ecc-context-monitor.js` has the
same fixed-suffix pattern and the same race; that fix lands in the
next commit so each can be reviewed against its own diff.
Salvages the useful statusline/context monitor work from stale PR #1504 while preserving the current continuous-learning hook runner wiring.
Adds the metrics bridge, context monitor, statusline script, shared cost/session bridge utilities, and tests. Fixes the reviewed false loop-detection hash collision for non-file tools, avoids default-session cost inflation, sanitizes statusline task lookup, and records hook payload session IDs in cost-tracker.
Jamkris ·
Affaan Mustafa ·