The daemon writes `.gstack/browse.json` via the standard atomic-rename
pattern: `writeFileSync(tmp, …) → renameSync(tmp, stateFile)`. Four
sites in server.ts use this pattern (initial daemon-startup state at
:2002, /tunnel/start handler at :1479, BROWSE_TUNNEL=1 inline tunnel
update at :2083, BROWSE_TUNNEL_LOCAL_ONLY=1 update at :2113), and all
four hard-code the same temp filename `${stateFile}.tmp`.
Under concurrent writers the shared filename races on the rename:
t0 Writer A: writeFileSync(stateFile + '.tmp', payloadA)
t1 Writer B: writeFileSync(stateFile + '.tmp', payloadB) // overwrites A
t2 Writer A: renameSync(stateFile + '.tmp', stateFile) // moves B's payload
t3 Writer B: renameSync(stateFile + '.tmp', stateFile) // ENOENT — file gone
Reproduced empirically with 15 concurrent CLIs against a fresh `.gstack/`:
[browse] Failed to start: ENOENT: no such file or directory,
rename '…/.gstack/browse.json.tmp' -> '…/.gstack/browse.json'
Pre-fix success rate: **0 / 15** under cold-start race.
Post-fix success rate: **15 / 15**, zero ENOENT.
Fix:
- New `tmpStatePath()` helper (server.ts:333) returns
`${stateFile}.tmp.${pid}.${randomBytes(4).toString('hex')}`
- All 4 call sites use `tmpStatePath()` instead of the shared literal
- Atomic rename still gives last-writer-wins semantics on the final
state.json content; only behavior change is that concurrent writers
no longer kill each other on the rename step
Source-level guard test (browse/test/server-tmp-state-path.test.ts)
locks two invariants: (1) no remaining `stateFile + '.tmp'` literals,
(2) every state-write `writeFileSync` call uses `tmpStatePath()`. Same
read-source-as-text pattern as terminal-agent.test.ts and
dual-listener.test.ts — no daemon required, runs in tier-1 free.
Test plan:
- [x] Targeted source-level guard test passes (3 / 0)
- [x] `bun run build` clean
- [x] Live regression: 15 concurrent CLIs against cold state →
15 / 15 healthy, 0 ENOENT (vs 0 / 15 pre-fix)
- [x] No `.tmp.*` orphans left behind after rename succeeds
- [x] Related test cluster (server-auth, dual-listener, cdp-mutex,
findport) — same pre-existing flakes as `main`, no new
regressions introduced
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Yashwant Kotipalli