fix(events): claim the IPC endpoint atomically before removing stale sockets (#209 follow-up)

[ScriptedAlchemy]

Summary

Addresses the unresolved P1 Codex finding on #209 (ipc.ts:287): two concurrently starting runtime processes could both observe a stale endpoint; after the first removed it and bound, the second's unconditional rm(endpoint) unlinked the first's LIVE socket, leaving a running but unreachable server.

Stale cleanup is now guarded by an atomic endpoint claim:

• An exclusive lockfile (<endpoint>.lock, open('wx')) serializes competing servers; the stale rm and the bind happen only while holding the claim, after a re-probe under the lock (a re-probed live endpoint fails with the existing live-server error instead of being removed).
• A held claim is awaited with bounded retries (100 × 10ms); an orphaned lock from a crashed process fails closed with a typed, actionable error rather than being stolen — stealing would recreate the exact unlink race this fixes.
• Claim release is identity-checked (dev/inode), mirroring removeOwnedEndpoint. The win32 path (no unix sockets) is untouched.

A test-only seam (createEventRuntimeServerForTest with an afterEndpointProbe hook) makes the race deterministic.

Tests

• does not unlink a concurrent winner after both servers probe a stale endpoint — freezes both racers in the historical probe-then-unlink window, lets one win, then asserts the loser fails with the live-server error and the winner still serves requests over its original socket.

Gates: scoped rstest (event-ipc), pnpm typecheck, pnpm lint, full pnpm build — all green.

[changeset-bot]

🦋 Changeset detected

Latest commit: 4c68b51

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
agent-bundle	Patch

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[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-01T21:39:05.758606Z	4c68b51	PR opened

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