## Why
Contention on the writer coordination lock can block writer cleanup indefinitely, preventing idle threads from unloading.
## What changed
Retry coordination lock acquisition every 50 ms and return `io::ErrorKind::TimedOut` after 30 seconds of contention. This lets cleanup release writer ownership and idle unloading finish even while another process holds coordination.
## Testing
Extend writer lock coverage to check the timeout error. Update the idle unload regression test to verify that the thread closes while coordination remains locked and can resume with its persisted turn after the lock is released.
GitOrigin-RevId: 513117fdaf3890283e7acdd149ce9abb66075b63
## Why
Idle thread unloading stopped waiting after ten seconds, leaving the thread loaded when resource cleanup took longer.
## What changed
Keep awaiting the same shutdown future after the ten-second deadline, emitting `codex.app_server.thread_shutdown_slow` as a warning. Once shutdown completes, remove the thread and send `thread/closed` without requiring another unload request.
## Testing
Add a regression test that blocks writer-lock cleanup past the warning deadline, verifies the thread remains loaded while cleanup is blocked, then releases the lock and checks for `thread/closed` and an empty loaded-thread list.
GitOrigin-RevId: 18c411f86fd69e710e472a4e3572d75f18682147
Dmitriy Kovalenko