## What changed
- Add `--exit-on-stdin-close` and the `CODEX_EXEC_SERVER_EXIT_ON_STDIN_CLOSE` environment variable as opt-in controls for remote exec servers.
- Gracefully drain active sessions and processes when the parent closes stdin, then flush telemetry before exiting.
- Remove the parent-lifetime environment variable from child process environments.
## Testing
- Cover parent disconnects after signal-listener failures.
- Exercise remote shutdown end to end, including child termination and final telemetry metrics.
- Verify that explicitly disabling the environment variable preserves local exec-server behavior.
GitOrigin-RevId: 63063bc097b54684c370bd545cd32d17c4e55d90
