## Why
Hook configurations can mark command handlers as asynchronous, but Codex previously skipped those handlers outside `SessionEnd`.
## What changed
- Run asynchronous command hooks in the background with a per-session concurrency limit, while keeping `SessionEnd` hooks synchronous.
- Prevent asynchronous hooks from blocking, stopping, rewriting, or otherwise controlling the operation that launched them.
- Deliver warnings and additional context at safe turn boundaries: inject results into an active turn after sampling, or buffer them ahead of the next user prompt when the session is idle.
- Preserve in-flight hooks across configuration reloads, scope spilled output to the thread, and abort outstanding work during session shutdown.
## Testing
Add unit and integration coverage for background scheduling, concurrency, output parsing, active and idle result delivery, configuration reloads, and shutdown cleanup.
GitOrigin-RevId: 8094552e4afe7b47b09a61bb575bb20f4e491d8d
6f647caa9b