## Why
Waiting for the event channel to close after `ShutdownComplete` retains the thread runtime because the thread owns its event sender. Remaining subscribers still need late notifications after shutdown.
## What changed
- Release runtime references after `ShutdownComplete` while keeping the listener command queue available for ordered notifications and late request resolutions.
- Preserve other subscribers when a client unsubscribes or disconnects from an unloaded thread, and serialize terminal cleanup with cold resumes.
- Return the thread-closing error when `thread/resume` encounters a terminated runtime or a listener that cannot complete the request.
- Close the status watch when removing a thread so a later load gets a fresh watch.
## Testing
Add regression coverage for listeners attached before and after shutdown, verifying runtime release, preservation of remaining subscribers, late notification delivery, and rejection of resumes against a terminated runtime. Add a test that removing and reloading a thread closes the old status watch.
GitOrigin-RevId: 6dda8f83a0fbe06c9a713e9801356753a0de172e
Charlie Marsh
7f4d53e928