## What changed
- Dispatch app-server turn interrupts in the background so the TUI can keep
processing thread events while an interrupt is pending.
- Coalesce repeated interrupt requests for the same active turn and clear the
pending state when the turn completes or the thread closes.
- Preserve the retry for stale active-turn IDs, surface interrupt failures as
warning notifications instead of exiting the TUI, and reset backtrack state
whenever an interrupt is handled.
## Testing
- Add an app-server integration test covering nonblocking event handling,
repeated-request coalescing, and pending-state cleanup.
- Verify that interrupting without an active turn clears backtrack state.
GitOrigin-RevId: 9ada247a739e2e0a63b425f75ebd6d054167d825
Eric Traut
62ba648136