## Why
Callers need to interrupt a specific active turn without discarding queued input. Tool callbacks must be able to await the interruption decision without blocking task cancellation.
## What changed
- Add `CodexThread::interrupt_if_no_pending_input` and `Op::InterruptIfNoPendingInput`.
- Check the turn identity and pending user input or mailbox items before taking the active task. Leave the turn running for stale or abandoned requests.
- Acknowledge the decision before joining cancellation, and unblock pending submissions when the active task is cancelled.
## Testing
Add regression coverage for successful interruption, stale turns, preservation of queued user input and agent mail, abandoned requests, and cancellation while the submission queue is full.
GitOrigin-RevId: 42e31c09369fb070ba1b4b3c64ef45334dd872d8
pmccrary-oai
04fc75adbe