* fix(tui): wait for an interrupted run before sending to its thread
Textual cannot stop a thread worker, so after an interrupt the agent
stream keeps running until its next event. A tool step already in
progress still completes and checkpoints while a new prompt runs on the
same thread; whichever run checkpoints last becomes the thread's state,
so the new turn could drop out of the conversation history.
Track when each worker actually starts and returns (Textual reports a
cancelled thread worker finished at once) and reject sends to a thread
whose interrupted worker is still running. Other threads stay usable,
and a worker cancelled before it started holds nothing.
* docs(changelog): reference #6350 for the interrupted TUI run fix
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Co-authored-by: Willem Jiang <willem.jiang@gmail.com>
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