Cancel a pending or in-progress async chat job.

Stops a running turn, or ends a turn that is waiting for your review by discarding its staged changes. Already-applied changes are preserved in the document; anything still pending is discarded. Use to abort work that is no longer wanted (e.g. the user changed their mind, or you want to retry with different parameters or model_tier). The response tells you whether the work was stopped here and now (stop_state: "stopped_here") or the stop was ACCEPTED and is being carried out by the instance running the turn (stop_state: "accepted") — in the accepted case poll get_job until metadata.stopped_unwound is true or the job reaches a terminal status. A turn that already finished cannot be stopped and returns 409 naming its status.