* fix(runtime): defer host cancellation through the whole terminal finalization
Cancelling run_agent() during an early terminal-finalization await (e.g.
the delivery-receipt write) escaped the surrounding `except Exception`
guards, because asyncio.CancelledError derives from BaseException. The
cancellation then skipped the remaining terminal tail: terminal status
persistence, the completion hook, task-stop notification, and the stream
END marker.
Add `_await_despite_host_cancellation`, which shields each terminal step
so the started awaitable keeps running under host cancellation, defers the
interruption (uncancelling the task), and re-awaits the shield until the
step completes. Apply it to the durable finalization stages; the original
interruption is still re-raised after publish_end.
* fix(runtime): bound terminal deferral and shield abort-path cancellation
* fix(runtime): retain owned finalization through cancellation
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Co-authored-by: Willem Jiang <willem.jiang@gmail.com>
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