When run_conversation encounters a non-retryable client error (401, 400,
etc.), it returns a dict with failed=True instead of raising. The gateway's
_run_and_close only branched on exceptions, so it always emitted run.completed
even for failed runs — clients could not distinguish success from failure.
Inspect the result dict before emitting: if failed=True, emit run.failed
with the error message; otherwise emit run.completed as before. The existing
except Exception path is unchanged for genuine programming errors.
Fixes#15561
297eaa3533