[SSR Agent] Issue Fix (22588): Fix silent hang in MessageBus.request when publish fails - #28816

In MessageBus.publish(), all errors are caught internally and emitted via this.emit('error', error). If there is an 'error' listener registered on the MessageBus (which is standard practice in production for logging/monitoring), this.emit will execute successfully and the promise returned by this.publish() will resolve rather than reject. Because of this, the .catch() block added here in request() will never be triggered when a publication error occurs (such as a policy check failure or invalid message structure). The request() promise will still silently hang. Additionally, asynchronous operations waiting for user input via the MessageBus should rely on the provided AbortSignal for cancellation, rather than implementing a separate timeout, to maintain consistency with existing patterns.

This test mocks messageBus.publish to reject using mockRejectedValue. However, in production, publish() catches all errors internally and resolves successfully (only emitting an 'error' event) if there is an 'error' listener registered. Therefore, this test does not accurately reflect production behavior where request() will still hang. Consider updating publish() to rethrow errors so that this test scenario matches real-world behavior.

In Node.js, emitting an 'error' event when there are no registered listeners causes the EventEmitter to throw an ERR_UNHANDLED_ERROR synchronously. Since this happens inside the catch block, it bypasses the original error and propagates the unhandled error wrapper to the caller of publish or request.

To preserve the original error for the caller while still supporting global error logging when listeners are present, check if there are any 'error' listeners before emitting.

    } catch (error) {
      if (this.listenerCount('error') > 0) {
        this.emit('error', error);
      }
      throw error;
    }