fix(server): fail fast when an executor produces no events

src/a2a/server/agent_execution/active_task.py

@@ -1003,6 +1003,11 @@ async def _mark_task_as_failed(self, exception: Exception) -> Task | None:
                 pass
         return task
 
+    @property
+    def task_created(self) -> bool:
+        """Whether a task exists, so ``get_task()`` will not block."""
+        return self._task_created.is_set()
+
     async def get_task(self) -> Task:
         """Get task from db."""
         await self._task_created.wait()

src/a2a/server/request_handlers/default_request_handler_v2.py

@@ -54,6 +54,7 @@
 from a2a.utils.errors import (
     ExtendedAgentCardNotConfiguredError,
     InternalError,
+    InvalidAgentResponseError,
     InvalidParamsError,
     PushNotificationNotSupportedError,
     TaskNotCancelableError,
@@ -444,6 +445,11 @@ async def on_message_send(  # noqa: D102
                 # pushed after a Message.
 
         if result is None:
+            if not active_task.task_created:
+                # A silent executor means get_task() would block forever.
+                raise InvalidAgentResponseError(
+                    message='Agent execution produced no events'
+                )
             logger.debug('Missing result for task %s', request_context.task_id)
             result = await active_task.get_task()
 

tests/server/request_handlers/test_default_request_handler_v2.py

@@ -2776,3 +2776,38 @@ async def test_on_message_send_stream_message_response_releases_active_task() ->
     assert [type(event) for event in events] == [Message]
     assert await _wait_until_released(handler, baseline) == set()
     assert handler._active_task_registry._active_tasks == {}
+
+
+class SilentExecutor(AgentExecutor):
+    """Returns normally without producing any event (issue #1330)."""
+
+    async def execute(self, context: RequestContext, event_queue: EventQueue):
+        return None
+
+    async def cancel(self, context: RequestContext, event_queue: EventQueue):
+        pass
+
+
+@pytest.mark.asyncio
+async def test_on_message_send_raises_when_agent_produces_no_events():
+    """A silent executor must fail fast instead of hanging forever (#1330)."""
+    request_handler = DefaultRequestHandlerV2(
+        agent_executor=SilentExecutor(),
+        task_store=InMemoryTaskStore(),
+        agent_card=create_default_agent_card(),
+    )
+    params = SendMessageRequest(
+        message=Message(
+            role=Role.ROLE_USER,
+            message_id='msg_silent',
+            parts=[Part(text='Hi')],
+        ),
+        configuration=SendMessageConfiguration(
+            accepted_output_modes=['text/plain']
+        ),
+    )
+
+    with pytest.raises(InvalidAgentResponseError, match='no events'):
+        await request_handler.on_message_send(
+            params, create_server_call_context()
+        )