fix: Append metadata and context id when processing TaskStatusUpdateEvent, and add more error logs

1. Fix the bug that during TaskManager.save_task_event, metadata from the updated task event is lost
2. During EventQueue processing, if any of the processing asyncio task failed with an unexpected
   exception, this exception is silently caught but never exposed to user or logged in the console.
   Add more error logs to make errors visible during debugging.

Author: pwwpche

src/a2a/server/events/event_consumer.py

@@ -138,6 +138,10 @@ async def consume_all(self) -> AsyncGenerator[Event]:
                 # python 3.12 and get a queue empty error on an open queue
                 if self.queue.is_closed():
                     break
+            except Exception as e:
+                logger.debug(f'Stopping event consumption due to exception: {e}')
+                self._exception = e
+                continue
 
     def agent_task_callback(self, agent_task: asyncio.Task[None]) -> None:
         """Callback to handle exceptions from the agent's execution task.

src/a2a/server/request_handlers/default_request_handler.py

@@ -248,7 +248,9 @@ async def on_message_send(
                 raise ServerError(
                     InternalError(message='Task ID mismatch in agent response')
                 )
-
+        except Exception as e:
+            logger.error(f'Agent execution failed. Error: {e}')
+            raise e
         finally:
             if interrupted:
                 # TODO: Track this disconnected cleanup task.

src/a2a/server/tasks/task_manager.py

@@ -130,7 +130,12 @@ async def save_task_event(
                     task.history = [task.status.message]
                 else:
                     task.history.append(task.status.message)
-
+            if event.contextId:
+                task.contextId = event.contextId
+            if event.metadata:
+                if not task.metadata:
+                    task.metadata = {}
+                task.metadata.update(event.metadata)
             task.status = event.status
         else:
             logger.debug('Appending artifact to task %s', task.id)

tests/server/tasks/test_task_manager.py

@@ -127,6 +127,29 @@ async def test_save_task_event_artifact_update(
     updated_task.artifacts = [new_artifact]
     mock_task_store.save.assert_called_once_with(updated_task)
 
+@pytest.mark.asyncio
+async def test_save_task_event_metadata_contextid_update(
+    task_manager: TaskManager, mock_task_store: AsyncMock
+) -> None:
+    """Test saving an metadata and context update for an existing task."""
+    initial_task = Task(**MINIMAL_TASK)
+    mock_task_store.get.return_value = initial_task
+    new_metadata = {"meta_key_test": "meta_value_test"}
+    new_context_id = 'new_context_id'
+    
+    event = TaskStatusUpdateEvent(
+        taskId=MINIMAL_TASK['id'],
+        contextId=new_context_id,
+        metadata=new_metadata,
+        status=TaskStatus(state=TaskState.working),
+        final=False,
+    )
+    await task_manager.save_task_event(event)
+
+    updated_task = mock_task_store.save.call_args.args[0]
+    assert updated_task.metadata == new_metadata
+    assert updated_task.contextId == new_context_id
+
 
 @pytest.mark.asyncio
 async def test_ensure_task_existing(