fix: filter thought parts from A2A client user-facing response

When an A2A server returns a completed response containing both thought
parts (metadata.adk_thought=true) and final answer parts, the client now
filters out thought parts before yielding the event to consumers.
Intermediate (submitted/working) events are preserved as-is since all
their parts are already marked as thoughts for streaming progress.

Fixes #4676

Author: weiguangli-io

src/google/adk/agents/remote_a2a_agent.py

@@ -531,6 +531,19 @@ async def _handle_a2a_response(
             invocation_id=ctx.invocation_id,
             branch=ctx.branch,
         )
+      # Filter out thought parts from user-facing response content.
+      # Intermediate (submitted/working) events have all parts marked as
+      # thought, so non_thought_parts will be empty and we preserve them.
+      if (
+          event.content is not None
+          and event.content.parts
+      ):
+        non_thought_parts = [
+            p for p in event.content.parts if not p.thought
+        ]
+        if non_thought_parts:
+          event.content.parts = non_thought_parts
+
       return event
     except A2AClientError as e:
       logger.error("Failed to handle A2A response: %s", e)

tests/unittests/agents/test_remote_a2a_agent.py

@@ -1324,6 +1324,163 @@ async def test_handle_a2a_response_with_partial_artifact_update(self):
 
     assert result is None
 
+  @pytest.mark.asyncio
+  async def test_handle_a2a_response_filters_thought_parts_from_completed_task(
+      self,
+  ):
+    """Test that thought parts are filtered from completed task response.
+
+    When an A2A server returns a completed task with both thought and
+    non-thought parts, the client should only include non-thought parts
+    in the user-facing event. Fixes #4676.
+    """
+    mock_a2a_task = Mock(spec=A2ATask)
+    mock_a2a_task.id = "task-123"
+    mock_a2a_task.context_id = "context-123"
+    mock_a2a_task.status = Mock(spec=A2ATaskStatus)
+    mock_a2a_task.status.state = TaskState.completed
+
+    # Create event with mixed thought/non-thought parts
+    thought_part = genai_types.Part(text="internal reasoning", thought=True)
+    answer_part = genai_types.Part(text="final answer")
+    mock_event = Event(
+        author=self.agent.name,
+        invocation_id=self.mock_context.invocation_id,
+        branch=self.mock_context.branch,
+        content=genai_types.Content(
+            role="model", parts=[thought_part, answer_part]
+        ),
+    )
+
+    with patch.object(
+        remote_a2a_agent,
+        "convert_a2a_task_to_event",
+        autospec=True,
+    ) as mock_convert:
+      mock_convert.return_value = mock_event
+
+      result = await self.agent._handle_a2a_response(
+          (mock_a2a_task, None), self.mock_context
+      )
+
+      # Only non-thought parts should remain
+      assert len(result.content.parts) == 1
+      assert result.content.parts[0].text == "final answer"
+      assert result.content.parts[0].thought is None
+
+  @pytest.mark.asyncio
+  async def test_handle_a2a_response_filters_thought_parts_from_status_update(
+      self,
+  ):
+    """Test that thought parts are filtered from completed status update.
+
+    Fixes #4676.
+    """
+    mock_a2a_task = Mock(spec=A2ATask)
+    mock_a2a_task.id = "task-123"
+    mock_a2a_task.context_id = "context-123"
+
+    mock_update = Mock(spec=TaskStatusUpdateEvent)
+    mock_update.status = Mock(spec=A2ATaskStatus)
+    mock_update.status.state = TaskState.completed
+    mock_update.status.message = Mock(spec=A2AMessage)
+
+    # Create event with mixed thought/non-thought parts
+    thought_part = genai_types.Part(text="thinking...", thought=True)
+    answer_part = genai_types.Part(text="the answer")
+    mock_event = Event(
+        author=self.agent.name,
+        invocation_id=self.mock_context.invocation_id,
+        branch=self.mock_context.branch,
+        content=genai_types.Content(
+            role="model", parts=[thought_part, answer_part]
+        ),
+    )
+
+    with patch(
+        "google.adk.agents.remote_a2a_agent.convert_a2a_message_to_event"
+    ) as mock_convert:
+      mock_convert.return_value = mock_event
+
+      result = await self.agent._handle_a2a_response(
+          (mock_a2a_task, mock_update), self.mock_context
+      )
+
+      # Only non-thought parts should remain
+      assert len(result.content.parts) == 1
+      assert result.content.parts[0].text == "the answer"
+
+  @pytest.mark.asyncio
+  async def test_handle_a2a_response_preserves_all_thought_parts_for_working(
+      self,
+  ):
+    """Test that working state events keep all parts as thoughts.
+
+    Intermediate events (working/submitted) should retain all parts
+    marked as thought for streaming progress display.
+    """
+    mock_a2a_task = Mock(spec=A2ATask)
+    mock_a2a_task.id = "task-123"
+    mock_a2a_task.context_id = "context-123"
+    mock_a2a_task.status = Mock(spec=A2ATaskStatus)
+    mock_a2a_task.status.state = TaskState.working
+
+    part = genai_types.Part(text="still thinking")
+    mock_event = Event(
+        author=self.agent.name,
+        invocation_id=self.mock_context.invocation_id,
+        branch=self.mock_context.branch,
+        content=genai_types.Content(role="model", parts=[part]),
+    )
+
+    with patch.object(
+        remote_a2a_agent,
+        "convert_a2a_task_to_event",
+        autospec=True,
+    ) as mock_convert:
+      mock_convert.return_value = mock_event
+
+      result = await self.agent._handle_a2a_response(
+          (mock_a2a_task, None), self.mock_context
+      )
+
+      # All parts should be marked as thought and preserved
+      assert len(result.content.parts) == 1
+      assert result.content.parts[0].thought is True
+
+  @pytest.mark.asyncio
+  async def test_handle_a2a_response_filters_thought_from_a2a_message(self):
+    """Test thought filtering for regular A2AMessage responses.
+
+    Fixes #4676.
+    """
+    mock_a2a_message = Mock(spec=A2AMessage)
+    mock_a2a_message.context_id = "context-123"
+
+    thought_part = genai_types.Part(text="reasoning", thought=True)
+    answer_part = genai_types.Part(text="response")
+    mock_event = Event(
+        author=self.agent.name,
+        invocation_id=self.mock_context.invocation_id,
+        branch=self.mock_context.branch,
+        content=genai_types.Content(
+            role="model", parts=[thought_part, answer_part]
+        ),
+    )
+
+    with patch(
+        "google.adk.agents.remote_a2a_agent.convert_a2a_message_to_event"
+    ) as mock_convert:
+      mock_convert.return_value = mock_event
+
+      result = await self.agent._handle_a2a_response(
+          mock_a2a_message, self.mock_context
+      )
+
+      # Only non-thought parts should remain
+      assert len(result.content.parts) == 1
+      assert result.content.parts[0].text == "response"
+
 
 class TestRemoteA2aAgentMessageHandlingFromFactory:
   """Test message handling functionality."""