fix: RemoteA2aAgent fails to send taskId in multi-turn scenarios

src/google/adk/agents/remote_a2a_agent.py

@@ -379,7 +379,7 @@ def _is_remote_response(self, event: Event) -> bool:
 
   def _construct_message_parts_from_session(
       self, ctx: InvocationContext
-  ) -> tuple[list[A2APart], Optional[str]]:
+  ) -> tuple[list[A2APart], Optional[str], Optional[str]]:
     """Construct A2A message parts from session events.
 
     Args:
@@ -391,6 +391,7 @@ def _construct_message_parts_from_session(
     """
     message_parts: list[A2APart] = []
     context_id = None
+    task_id = None
 
     events_to_process = []
     for event in reversed(ctx.session.events):
@@ -400,6 +401,10 @@ def _construct_message_parts_from_session(
         if event.custom_metadata:
           metadata = event.custom_metadata
           context_id = metadata.get(A2A_METADATA_PREFIX + "context_id")
+          # Always forward task_id if present. The remote agent (server) owns task
+          # lifecycle and will reject or ignore a stale task_id if the task is no
+          # longer open. Filtering by state client-side is error-prone.
+          task_id = metadata.get(A2A_METADATA_PREFIX + "task_id")
         # Historical note: this behavior originally always applied, regardless
         # of whether the agent was stateful or stateless. However, only stateful
         # agents can be expected to have previous events in the remote session.
@@ -427,7 +432,7 @@ def _construct_message_parts_from_session(
         else:
           logger.warning("Failed to convert part to A2A format: %s", part)
 
-    return message_parts, context_id
+    return message_parts, context_id, task_id
 
   async def _handle_a2a_response(
       self, a2a_response: A2AClientEvent | A2AMessage, ctx: InvocationContext
@@ -624,7 +629,7 @@ async def _run_async_impl(
     # Create A2A request for function response or regular message
     a2a_request = self._create_a2a_request_for_user_function_response(ctx)
     if not a2a_request:
-      message_parts, context_id = self._construct_message_parts_from_session(
+      message_parts, context_id, task_id = self._construct_message_parts_from_session(
           ctx
       )
 
@@ -645,6 +650,7 @@ async def _run_async_impl(
           parts=message_parts,
           role="user",
           context_id=context_id,
+          task_id=task_id,
       )
 
     logger.debug(build_a2a_request_log(a2a_request))

tests/unittests/agents/test_remote_a2a_agent.py

@@ -615,7 +615,7 @@ def test_construct_message_parts_from_session_success(self):
       mock_a2a_part = Mock()
       self.mock_genai_part_converter.return_value = mock_a2a_part
 
-      parts, context_id = self.agent._construct_message_parts_from_session(
+      parts, context_id, task_id = self.agent._construct_message_parts_from_session(
           self.mock_context
       )
 
@@ -649,7 +649,7 @@ def test_construct_message_parts_from_session_success_multiple_parts(self):
           mock_a2a_part2,
       ]
 
-      parts, context_id = self.agent._construct_message_parts_from_session(
+      parts, context_id, task_id = self.agent._construct_message_parts_from_session(
           self.mock_context
       )
 
@@ -660,7 +660,7 @@ def test_construct_message_parts_from_session_empty_events(self):
     """Test message parts construction with empty events."""
     self.mock_session.events = []
 
-    parts, context_id = self.agent._construct_message_parts_from_session(
+    parts, context_id, task_id = self.agent._construct_message_parts_from_session(
         self.mock_context
     )
 
@@ -718,7 +718,7 @@ def mock_converter(part):
         "google.adk.agents.remote_a2a_agent._present_other_agent_message"
     ) as mock_present:
       mock_present.side_effect = lambda event: event
-      parts, context_id = self.agent._construct_message_parts_from_session(
+      parts, context_id, task_id = self.agent._construct_message_parts_from_session(
           self.mock_context
       )
       assert len(parts) == 1
@@ -768,7 +768,7 @@ def mock_converter(part):
         "google.adk.agents.remote_a2a_agent._present_other_agent_message"
     ) as mock_present:
       mock_present.side_effect = lambda event: event
-      parts, context_id = self.agent._construct_message_parts_from_session(
+      parts, context_id, task_id = self.agent._construct_message_parts_from_session(
           self.mock_context
       )
       assert len(parts) == 3
@@ -823,7 +823,7 @@ def mock_converter(part):
         "google.adk.agents.remote_a2a_agent._present_other_agent_message"
     ) as mock_present:
       mock_present.side_effect = lambda event: event
-      parts, context_id = self.agent._construct_message_parts_from_session(
+      parts, context_id, task_id = self.agent._construct_message_parts_from_session(
           self.mock_context
       )
       assert len(parts) == 1
@@ -954,7 +954,7 @@ def mock_converter(part):
 
       self.mock_genai_part_converter.side_effect = mock_converter
 
-      parts, context_id = self.agent._construct_message_parts_from_session(
+      parts, context_id, task_id = self.agent._construct_message_parts_from_session(
           self.mock_context
       )
 
@@ -1373,12 +1373,12 @@ def test_construct_message_parts_from_session_success(self):
       mock_convert.return_value = mock_event
 
       with patch.object(
-          self.agent, "_genai_part_converter"
+         self.agent, "_genai_part_converter"
       ) as mock_convert_part:
         mock_a2a_part = Mock()
         mock_convert_part.return_value = mock_a2a_part
 
-        parts, context_id = self.agent._construct_message_parts_from_session(
+        parts, context_id, task_id = self.agent._construct_message_parts_from_session(
             self.mock_context
         )
 
@@ -1390,7 +1390,7 @@ def test_construct_message_parts_from_session_empty_events(self):
     """Test message parts construction with empty events."""
     self.mock_session.events = []
 
-    parts, context_id = self.agent._construct_message_parts_from_session(
+    parts, context_id, task_id = self.agent._construct_message_parts_from_session(
         self.mock_context
     )
 
@@ -1966,10 +1966,7 @@ async def test_run_async_impl_no_message_parts(self):
         with patch.object(
             self.agent, "_construct_message_parts_from_session"
         ) as mock_construct:
-          mock_construct.return_value = (
-              [],
-              None,
-          )  # Tuple with empty parts and no context_id
+          mock_construct.return_value =([], None, None)  # Tuple with empty parts and no context_id
 
           events = []
           async for event in self.agent._run_async_impl(self.mock_context):
@@ -1999,7 +1996,8 @@ async def test_run_async_impl_successful_request(self):
           mock_construct.return_value = (
               [mock_a2a_part],
               "context-123",
-          )  # Tuple with parts and context_id
+              None,
+          )  # Tuple with parts and context_id , no task_id
 
           # Mock A2A client
           mock_a2a_client = create_autospec(spec=A2AClient, instance=True)
@@ -2071,6 +2069,7 @@ async def test_run_async_impl_a2a_client_error(self):
           mock_construct.return_value = (
               [mock_a2a_part],
               "context-123",
+              None,
           )  # Tuple with parts and context_id
 
           # Mock A2A client that throws an exception
@@ -2138,6 +2137,7 @@ async def test_run_async_impl_with_meta_provider(self):
           mock_construct.return_value = (
               [mock_a2a_part],
               "context-123",
+              None,
           )  # Tuple with parts and context_id
 
           # Mock A2A client
@@ -2242,10 +2242,8 @@ async def test_run_async_impl_no_message_parts(self):
         with patch.object(
             self.agent, "_construct_message_parts_from_session"
         ) as mock_construct:
-          mock_construct.return_value = (
-              [],
-              None,
-          )  # Tuple with empty parts and no context_id
+          mock_construct.return_value = ([], None, None)
+          # Tuple with empty parts and no context_id
 
           events = []
           async for event in self.agent._run_async_impl(self.mock_context):
@@ -2275,6 +2273,7 @@ async def test_run_async_impl_successful_request(self):
           mock_construct.return_value = (
               [mock_a2a_part],
               "context-123",
+              None,
           )  # Tuple with parts and context_id
 
           # Mock A2A client
@@ -2349,6 +2348,7 @@ async def test_run_async_impl_a2a_client_error(self):
           mock_construct.return_value = (
               [mock_a2a_part],
               "context-123",
+              None,
           )  # Tuple with parts and context_id
 
           # Mock A2A client that throws an exception