fix: Prevent stopping event processing on events with None content

PiperOrigin-RevId: 856706510

src/google/adk/agents/remote_a2a_agent.py

@@ -348,6 +348,13 @@ class RemoteA2aAgent(BaseAgent):
 
     return a2a_message
 
+  def _is_remote_response(self, event: Event) -> bool:
+    return (
+        event.author == self.name
+        and event.custom_metadata
+        and event.custom_metadata.get(A2A_METADATA_PREFIX + "response", False)
+    )
+
   def _construct_message_parts_from_session(
       self, ctx: InvocationContext
   ) -> tuple[list[A2APart], Optional[str]]:
@@ -365,7 +372,7 @@ class RemoteA2aAgent(BaseAgent):
 
     events_to_process = []
     for event in reversed(ctx.session.events):
-      if event.author == self.name:
+      if self._is_remote_response(event):
         # stop on content generated by current a2a agent given it should already
         # be in remote session
         if event.custom_metadata:
@@ -496,6 +503,8 @@ class RemoteA2aAgent(BaseAgent):
             invocation_id=ctx.invocation_id,
             branch=ctx.branch,
         )
+      event.custom_metadata = event.custom_metadata or {}
+      event.custom_metadata[A2A_METADATA_PREFIX + "response"] = True
       return event
     except A2AClientError as e:
       logger.error("Failed to handle A2A response: %s", e)

tests/unittests/agents/test_remote_a2a_agent.py

@@ -683,7 +683,16 @@ class TestRemoteA2aAgentMessageHandling:
     agent1 = Mock()
     agent1.content = content2
     agent1.author = self.agent.name
-    agent1.custom_metadata = None
+    agent1.custom_metadata = {
+        A2A_METADATA_PREFIX + "response": True,
+    }
+
+    agent2 = Mock()
+    agent2.content = None
+    agent2.author = self.agent.name
+    # Just actions, no content. Not marked as a response.
+    agent2.actions = Mock()
+    agent2.custom_metadata = None
 
     part3 = Mock()
     part3.text = "User 2"
@@ -694,7 +703,7 @@ class TestRemoteA2aAgentMessageHandling:
     user2.author = "user"
     user2.custom_metadata = None
 
-    self.mock_session.events = [user1, agent1, user2]
+    self.mock_session.events = [user1, agent1, user2, agent2]
 
     def mock_converter(part):
       mock_a2a_part = Mock()
@@ -785,7 +794,10 @@ class TestRemoteA2aAgentMessageHandling:
     agent1 = Mock()
     agent1.content = content2
     agent1.author = self.agent.name
-    agent1.custom_metadata = {A2A_METADATA_PREFIX + "context_id": "ctx-1"}
+    agent1.custom_metadata = {
+        A2A_METADATA_PREFIX + "response": True,
+        A2A_METADATA_PREFIX + "context_id": "ctx-1",
+    }
 
     part3 = Mock()
     part3.text = "User 2"