fix: Update remote_a2a_agent to better handle streaming events and avoid duplicate responses

Currently, the A2A Task -> ADK event conversion is producing the same events on the last two update events (the last is a status update marking the task complete)

The change here based on A2AClientEvent(task, update):
 - if the update == None: handle the non-streaming task case and also streaming case for the initial task creation event
 - if the update = TaskStatusUpdateEvent AND a message is set: emit an event with that message
 - if a task status update AND no message is set: don't emit event (for example, the final status update)
 - if the update is ArtifactUpdateEvent and it's final artifact: emit the event

PiperOrigin-RevId: 812878869

src/google/adk/agents/remote_a2a_agent.py

@@ -36,6 +36,8 @@ try:
   from a2a.types import Message as A2AMessage
   from a2a.types import Part as A2APart
   from a2a.types import Role
+  from a2a.types import TaskArtifactUpdateEvent as A2ATaskArtifactUpdateEvent
+  from a2a.types import TaskStatusUpdateEvent as A2ATaskStatusUpdateEvent
   from a2a.types import TransportProtocol as A2ATransport
 except ImportError as e:
   import sys
@@ -393,7 +395,7 @@ class RemoteA2aAgent(BaseAgent):
 
   async def _handle_a2a_response(
       self, a2a_response: A2AClientEvent | A2AMessage, ctx: InvocationContext
-  ) -> Event:
+  ) -> Optional[Event]:
     """Handle A2A response and convert to Event.
 
     Args:
@@ -401,14 +403,37 @@ class RemoteA2aAgent(BaseAgent):
       ctx: The invocation context
 
     Returns:
-      Event object representing the response
+      Event object representing the response, or None if no event should be
+      emitted.
     """
     try:
       if isinstance(a2a_response, tuple):
-        # ClientEvent is a tuple of the absolute Task state and the last update.
-        # We only need the Task state.
-        task = a2a_response[0]
-        event = convert_a2a_task_to_event(task, self.name, ctx)
+        task, update = a2a_response
+        if update is None:
+          # This is the initial response for a streaming task or the complete
+          # response for a non-streaming task, which is the full task state.
+          # We process this to get the initial message.
+          event = convert_a2a_task_to_event(task, self.name, ctx)
+        elif isinstance(update, A2ATaskStatusUpdateEvent) and update.message:
+          # This is a streaming task status update with a message.
+          event = convert_a2a_message_to_event(update.message, self.name, ctx)
+        elif isinstance(update, A2ATaskArtifactUpdateEvent) and (
+            not update.append or update.last_chunk
+        ):
+          # This is a streaming task artifact update.
+          # We only handle full artifact updates and ignore partial updates.
+          # Note: Depends on the server implementation, there is no clear
+          # definition of what a partial update is currently. We use the two
+          # signals:
+          # 1. append: True for partial updates, False for full updates.
+          # 2. last_chunk: True for full updates, False for partial updates.
+          event = convert_a2a_task_to_event(task, self.name, ctx)
+        else:
+          # This is a streaming update without a message (e.g. status change)
+          # or an partial artifact update. We don't emit an event for these
+          # for now.
+          return None
+
         event.custom_metadata = event.custom_metadata or {}
         event.custom_metadata[A2A_METADATA_PREFIX + "task_id"] = task.id
         if task.context_id:
@@ -416,7 +441,7 @@ class RemoteA2aAgent(BaseAgent):
               task.context_id
           )
 
-      # Otherwise, it's a regular A2AMessage.
+      # Otherwise, it's a regular A2AMessage for non-streaming responses.
       elif isinstance(a2a_response, A2AMessage):
         event = convert_a2a_message_to_event(a2a_response, self.name, ctx)
         event.custom_metadata = event.custom_metadata or {}
@@ -492,6 +517,8 @@ class RemoteA2aAgent(BaseAgent):
         logger.debug(build_a2a_response_log(a2a_response))
 
         event = await self._handle_a2a_response(a2a_response, ctx)
+        if not event:
+          continue
 
         # Add metadata about the request and response
         event.custom_metadata = event.custom_metadata or {}