Python: [Bug]: Inconsistent handling of response_id in returned messages by A2AAgent

[lixiaoqiang]

Description

The A2AAgent handles the response_id inconsistently when processing returned messages.
If the returned message type is A2AMessage, it sets response_id to A2AMessage.message_id; otherwise, it sets response_id to task.id.
This results in inconsistent response_id values.
Current code:

        async for item in a2a_stream:
            if isinstance(item, A2AMessage):
                # Process A2A Message
                contents = self._parse_contents_from_a2a(item.parts)
                update = AgentResponseUpdate(
                    contents=contents,
                    role="assistant" if item.role == A2ARole.agent else "user",
                    response_id=str(getattr(item, "message_id", uuid.uuid4())),
                    additional_properties=item.metadata,
                    raw_representation=item,
                )
                all_updates.append(update)
                yield update

I think it should be handled as follows:

        async for item in a2a_stream:
            if isinstance(item, A2AMessage):
                # Process A2A Message
                contents = self._parse_contents_from_a2a(item.parts)
                update = AgentResponseUpdate(
                    contents=contents,
                    role="assistant" if item.role == A2ARole.agent else "user",
                    response_id=item.task_id or uuid.uuid4(),
                    message_id=item.message_id,
                    additional_properties=item.metadata,
                    raw_representation=item,
                )
                all_updates.append(update)
                yield update

Code Sample

Error Messages / Stack Traces

Package Versions

agent-framework-core:1.0.1

Python Version

python 3.13

Additional Context

No response

[LEDazzio01]

I'd like to take this one — I have context in the A2A module from PR #5213 (session context_id propagation) and can investigate the response_id inconsistency.