Python: [Bug]: AG-UI EventEncoder._encode_sse cannot handle AgentResponseUpdate

[lixiaoqiang]

Description

EventEncoder._encode_sse uses module_dump_json to return data. When the event type is AgentResponseUpdate, AgentResponseUpdate fails to serialize/export.
Error Message:
AttributeError: 'AgentResponseUpdate' object has no attribute 'model_dump_json'

Code Sample

Error Messages / Stack Traces

Package Versions

agent-framework-ag-ui=1.0.0b260311

Python Version

3.13

Additional Context

No response

[LEDazzio01]

I'd like to pick this up. The root cause is that EventEncoder.encode() (from ag_ui.encoder) calls model_dump_json(), but AgentResponseUpdate is not a Pydantic model — it extends SerializationMixin and uses to_json() instead.

I'll add a defensive guard in _endpoint.py's event_generator() to skip non-BaseEvent objects before they reach the encoder, with appropriate logging. PR incoming.