Fixes#2804
The useStream hook tracks messages-tuple mode which captures ALL LLM
events, including the internal summarization LLM call. This caused the
English summary text to briefly appear as an AI message in the UI before
the REMOVE_ALL_MESSAGES state update replaced it.
Fix by overriding _create_summary/_acreate_summary to pass callbacks=[]
when invoking the summary model, preventing LangGraph from forwarding
the internal LLM events to the frontend stream. Also add
hide_from_ui=True to the summary HumanMessage's additional_kwargs as a
belt-and-suspenders safety net alongside the existing name=summary
check.
Willem Jiang