fix: enable weave tracing on chat widget

[dmadisetti]

📝 Summary

Currently weave tracing fails on the following code:

chat_client = OpenAI()

@weave.op()
def handle_chat(messages, config):
    """Wrapper that ensures string return for marimo."""
    user_msg = messages[-1].content
    chat_messages = [{"role": "user", "content": user_msg}]

    response = chat_client.chat.completions.create(
        model="gpt-4o-mini",
        messages=[get_system_prompt()] + chat_messages,
        tools=get_robot_tools(),
    )

    msg = response.choices[0].message
    return msg.content

chat = mo.ui.chat(
    handle_chat
)
chat

This is because weave.op returns a BoxedStr(str) which the causes pydantic to fail. As such, we force a conversion to string even if isinstance(chunk, str).

[vercel]

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Jan 31, 2026 10:09pm

[dmadisetti]

Optional deps look like they'll be fixed with #8077
Going to merge for pixi lock

[github-actions]

🚀 Development release published. You may be able to view the changes at https://marimo.app?v=0.19.8-dev5