langchain - 💡(How to fix) Fix stream_events(version="v3"): reasoning content dropped from AIMessage when message also contains a tool_call

import asyncio
from langchain.agents import create_agent
from langchain_google_genai import ChatGoogleGenerativeAI
from langchain_core.tools import tool
from langchain_core.messages import AIMessage


@tool
def get_weather(city: str) -> str:
    """Get the weather for a city."""
    return f"Sunny in {city}"


async def main():
    llm = ChatGoogleGenerativeAI(
        model="gemini-2.5-pro",
        thinking_budget=2048,
        include_thoughts=True,
    )
    agent = create_agent(llm, [get_weather])

    run = await agent.astream_events(
        {"messages": [{"role": "user",
                       "content": "What is the weather in San Francisco?"}]},
        version="v3",
    )

    print("============ STREAM ============")
    async for chat_stream in run.messages:
        print("\n--- streamed AIMessage ---")
        print("[reasoning] ", end="", flush=True)
        async for chunk in chat_stream.reasoning:
            print(chunk, end="", flush=True)
        print("\n[text] ", end="", flush=True)
        async for chunk in chat_stream.text:
            print(chunk, end="", flush=True)
        print()

    final = await run.output()
    print("\n\n============ final state ============")
    for m in final["messages"]:
        if isinstance(m, AIMessage):
            print("\n--- AIMessage ---")
            print("content:   ", m.content)
            print("tool_calls:", m.tool_calls)


asyncio.run(main())

---

============ STREAM ============

--- streamed AIMessage #1 ---
[reasoning] **Querying the Weather**

I'm zeroing in on the task at hand. The user wants San Francisco's weather. I've pinpointed the `get_weather` tool as the solution. Now, I'm just formulating the correct tool call. Specifically, I'm setting the `city` parameter to "San Francisco" and will wrap the tool call in a `print` statement.


**Formulating the Code**

I'm solidifying the final code block. I've got the `get_weather` tool call prepared and the city parameter set. The next step is to neatly package this tool call within the `print` function. Then, I'll ensure it's accurately embedded within the `tool_code` block before submitting the response.



[text]

--- streamed AIMessage #2 ---
[reasoning]
[text] Sunny in San Francisco

--- streamed AIMessage #3 ---
[reasoning]
[text] The weather in San Francisco is sunny.



============ final state ============

--- AIMessage ---
content:    [{'type': 'tool_call', 'id': '6d665264-4fd0-46a3-889e-f04e47548ed0', 'name': 'get_weather', 'args': {'city': 'San Francisco'}}]
tool_calls: [{'name': 'get_weather', 'args': {'city': 'San Francisco'}, 'id': '6d665264-4fd0-46a3-889e-f04e47548ed0', 'type': 'tool_call'}] **<--- Missing reasoning**

--- AIMessage ---
content:    [{'type': 'text', 'text': 'The weather in San Francisco is sunny.\n', 'index': 0}]
tool_calls: []