BUG: TypeError: 'ChatMessage' object is not iterable when use **ChatOpenAI & CodeAgent**

[LivinLuo1993]

Problem
simple test code,while meeting something worong, when use ChatOpenAI & CodeAgent

from langchain_openai import ChatOpenAI
from smolagents import (
    CodeAgent, 
    LiteLLMModel, 
    OpenAIModel,
    WebSearchTool
)

model = ChatOpenAI(
            model_name="Qwen/Qwen3-30B-A3B-thinking-2507",
            api_key=os.getenv("MODELSCOPE_API_KEY"),
            base_url=os.getenv("MODELSCOPE_BASE_URL"),
            temperature=0.2,  # 随机性，0-1之间，值越高回复越多样
            max_tokens=1024,  # 最大生成token数
            streaming=True,
        )

print(model.invoke("你好"))
agent = CodeAgent(
    model=model,
    tools=[],
    planning_interval=3
)

print(agent.run("你好"))

Actual behavior and error logs
print(agent.run("你好"))
^^^^^^^^^^^^^^^
File "D:\miniconda3\envs\agent_mcp_skill\Lib\site-packages\smolagents\agents.py", line 498, in run
steps = list(self._run_stream(task=self.task, max_steps=max_steps, images=images))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "D:\miniconda3\envs\agent_mcp_skill\Lib\site-packages\smolagents\agents.py", line 554, in _run_stream
for element in self._generate_planning_step(
File "D:\miniconda3\envs\agent_mcp_skill\Lib\site-packages\smolagents\agents.py", line 671, in _generate_planning_step
plan_message = self.model.generate(input_messages, stop_sequences=["<end_plan>"])
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "D:\miniconda3\envs\agent_mcp_skill\Lib\site-packages\langchain_core\language_models\chat_models.py", line 913, in generate
_format_for_tracing(message_list) for message_list in messages
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "D:\miniconda3\envs\agent_mcp_skill\Lib\site-packages\langchain_core\language_models\chat_models.py", line 129, in _format_for_tracing
for message in messages:
TypeError: 'ChatMessage' object is not iterable

Expected behavior
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Environment:
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• OS: [e.g., Linux, macOS, Windows]
• Python version: [e.g., 3.10]
• Package version: (output of pip show smolagents)

Additional context (optional)
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Checklist

• I have searched the existing issues and have not found a similar bug report.
• I have provided a minimal, reproducible example.
• I have provided the full traceback of the error.
• I have provided my environment details.
• I am willing to work on this issue and submit a pull request. (optional)