feat(llm): migrate model calls to LangChain ChatOpenAI

test/agent/test_workflow_prompts.py

@@ -104,14 +104,14 @@ async def test_openai_adapter_preserves_message_roles():
     from unittest.mock import AsyncMock
     from src.agent.llm import OpenAILLMService
 
-    create = AsyncMock(return_value=SimpleNamespace(choices=[
-        SimpleNamespace(message=SimpleNamespace(content="<state>1002</state>收到。"))
-    ]))
+    from langchain_core.messages import AIMessage
+
+    create = AsyncMock(return_value=AIMessage(content="<state>1002</state>收到。"))
     llm = OpenAILLMService(model="test", api_key="test", max_retries=0)
-    llm._client = SimpleNamespace(chat=SimpleNamespace(completions=SimpleNamespace(create=create)))
+    llm._client = SimpleNamespace(ainvoke=create)
     history = [{"role": "assistant", "content": "之前的问题"}]
     await llm.complete("系统提示词", "本轮输入", history=history)
-    assert create.call_args.kwargs["messages"] == [
+    assert create.call_args.args[0] == [
         {"role": "system", "content": "系统提示词"},
         {"role": "assistant", "content": "之前的问题"},
         {"role": "user", "content": "本轮输入"},