add langgraph use

examples/stream_modes/messages_demo.py

@@ -0,0 +1,43 @@
+from typing import TypedDict
+
+from langgraph.graph import StateGraph, START
+from langchain_core.messages import HumanMessage
+
+from langgraph_qwen import ChatQwenOpenAICompat
+
+
+class SimpleState(TypedDict):
+    topic: str
+    joke: str
+
+
+model = ChatQwenOpenAICompat(temperature=0)
+
+
+def call_model(state: SimpleState):
+    llm_response = model.invoke([HumanMessage(content=f"Generate a joke about {state['topic']}")])
+    return {"joke": llm_response.content}
+
+
+graph = (
+    StateGraph(SimpleState)
+    .add_node("call_model", call_model)
+    .add_edge(START, "call_model")
+    .compile()
+)
+
+
+def main():
+    print("=" * 60)
+    print("💬 LangGraph stream_mode='messages' 示例（捕获 LLM tokens）")
+    print("=" * 60)
+    for msg, meta in graph.stream({"topic": "cats"}, stream_mode="messages"):
+        if hasattr(msg, "content") and msg.content:
+            node = meta.get("langgraph_node", "unknown")
+            print(f"[{node}] {msg.content}", end="", flush=True)
+    print("\n\n✅ 完成！")
+
+
+if __name__ == "__main__":
+    main()
+