修改引用逻辑，修改长期记忆bug

app/nodes/tool_call.py

@@ -6,15 +6,13 @@
 import asyncio
 from typing import Any, Dict
 from langchain_core.messages import AIMessage, ToolMessage
-from langgraph.runtime import Runtime
 from langgraph.config import get_stream_writer
 
 # 本地模块
-from app.graph.state import MessagesState, GraphContext
+from app.graph.state import MessagesState
 from app.utils.logging import log_state_change
 from app.logger import debug, info
 
-
 def create_tool_call_node(tools_by_name: Dict[str, Any]):
     """
     工厂函数：创建工具执行节点