修改引用逻辑，修改长期记忆bug

app/graph/retrieve_memory.py

@@ -4,15 +4,13 @@
 """
 
 from typing import Any, Dict
-from langgraph.runtime import Runtime
 
 # 本地模块
-from app.graph.state import MessagesState, GraphContext
+from app.graph.state import MessagesState
 from app.memory.mem0_client import Mem0Client
 from app.utils.logging import log_state_change
 from app.logger import debug
 
-
 def create_retrieve_memory_node(mem0_client: Mem0Client):
     """
     工厂函数：创建记忆检索节点