修复导入错误：更新 router.py 到 MainGraphState

backend/app/main_graph/nodes/router.py

@@ -8,11 +8,11 @@ from langchain_core.messages import AIMessage
 
 # 本地模块
 from app.config import ENABLE_GRAPH_TRACE, MEMORY_SUMMARIZE_INTERVAL
-from app.main_graph.state import MessagesState
+from app.main_graph.state import MainGraphState
 from app.logger import info
 
 
-def should_continue(state: MessagesState) -> Literal['tool_node', 'summarize', 'finalize']:
+def should_continue(state: MainGraphState) -> Literal['tool_node', 'summarize', 'finalize']:
     """
     决定下一步：工具调用、生成摘要还是结束
     
@@ -22,7 +22,7 @@ def should_continue(state: MessagesState) -> Literal['tool_node', 'summarize', '
     Returns:
         下一个节点名称
     """
-    last_message = state["messages"][-1]
+    last_message = state.messages[-1]
 
     # 1. 如果需要调用工具，优先进入工具节点
     if isinstance(last_message, AIMessage) and last_message.tool_calls:
@@ -32,7 +32,7 @@ def should_continue(state: MessagesState) -> Literal['tool_node', 'summarize', '
 
     # 2. 如果是 AI 的最终回复，判断是否达到摘要生成阈值
     if isinstance(last_message, AIMessage):
-        turns = state.get("turns_since_last_summary", 0)
+        turns = state.turns_since_last_summary
         if turns >= MEMORY_SUMMARIZE_INTERVAL:
             if ENABLE_GRAPH_TRACE:
                 info(f"🔀 [路由决策] 收到 AI 最终回复，已达摘要阈值({turns}/{MEMORY_SUMMARIZE_INTERVAL}) → 转向 'summarize'")