重构：继续移除对 debug_info 的依赖，主要模块已完成迁移

backend/app/main_graph/nodes/hybrid_router.py

@@ -219,11 +219,11 @@ def route_from_hybrid_decision(state: MainGraphState) -> str:
 
 
 def check_fast_path_success(state: MainGraphState) -> str:
-    """检查快速路径是否成功"""
-    if state.debug_info.get("fast_path_failed"):
+    """检查快速路径是否成功 - 使用新的结构化字段"""
+    if state.fast_path.failed:
         info("[Fast Path Check] 快速路径失败，升级到 React 循环")
         return "escalate"
-
+    
     info("[Fast Path Check] 快速路径成功，进入 llm_call")
     return "llm_call"