修复循环推理bug

backend/app/core/intent.py

@@ -151,6 +151,20 @@ class ReactIntentReasoner:
             result.reasoning = "已获取足够信息，直接回答"
             return result
 
+        # 检查 RAG 是否多次失败（reasoning_history 中有失败的 RAG 记录）
+        # 失败的 RAG 记录特征：confidence = 0.0
+        rag_history = context.get("reasoning_history", [])
+        rag_fail_count = sum(
+            1 for h in rag_history
+            if h.get("action") in ("RETRIEVE_RAG", "RE_RETRIEVE_RAG") and h.get("confidence", 1.0) == 0.0
+        )
+        if rag_fail_count >= 2:
+            # RAG 多次失败，应该直接回答而不是继续重试
+            result.action = ReasoningAction.DIRECT_RESPONSE
+            result.confidence = 0.7
+            result.reasoning = f"RAG 已尝试 {rag_fail_count} 次均失败，知识库无相关内容，直接基于常识回答"
+            return result
+
         # 策略1：尝试使用 LLM 推理
         try:
             llm_result = await self._reason_with_llm(query, context)
@@ -347,7 +361,7 @@ _reasoner: Optional[ReactIntentReasoner] = None
 _small_reasoner: Optional[ReactIntentReasoner] = None
 
 
-def _get_reasoner(use_small_llm: bool = False) -> ReactIntentReasoner:
+def _get_reasoner(use_small_llm: bool = True) -> ReactIntentReasoner:
     """
     获取推理器实例
     
@@ -371,7 +385,7 @@ def _get_reasoner(use_small_llm: bool = False) -> ReactIntentReasoner:
 async def react_reason_async(
     query: str,
     context: Optional[Dict[str, Any]] = None,
-    use_small_llm: bool = False
+    use_small_llm: bool =  True
 ) -> ReasoningResult:
     """
     便捷函数：异步 React 推理（推荐使用）