Clarify chat retrieval failures

ai_knowledge_base_v2/apps/backend/app/services/chat_service.py

@@ -107,7 +107,7 @@ class ChatService:
             db.commit()
             raise HTTPException(
                 status_code=status.HTTP_502_BAD_GATEWAY,
-                detail="外部服务暂时不可用，请稍后再试",
+                detail=str(exc),
             ) from exc
         cost_ms = int((perf_counter() - started_at) * 1000)
 

ai_knowledge_base_v2/apps/backend/app/services/feishu_service.py

@@ -267,8 +267,14 @@ class FeishuKnowledgeService:
         if config.search_url:
             try:
                 return cls._retrieve_from_search(question, scopes, config)
-            except ExternalServiceError:
-                pass
+            except ExternalServiceError as exc:
+                try:
+                    return cls._retrieve_from_feishu(question, scopes)
+                except ExternalServiceError as fallback_exc:
+                    raise ExternalServiceError(
+                        f"{exc}；飞书直读也失败：{fallback_exc}",
+                        provider="feishu",
+                    ) from fallback_exc
         return cls._retrieve_from_feishu(question, scopes)
 
     @classmethod
@@ -298,19 +304,34 @@ class FeishuKnowledgeService:
         """从飞书知识库检索文档内容"""
         from app.services.rag_service import RetrievedChunk
 
+        settings = get_settings()
+        if not settings.feishu_app_id or not settings.feishu_app_secret:
+            raise ExternalServiceError(
+                "未配置飞书应用凭证，无法读取飞书知识库。请配置 FEISHU_APP_ID/FEISHU_APP_SECRET，"
+                "或在系统配置中填写可用的飞书搜索接口地址。",
+                provider="feishu",
+            )
+
         # 收集所有文档片段
         all_chunks: list[tuple[KnowledgeScope, str, str, str | None]] = []
+        load_errors: list[str] = []
 
         for scope in scopes:
             try:
                 documents = cls._load_documents(scope)
-            except ExternalServiceError:
+            except ExternalServiceError as exc:
+                load_errors.append(f"{scope.name}：{exc}")
                 continue
 
             for title, content, source_url in documents:
                 all_chunks.append((scope, title, content, source_url))
 
         if not all_chunks:
+            if load_errors:
+                raise ExternalServiceError(
+                    "飞书知识库读取失败：" + "；".join(load_errors[:3]),
+                    provider="feishu",
+                )
             return []
 
         # 关键词匹配评分（简单但够用的检索方式）