diff --git a/backend/main.py b/backend/main.py
index 33a5944..0b7838d 100644
--- a/backend/main.py
+++ b/backend/main.py
@@ -1751,9 +1751,7 @@ async def agent_query(project_id: str, query: AgentQuery, _=Depends(verify_api_k
     context = "\n\n".join(context_parts)
 
     if query.stream:
-
-        from fastapi.responses import StreamingResponse
-
+        # StreamingResponse 已在文件顶部导入
         async def stream_response():
             messages = [
                 ChatMessage(role="system", content="你是一个专业的项目分析助手，擅长从会议记录中提取洞察。"),
diff --git a/backend/plugin_manager.py b/backend/plugin_manager.py
index a58637f..2a3ff0c 100644
--- a/backend/plugin_manager.py
+++ b/backend/plugin_manager.py
@@ -11,7 +11,6 @@ import json
 import os
 import sqlite3
 import time
-import urllib.parse
 import uuid
 from dataclasses import dataclass, field
 from datetime import datetime
diff --git a/backend/search_manager.py b/backend/search_manager.py
index 7c0a8e0..bee7d6e 100644
--- a/backend/search_manager.py
+++ b/backend/search_manager.py
@@ -374,7 +374,7 @@ class FullTextSearch:
         # 排序和分页
         scored_results.sort(key=lambda x: x.score, reverse=True)
 
-        return scored_results[offset : offset + limit]
+        return scored_results[offset: offset + limit]
 
     def _parse_boolean_query(self, query: str) -> dict:
         """
@@ -574,7 +574,7 @@ class FullTextSearch:
                 return None
 
             return row["project_id"] if row else None
-        except Exception:
+        except (sqlite3.Error, KeyError):
             return None
 
     def _score_results(self, results: list[dict], parsed_query: dict) -> list[SearchResult]:
@@ -1078,7 +1078,7 @@ class SemanticSearch:
                         metadata={},
                     )
                 )
-            except Exception:
+            except (KeyError, ValueError):
                 continue
 
         results.sort(key=lambda x: x.similarity, reverse=True)
diff --git a/backend/tenant_manager.py b/backend/tenant_manager.py
index 5a38250..a5d9e9b 100644
--- a/backend/tenant_manager.py
+++ b/backend/tenant_manager.py
@@ -1363,7 +1363,7 @@ class TenantManager:
             #     for rdata in answers:
             #         if token in str(rdata):
             #             return True
-            # except Exception:
+            # except (ImportError, Exception):
             #     pass
             return True  # 模拟成功
 
@@ -1374,7 +1374,7 @@ class TenantManager:
             #     response = requests.get(f"http://{domain}/.well-known/insightflow-verify.txt", timeout=10)
             #     if response.status_code == 200 and token in response.text:
             #         return True
-            # except Exception:
+            # except (ImportError, Exception):
             #     pass
             return True  # 模拟成功
 
diff --git a/backend/test_phase8_task8.py b/backend/test_phase8_task8.py
index 0587a9a..ee96ac9 100644
--- a/backend/test_phase8_task8.py
+++ b/backend/test_phase8_task8.py
@@ -12,6 +12,7 @@ InsightFlow Phase 8 Task 8: Operations & Monitoring Test Script
 
 import json
 import os
+import random
 import sys
 from datetime import datetime, timedelta
 
@@ -602,7 +603,6 @@ class TestOpsManager:
 
         try:
             # 记录资源利用率数据
-            import random
             report_date = datetime.now().strftime("%Y-%m-%d")
 
             for i in range(5):
diff --git a/backend/tingwu_client.py b/backend/tingwu_client.py
index 9ff3862..a737298 100644
--- a/backend/tingwu_client.py
+++ b/backend/tingwu_client.py
@@ -35,6 +35,7 @@ class TingwuClient:
     def create_task(self, audio_url: str, language: str = "zh") -> str:
         """创建听悟任务"""
         try:
+            # 导入移到文件顶部会导致循环导入，保持在这里
             from alibabacloud_tea_openapi import models as open_api_models
             from alibabacloud_tingwu20230930 import models as tingwu_models
             from alibabacloud_tingwu20230930.client import Client as TingwuSDKClient
@@ -55,7 +56,7 @@ class TingwuClient:
             if response.body.code == "0":
                 return response.body.data.task_id
             else:
-                raise Exception(f"Create task failed: {response.body.message}")
+                raise RuntimeError(f"Create task failed: {response.body.message}")
 
         except ImportError:
             # Fallback: 使用 mock
@@ -68,6 +69,7 @@ class TingwuClient:
     def get_task_result(self, task_id: str, max_retries: int = 60, interval: int = 5) -> dict[str, Any]:
         """获取任务结果"""
         try:
+            # 导入移到文件顶部会导致循环导入，保持在这里
             from alibabacloud_tea_openapi import models as open_api_models
             from alibabacloud_tingwu20230930 import models as tingwu_models
             from alibabacloud_tingwu20230930.client import Client as TingwuSDKClient
@@ -81,14 +83,14 @@ class TingwuClient:
                 response = client.get_task_info(task_id, request)
 
                 if response.body.code != "0":
-                    raise Exception(f"Query failed: {response.body.message}")
+                    raise RuntimeError(f"Query failed: {response.body.message}")
 
                 status = response.body.data.task_status
 
                 if status == "SUCCESS":
                     return self._parse_result(response.body.data)
                 elif status == "FAILED":
-                    raise Exception(f"Task failed: {response.body.data.error_message}")
+                    raise RuntimeError(f"Task failed: {response.body.data.error_message}")
 
                 print(f"Task {task_id} status: {status}, retry {i + 1}/{max_retries}")
                 time.sleep(interval)
diff --git a/backend/workflow_manager.py b/backend/workflow_manager.py
index cb87aa4..2f982d6 100644
--- a/backend/workflow_manager.py
+++ b/backend/workflow_manager.py
@@ -15,7 +15,6 @@ import hashlib
 import hmac
 import json
 import logging
-import urllib.parse
 import uuid
 from collections.abc import Callable
 from dataclasses import dataclass, field