diff --git a/modules/mcp_client_manager.py b/modules/mcp_client_manager.py
index c558a4b..54bf2ad 100644
--- a/modules/mcp_client_manager.py
+++ b/modules/mcp_client_manager.py
@@ -1073,6 +1073,11 @@ class MCPClientManager:
         tools: List[Dict[str, Any]] = []
         alias_map: Dict[str, MCPToolBinding] = {}
 
+        # 防止“外部直接改配置文件但进程内缓存没刷新”：
+        # 这里在常规构建阶段主动重载一次，避免后续 discover/update 把旧缓存反写回磁盘。
+        if ensure_discovery:
+            self.registry.reload()
+
         servers = self.registry.list_enabled_servers()
         for server in servers:
             sid = str(server.get("id") or "").strip()
diff --git a/test/test_mcp_integration.py b/test/test_mcp_integration.py
index ef14d85..3a07c4d 100644
--- a/test/test_mcp_integration.py
+++ b/test/test_mcp_integration.py
@@ -210,6 +210,49 @@ class MCPIntegrationTest(unittest.TestCase):
         self.assertIn("extra_stdio", by_id, sync_result)
         self.assertTrue(by_id["extra_stdio"].get("success"), sync_result)
 
+    def test_build_openai_tools_reload_external_file_changes(self):
+        # 模拟外部直接改配置文件（registry._cache 仍是旧内容）
+        payload = {
+            "servers": [
+                {
+                    "id": "demo_stdio",
+                    "name": "Demo MCP",
+                    "transport": "stdio",
+                    "enabled": True,
+                    "command": sys.executable,
+                    "args": [str(self.demo_script)],
+                    "timeout_seconds": 10,
+                },
+                {
+                    "id": "extra_stdio",
+                    "name": "Extra MCP",
+                    "transport": "stdio",
+                    "enabled": True,
+                    "command": sys.executable,
+                    "args": [str(self.demo_script)],
+                    "timeout_seconds": 10,
+                },
+            ]
+        }
+        self.registry_path.write_text(json.dumps(payload, ensure_ascii=False, indent=2), encoding="utf-8")
+
+        tools, alias_map = self.manager.build_openai_tools(
+            ensure_discovery=True,
+            discovery_timeout_seconds=10,
+        )
+        self.assertTrue(tools)
+        self.assertTrue(alias_map)
+        self.assertTrue(
+            any(getattr(binding, "server_id", "") == "extra_stdio" for binding in alias_map.values()),
+            alias_map,
+        )
+
+        # 关键断言：外部新增服务不应被旧缓存反写覆盖
+        after = json.loads(self.registry_path.read_text(encoding="utf-8"))
+        ids = {str((item or {}).get("id") or "") for item in (after.get("servers") or [])}
+        self.assertIn("demo_stdio", ids)
+        self.assertIn("extra_stdio", ids)
+
     def test_stdio_container_path_rewrite_from_workspace(self):
         fake_session = SimpleNamespace(
             mode="docker",