fix(mcp): 修复前端空输入重置为不超时，增加超时路径单元测试

P3: 清空输入框时回退到默认值 300 而非 0；新增两个 tokio 测试覆盖有超时和无超时(error pass-through)路径

src/mcp/tool_adapter.rs

@@ -281,4 +281,49 @@ mod tests {
         // Empty stays empty
         assert_eq!(sanitize_tool_name(""), "");
     }
+
+    #[tokio::test]
+    async fn test_execute_returns_error_when_server_not_connected() {
+        // McpClientManager with no connected servers — call should fail immediately
+        // with "not connected" error, not hang or timeout.
+        let manager = Arc::new(McpClientManager::new());
+        let schema: serde_json::Map<String, serde_json::Value> =
+            serde_json::json!({"type": "object"})
+                .as_object()
+                .unwrap()
+                .clone();
+        let tool_info = Tool::new("echo", "Echo tool", schema);
+        let wrapper = McpToolWrapper::new(manager, "ghost".to_string(), tool_info, 300);
+
+        let result = wrapper.execute(serde_json::json!({})).await;
+        assert!(result.is_err());
+        let msg = result.unwrap_err().to_string();
+        assert!(
+            msg.contains("not connected"),
+            "expected 'not connected' error, got: {msg}"
+        );
+    }
+
+    #[tokio::test]
+    async fn test_timeout_zero_does_not_wrap() {
+        // With timeout_secs = 0, the wrapper should pass through directly
+        // without tokio::time::timeout. The call still fails because no server
+        // is connected, but the error path is the non-timeout branch.
+        let manager = Arc::new(McpClientManager::new());
+        let schema: serde_json::Map<String, serde_json::Value> =
+            serde_json::json!({"type": "object"})
+                .as_object()
+                .unwrap()
+                .clone();
+        let tool_info = Tool::new("echo", "Echo tool", schema);
+        let wrapper = McpToolWrapper::new(manager, "ghost".to_string(), tool_info, 0);
+
+        let result = wrapper.execute(serde_json::json!({})).await;
+        assert!(result.is_err());
+        let msg = result.unwrap_err().to_string();
+        assert!(
+            msg.contains("not connected"),
+            "expected 'not connected' error, got: {msg}"
+        );
+    }
 }

web/src/components/Settings/tabs/McpTab.tsx

@@ -63,7 +63,10 @@ export function McpTab({ config, update, setToast }: Props) {
           <input
             type="number"
             value={config.mcp_tool_timeout_secs ?? 300}
-            onChange={(e) => update('mcp_tool_timeout_secs', Number(e.target.value))}
+            onChange={(e) => {
+              const v = e.target.value;
+              update('mcp_tool_timeout_secs', v === '' ? 300 : Number(v));
+            }}
             className={inputCls}
             min={0}
             step={30}