feat: stage sidebar submenu panel visibility

test/sidebar-submenu-panel-and-theme-mode.node-test.js

@@ -44,3 +44,26 @@ test('侧边栏样式：收起时不应在页面按钮下方显示目录子菜
     '收起态的 submenu 应明确设置为 display: none'
   );
 });
+
+test('侧边栏目录面板：应默认隐藏，并通过独立状态类延后淡入', () => {
+  const repoRoot = path.resolve(__dirname, '..');
+  const sidebarStylePath = path.join(repoRoot, 'assets', 'styles', '_sidebar.css');
+  const uiPath = path.join(repoRoot, 'src', 'runtime', 'app', 'ui.js');
+  const styleContent = fs.readFileSync(sidebarStylePath, 'utf8');
+  const uiContent = fs.readFileSync(uiPath, 'utf8');
+
+  assert.match(
+    styleContent,
+    /\.sidebar-submenu-panel\s*\{[\s\S]*opacity:\s*0;[\s\S]*visibility:\s*hidden;/m,
+    '目录面板默认应处于隐藏状态'
+  );
+  assert.match(
+    styleContent,
+    /\.sidebar\.submenu-panel-visible \.sidebar-submenu-panel:not\(:empty\)\s*\{[\s\S]*opacity:\s*1;[\s\S]*visibility:\s*visible;/m,
+    '目录面板应通过 submenu-panel-visible 状态类显现'
+  );
+  assert.ok(
+    uiContent.includes('submenu-panel-visible'),
+    'src/runtime/app/ui.js 应控制 submenu-panel-visible 状态类'
+  );
+});