feat: add renderSidebar — populates sidebar list from session data

frontend/app.js

@@ -339,6 +339,35 @@ function buildSidebarHTML(session, currentSession) {
   );
 }
 
+/**
+ * Render the session sidebar list. Only renders in fullscreen view.
+ * Shows empty state when no sessions exist.
+ * Binds click handlers on each sidebar-item to switch sessions.
+ * @param {object[]} sessions
+ * @param {string|null} currentSession - name of the currently active session
+ */
+function renderSidebar(sessions, currentSession) {
+  if (_viewMode !== 'fullscreen') return;
+
+  const list = $('sidebar-list');
+  if (!list) return;
+
+  if (!sessions || sessions.length === 0) {
+    list.innerHTML = '<div class="sidebar-empty">No sessions</div>';
+    return;
+  }
+
+  list.innerHTML = sessions.map((session) => buildSidebarHTML(session, currentSession)).join('');
+
+  // Bind click handlers on each sidebar item
+  list.querySelectorAll('.sidebar-item').forEach((item) => {
+    const name = item.dataset.session;
+    on(item, 'click', () => {
+      if (name !== currentSession) openSession(name);
+    });
+  });
+}
+
 /**
  * Render the session grid. Shows empty state when no sessions exist.
  * On mobile, sorts sessions by priority before rendering.
@@ -937,6 +966,7 @@ if (typeof module !== 'undefined' && module.exports) {
     escapeHtml,
     buildTileHTML,
     buildSidebarHTML,
+    renderSidebar,
     renderGrid,
     requestNotificationPermission,
     handleBellTransitions,

frontend/tests/test_app.mjs

@@ -1692,3 +1692,77 @@ test('buildSidebarHTML includes snapshot preview in a pre element', () => {
   const html = app.buildSidebarHTML(session, '');
   assert.ok(/<pre>[\s\S]*line1[\s\S]*<\/pre>/.test(html), 'snapshot content should be inside a <pre> element');
 });
+
+// --- renderSidebar ---
+
+test('renderSidebar populates sidebar-list innerHTML when viewMode is fullscreen', () => {
+  let capturedHTML = '';
+  const mockList = {
+    get innerHTML() { return capturedHTML; },
+    set innerHTML(v) { capturedHTML = v; },
+    querySelectorAll: () => [],
+  };
+  const origGetById = globalThis.document.getElementById;
+  globalThis.document.getElementById = (id) => {
+    if (id === 'sidebar-list') return mockList;
+    return null;
+  };
+
+  app._setViewMode('fullscreen');
+  const sessions = [
+    { name: 'session-a', snapshot: '', bell: { unseen_count: 0 } },
+    { name: 'session-b', snapshot: '', bell: { unseen_count: 0 } },
+  ];
+  app.renderSidebar(sessions, 'session-a');
+
+  assert.ok(capturedHTML.includes('sidebar-item'), 'innerHTML should contain sidebar-item');
+  assert.ok(capturedHTML.includes('sidebar-item--active'), 'innerHTML should contain sidebar-item--active for active session');
+
+  globalThis.document.getElementById = origGetById;
+  app._setViewMode('grid');
+});
+
+test('renderSidebar renders empty message when sessions array is empty', () => {
+  let capturedHTML = '';
+  const mockList = {
+    get innerHTML() { return capturedHTML; },
+    set innerHTML(v) { capturedHTML = v; },
+    querySelectorAll: () => [],
+  };
+  const origGetById = globalThis.document.getElementById;
+  globalThis.document.getElementById = (id) => {
+    if (id === 'sidebar-list') return mockList;
+    return null;
+  };
+
+  app._setViewMode('fullscreen');
+  app.renderSidebar([], null);
+
+  assert.ok(capturedHTML.includes('sidebar-empty'), 'innerHTML should contain sidebar-empty class');
+  assert.ok(capturedHTML.includes('No sessions'), 'innerHTML should contain "No sessions" text');
+
+  globalThis.document.getElementById = origGetById;
+  app._setViewMode('grid');
+});
+
+test('renderSidebar does nothing when view is not fullscreen', () => {
+  let innerHTMLSet = false;
+  const mockList = {
+    get innerHTML() { return ''; },
+    set innerHTML(v) { innerHTMLSet = true; },
+    querySelectorAll: () => [],
+  };
+  const origGetById = globalThis.document.getElementById;
+  globalThis.document.getElementById = (id) => {
+    if (id === 'sidebar-list') return mockList;
+    return null;
+  };
+
+  app._setViewMode('grid');
+  const sessions = [{ name: 'session-a', snapshot: '', bell: { unseen_count: 0 } }];
+  app.renderSidebar(sessions, null);
+
+  assert.strictEqual(innerHTMLSet, false, 'innerHTML setter should never be called when not in fullscreen');
+
+  globalThis.document.getElementById = origGetById;
+});