feat: pre-render sidebar on openSession before first poll tick

frontend/app.js

@@ -360,12 +360,14 @@ function renderSidebar(sessions, currentSession) {
   list.innerHTML = sessions.map((session) => buildSidebarHTML(session, currentSession)).join('');
 
   // Bind click handlers on each sidebar item
-  list.querySelectorAll('.sidebar-item').forEach((item) => {
+  if (typeof list.querySelectorAll === 'function') {
-    const name = item.dataset.session;
+    list.querySelectorAll('.sidebar-item').forEach((item) => {
-    on(item, 'click', () => {
+      const name = item.dataset.session;
-      if (name !== currentSession) openSession(name);
+      on(item, 'click', () => {
+        if (name !== currentSession) openSession(name);
+      });
     });
-  });
+  }
 }
 
 const SIDEBAR_KEY = 'muxplex.sidebarOpen';
@@ -604,6 +606,10 @@ async function openSession(name, opts = {}) {
   _viewingSession = name;
   _viewMode = 'fullscreen';
 
+  // Pre-render sidebar with current sessions before first poll tick
+  initSidebar();
+  renderSidebar(_currentSessions, name);
+
   // Update expanded header
   const nameEl = $('expanded-session-name');
   if (nameEl) nameEl.textContent = name;
@@ -638,6 +644,9 @@ async function openSession(name, opts = {}) {
     }
     // Mount terminal AFTER view is visible so FitAddon measures real dimensions
     if (window._openTerminal) window._openTerminal(name);
+    // Re-render sidebar after DOM is visible and dimensions are correct
+    initSidebar();
+    renderSidebar(_currentSessions, name);
   }, 260);
 
   // Mobile pill

frontend/tests/test_app.mjs

@@ -1927,6 +1927,16 @@ test('toggleSidebar removes sidebar--collapsed class when opening (from closed)
   globalThis.document.getElementById = origGetById;
 });
 
+// --- Guard: initSidebar and renderSidebar are exported and callable ---
+
+test('initSidebar is exported and callable', () => {
+  assert.strictEqual(typeof app.initSidebar, 'function', 'initSidebar should be a function');
+});
+
+test('renderSidebar is exported and callable', () => {
+  assert.strictEqual(typeof app.renderSidebar, 'function', 'renderSidebar should be a function');
+});
+
 // --- bindStaticEventListeners sidebar toggle buttons ---
 
 test('bindStaticEventListeners binds sidebar-toggle-btn and sidebar-collapse-btn click to toggleSidebar', () => {