diff --git a/public/app.js b/public/app.js
index 9ab01b8..74efd61 100644
--- a/public/app.js
+++ b/public/app.js
@@ -531,6 +531,22 @@ terminalStopBtn.addEventListener('click', () => {
 
 
 // --- Poll for active PTY sessions ---
+// Adaptive cadence: poll fast (3s) only while PTYs are running; when idle, back
+// off to 30s. Every renderer path that starts a session (launchNewSession,
+// openSession, launchTerminalSession, onSessionDetected/Forked) calls
+// pollActiveSessions() explicitly, which re-arms the fast cadence immediately.
+// The 30s idle floor still catches sessions started outside the renderer
+// (scheduler-spawned PTYs, other windows) within at most 30s.
+const POLL_FAST_MS = 3000;
+const POLL_IDLE_MS = 30000;
+let pollTimer = null;
+
+function scheduleActiveSessionsPoll() {
+  if (pollTimer) clearTimeout(pollTimer);
+  const delay = activePtyIds.size > 0 ? POLL_FAST_MS : POLL_IDLE_MS;
+  pollTimer = setTimeout(pollActiveSessions, delay);
+}
+
 async function pollActiveSessions() {
   try {
     const ids = await window.api.getActiveSessions();
@@ -538,6 +554,7 @@ async function pollActiveSessions() {
     updateRunningIndicators();
     updateTerminalHeader();
   } catch {}
+  scheduleActiveSessionsPoll();
 }
 
 function updateRunningIndicators() {
@@ -592,10 +609,11 @@ function updatePtyTitle() {
   terminalHeaderPtyTitle.style.display = title ? '' : 'none';
 }
 
-setInterval(pollActiveSessions, 3000);
+scheduleActiveSessionsPoll();
 
 // Refresh sidebar timeago labels every 30s so "just now" ticks forward
 setInterval(() => {
+  if (lastActivityTime.size === 0) return;
   for (const [sessionId, time] of lastActivityTime) {
     const item = document.getElementById('si-' + sessionId);
     if (!item) continue;