Don't stream by default

web/app.js

@@ -99,11 +99,8 @@ async function discoverServices() {
     // Initial read so values show immediately
     parseTelemetry(await chars.telemetry.readValue());
 
-    // IMU stream notify (~100 Hz)
+    // IMU stream — subscribed on demand via play button
     chars.imuStream.addEventListener('characteristicvaluechanged', e => parseImuStream(e.target.value));
-    await chars.imuStream.startNotifications();
-    document.getElementById('vizLive').classList.add('on');
-    log('IMU stream subscribed','ok');
 
     log('Config service ready (4 chars)','ok');
   } catch(e) {
@@ -396,7 +393,7 @@ function onDisconnected() {
   document.getElementById('battBar').style.display='none';
   document.getElementById('badgeCharging').classList.remove('show');
   document.getElementById('badgeFull').classList.remove('show');
-  document.getElementById('vizLive').classList.remove('on');
+  imuSubscribed = false; vizPaused = true; vizUpdateIndicator();
   clearTelemetry();
   if (!userDisconnected && document.getElementById('autoReconnect').checked && savedDevice) {
     log('Auto-reconnecting…','info');
@@ -426,8 +423,43 @@ const canvas = document.getElementById('vizCanvas');
 const ctx    = canvas.getContext('2d');
 const TRAIL_LEN = 120;
 let cursorX = canvas.width/2, cursorY = canvas.height/2, trail = [];
+let vizPaused = true;
+let imuSubscribed = false;
+
+function vizUpdateIndicator() {
+  const el = document.getElementById('vizLive');
+  if (!imuSubscribed || vizPaused) {
+    el.classList.remove('on');
+    el.classList.add('paused');
+    el.textContent = '⏸ PAUSED';
+  } else {
+    el.classList.add('on');
+    el.classList.remove('paused');
+    el.textContent = '● LIVE';
+  }
+  document.getElementById('vizPauseBtn').style.display = (!vizPaused && imuSubscribed) ? '' : 'none';
+  document.getElementById('vizPlayBtn').style.display  = (vizPaused || !imuSubscribed) ? '' : 'none';
+}
+
+async function vizSetPaused(paused) {
+  vizPaused = paused;
+  if (!paused && chars.imuStream && !imuSubscribed) {
+    try {
+      await chars.imuStream.startNotifications();
+      imuSubscribed = true;
+      log('IMU stream subscribed','ok');
+    } catch(e) { log(`IMU stream start failed: ${e.message}`,'err'); vizPaused = true; }
+  } else if (paused && imuSubscribed) {
+    try {
+      await chars.imuStream.stopNotifications();
+      imuSubscribed = false;
+    } catch(e) { log(`IMU stream stop failed: ${e.message}`,'err'); }
+  }
+  vizUpdateIndicator();
+}
 
 function parseImuStream(dv) {
+  if (vizPaused) return;
   let view;
   try {
     view = dv instanceof DataView ? new DataView(dv.buffer, dv.byteOffset, dv.byteLength) : new DataView(dv);