diff --git a/public/sw.js b/public/sw.js
index 417a76e..65f4c70 100644
--- a/public/sw.js
+++ b/public/sw.js
@@ -1,23 +1,139 @@
-// /sw.js (simple test worker)
-self.addEventListener('install', event => {
+// /sw.js
+// Service worker that detects if it was restarted (killed) between pings.
+// - Uses IndexedDB to persist restartCount and lastPingRestartCount
+// - Replies to message {type: 'PING'} by responding on the provided MessagePort
+//   with a {type:'PONG', ...} payload the sune logs already.
+
+// Basic small IDB helper (promisified key-value store)
+const DB_NAME = 'sune-sw-test-db';
+const STORE = 'kv';
+
+function openDb() {
+  return new Promise((resolve, reject) => {
+    const req = indexedDB.open(DB_NAME, 1);
+    req.onupgradeneeded = () => {
+      const db = req.result;
+      if (!db.objectStoreNames.contains(STORE)) {
+        db.createObjectStore(STORE, { keyPath: 'k' });
+      }
+    };
+    req.onsuccess = () => resolve(req.result);
+    req.onerror = () => reject(req.error);
+  });
+}
+
+async function idbGet(key) {
+  const db = await openDb();
+  return new Promise((resolve, reject) => {
+    const tx = db.transaction(STORE, 'readonly');
+    const s = tx.objectStore(STORE);
+    const r = s.get(key);
+    r.onsuccess = () => resolve(r.result ? r.result.v : undefined);
+    r.onerror = () => reject(r.error);
+  });
+}
+
+async function idbPut(key, value) {
+  const db = await openDb();
+  return new Promise((resolve, reject) => {
+    const tx = db.transaction(STORE, 'readwrite');
+    const s = tx.objectStore(STORE);
+    const r = s.put({ k: key, v: value });
+    r.onsuccess = () => resolve();
+    r.onerror = () => reject(r.error);
+  });
+}
+
+// Instance info set at startup
+const INSTANCE_ID = (self.crypto && self.crypto.randomUUID) ? crypto.randomUUID() : String(Math.random()).slice(2);
+const STARTED_AT = Date.now();
+const VERSION = '1.0.0'; // bump if you change behavior
+
+// Keys used in IDB
+const KEY_RESTART_COUNT = 'restartCount';
+const KEY_LAST_PING_RESTART_COUNT = 'lastPingRestartCount';
+const KEY_LAST_PING_TIME = 'lastPingTime';
+
+// On install/activate: increment persistent restart counter so we can detect restarts.
+self.addEventListener('install', (ev) => {
+  // activate immediately so testing is easier
   self.skipWaiting();
 });
 
-self.addEventListener('activate', event => {
-  event.waitUntil(self.clients.claim());
+self.addEventListener('activate', (ev) => {
+  ev.waitUntil((async () => {
+    // claim clients quickly
+    await self.clients.claim();
+
+    try {
+      const current = (await idbGet(KEY_RESTART_COUNT)) || 0;
+      const next = current + 1;
+      await idbPut(KEY_RESTART_COUNT, next);
+      console.log(`[sw] activated — instance=${INSTANCE_ID} start=${new Date(STARTED_AT).toISOString()} restartCount=${next}`);
+    } catch (err) {
+      console.error('[sw] activate idb error', err);
+    }
+  })());
 });
 
-self.addEventListener('message', event => {
-  const data = event.data || {};
-  if (data?.type === 'PING') {
-    // prefer replying on the message port if provided
-    if (event.ports && event.ports[0]) {
-      event.ports[0].postMessage({type: 'PONG', ts: Date.now(), ok: true});
-    } else {
-      // fallback: broadcast to all clients
-      self.clients.matchAll().then(clients => {
-        clients.forEach(c => c.postMessage({type: 'PONG', ts: Date.now(), ok: true}));
-      });
+// Helper to reply on message port or broadcast fallback
+async function replyToMessage(event, payload) {
+  // Prefer using provided MessagePort (sune sends one)
+  if (event.ports && event.ports[0]) {
+    try {
+      event.ports[0].postMessage(payload);
+      return;
+    } catch (err) {
+      console.warn('[sw] reply via port failed', err);
     }
   }
-});
+
+  // Fallback: send to the client who sent the message (if event.source) or broadcast
+  try {
+    if (event.source && typeof event.source.postMessage === 'function') {
+      event.source.postMessage(payload);
+      return;
+    }
+  } catch (err) {
+    // ignore
+  }
+
+  // Last resort: broadcast to all clients
+  const clients = await self.clients.matchAll({ includeUncontrolled: true });
+  for (const c of clients) {
+    try { c.postMessage(payload); } catch (e) { /* ignore per-client errors */ }
+  }
+}
+
+// Message handler
+self.addEventListener('message', (event) => {
+  const data = event.data || {};
+  if (data && data.type === 'PING') {
+    (async () => {
+      try {
+        const now = Date.now();
+        const restartCount = (await idbGet(KEY_RESTART_COUNT)) || 0;
+        const lastPingRestartCount = (await idbGet(KEY_LAST_PING_RESTART_COUNT));
+        const lastPingTime = (await idbGet(KEY_LAST_PING_TIME)) || null;
+
+        // If there was a previously-recorded lastPingRestartCount and current restartCount
+        // is greater, that means the worker was restarted since the last ping.
+        const lostConnection = (typeof lastPingRestartCount !== 'undefined') && (restartCount > lastPingRestartCount);
+
+        // Build response payload
+        const payload = {
+          type: 'PONG',
+          ts: data.ts || null,
+          now,
+          sw: {
+            version: VERSION,
+            instanceId: INSTANCE_ID,
+            startedAt: STARTED_AT,
+            restartCount,
+          },
+          lastPing: {
+            time: lastPingTime,
+            lastPingRestartCount: lastPingRestartCount
+          },
+          lostConnectionSinceLastPing: !!lostConnection,
+          note: lostConnection ? '