sw.js

// picoTracker Librarian service worker — cache-first with background
// refresh, so the app opens instantly offline and still picks up
// deployed updates on the next visit.
const CACHE = 'pt-librarian-v1-5-2';
const ASSETS = ['./', 'index.html', 'manifest.webmanifest', 'icon-192.png', 'icon-512.png'];

self.addEventListener('install', e => {
  e.waitUntil(caches.open(CACHE).then(c => c.addAll(ASSETS)).catch(() => {}));
  self.skipWaiting();
});
self.addEventListener('activate', e => {
  e.waitUntil(caches.keys().then(keys =>
    Promise.all(keys.filter(k => k !== CACHE).map(k => caches.delete(k)))));
  self.clients.claim();
});
self.addEventListener('fetch', e => {
  if (e.request.method !== 'GET') return;
  e.respondWith(
    caches.match(e.request).then(cached => {
      const refresh = fetch(e.request).then(res => {
        if (res.ok) caches.open(CACHE).then(c => c.put(e.request, res.clone()));
        return res;
      }).catch(() => cached);
      return cached || refresh;
    })
  );
});