frontend/public/sw.js

const CACHE_NAME = 'pneumonia-ai-v1';
const PRECACHE_URLS = [
  '/',
  '/index.html',
  '/manifest.json',
  '/apple-touch-icon.svg',
  '/favicon.svg',
  '/social-preview.png'
];

self.addEventListener('install', event => {
  event.waitUntil(
    caches.open(CACHE_NAME).then(cache => cache.addAll(PRECACHE_URLS))
  );
  self.skipWaiting();
});

self.addEventListener('activate', event => {
  event.waitUntil(
    caches.keys().then(keys => Promise.all(
      keys.filter(k => k !== CACHE_NAME).map(k => caches.delete(k))
    ))
  );
  self.clients.claim();
});

self.addEventListener('fetch', event => {
  if (event.request.method !== 'GET') return;
  event.respondWith(
    caches.match(event.request).then(response => {
      if (response) return response;
      return fetch(event.request).then(networkRes => {
        return caches.open(CACHE_NAME).then(cache => {
          cache.put(event.request, networkRes.clone());
          return networkRes;
        });
      }).catch(() => caches.match('/index.html'));
    })
  );
});