refactor: Simplify prefetch by moving to activate event

Remove message-based prefetch in favor of prefetching on activate:
- Remove PREFETCH_ASSETS message listener from service worker
- Remove prefetchAssets() call and idle callback from pushHelper.js
- Call prefetchAssets() directly in activate event

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/javascript/dashboard/helper/pushHelper.js

@@ -2,13 +2,6 @@ import NotificationSubscriptions from '../api/notificationSubscription';
 import auth from '../api/auth';
 import { useAlert } from 'dashboard/composables';
 
-/**
- * Request the service worker to prefetch all assets in the manifest.
- */
-const prefetchAssets = () => {
-  navigator.serviceWorker?.controller?.postMessage({ type: 'PREFETCH_ASSETS' });
-};
-
 export const verifyServiceWorkerExistence = (callback = () => {}) => {
   if (!('serviceWorker' in navigator)) {
     // Service Worker isn't supported on this browser, disable or hide UI.
@@ -41,14 +34,6 @@ export const verifyServiceWorkerExistence = (callback = () => {}) => {
         });
       });
 
-      // Trigger asset prefetch during idle time
-      if ('requestIdleCallback' in window) {
-        window.requestIdleCallback(() => prefetchAssets(), { timeout: 5000 });
-      } else {
-        // Fallback: prefetch after 3 seconds
-        setTimeout(prefetchAssets, 3000);
-      }
-
       callback(registration);
     })
     .catch(registrationError => {

app/javascript/service-worker/sw-runtime.js

@@ -122,12 +122,7 @@ self.addEventListener('install', () => self.skipWaiting());
 
 self.addEventListener('activate', event => {
   event.waitUntil(
-    Promise.all([
-      // Clean up stale assets not in current manifest
-      cleanupStaleAssets(),
-      // Take control of all clients
-      self.clients.claim(),
-    ])
+    Promise.all([cleanupStaleAssets(), prefetchAssets(), self.clients.claim()])
   );
 });
 
@@ -164,10 +159,3 @@ async function cleanupStaleAssets() {
 
   await Promise.all(deletions);
 }
-
-self.addEventListener('message', async event => {
-  if (event.data?.type === 'PREFETCH_ASSETS') {
-    await prefetchAssets();
-    event.ports[0]?.postMessage({ type: 'PREFETCH_COMPLETE' });
-  }
-});