fix: preserve offline workflows across activation (Closes #977)

frontend/service-worker.js

@@ -1,7 +1,7 @@
 const BASE = new URL('./', self.location.href).pathname;
 importScripts(BASE + 'static/private-data-registry.js');
 importScripts(BASE + 'static/background-issue-sync.js');
-const CACHE = 'stackchain-dashboard-shell-v113';
+const CACHE = 'stackchain-dashboard-shell-v114';
 const OFFLINE_LEASE_URL = new URL(BASE + '__offline-session-lease', self.location.origin).href;
 const OUTAGE_STATUSES = new Set([500, 502, 503, 504]);
 const NAVIGATION_TIMEOUT_MS = self.__STACKCHAIN_NAVIGATION_TIMEOUT_MS || 4000;
@@ -366,15 +366,29 @@ self.addEventListener('install', event => {
   event.waitUntil(caches.open(CACHE).then(cache => cache.addAll(SHELL)).then(() => self.skipWaiting()));
 });
 
+async function warmOptionalFeature(cache, staleCacheNames, asset) {
+  for (const cacheName of staleCacheNames) {
+    const staleCache = await caches.open(cacheName);
+    const cached = await staleCache.match(asset);
+    if (cached) {
+      await cache.put(asset, cached);
+      return;
+    }
+  }
+  await cache.add(asset);
+}
+
 self.addEventListener('activate', event => {
   event.waitUntil((async () => {
     const keys = await caches.keys();
-    await Promise.all(
-      keys.filter(key => key.startsWith('stackchain-dashboard-') && key !== CACHE)
-        .map(key => caches.delete(key))
+    const staleCacheNames = keys.filter(
+      key => key.startsWith('stackchain-dashboard-') && key !== CACHE
     );
     const cache = await caches.open(CACHE);
-    await Promise.allSettled(OPTIONAL_FEATURES.map(asset => cache.add(asset)));
+    await Promise.allSettled(
+      OPTIONAL_FEATURES.map(asset => warmOptionalFeature(cache, staleCacheNames, asset))
+    );
+    await Promise.all(staleCacheNames.map(key => caches.delete(key)));
     await self.clients.claim();
   })());
 });