Fail closed when worker update status is unavailable

frontend/sw-update.js

@@ -161,6 +161,9 @@
       const reg = root.navigator && await root.navigator.serviceWorker.getRegistration();
       const worker = reg && (reg.waiting || reg.active);
       const status = await askCacheStatus(worker);
+      // Unknown protocol is a retryable failure, never an empty successful
+      // legacy refresh followed by a reload into the old persistent manifest.
+      if (worker && !status) throw new Error('Worker update status unavailable; try again');
       if (status && status.assetSync) {
         const result = await core.syncAssets(m,{cache,fetchFn:opts.fetchFn});
         if (!reg.waiting) await core.commit(m,cache);