Merge Phase 6 and reconcile offline completion, response capture and contract tests

frontend/lazy.js

@@ -123,6 +123,24 @@
       for (const type of ['pointerenter', 'focus', 'touchstart']) element.addEventListener(type, () => load(name).catch(() => {}), { once: true, passive: true });
     },
   };
+  // Own this response once. Classic-script and fetch preloads do not share
+  // their cached bodies in WebKit; the later bootstrap consumes this promise.
+  const agent=root.navigator.userAgent || '';
+  api.captureApp=!!(manifest.appCache && !root.navigator.serviceWorker?.controller && root.crypto?.subtle && /AppleWebKit\//.test(agent) && !/(?:Chrome|Chromium|Edg|OPR)\//.test(agent));
+  if(api.captureApp) {
+    api.appResponse=(async()=>{
+      const key=url('/app.js');
+      try {
+        const cache=await root.caches?.open('ytplayer-assets'), held=await cache?.match(key);
+        if(held?.headers.get('X-Asset-Hash')===manifest.files['/app.js']?.h && held)return held;
+      } catch {}
+      return root.fetch(key,{credentials:'same-origin'});
+    })();
+    api.appResponse.catch(()=>{});
+  } else if(manifest.appCache) {
+    // Preserve native script/code-cache reuse in engines without the WebKit gap.
+    const preload=doc.createElement('link');preload.rel='preload';preload.as='script';preload.fetchPriority='low';preload.href=url('/app.js');doc.head.append(preload);
+  }
   root.Lazy = api;
   root.navigator.serviceWorker?.addEventListener('message',event=>{
     if(event.data?.type==='ASSET_LAYOUT_REQUEST') event.source?.postMessage({type:'LAYOUT',value:api.layout});