Cache the page-owned app response before starting the worker

frontend/app-seams.test.js

@@ -30,7 +30,7 @@ test('Phase 4 preserves the exact player, continuity, tracking and queue bodies'
 test('eager shell and Settings definitions load before app state and defer reading it',()=>{
  const html=readFileSync(join(__dirname,'index.html'),'utf8');
  for(const file of ['shell-core.js','views-core.js','section-rail.js']) {
-  assert.ok(html.indexOf('src="'+file+'"')<html.indexOf('src="app.js"'));
+  assert.ok(html.indexOf('src="'+file+'"')<html.indexOf('src="app-bootstrap.js"'));
   const vm=require('node:vm');const context=vm.createContext({window:{},document:{}});
   // Evaluation before any data/$/els/Player declaration must be safe.
   vm.runInContext(readFileSync(join(__dirname,file),'utf8'),context);