Enforce stale core contracts in the worker without native startup I/O

frontend/asset-sync-core.test.js

@@ -45,3 +45,10 @@ test('removing group membership retains the old tab URL even if the physical fil
  const previous=manifest(),current=manifest();current.groups.core.files=['/index.html'];
  assert.ok(core.retained(current,previous).has('/a.js?v=a'));
 });
+
+
+test('stale app core requires every feature contract to match the new shell',()=>{
+ const old={files:{'/app.js':{h:'old'}},groups:{core:{contract:1,files:['/app.js']},extra:{contract:1,files:[]}}};
+ const next=structuredClone(old);next.files['/app.js'].h='new';next.groups.extra.contract=2;
+ assert.equal(core.fallback(next,old,'/app.js'),null);next.groups.extra.contract=1;assert.equal(core.fallback(next,old,'/app.js'),'/app.js?v=old');
+});