fix(web): ignore a missing documentElement when marking the home screen revealed

frontend/src/hooks/use-home-shell-registration.ts

@@ -82,7 +82,9 @@ export function useHomeShellRegistration(params: HomeShellRegistrationParams) {
 
   useEffect(() => {
     // The inline dead-screen script stands down only after the app has revealed.
-    if (!hydrated || typeof document === "undefined") return;
+    // Shell tests mount this hook without a documentElement; missing it must not
+    // throw, or the registration effect never gets to run.
+    if (!hydrated || typeof document === "undefined" || !document.documentElement) return;
     document.documentElement.dataset.hydrated = "1";
   }, [hydrated]);
 

frontend/tests/first-paint-fallback-contract.test.ts

@@ -192,6 +192,7 @@ test("fallback script is classic ES5 and waits past the bootstrap budgets", () =
 
   assert.match(layout, /firstPaintFallbackBootScript\(\)/);
   assert.doesNotMatch(layout, /firstPaintFallbackBootScript\(\)[\s\S]{0,80}type\s*=\s*["']module["']/);
+  assert.match(hook, /!document\.documentElement\) return/);
   assert.match(hook, /document\.documentElement\.dataset\.hydrated = "1"/);
   assert.equal(page.includes("dataset.hydrated"), false);
   assert.match(page, /连接云端服务超时/);