quiz seo image and authguard

components/quiz/quiz-button.tsx

@@ -5,6 +5,7 @@
  *
  * Asks the BFF whether this page has a published quiz and renders nothing if
  * not, so it can sit on every content page without leaving an empty slot.
+ * Quizzes are for signed-in readers only, so signed out it never asks.
  * Its label tracks progress: Take quiz → Continue quiz → View results.
  */
 
@@ -24,10 +25,12 @@ export function QuizButton({
   className?: string;
 }) {
   const { user } = useAuth();
+  const userId = user?.id;
   const [card, setCard] = useState<QuizCard | null>(null);
 
   // Re-asked when the user changes, so progress appears right after sign-in.
   useEffect(() => {
+    if (!userId) return;
     let cancelled = false;
     quiz
       .forPath(path)
@@ -40,9 +43,10 @@ export function QuizButton({
     return () => {
       cancelled = true;
     };
-  }, [path, user?.id]);
+  }, [path, userId]);
 
-  if (!card) return null;
+  // A card left over from before sign-out is ignored rather than cleared.
+  if (!card || !user) return null;
 
   const done = card.my.state === "completed";
   return (