banner and intro fix

app/page.tsx

@@ -31,6 +31,8 @@ import { openCookieBanner } from "@/components/CookieBanner";
 
 // Type for the mouse-pointer position used to move the background glow.
 type PointerState = { x: number; y: number };
+const INTRO_SEEN_KEY = "novarix-intro-seen";
+const INTRO_EVENT = "novarix:start-intro";
 
 export default function HomePage() {
   // ---------------------------------------------------------------------------
@@ -40,43 +42,72 @@ export default function HomePage() {
   //  pointer    — the mouse position (in % of page width/height). Used by the
   //               soft glow that follows the cursor in the background.
   // ---------------------------------------------------------------------------
-  const [showIntro, setShowIntro] = useState(false);
+  const [showIntro, setShowIntro] = useState(() => {
+    if (typeof document === "undefined") return false;
+    return document.documentElement.dataset.showIntro === "1";
+  });
   const [pointer, setPointer] = useState<PointerState>({ x: 50, y: 22 });
 
   // ---------------------------------------------------------------------------
   //  INTRO OVERLAY EFFECT
   //  Plays the animated logo + wordmark the first time someone visits the
-  //  site in this browser tab. We remember they've seen it using
-  //  sessionStorage so it doesn't replay on every navigation. The intro lasts
-  //  a little under 4 seconds, with a softer fade into the main page.
+  //  site in this browser tab. We decide before hydration whether to play it,
+  //  which avoids the homepage flashing briefly before the intro appears.
+  //  After the user accepts cookies on their first visit, we trigger the intro
+  //  immediately from the banner close action.
   // ---------------------------------------------------------------------------
   useEffect(() => {
+    function playIntro() {
+      document.documentElement.dataset.showIntro = "1";
+      setShowIntro(true);
+      try {
+        window.sessionStorage.setItem(INTRO_SEEN_KEY, "true");
+      } catch {
+        /* storage unavailable — silently ignore */
+      }
+
+      const timer = window.setTimeout(() => {
+        document.documentElement.dataset.showIntro = "0";
+        setShowIntro(false);
+      }, 3950);
+
+      return timer;
+    }
+
+    let timer: number | null = null;
+
     try {
-      const introSeen = window.sessionStorage.getItem("novarix-intro-seen");
-      // Only set the "seen" flag if the user has accepted cookies. Without
-      // consent we still play the intro — we just don't remember it played.
+      const introSeen = window.sessionStorage.getItem(INTRO_SEEN_KEY);
       const consent = window.localStorage.getItem("novarix-cookie-consent");
+      const shouldPlayNow =
+        document.documentElement.dataset.showIntro === "1" &&
+        consent === "ack" &&
+        !introSeen;
 
-      if (!introSeen) {
-        // Sync once with sessionStorage on first client mount.
+      if (shouldPlayNow) {
+        timer = playIntro();
+      } else {
+        document.documentElement.dataset.showIntro = "0";
         // eslint-disable-next-line react-hooks/set-state-in-effect
-        setShowIntro(true);
-        if (consent === "ack") {
-          window.sessionStorage.setItem("novarix-intro-seen", "true");
-        }
-
-        // The SVG's built-in stroke + fill animation lasts ~3s.
-        // We hold a little longer so the page underneath can ease in while
-        // the overlay fades away.
-        const timer = window.setTimeout(() => {
-          setShowIntro(false);
-        }, 3950);
-
-        return () => window.clearTimeout(timer);
+        setShowIntro(false);
       }
     } catch {
-      /* storage unavailable — silently skip the intro */
+      document.documentElement.dataset.showIntro = "0";
+      // eslint-disable-next-line react-hooks/set-state-in-effect
+      setShowIntro(false);
     }
+
+    function handleStartIntro() {
+      if (timer !== null) window.clearTimeout(timer);
+      timer = playIntro();
+    }
+
+    window.addEventListener(INTRO_EVENT, handleStartIntro);
+
+    return () => {
+      if (timer !== null) window.clearTimeout(timer);
+      window.removeEventListener(INTRO_EVENT, handleStartIntro);
+    };
   }, []);
 
   // ---------------------------------------------------------------------------