Fix /set offline cache: save markers and page assets on first visit

The worker isn't controlling the page on the first visit, so warm-up fetches
bypassed it and no images were cached. The page now writes markers, its own
JS/CSS/fonts and /set/ straight into the cache and only then shows
'Works offline'.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

components/set/MarkerPicker.tsx

@@ -8,6 +8,8 @@ type Showing = { src: string; label: string; detail: string; screen?: MarkerScre
 
 const KIND_LABEL: Record<Kind, string> = { phone: "Phones", tablet: "Tablets", laptop: "Laptops", monitor: "Monitors" };
 const MODE_KEY = "ttvfx-set-mode";
+// Must match CACHE in public/set/sw.js
+const OFFLINE_CACHE = "ttvfx-set-v1";
 
 function detectScreen() {
   const dpr = window.devicePixelRatio || 1;
@@ -139,18 +141,35 @@ export default function MarkerPicker({ screens, extras }: { screens: MarkerScree
     if (!showing && document.fullscreenElement) document.exitFullscreen?.().catch(() => {});
   }, [showing]);
 
-  // Offline: register the service worker, then warm its cache with every marker
+  // Offline: register the service worker, then put every marker plus this page's own
+  // scripts/styles/fonts straight into its cache. Writing from the page (rather than
+  // relying on the worker intercepting fetches) also covers the very first visit,
+  // before the worker controls the page.
   useEffect(() => {
-    if (process.env.NODE_ENV !== "production" || !("serviceWorker" in navigator)) return;
-    navigator.serviceWorker
-      .register("/set/sw.js", { scope: "/set/" })
-      .then(async () => {
+    if (process.env.NODE_ENV !== "production" || !("serviceWorker" in navigator) || !("caches" in window)) return;
+    let cancelled = false;
+    (async () => {
+      try {
+        await navigator.serviceWorker.register("/set/sw.js", { scope: "/set/" });
+        await navigator.serviceWorker.ready;
+        if (cancelled) return;
         setOffline("saving");
-        const urls = [...screens.flatMap((s) => [s.full, s.edge]), ...extras.map((e) => e.src)].filter(Boolean) as string[];
-        await Promise.all(urls.map((u) => fetch(u).catch(() => null)));
-        setOffline("ready");
-      })
-      .catch(() => {});
+        const markers = [...screens.flatMap((s) => [s.full, s.edge]), ...extras.map((e) => e.src)].filter(Boolean) as string[];
+        const assets = performance
+          .getEntriesByType("resource")
+          .map((e) => new URL(e.name))
+          .filter((u) => u.origin === location.origin && /^\/(_next\/|icon|apple-icon)/.test(u.pathname))
+          .map((u) => u.pathname + u.search);
+        const cache = await caches.open(OFFLINE_CACHE);
+        await cache.addAll(["/set/", ...new Set([...markers, ...assets])]);
+        if (!cancelled) setOffline("ready");
+      } catch {
+        if (!cancelled) setOffline("idle");
+      }
+    })();
+    return () => {
+      cancelled = true;
+    };
   }, [screens, extras]);
 
   const showScreen = (s: MarkerScreen) => {