feat(web): Core Refactor Phase A — extract sampling and cache modules; add adaptive TTL + eviction heuristics, Redis PoC, and metrics wiring. Tests added for TTL, eviction, exports, splash-adaptive, card index, and service worker. Docs+roadmap updated.

code/web/static/sw.js

@@ -1,10 +1,85 @@
-// Minimal service worker (stub). Controlled by ENABLE_PWA.
+// Service Worker for MTG Deckbuilder
+// Versioned via ?v=<catalog_hash> appended at registration time.
+// Strategies:
+// 1. Precache core shell assets (app shell + styles + manifest).
+// 2. Runtime cache (stale-while-revalidate) for theme list & preview fragments.
+// 3. Version bump (catalog hash change) triggers old cache purge.
+
+const VERSION = (new URL(self.location.href)).searchParams.get('v') || 'dev';
+const PRECACHE = `precache-v${VERSION}`;
+const RUNTIME = `runtime-v${VERSION}`;
+const CORE_ASSETS = [
+  '/',
+  '/themes/',
+  '/static/styles.css',
+  '/static/app.js',
+  '/static/manifest.webmanifest',
+  '/static/favicon.png'
+];
+
+// Utility: limit entries in a cache (simple LRU-esque trim by deletion order)
+async function trimCache(cacheName, maxEntries){
+  const cache = await caches.open(cacheName);
+  const keys = await cache.keys();
+  if(keys.length <= maxEntries) return;
+  const remove = keys.slice(0, keys.length - maxEntries);
+  await Promise.all(remove.map(k => cache.delete(k)));
+}
+
 self.addEventListener('install', event => {
-  self.skipWaiting();
+  event.waitUntil(
+    caches.open(PRECACHE).then(cache => cache.addAll(CORE_ASSETS)).then(() => self.skipWaiting())
+  );
 });
+
 self.addEventListener('activate', event => {
-  event.waitUntil(clients.claim());
+  event.waitUntil((async () => {
+    // Remove old versioned caches
+    const keys = await caches.keys();
+    await Promise.all(keys.filter(k => (k.startsWith('precache-v') || k.startsWith('runtime-v')) && !k.endsWith(VERSION)).map(k => caches.delete(k)));
+    await clients.claim();
+  })());
 });
+
+function isPreviewRequest(url){
+  return /\/themes\/preview\//.test(url.pathname);
+}
+function isThemeList(url){
+  return url.pathname === '/themes/' || url.pathname.startsWith('/themes?');
+}
+
 self.addEventListener('fetch', event => {
-  // Pass-through; caching strategy can be added later.
+  const req = event.request;
+  const url = new URL(req.url);
+  if(req.method !== 'GET') return; // Non-GET pass-through
+
+  // Core assets: cache-first
+  if(CORE_ASSETS.includes(url.pathname)){
+    event.respondWith(
+      caches.open(PRECACHE).then(cache => cache.match(req).then(found => {
+        return found || fetch(req).then(resp => { cache.put(req, resp.clone()); return resp; });
+      }))
+    );
+    return;
+  }
+
+  // Theme list / preview fragments: stale-while-revalidate
+  if(isPreviewRequest(url) || isThemeList(url)){
+    event.respondWith((async () => {
+      const cache = await caches.open(RUNTIME);
+      const cached = await cache.match(req);
+      const fetchPromise = fetch(req).then(resp => {
+        if(resp && resp.status === 200){ cache.put(req, resp.clone()); trimCache(RUNTIME, 120).catch(()=>{}); }
+        return resp;
+      }).catch(() => cached);
+      return cached || fetchPromise;
+    })());
+    return;
+  }
+});
+
+self.addEventListener('message', event => {
+  if(event.data && event.data.type === 'SKIP_WAITING'){
+    self.skipWaiting();
+  }
 });