feat(pwa): Service-Worker-Gerüst mit Shell-Cache + Fetch-Dispatch

src/service-worker.ts installiert die App-Shell-Assets (build +
files aus $service-worker) beim install-Event in kochwas-shell-
<version>, räumt alte Shell-Caches beim activate und dispatcht
jeden Fetch via resolveStrategy — shell/images cache-first, swr
stale-while-revalidate, network-only unangetastet. Pre-Cache-
Orchestrator kommt in Task 9.

Client-seitig registriert sw-register.ts den SW und verdrahtet
Messages vom SW in den sync-status-Store.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/service-worker.ts

@@ -2,88 +2,78 @@
 /// <reference no-default-lib="true"/>
 /// <reference lib="esnext" />
 /// <reference lib="webworker" />
-
 import { build, files, version } from '$service-worker';
+import { resolveStrategy } from '$lib/sw/cache-strategy';
 
-const sw = self as unknown as ServiceWorkerGlobalScope;
+declare const self: ServiceWorkerGlobalScope;
 
-const APP_CACHE = `kochwas-app-${version}`;
-const IMAGE_CACHE = `kochwas-images-v1`;
-const APP_ASSETS = [...build, ...files];
+const SHELL_CACHE = `kochwas-shell-${version}`;
+const DATA_CACHE = 'kochwas-data-v1';
+const IMAGES_CACHE = 'kochwas-images-v1';
 
-sw.addEventListener('install', (event) => {
-  event.waitUntil(
-    caches.open(APP_CACHE).then((cache) => cache.addAll(APP_ASSETS))
-  );
-  // Activate new worker without waiting for old clients to close.
-  void sw.skipWaiting();
-});
+// App-Shell-Assets (Build-Output + statische Dateien, die SvelteKit kennt)
+const SHELL_ASSETS = [...build, ...files];
 
-sw.addEventListener('activate', (event) => {
+self.addEventListener('install', (event) => {
   event.waitUntil(
     (async () => {
-      const keys = await caches.keys();
-      await Promise.all(
-        keys
-          .filter((k) => k.startsWith('kochwas-app-') && k !== APP_CACHE)
-          .map((k) => caches.delete(k))
-      );
-      await sw.clients.claim();
+      const cache = await caches.open(SHELL_CACHE);
+      await cache.addAll(SHELL_ASSETS);
+      await self.skipWaiting();
     })()
   );
 });
 
-sw.addEventListener('fetch', (event) => {
+self.addEventListener('activate', (event) => {
+  event.waitUntil(
+    (async () => {
+      // Alte Shell-Caches (vorherige Versionen) räumen
+      const keys = await caches.keys();
+      await Promise.all(
+        keys
+          .filter((k) => k.startsWith('kochwas-shell-') && k !== SHELL_CACHE)
+          .map((k) => caches.delete(k))
+      );
+      await self.clients.claim();
+    })()
+  );
+});
+
+self.addEventListener('fetch', (event) => {
   const req = event.request;
-  if (req.method !== 'GET') return;
+  if (new URL(req.url).origin !== self.location.origin) return; // Cross-Origin unangetastet
 
-  const url = new URL(req.url);
-  if (url.origin !== location.origin) return;
+  const strategy = resolveStrategy({ url: req.url, method: req.method });
+  if (strategy === 'network-only') return;
 
-  // Images served from /images/* — cache-first with background update
-  if (url.pathname.startsWith('/images/')) {
-    event.respondWith(
-      (async () => {
-        const cache = await caches.open(IMAGE_CACHE);
-        const cached = await cache.match(req);
-        const network = fetch(req)
-          .then((res) => {
-            if (res.ok) void cache.put(req, res.clone());
-            return res;
-          })
-          .catch(() => undefined);
-        return cached ?? (await network) ?? new Response('Offline', { status: 503 });
-      })()
-    );
-    return;
-  }
-
-  // App shell assets (build/* and static files) — cache-first
-  if (APP_ASSETS.includes(url.pathname)) {
-    event.respondWith(
-      (async () => {
-        const cache = await caches.open(APP_CACHE);
-        const cached = await cache.match(req);
-        return cached ?? fetch(req);
-      })()
-    );
-    return;
-  }
-
-  // API and HTML pages — network-first, fall back to cache for HTML
-  if (req.destination === 'document') {
-    event.respondWith(
-      (async () => {
-        try {
-          const res = await fetch(req);
-          const cache = await caches.open(APP_CACHE);
-          if (res.ok) void cache.put(req, res.clone());
-          return res;
-        } catch {
-          const cached = await caches.match(req);
-          return cached ?? new Response('Offline', { status: 503 });
-        }
-      })()
-    );
+  if (strategy === 'shell') {
+    event.respondWith(cacheFirst(req, SHELL_CACHE));
+  } else if (strategy === 'images') {
+    event.respondWith(cacheFirst(req, IMAGES_CACHE));
+  } else if (strategy === 'swr') {
+    event.respondWith(staleWhileRevalidate(req, DATA_CACHE));
   }
 });
+
+async function cacheFirst(req: Request, cacheName: string): Promise<Response> {
+  const cache = await caches.open(cacheName);
+  const hit = await cache.match(req);
+  if (hit) return hit;
+  const fresh = await fetch(req);
+  if (fresh.ok) cache.put(req, fresh.clone()).catch(() => {});
+  return fresh;
+}
+
+async function staleWhileRevalidate(req: Request, cacheName: string): Promise<Response> {
+  const cache = await caches.open(cacheName);
+  const hit = await cache.match(req);
+  const fetchPromise = fetch(req)
+    .then((res) => {
+      if (res.ok) cache.put(req, res.clone()).catch(() => {});
+      return res;
+    })
+    .catch(() => hit ?? Response.error());
+  return hit ?? fetchPromise;
+}
+
+export {};