Feature 06: PWA shell and offline (#58)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>

web/src/sw/apiStrategy.ts

@@ -0,0 +1,16 @@
+// The network-first strategy for API reads, kept apart from src/sw.ts so the
+// tests can run it without a service worker.
+import type { WorkboxPlugin } from 'workbox-core/types'
+import { NetworkFirst } from 'workbox-strategies'
+import { cacheNames, markCacheFallback, networkTimeoutSeconds } from './routes'
+
+// NetworkFirst reads its cache only when the network fails or times out, so
+// every cached response it uses is a fallback.
+const markFallback: WorkboxPlugin = {
+  cachedResponseWillBeUsed: async ({ cachedResponse }) =>
+    cachedResponse === undefined ? undefined : markCacheFallback(cachedResponse),
+}
+
+export function createApiStrategy(): NetworkFirst {
+  return new NetworkFirst({ cacheName: cacheNames.api, networkTimeoutSeconds, plugins: [markFallback] })
+}