fix(pwa): harden service worker fetch handler to prevent ERR_FAILED

public/sw.js

@@ -1,9 +1,9 @@
-const CACHE_NAME = "checkflow-v1";
-const STATIC_ASSETS = ["/", "/login", "/register", "/manifest.json", "/icons/icon.svg"];
+const CACHE_NAME = "checkflow-v2";
+const STATIC_ASSETS = ["/manifest.json", "/icons/icon.svg"];
 
 self.addEventListener("install", (event) => {
   event.waitUntil(
-    caches.open(CACHE_NAME).then((cache) => cache.addAll(STATIC_ASSETS))
+    caches.open(CACHE_NAME).then((cache) => cache.addAll(STATIC_ASSETS)).catch(() => {})
   );
   self.skipWaiting();
 });
@@ -21,14 +21,37 @@ self.addEventListener("fetch", (event) => {
   const { request } = event;
   const url = new URL(request.url);
 
-  // Network-first for API
-  if (url.pathname.startsWith("/api")) {
-    event.respondWith(fetch(request).catch(() => new Response(JSON.stringify({ error: "Offline" }), { headers: { "Content-Type": "application/json" } })));
+  // Only handle http/https GET requests to the same origin
+  if (request.method !== "GET" || !url.protocol.startsWith("http") || url.origin !== self.location.origin) {
     return;
   }
 
-  // Cache-first for static
+  // Network-first for API & navigation routes to avoid stale/failed page loads
+  if (url.pathname.startsWith("/api") || request.mode === "navigate") {
     event.respondWith(
-    caches.match(request).then((cached) => cached || fetch(request))
+      fetch(request).catch(() => {
+        if (url.pathname.startsWith("/api")) {
+          return new Response(JSON.stringify({ error: "Offline or service unavailable" }), {
+            headers: { "Content-Type": "application/json" },
+          });
+        }
+        return caches.match(request).then((cached) => cached || Response.error());
+      })
+    );
+    return;
+  }
+
+  // Cache-first for static assets with safe network fallback
+  event.respondWith(
+    caches.match(request).then((cached) => {
+      if (cached) return cached;
+      return fetch(request).then((response) => {
+        if (response && response.status === 200 && response.type === "basic") {
+          const clone = response.clone();
+          caches.open(CACHE_NAME).then((cache) => cache.put(request, clone)).catch(() => {});
+        }
+        return response;
+      }).catch(() => Response.error());
+    })
   );
 });