Offline trip day tracker: app, service worker, manifest, icon

manifest.webmanifest

@@ -0,0 +1,15 @@
+{
+  "name": "Business Trip Day Tracker",
+  "short_name": "Trip Log",
+  "description": "Offline day-by-day record of a business trip for tax substantiation.",
+  "start_url": "./index.html",
+  "scope": "./",
+  "display": "standalone",
+  "orientation": "portrait",
+  "background_color": "#0b1220",
+  "theme_color": "#0b1220",
+  "icons": [
+    { "src": "icon-512.png", "sizes": "512x512", "type": "image/png", "purpose": "any" },
+    { "src": "icon-512.png", "sizes": "512x512", "type": "image/png", "purpose": "maskable" }
+  ]
+}

sw.js

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+/* Business Trip Day Tracker — offline shell.
+   Cache-first on purpose: this app is a static document whose whole point is
+   working in airplane mode, so a stale-by-a-day shell beats a failed load.
+   Bump CACHE when index.html changes; activate() drops every older cache. */
+var CACHE = "trip-tracker-v3";
+var ASSETS = ["./", "./index.html", "./manifest.webmanifest", "./icon-512.png"];
+
+self.addEventListener("install", function(e){
+  e.waitUntil(
+    caches.open(CACHE).then(function(c){
+      /* addAll is all-or-nothing; one 404 would leave us with no offline copy
+         at all, so fetch them individually and keep whatever succeeds. */
+      return Promise.all(ASSETS.map(function(u){
+        return fetch(u, {cache:"reload"})
+          .then(function(r){ if(r && r.ok) return c.put(u, r); })
+          .catch(function(){});
+      }));
+    }).then(function(){ return self.skipWaiting(); })
+  );
+});
+
+self.addEventListener("activate", function(e){
+  e.waitUntil(
+    caches.keys().then(function(keys){
+      return Promise.all(keys.map(function(k){
+        return k === CACHE ? null : caches.delete(k);
+      }));
+    }).then(function(){ return self.clients.claim(); })
+  );
+});
+
+self.addEventListener("fetch", function(e){
+  var req = e.request;
+  if(req.method !== "GET") return;
+  if(new URL(req.url).origin !== self.location.origin) return;
+
+  e.respondWith(
+    caches.match(req, {ignoreSearch:true}).then(function(hit){
+      if(hit) return hit;
+      return fetch(req).then(function(res){
+        if(res && res.ok){
+          var copy = res.clone();
+          caches.open(CACHE).then(function(c){ c.put(req, copy); });
+        }
+        return res;
+      }).catch(function(){
+        /* Offline and not cached — a navigation still gets the app shell. */
+        if(req.mode === "navigate") return caches.match("./index.html");
+        throw new Error("offline");
+      });
+    })
+  );
+});