diff --git a/STATUS.md b/STATUS.md
index 3e17e7d..715db8a 100644
--- a/STATUS.md
+++ b/STATUS.md
@@ -28,6 +28,7 @@ Living progress tracker. Update at the end of each task. Codex and Claude Code b
 - **31 — Public share viewer**. Made `actorId` nullable in `activity_log` (migration `0010_nullable_actor_id.sql`, `onDelete: "set null"`) for anonymous share-page mutations. Added `logShareActivity` to `_core/activity.ts` (no session, explicit `householdId`). Added `householdId` to `resolveShareToken` return. Added `renderSharedView` to `EntityTypeRegistration` type. Each module implements `loadForShare` (bare DB queries, no session) and `renderSharedView`: calendar shows upcoming 90-day events or single-event details, lists shows items with optional toggle, notes shows title + body. `toggleShareListItem` server action lives in `lists/server/share-actions.ts` — validates token write capability, verifies item→list→household chain, logs `share.toggle` with `actorId = null`. `/app/s/[token]/page.tsx` resolves token, dispatches to `loadForShare` + `renderSharedView`, returns friendly error for invalid/expired tokens, sets `noindex`. Middleware `/s/*` exemption confirmed present. `pnpm typecheck`, `pnpm lint`, `pnpm build`, and all 4 E2E specs pass.
 
 - **50 — PWA shell**. `public/manifest.webmanifest` (name, short_name, icons, theme_color, display: standalone, start_url `/`). Placeholder PNG icons at 180, 192, 384, 512 (regular + maskable) generated by `scripts/generate-icons.mjs` (`pnpm gen:icons`); `public/icon.svg` committed as source. Hand-rolled service worker at `public/sw.js`: precaches `offline.html` on install, cache-first for `/_next/static/`, network-first for navigation with offline fallback, network-only for API routes. `src/components/pwa-register.tsx` registers the SW client-side. `src/components/install-prompt.tsx` shows a dismissible banner: `beforeinstallprompt` on Android/Chrome, a one-time "Add to Home Screen" hint on iOS (detected via UA + `navigator.maxTouchPoints`, suppressed in standalone mode). Root layout exports `viewport` (themeColor), updated `metadata` (manifest, appleWebApp, apple-touch-icon), and mounts both new components. `pnpm typecheck`, `pnpm lint`, `pnpm build` all clean.
+- **51 — Offline shell + service worker caching**. `next.config.ts` generates `public/sw.js` as a side effect on every `next build` / `next dev` invocation, embedding a build timestamp as `CACHE_VERSION` (stable `"dev"` string in development to avoid hot-reload cache churn; epoch milliseconds in production). SW strategies: stale-while-revalidate for `/_next/static/` chunks and navigation HTML (cached page served instantly, network update fires in background); network-first with 2-second abort timeout for API GETs falling back to cache; network-only for mutations (POST/PATCH/DELETE/PUT) — if offline, all controlled clients receive `{ type: "OFFLINE_MUTATION" }` via `postMessage` and a synthetic 503 is returned. Activate handler evicts all `famapp-*` caches whose suffix doesn't match the current version, then claims clients. `pwa-register.tsx` extended with three inline toasts: amber "offline" banner (persistent, driven by `navigator.onLine` + `online`/`offline` events), red "changes can't be saved" toast (auto-dismisses in 4 s, driven by SW postMessage), and indigo "new version available — refresh" bottom toast (driven by `controllerchange` with `hadController` guard). `pnpm typecheck`, `pnpm build` pass.
 
 ## Next up
 
diff --git a/next.config.ts b/next.config.ts
index a8b7383..7a5fbd1 100644
--- a/next.config.ts
+++ b/next.config.ts
@@ -1,4 +1,146 @@
 import type { NextConfig } from "next";
+import { writeFileSync } from "fs";
+import { resolve } from "path";
+
+// Stable in dev to avoid cache churn on hot-reload; unique per production build.
+const BUILD_TIME =
+  process.env.NODE_ENV === "development" ? "dev" : String(Date.now());
+
+writeFileSync(resolve(process.cwd(), "public/sw.js"), buildSwContent(BUILD_TIME));
+
+function buildSwContent(version: string): string {
+  return `// famapp service worker — v${version}
+// Generated at build time. Do not edit directly.
+const CACHE_VERSION = "${version}";
+const SHELL = "famapp-shell-" + CACHE_VERSION;
+const API = "famapp-api-" + CACHE_VERSION;
+const OFFLINE = "/offline.html";
+
+// --- install: precache the offline fallback ---
+
+self.addEventListener("install", (e) => {
+  e.waitUntil(caches.open(SHELL).then((c) => c.add(OFFLINE)));
+  self.skipWaiting();
+});
+
+// --- activate: evict old-version caches, claim clients ---
+
+self.addEventListener("activate", (e) => {
+  e.waitUntil(
+    caches
+      .keys()
+      .then((keys) =>
+        Promise.all(
+          keys
+            .filter(
+              (k) =>
+                k.startsWith("famapp-") && !k.endsWith("-" + CACHE_VERSION)
+            )
+            .map((k) => caches.delete(k))
+        )
+      )
+      .then(() => self.clients.claim())
+  );
+});
+
+// --- fetch: strategy dispatch ---
+
+self.addEventListener("fetch", (e) => {
+  const { request } = e;
+  const url = new URL(request.url);
+
+  // Mutations — network-only; notify clients if the network is unreachable.
+  if (request.method !== "GET") {
+    e.respondWith(
+      fetch(request).catch(() => {
+        self.clients
+          .matchAll({ includeUncontrolled: true })
+          .then((cs) =>
+            cs.forEach((c) => c.postMessage({ type: "OFFLINE_MUTATION" }))
+          );
+        return new Response(JSON.stringify({ error: "offline" }), {
+          status: 503,
+          headers: { "Content-Type": "application/json" },
+        });
+      })
+    );
+    return;
+  }
+
+  // Auth endpoints — always network-only.
+  if (url.pathname.startsWith("/api/auth/")) return;
+
+  // Next.js immutable static chunks — stale-while-revalidate.
+  if (url.pathname.startsWith("/_next/static/")) {
+    e.respondWith(staleWhileRevalidate(request, SHELL));
+    return;
+  }
+
+  // API GETs — network-first with 2-second timeout, fall back to cache.
+  if (url.pathname.startsWith("/api/")) {
+    e.respondWith(networkFirstWithTimeout(request, API, 2000));
+    return;
+  }
+
+  // Navigation — stale-while-revalidate; fall back to offline page.
+  if (request.mode === "navigate") {
+    e.respondWith(navigateWithFallback(request));
+    return;
+  }
+});
+
+// --- strategy helpers ---
+
+async function staleWhileRevalidate(request, cacheName) {
+  const cache = await caches.open(cacheName);
+  const cached = await cache.match(request);
+  const update = fetch(request)
+    .then((res) => {
+      if (res.ok) cache.put(request, res.clone());
+      return res;
+    })
+    .catch(() => null);
+  // Serve cached immediately; let update happen in the background.
+  return cached ?? (await update);
+}
+
+async function networkFirstWithTimeout(request, cacheName, ms) {
+  const cache = await caches.open(cacheName);
+  const ac = new AbortController();
+  const timer = setTimeout(() => ac.abort(), ms);
+  try {
+    const res = await fetch(request, { signal: ac.signal });
+    clearTimeout(timer);
+    if (res.ok) cache.put(request, res.clone());
+    return res;
+  } catch {
+    clearTimeout(timer);
+    return (await cache.match(request)) ?? new Response(null, { status: 503 });
+  }
+}
+
+async function navigateWithFallback(request) {
+  const cache = await caches.open(SHELL);
+  const cached = await cache.match(request);
+  const networkFetch = fetch(request)
+    .then((res) => {
+      if (res.ok) cache.put(request, res.clone());
+      return res;
+    })
+    .catch(() => null);
+  if (cached) {
+    // Return cached immediately; revalidate in the background.
+    networkFetch;
+    return cached;
+  }
+  const net = await networkFetch;
+  if (net) return net;
+  return (
+    (await cache.match(OFFLINE)) ?? new Response("Offline", { status: 503 })
+  );
+}
+`;
+}
 
 const nextConfig: NextConfig = {
   reactStrictMode: true,
diff --git a/public/sw.js b/public/sw.js
index f50512a..7a1faf6 100644
--- a/public/sw.js
+++ b/public/sw.js
@@ -1,69 +1,130 @@
-// famapp service worker — app-shell pattern
-// Caches a minimal offline fallback on install.
-// Navigation requests: network-first with offline fallback.
-// Next.js static chunks: cache-first.
-// API routes: network-only (pass through).
-
-const CACHE = "famapp-shell-v1";
+// famapp service worker — v1778101829038
+// Generated at build time. Do not edit directly.
+const CACHE_VERSION = "1778101829038";
+const SHELL = "famapp-shell-" + CACHE_VERSION;
+const API = "famapp-api-" + CACHE_VERSION;
 const OFFLINE = "/offline.html";
 
-// --- install: precache offline shell ---
+// --- install: precache the offline fallback ---
 
-self.addEventListener("install", (event) => {
-  event.waitUntil(
-    caches.open(CACHE).then((cache) => cache.add(OFFLINE))
-  );
+self.addEventListener("install", (e) => {
+  e.waitUntil(caches.open(SHELL).then((c) => c.add(OFFLINE)));
   self.skipWaiting();
 });
 
-// --- activate: evict old caches ---
+// --- activate: evict old-version caches, claim clients ---
 
-self.addEventListener("activate", (event) => {
-  event.waitUntil(
+self.addEventListener("activate", (e) => {
+  e.waitUntil(
     caches
       .keys()
       .then((keys) =>
-        Promise.all(keys.filter((k) => k !== CACHE).map((k) => caches.delete(k)))
+        Promise.all(
+          keys
+            .filter(
+              (k) =>
+                k.startsWith("famapp-") && !k.endsWith("-" + CACHE_VERSION)
+            )
+            .map((k) => caches.delete(k))
+        )
       )
+      .then(() => self.clients.claim())
   );
-  self.clients.claim();
 });
 
-// --- fetch ---
-
-self.addEventListener("fetch", (event) => {
-  const { request } = event;
-  if (request.method !== "GET") return;
+// --- fetch: strategy dispatch ---
 
+self.addEventListener("fetch", (e) => {
+  const { request } = e;
   const url = new URL(request.url);
 
-  // API routes — always go to network, never cache.
-  if (url.pathname.startsWith("/api/")) return;
-
-  // NextAuth — network-only.
-  if (url.pathname.startsWith("/api/auth/")) return;
-
-  // Next.js immutable static assets — cache-first.
-  if (url.pathname.startsWith("/_next/static/")) {
-    event.respondWith(
-      caches.match(request).then(
-        (cached) =>
-          cached ??
-          fetch(request).then((res) => {
-            const clone = res.clone();
-            caches.open(CACHE).then((c) => c.put(request, clone));
-            return res;
-          })
-      )
+  // Mutations — network-only; notify clients if the network is unreachable.
+  if (request.method !== "GET") {
+    e.respondWith(
+      fetch(request).catch(() => {
+        self.clients
+          .matchAll({ includeUncontrolled: true })
+          .then((cs) =>
+            cs.forEach((c) => c.postMessage({ type: "OFFLINE_MUTATION" }))
+          );
+        return new Response(JSON.stringify({ error: "offline" }), {
+          status: 503,
+          headers: { "Content-Type": "application/json" },
+        });
+      })
     );
     return;
   }
 
-  // Navigation requests — network-first, serve offline shell if unreachable.
+  // Auth endpoints — always network-only.
+  if (url.pathname.startsWith("/api/auth/")) return;
+
+  // Next.js immutable static chunks — stale-while-revalidate.
+  if (url.pathname.startsWith("/_next/static/")) {
+    e.respondWith(staleWhileRevalidate(request, SHELL));
+    return;
+  }
+
+  // API GETs — network-first with 2-second timeout, fall back to cache.
+  if (url.pathname.startsWith("/api/")) {
+    e.respondWith(networkFirstWithTimeout(request, API, 2000));
+    return;
+  }
+
+  // Navigation — stale-while-revalidate; fall back to offline page.
   if (request.mode === "navigate") {
-    event.respondWith(
-      fetch(request).catch(() => caches.match(OFFLINE))
-    );
+    e.respondWith(navigateWithFallback(request));
     return;
   }
 });
+
+// --- strategy helpers ---
+
+async function staleWhileRevalidate(request, cacheName) {
+  const cache = await caches.open(cacheName);
+  const cached = await cache.match(request);
+  const update = fetch(request)
+    .then((res) => {
+      if (res.ok) cache.put(request, res.clone());
+      return res;
+    })
+    .catch(() => null);
+  // Serve cached immediately; let update happen in the background.
+  return cached ?? (await update);
+}
+
+async function networkFirstWithTimeout(request, cacheName, ms) {
+  const cache = await caches.open(cacheName);
+  const ac = new AbortController();
+  const timer = setTimeout(() => ac.abort(), ms);
+  try {
+    const res = await fetch(request, { signal: ac.signal });
+    clearTimeout(timer);
+    if (res.ok) cache.put(request, res.clone());
+    return res;
+  } catch {
+    clearTimeout(timer);
+    return (await cache.match(request)) ?? new Response(null, { status: 503 });
+  }
+}
+
+async function navigateWithFallback(request) {
+  const cache = await caches.open(SHELL);
+  const cached = await cache.match(request);
+  const networkFetch = fetch(request)
+    .then((res) => {
+      if (res.ok) cache.put(request, res.clone());
+      return res;
+    })
+    .catch(() => null);
+  if (cached) {
+    // Return cached immediately; revalidate in the background.
+    networkFetch;
+    return cached;
+  }
+  const net = await networkFetch;
+  if (net) return net;
+  return (
+    (await cache.match(OFFLINE)) ?? new Response("Offline", { status: 503 })
+  );
+}
diff --git a/src/components/pwa-register.tsx b/src/components/pwa-register.tsx
index 20dbbba..39d3613 100644
--- a/src/components/pwa-register.tsx
+++ b/src/components/pwa-register.tsx
@@ -1,28 +1,115 @@
 "use client";
 
-import { useEffect } from "react";
+import { useEffect, useState } from "react";
 
 export function PwaRegister() {
+  const [showUpdate, setShowUpdate] = useState(false);
+  // Lazy init reads navigator.onLine on the client; SSR always returns false.
+  const [isOffline, setIsOffline] = useState(
+    () => typeof navigator !== "undefined" && !navigator.onLine
+  );
+  const [mutationFailed, setMutationFailed] = useState(false);
+
   useEffect(() => {
-    if (!("serviceWorker" in navigator)) return;
+    const handleOffline = () => setIsOffline(true);
+    const handleOnline = () => setIsOffline(false);
+    window.addEventListener("offline", handleOffline);
+    window.addEventListener("online", handleOnline);
+
+    if (!("serviceWorker" in navigator)) {
+      return () => {
+        window.removeEventListener("offline", handleOffline);
+        window.removeEventListener("online", handleOnline);
+      };
+    }
+
+    // Capture whether a SW already controls this page before registering.
+    // If true and the controller later changes, a new build has deployed.
+    const hadController = !!navigator.serviceWorker.controller;
 
     navigator.serviceWorker
       .register("/sw.js", { scope: "/" })
-      .then((reg) => {
-        reg.addEventListener("updatefound", () => {
-          const next = reg.installing;
-          if (!next) return;
-          next.addEventListener("statechange", () => {
-            if (next.state === "installed" && navigator.serviceWorker.controller) {
-              // New version available — the next navigation will pick it up
-              // because skipWaiting() is called in the SW install handler.
-              console.info("[famapp] Service worker updated.");
-            }
-          });
-        });
-      })
       .catch((err) => console.warn("[famapp] SW registration failed:", err));
+
+    const handleControllerChange = () => {
+      if (hadController) setShowUpdate(true);
+    };
+    navigator.serviceWorker.addEventListener(
+      "controllerchange",
+      handleControllerChange
+    );
+
+    const handleMessage = (e: MessageEvent) => {
+      if (e.data?.type === "OFFLINE_MUTATION") {
+        setMutationFailed(true);
+        setTimeout(() => setMutationFailed(false), 4000);
+      }
+    };
+    navigator.serviceWorker.addEventListener("message", handleMessage);
+
+    return () => {
+      window.removeEventListener("offline", handleOffline);
+      window.removeEventListener("online", handleOnline);
+      navigator.serviceWorker.removeEventListener(
+        "controllerchange",
+        handleControllerChange
+      );
+      navigator.serviceWorker.removeEventListener("message", handleMessage);
+    };
   }, []);
 
-  return null;
+  return (
+    <>
+      {isOffline && (
+        <div
+          role="status"
+          className="fixed top-4 left-1/2 -translate-x-1/2 z-50 flex items-center gap-3 rounded-lg bg-amber-50 px-4 py-3 text-amber-900 shadow-lg ring-1 ring-amber-200 dark:bg-amber-950 dark:text-amber-100 dark:ring-amber-800"
+        >
+          <span className="text-sm font-medium">
+            You&rsquo;re offline — showing cached content
+          </span>
+          <button
+            onClick={() => setIsOffline(false)}
+            aria-label="Dismiss"
+            className="text-sm opacity-60 hover:opacity-100"
+          >
+            ✕
+          </button>
+        </div>
+      )}
+
+      {mutationFailed && !isOffline && (
+        <div
+          role="alert"
+          className="fixed top-4 left-1/2 -translate-x-1/2 z-50 flex items-center gap-3 rounded-lg bg-destructive px-4 py-3 text-destructive-foreground shadow-lg"
+        >
+          <span className="text-sm font-medium">
+            Changes can&rsquo;t be saved while offline
+          </span>
+        </div>
+      )}
+
+      {showUpdate && (
+        <div
+          role="status"
+          className="fixed bottom-6 left-1/2 -translate-x-1/2 z-50 flex items-center gap-3 rounded-lg bg-primary px-4 py-3 text-primary-foreground shadow-lg"
+        >
+          <span className="text-sm font-medium">New version available</span>
+          <button
+            onClick={() => window.location.reload()}
+            className="text-sm font-semibold underline underline-offset-2"
+          >
+            Refresh
+          </button>
+          <button
+            onClick={() => setShowUpdate(false)}
+            aria-label="Dismiss"
+            className="text-sm opacity-60 hover:opacity-100"
+          >
+            ✕
+          </button>
+        </div>
+      )}
+    </>
+  );
 }