diff --git a/src/app/infrastructure/storage-persist.test.ts b/src/app/infrastructure/storage-persist.test.ts
new file mode 100644
index 0000000..9513e9b
--- /dev/null
+++ b/src/app/infrastructure/storage-persist.test.ts
@@ -0,0 +1,75 @@
+import { afterEach, describe, expect, test, vi } from 'vitest';
+import { requestPersistentStorage } from './storage-persist';
+
+const realNavigator = globalThis.navigator;
+
+/** Swap `navigator` for one exposing the given `storage` (or none). */
+function withStorage(storage: unknown) {
+  Object.defineProperty(globalThis, 'navigator', {
+    value: storage === undefined ? {} : { storage },
+    configurable: true,
+  });
+}
+
+afterEach(() => {
+  Object.defineProperty(globalThis, 'navigator', { value: realNavigator, configurable: true });
+  vi.restoreAllMocks();
+});
+
+describe('requestPersistentStorage', () => {
+  test('reports unsupported when the StorageManager API is absent', async () => {
+    withStorage(undefined);
+    expect(await requestPersistentStorage()).toEqual({ supported: false });
+  });
+
+  test('reports unsupported when persist/persisted are missing', async () => {
+    withStorage({ estimate: () => Promise.resolve({}) });
+    expect(await requestPersistentStorage()).toEqual({ supported: false });
+  });
+
+  test('does not re-request when already persisted', async () => {
+    const persist = vi.fn();
+    withStorage({ persisted: vi.fn().mockResolvedValue(true), persist });
+    expect(await requestPersistentStorage()).toEqual({
+      supported: true,
+      persisted: true,
+      alreadyPersisted: true,
+    });
+    expect(persist).not.toHaveBeenCalled();
+  });
+
+  test('requests persistence once and reports granted', async () => {
+    const persist = vi.fn().mockResolvedValue(true);
+    withStorage({ persisted: vi.fn().mockResolvedValue(false), persist });
+    expect(await requestPersistentStorage()).toEqual({
+      supported: true,
+      persisted: true,
+      alreadyPersisted: false,
+    });
+    expect(persist).toHaveBeenCalledTimes(1);
+  });
+
+  test('reports not granted when the request is denied', async () => {
+    withStorage({
+      persisted: vi.fn().mockResolvedValue(false),
+      persist: vi.fn().mockResolvedValue(false),
+    });
+    expect(await requestPersistentStorage()).toEqual({
+      supported: true,
+      persisted: false,
+      alreadyPersisted: false,
+    });
+  });
+
+  test('never rejects — a thrown request resolves to not-persisted', async () => {
+    withStorage({
+      persisted: vi.fn().mockRejectedValue(new Error('blocked')),
+      persist: vi.fn(),
+    });
+    expect(await requestPersistentStorage()).toEqual({
+      supported: true,
+      persisted: false,
+      alreadyPersisted: false,
+    });
+  });
+});
diff --git a/src/app/infrastructure/storage-persist.ts b/src/app/infrastructure/storage-persist.ts
new file mode 100644
index 0000000..17ebdc2
--- /dev/null
+++ b/src/app/infrastructure/storage-persist.ts
@@ -0,0 +1,45 @@
+/**
+ * Persistent-storage request (web.dev → council; see reference/principles/web-dev.md).
+ *
+ * By default browser storage is **best-effort**: under storage pressure the
+ * browser may evict the whole origin's IndexedDB + Cache API data. For a
+ * local-first app whose workspace lives only in the browser, that is data loss.
+ * `navigator.storage.persist()` asks the browser not to evict us.
+ *
+ * Behaviour per web.dev guidance:
+ *   - feature-detect; do nothing where the API is absent (never throw),
+ *   - check `persisted()` first and request **at most once** — don't nag,
+ *   - stay silent on denial: Chromium decides automatically from heuristics
+ *     (installed / engagement / notifications), and there is nothing the user
+ *     can act on, so no toast.
+ *
+ * Browser-only; the rest of the app reaches it through `orchestration/pwa`.
+ */
+
+export type PersistResult =
+  | { supported: false }
+  | { supported: true; persisted: boolean; alreadyPersisted: boolean };
+
+/**
+ * Ensure persistent storage, requesting it once if not already granted.
+ * Resolves to the outcome; never rejects.
+ */
+export async function requestPersistentStorage(): Promise<PersistResult> {
+  const storage = typeof navigator !== 'undefined' ? navigator.storage : undefined;
+  if (
+    !storage ||
+    typeof storage.persist !== 'function' ||
+    typeof storage.persisted !== 'function'
+  ) {
+    return { supported: false };
+  }
+  try {
+    const alreadyPersisted = await storage.persisted();
+    if (alreadyPersisted) return { supported: true, persisted: true, alreadyPersisted: true };
+    const persisted = await storage.persist();
+    return { supported: true, persisted, alreadyPersisted: false };
+  } catch {
+    // A rejected request is not actionable by the user — report not-persisted.
+    return { supported: true, persisted: false, alreadyPersisted: false };
+  }
+}
diff --git a/src/app/orchestration/pwa.ts b/src/app/orchestration/pwa.ts
new file mode 100644
index 0000000..05a99f4
--- /dev/null
+++ b/src/app/orchestration/pwa.ts
@@ -0,0 +1,49 @@
+/**
+ * PWA wiring (web.dev → council; see reference/principles/web-dev.md).
+ *
+ * Two startup concerns, both browser-only and called once from `main.tsx`:
+ *
+ *  - **Service-worker update prompt.** The build uses `registerType: 'prompt'`
+ *    (vite.config), so a freshly-installed service worker parks in the *waiting*
+ *    state and never takes over until the app explicitly reloads. Without
+ *    consuming the registration that posture silently means "never update", so we
+ *    surface `onNeedRefresh` as a **durable** info toast with a **Reload** action
+ *    that calls `updateSW()` (web.dev "update" flow via vite-plugin-pwa).
+ *  - **Persistent storage.** Request it once at startup so the local-first
+ *    workspace is not evicted under pressure (see `infrastructure/storage-persist`).
+ *
+ * The `virtual:pwa-register` import is provided by vite-plugin-pwa at build time;
+ * it is only imported here (not in tested modules) so the test runner never has
+ * to resolve the virtual module.
+ */
+
+import { registerSW } from 'virtual:pwa-register';
+import { notify } from '../stores/NotificationStore';
+import { requestPersistentStorage } from '../infrastructure/storage-persist';
+
+/** Register the service worker and prompt the user when an update is ready. */
+export function registerServiceWorker(): void {
+  const updateSW = registerSW({
+    onNeedRefresh() {
+      notify({
+        kind: 'info',
+        title: 'Update available',
+        message: 'A new version of Astrolabe is ready.',
+        durable: true, // wait for the user — don't time out an update offer
+        action: { label: 'Reload', onClick: () => void updateSW(true) },
+      });
+    },
+    onOfflineReady() {
+      notify({
+        kind: 'success',
+        title: 'Ready to work offline',
+        message: 'Astrolabe is cached and will work without a connection.',
+      });
+    },
+  });
+}
+
+/** Ask the browser to keep our storage from being evicted (fire-and-forget). */
+export function initPersistentStorage(): void {
+  void requestPersistentStorage();
+}
diff --git a/src/main.tsx b/src/main.tsx
index 685e2d9..85253aa 100644
--- a/src/main.tsx
+++ b/src/main.tsx
@@ -4,6 +4,7 @@ import { initPanes, wirePanes } from './app/orchestration/panes';
 import { initPreviewFitMode, wirePreviewFitMode } from './app/orchestration/preferences';
 import { initSettings, wireSettings } from './app/orchestration/settings';
 import { initSnippetSort, wireSnippetSort } from './app/orchestration/snippet-sort';
+import { initPersistentStorage, registerServiceWorker } from './app/orchestration/pwa';
 import { initApp } from './app/orchestration/startup';
 import { initTheme, wireTheme } from './app/orchestration/theme';
 import '../styles/base.css';
@@ -37,4 +38,9 @@ wireSettings();
 // hydration resolves.
 void initApp();
 
+// PWA: register the service worker (prompt the user to reload on an update) and
+// request persistent storage so the local-first workspace isn't evicted (web.dev).
+registerServiceWorker();
+initPersistentStorage();
+
 createRoot(document.getElementById('app')!).render(<App />);