diff --git a/README.md b/README.md
index 03318e4..f984626 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,8 @@ Built with Svelte for speed and simplicity. No overwhelming features, no endless
 - 🎯 **Reorder by drag or keyboard** - Drag with a mouse, long-press and drag on touch, or use `Alt+↑`/`Alt+↓`
 - 💾 **Persistent storage** - All tasks saved locally in your browser
 - 📊 **Task statistics** - See how many tasks remain at a glance
+- 📱 **Installable and works offline** - Add it to your home screen or dock and it runs with no connection
+- 📦 **Export and import** - Take your tasks with you, or keep a backup
 
 ## 🚀 Getting Started
 
@@ -98,6 +100,22 @@ The date, storage, rollover, task and undo logic lives in `src/lib/` as plain mo
 - **Carry-over**: When a new day begins, whatever you didn't finish moves into Today. Completed tasks are cleared away with the day they belonged to. It works across gaps too. If you don't open Negotium for a week, everything still outstanding is waiting for you.
 - **While it's open**: The app notices the day change on its own, so a tab left open overnight rolls over without a reload.
 
+### Installing It
+
+Negotium is a PWA, so it installs like an app and runs without a connection.
+
+- **iPhone and iPad**: open it in Safari, tap Share, then Add to Home Screen
+- **Android**: Chrome offers Install from the menu, or prompts you directly
+- **Desktop**: Chrome and Edge show an install button in the address bar
+
+Once installed it opens in its own window with no browser chrome, and works on a plane. The app never needed the network for anything beyond loading itself.
+
+### Backing Up and Moving Between Devices
+
+Everything lives in one browser's storage, so `Export` writes it all to a JSON file you can keep or carry somewhere else. `Import` reads that file back.
+
+Import only ever adds. Tasks already present are left alone, so importing the same file twice changes nothing and importing into a list you're already using can't lose anything. The flip side is that import restores rather than reverts: it won't undo work you did after the export.
+
 ### Theme Toggle
 - Click the sun/moon icon in the header to switch themes
 - Your preference is saved automatically and restored on reload
@@ -121,6 +139,7 @@ All data is stored locally in your browser using localStorage:
 - **No server required**: Everything runs entirely client-side
 - **Privacy first**: Your data never leaves your device
 - **Self-pruning**: Past days are removed as their unfinished tasks carry forward, so storage doesn't grow without bound
+- **Yours to take**: Export writes everything to a JSON file, so your tasks aren't trapped in one browser
 
 Earlier versions keyed tasks by a different date format (`negotium-tasks-Sat Aug 15 2026`). Those convert automatically the first time you open this version. Nothing to do, and nothing is lost.
 
diff --git a/index.html b/index.html
index 4aca175..ecd5b68 100644
--- a/index.html
+++ b/index.html
@@ -2,10 +2,17 @@
 <html lang="en">
 <head>
     <meta charset="UTF-8">
-    <meta name="viewport" content="width=device-width, initial-scale=1.0">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0, viewport-fit=cover">
     <title>Negotium - Your Productivity Companion</title>
     <meta name="description" content="A clean, minimal to-do list application with smooth animations and dark/light mode support">
     <link rel="icon" type="image/svg+xml" href="data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none'><path d='M12.37 8.87988H17.62' stroke='%23607afb' stroke-width='1.5' stroke-linecap='round' stroke-linejoin='round'/><path d='M6.38 8.87988L7.13 9.62988L9.38 7.37988' stroke='%23607afb' stroke-width='1.5' stroke-linecap='round' stroke-linejoin='round'/><path d='M12.37 15.8799H17.62' stroke='%23607afb' stroke-width='1.5' stroke-linecap='round' stroke-linejoin='round'/><path d='M6.38 15.8799L7.13 16.6299L9.38 14.3799' stroke='%23607afb' stroke-width='1.5' stroke-linecap='round' stroke-linejoin='round'/><path d='M9 22H15C20 22 22 20 22 15V9C22 4 20 2 15 2H9C4 2 2 4 2 9V15C2 20 4 22 9 22Z' stroke='%23607afb' stroke-width='1.5' stroke-linecap='round' stroke-linejoin='round'/></svg>">
+    <link rel="manifest" href="/manifest.webmanifest">
+    <link rel="apple-touch-icon" href="/apple-touch-icon.png">
+    <meta name="apple-mobile-web-app-capable" content="yes">
+    <meta name="apple-mobile-web-app-title" content="Negotium">
+    <!-- Two of these, so the phone's status bar matches whichever theme is on. -->
+    <meta name="theme-color" content="#F8FAFB" media="(prefers-color-scheme: light)">
+    <meta name="theme-color" content="#121212" media="(prefers-color-scheme: dark)">
     <script>
         // Runs before first paint so dark-mode users never see a light flash.
         // App.svelte seeds its own state from the class this sets, keeping one
diff --git a/public/apple-touch-icon.png b/public/apple-touch-icon.png
new file mode 100644
index 0000000..90263c7
Binary files /dev/null and b/public/apple-touch-icon.png differ
diff --git a/public/icon-maskable.svg b/public/icon-maskable.svg
new file mode 100644
index 0000000..af5a3cd
--- /dev/null
+++ b/public/icon-maskable.svg
@@ -0,0 +1,10 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" width="512" height="512">
+  <rect width="512" height="512" fill="#607afb"/>
+  <g transform="translate(115.2 115.2) scale(11.73)">
+  <path d="M12.37 8.87988H17.62" stroke="#FFFFFF" stroke-width="1.6" stroke-linecap="round" stroke-linejoin="round"/>
+  <path d="M6.38 8.87988L7.13 9.62988L9.38 7.37988" stroke="#FFFFFF" stroke-width="1.6" stroke-linecap="round" stroke-linejoin="round"/>
+  <path d="M12.37 15.8799H17.62" stroke="#FFFFFF" stroke-width="1.6" stroke-linecap="round" stroke-linejoin="round"/>
+  <path d="M6.38 15.8799L7.13 16.6299L9.38 14.3799" stroke="#FFFFFF" stroke-width="1.6" stroke-linecap="round" stroke-linejoin="round"/>
+  <path d="M9 22H15C20 22 22 20 22 15V9C22 4 20 2 15 2H9C4 2 2 4 2 9V15C2 20 4 22 9 22Z" stroke="#FFFFFF" stroke-width="1.6" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+</svg>
diff --git a/public/icon.svg b/public/icon.svg
new file mode 100644
index 0000000..8009f10
--- /dev/null
+++ b/public/icon.svg
@@ -0,0 +1,10 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" width="512" height="512">
+  <rect width="512" height="512" rx="96" fill="#607afb"/>
+  <g transform="translate(87.04 87.04) scale(14.58)">
+  <path d="M12.37 8.87988H17.62" stroke="#FFFFFF" stroke-width="1.6" stroke-linecap="round" stroke-linejoin="round"/>
+  <path d="M6.38 8.87988L7.13 9.62988L9.38 7.37988" stroke="#FFFFFF" stroke-width="1.6" stroke-linecap="round" stroke-linejoin="round"/>
+  <path d="M12.37 15.8799H17.62" stroke="#FFFFFF" stroke-width="1.6" stroke-linecap="round" stroke-linejoin="round"/>
+  <path d="M6.38 15.8799L7.13 16.6299L9.38 14.3799" stroke="#FFFFFF" stroke-width="1.6" stroke-linecap="round" stroke-linejoin="round"/>
+  <path d="M9 22H15C20 22 22 20 22 15V9C22 4 20 2 15 2H9C4 2 2 4 2 9V15C2 20 4 22 9 22Z" stroke="#FFFFFF" stroke-width="1.6" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+</svg>
diff --git a/public/manifest.webmanifest b/public/manifest.webmanifest
new file mode 100644
index 0000000..3c3071b
--- /dev/null
+++ b/public/manifest.webmanifest
@@ -0,0 +1,30 @@
+{
+  "name": "Negotium",
+  "short_name": "Negotium",
+  "description": "A minimal to-do list for today and tomorrow.",
+  "start_url": "/",
+  "scope": "/",
+  "display": "standalone",
+  "background_color": "#F8FAFB",
+  "theme_color": "#607afb",
+  "icons": [
+    {
+      "src": "/icon.svg",
+      "sizes": "any",
+      "type": "image/svg+xml",
+      "purpose": "any"
+    },
+    {
+      "src": "/icon-maskable.svg",
+      "sizes": "any",
+      "type": "image/svg+xml",
+      "purpose": "maskable"
+    },
+    {
+      "src": "/apple-touch-icon.png",
+      "sizes": "180x180",
+      "type": "image/png",
+      "purpose": "any"
+    }
+  ]
+}
diff --git a/public/sw.js b/public/sw.js
new file mode 100644
index 0000000..f0af2c1
--- /dev/null
+++ b/public/sw.js
@@ -0,0 +1,80 @@
+// Negotium's service worker. Small on purpose: this app is one HTML file, one
+// JS bundle, one stylesheet and a couple of icons.
+//
+// The strategy leans on a property of the build: Vite fingerprints assets by
+// content, so index-CE76Mg_z.js can never change meaning. That splits cleanly
+// in two:
+//
+//   Documents  -> network first, cache as fallback. A new deploy is picked up
+//                 the moment you are online, so nobody gets welded to a stale
+//                 build. Offline, the last good copy is served.
+//   Everything -> cache first. Fingerprinted files are immutable, and a new
+//   else         build simply asks for new filenames.
+//
+// Bump CACHE when the caching logic itself changes; old caches are dropped on
+// activate.
+
+const CACHE = 'negotium-v1'
+
+self.addEventListener('install', (event) => {
+  // The shell is cached on first fetch rather than precached, which keeps this
+  // file free of a build-generated asset manifest.
+  event.waitUntil(self.skipWaiting())
+})
+
+self.addEventListener('activate', (event) => {
+  event.waitUntil(
+    (async () => {
+      const names = await caches.keys()
+      await Promise.all(names.filter((name) => name !== CACHE).map((name) => caches.delete(name)))
+      await self.clients.claim()
+    })(),
+  )
+})
+
+async function networkFirst(request) {
+  const cache = await caches.open(CACHE)
+
+  try {
+    const response = await fetch(request)
+    if (response && response.ok) cache.put(request, response.clone())
+    return response
+  } catch {
+    const cached = await cache.match(request)
+    if (cached) return cached
+
+    // A deep link visited offline that was never cached: fall back to the app
+    // shell, which is all this app needs to boot.
+    const shell = await cache.match('/index.html')
+    if (shell) return shell
+
+    throw new Error('offline and nothing cached')
+  }
+}
+
+async function cacheFirst(request) {
+  const cache = await caches.open(CACHE)
+
+  const cached = await cache.match(request)
+  if (cached) return cached
+
+  const response = await fetch(request)
+  if (response && response.ok) cache.put(request, response.clone())
+  return response
+}
+
+self.addEventListener('fetch', (event) => {
+  const { request } = event
+
+  if (request.method !== 'GET') return
+
+  const url = new URL(request.url)
+  if (url.origin !== self.location.origin) return
+
+  if (request.mode === 'navigate' || request.destination === 'document') {
+    event.respondWith(networkFirst(request))
+    return
+  }
+
+  event.respondWith(cacheFirst(request))
+})
diff --git a/src/App.svelte b/src/App.svelte
index e587195..5cda81d 100644
--- a/src/App.svelte
+++ b/src/App.svelte
@@ -11,6 +11,7 @@
   import * as taskOps from './lib/tasks.js';
   import { createUndoStack, applyUndo } from './lib/undo.js';
   import { shouldHandleUndo } from './lib/shortcuts.js';
+  import { buildExport, serialize, parseImport, mergeImport } from './lib/backup.js';
 
   const storage = createStorage();
   const undoStack = createUndoStack();
@@ -83,6 +84,63 @@
     darkMode = !darkMode;
   }
 
+  let fileInput;
+  let status = $state('');
+  let statusIsError = $state(false);
+  let statusTimer = null;
+
+  function showStatus(message, isError = false) {
+    status = message;
+    statusIsError = isError;
+    clearTimeout(statusTimer);
+    statusTimer = setTimeout(() => { status = ''; }, STATUS_MS);
+  }
+
+  function exportTasks() {
+    const text = serialize(buildExport(storage));
+    const url = URL.createObjectURL(new Blob([text], { type: 'application/json' }));
+
+    const link = document.createElement('a');
+    link.href = url;
+    link.download = `negotium-${todayKey}.json`;
+    link.click();
+    URL.revokeObjectURL(url);
+
+    showStatus('Exported.');
+  }
+
+  async function importTasks(event) {
+    const file = event.target.files?.[0];
+    // Reset first, so picking the same file twice still fires a change event.
+    event.target.value = '';
+    if (!file) return;
+
+    let parsed;
+    try {
+      parsed = parseImport(await file.text());
+    } catch {
+      showStatus("That file couldn't be read.", true);
+      return;
+    }
+
+    if (!parsed.ok) {
+      showStatus(parsed.error, true);
+      return;
+    }
+
+    const { imported, duplicates, days } = mergeImport(storage, parsed);
+    tasks = storage.loadTasks(selectedKey);
+
+    if (imported === 0) {
+      showStatus(duplicates > 0 ? 'Already up to date.' : 'Nothing to import.');
+      return;
+    }
+
+    const taskWord = imported === 1 ? 'task' : 'tasks';
+    const dayWord = days === 1 ? 'day' : 'days';
+    showStatus(`Imported ${imported} ${taskWord} across ${days} ${dayWord}.`);
+  }
+
   /** Scoped to the input. Previously this also sat on window, so Enter while a
    *  task was focused would toggle that task *and* add whatever was in the
    *  input. */
@@ -126,6 +184,7 @@
   const DRAG_THRESHOLD_PX = 8;
   const LONG_PRESS_MS = 400;
   const SETTLE_MS = 240;
+  const STATUS_MS = 4000;
 
   let drag = null;
 
@@ -534,6 +593,22 @@
           {/if}
         {/key}
       </div>
+
+      <footer class="data-footer">
+        <button class="data-link" onclick={exportTasks}>Export</button>
+        <span class="data-sep" aria-hidden="true">·</span>
+        <button class="data-link" onclick={() => fileInput.click()}>Import</button>
+        <input
+          bind:this={fileInput}
+          type="file"
+          accept="application/json,.json"
+          class="visually-hidden"
+          onchange={importTasks}
+        />
+        <span class="data-status" class:error={statusIsError} role="status" aria-live="polite">
+          {status}
+        </span>
+      </footer>
     </div>
   </main>
 </div>
diff --git a/src/lib/backup.js b/src/lib/backup.js
new file mode 100644
index 0000000..b2aaf41
--- /dev/null
+++ b/src/lib/backup.js
@@ -0,0 +1,123 @@
+import { isKey } from './dates.js'
+
+const APP = 'negotium'
+const FORMAT_VERSION = 1
+
+/** Everything currently stored, as a plain object ready to serialize. */
+export function buildExport(storage, now = new Date()) {
+  const days = {}
+
+  for (const dateKey of storage.listTaskKeys().sort()) {
+    const tasks = storage.loadTasks(dateKey)
+    if (tasks.length > 0) days[dateKey] = tasks
+  }
+
+  return {
+    app: APP,
+    version: FORMAT_VERSION,
+    exportedAt: now.toISOString(),
+    days,
+  }
+}
+
+export function serialize(data) {
+  return JSON.stringify(data, null, 2)
+}
+
+/** Keeps only the fields we know about, so an edited file can't smuggle
+ *  anything unexpected into storage. Returns null if the task is unusable. */
+function cleanTask(raw) {
+  if (!raw || typeof raw !== 'object') return null
+
+  const hasId = typeof raw.id === 'string' || typeof raw.id === 'number'
+  const text = typeof raw.text === 'string' ? raw.text.trim() : ''
+  if (!hasId || !text) return null
+
+  return {
+    id: String(raw.id),
+    text,
+    completed: Boolean(raw.completed),
+    createdAt: typeof raw.createdAt === 'number' ? raw.createdAt : Date.now(),
+  }
+}
+
+/**
+ * Validates a file's contents without touching storage.
+ *
+ * Anything malformed is skipped rather than failing the whole import: one bad
+ * row in a hand-edited file shouldn't cost someone the other two hundred.
+ */
+export function parseImport(text) {
+  let raw
+  try {
+    raw = JSON.parse(text)
+  } catch {
+    return { ok: false, error: "That file isn't a valid JSON file." }
+  }
+
+  if (!raw || typeof raw !== 'object' || Array.isArray(raw)) {
+    return { ok: false, error: "That file doesn't look like a Negotium export." }
+  }
+
+  if (raw.app !== APP || !raw.days || typeof raw.days !== 'object' || Array.isArray(raw.days)) {
+    return { ok: false, error: "That file doesn't look like a Negotium export." }
+  }
+
+  const days = {}
+  let taskCount = 0
+  let skipped = 0
+
+  for (const [dateKey, value] of Object.entries(raw.days)) {
+    if (!isKey(dateKey) || !Array.isArray(value)) continue
+
+    const tasks = []
+    for (const entry of value) {
+      const task = cleanTask(entry)
+      if (task) tasks.push(task)
+      else skipped += 1
+    }
+
+    if (tasks.length > 0) {
+      days[dateKey] = tasks
+      taskCount += tasks.length
+    }
+  }
+
+  return { ok: true, days, taskCount, skipped }
+}
+
+/**
+ * Adds parsed tasks to storage. Additive by design: a task whose id is already
+ * present is left alone, so importing the same file twice changes nothing and
+ * importing into a live list can't lose work. The trade is that import cannot
+ * be used to roll back to an earlier state.
+ */
+export function mergeImport(storage, parsed) {
+  if (!parsed?.ok) return { imported: 0, duplicates: 0, days: 0 }
+
+  let imported = 0
+  let duplicates = 0
+  let days = 0
+
+  for (const [dateKey, incoming] of Object.entries(parsed.days)) {
+    const existing = storage.loadTasks(dateKey)
+    const seen = new Set(existing.map(task => String(task.id)))
+
+    const additions = []
+    for (const task of incoming) {
+      if (seen.has(task.id)) duplicates += 1
+      else {
+        additions.push(task)
+        seen.add(task.id)
+      }
+    }
+
+    if (additions.length > 0) {
+      storage.saveTasks(dateKey, [...existing, ...additions])
+      imported += additions.length
+      days += 1
+    }
+  }
+
+  return { imported, duplicates, days }
+}
diff --git a/src/lib/backup.test.js b/src/lib/backup.test.js
new file mode 100644
index 0000000..289d498
--- /dev/null
+++ b/src/lib/backup.test.js
@@ -0,0 +1,178 @@
+import { describe, it, expect } from 'vitest'
+import { createStorage, createMemoryStore } from './storage.js'
+import { buildExport, serialize, parseImport, mergeImport } from './backup.js'
+
+const task = (id, text = id, completed = false) => ({ id, text, completed, createdAt: 1000 })
+
+const setup = (seed = {}) => {
+  const backend = createMemoryStore()
+  for (const [day, tasks] of Object.entries(seed)) {
+    backend.setItem(`negotium-tasks-${day}`, JSON.stringify(tasks))
+  }
+  return createStorage(backend)
+}
+
+const file = (days, extra = {}) =>
+  JSON.stringify({ app: 'negotium', version: 1, exportedAt: '2026-08-16T00:00:00.000Z', days, ...extra })
+
+describe('buildExport', () => {
+  it('stamps the app, version and time', () => {
+    const result = buildExport(setup(), new Date(Date.UTC(2026, 7, 16, 12)))
+    expect(result.app).toBe('negotium')
+    expect(result.version).toBe(1)
+    expect(result.exportedAt).toBe('2026-08-16T12:00:00.000Z')
+  })
+
+  it('includes every stored day', () => {
+    const storage = setup({ '2026-08-16': [task('a')], '2026-08-17': [task('b')] })
+    expect(Object.keys(buildExport(storage).days).sort()).toEqual(['2026-08-16', '2026-08-17'])
+  })
+
+  it('omits days holding no tasks', () => {
+    const storage = setup({ '2026-08-16': [task('a')], '2026-08-17': [] })
+    expect(Object.keys(buildExport(storage).days)).toEqual(['2026-08-16'])
+  })
+
+  it('exports an empty days object when nothing is stored', () => {
+    expect(buildExport(setup()).days).toEqual({})
+  })
+
+  it('serializes to text a human can read', () => {
+    const text = serialize(buildExport(setup({ '2026-08-16': [task('a')] })))
+    expect(text).toContain('\n')
+    expect(JSON.parse(text).days['2026-08-16']).toHaveLength(1)
+  })
+})
+
+describe('parseImport', () => {
+  it('rejects text that is not JSON', () => {
+    const result = parseImport('{not json')
+    expect(result.ok).toBe(false)
+    expect(result.error).toMatch(/valid JSON/i)
+  })
+
+  it('rejects a file from somewhere else', () => {
+    const result = parseImport(JSON.stringify({ app: 'other', days: {} }))
+    expect(result.ok).toBe(false)
+    expect(result.error).toMatch(/negotium/i)
+  })
+
+  it('rejects a file with no days object', () => {
+    expect(parseImport(JSON.stringify({ app: 'negotium' })).ok).toBe(false)
+  })
+
+  it('rejects a top-level array', () => {
+    expect(parseImport('[]').ok).toBe(false)
+  })
+
+  it('accepts a valid file and counts what it found', () => {
+    const result = parseImport(file({ '2026-08-16': [task('a'), task('b')], '2026-08-17': [task('c')] }))
+    expect(result.ok).toBe(true)
+    expect(result.taskCount).toBe(3)
+    expect(Object.keys(result.days)).toHaveLength(2)
+  })
+
+  it('ignores unknown top-level fields', () => {
+    const result = parseImport(file({ '2026-08-16': [task('a')] }, { somethingElse: 42 }))
+    expect(result.ok).toBe(true)
+    expect(result.taskCount).toBe(1)
+  })
+
+  it('skips days whose key is not a date', () => {
+    const result = parseImport(file({ 'not-a-date': [task('a')], '2026-08-16': [task('b')] }))
+    expect(Object.keys(result.days)).toEqual(['2026-08-16'])
+  })
+
+  it('skips a day that is not an array', () => {
+    const result = parseImport(file({ '2026-08-16': { nope: true } }))
+    expect(result.days).toEqual({})
+  })
+
+  it('skips tasks with no usable text and counts them', () => {
+    const result = parseImport(file({ '2026-08-16': [task('a'), { id: 'b' }, { id: 'c', text: '   ' }] }))
+    expect(result.taskCount).toBe(1)
+    expect(result.skipped).toBe(2)
+  })
+
+  it('skips tasks with no id', () => {
+    const result = parseImport(file({ '2026-08-16': [{ text: 'orphan' }] }))
+    expect(result.taskCount).toBe(0)
+    expect(result.skipped).toBe(1)
+  })
+
+  it('coerces completed to a boolean', () => {
+    const result = parseImport(file({ '2026-08-16': [{ id: 'a', text: 'x', completed: 'yes' }] }))
+    expect(result.days['2026-08-16'][0].completed).toBe(true)
+  })
+
+  it('trims task text', () => {
+    const result = parseImport(file({ '2026-08-16': [{ id: 'a', text: '  spaced  ' }] }))
+    expect(result.days['2026-08-16'][0].text).toBe('spaced')
+  })
+
+  it('drops fields it does not recognise', () => {
+    const result = parseImport(file({ '2026-08-16': [{ id: 'a', text: 'x', evil: '<script>' }] }))
+    expect(result.days['2026-08-16'][0]).not.toHaveProperty('evil')
+  })
+})
+
+describe('mergeImport', () => {
+  it('imports into an empty store', () => {
+    const storage = setup()
+    const parsed = parseImport(file({ '2026-08-16': [task('a'), task('b')] }))
+    const result = mergeImport(storage, parsed)
+
+    expect(result.imported).toBe(2)
+    expect(storage.loadTasks('2026-08-16').map(t => t.id)).toEqual(['a', 'b'])
+  })
+
+  it('appends to a day that already has tasks', () => {
+    const storage = setup({ '2026-08-16': [task('existing')] })
+    mergeImport(storage, parseImport(file({ '2026-08-16': [task('new')] })))
+    expect(storage.loadTasks('2026-08-16').map(t => t.id)).toEqual(['existing', 'new'])
+  })
+
+  it('never overwrites a task already present', () => {
+    const storage = setup({ '2026-08-16': [task('a', 'mine')] })
+    mergeImport(storage, parseImport(file({ '2026-08-16': [task('a', 'theirs')] })))
+
+    const stored = storage.loadTasks('2026-08-16')
+    expect(stored).toHaveLength(1)
+    expect(stored[0].text).toBe('mine')
+  })
+
+  it('reports duplicates as skipped', () => {
+    const storage = setup({ '2026-08-16': [task('a')] })
+    const result = mergeImport(storage, parseImport(file({ '2026-08-16': [task('a'), task('b')] })))
+    expect(result.imported).toBe(1)
+    expect(result.duplicates).toBe(1)
+  })
+
+  it('is a no-op the second time the same file is imported', () => {
+    const storage = setup()
+    const parsed = parseImport(file({ '2026-08-16': [task('a'), task('b')] }))
+
+    mergeImport(storage, parsed)
+    const second = mergeImport(storage, parsed)
+
+    expect(second.imported).toBe(0)
+    expect(storage.loadTasks('2026-08-16')).toHaveLength(2)
+  })
+
+  it('counts the days it touched', () => {
+    const storage = setup()
+    const parsed = parseImport(file({ '2026-08-16': [task('a')], '2026-08-17': [task('b')] }))
+    expect(mergeImport(storage, parsed).days).toBe(2)
+  })
+
+  it('round-trips an export back into an empty store', () => {
+    const source = setup({ '2026-08-16': [task('a'), task('b')], '2026-08-17': [task('c')] })
+    const text = serialize(buildExport(source))
+
+    const target = setup()
+    mergeImport(target, parseImport(text))
+
+    expect(target.loadTasks('2026-08-16')).toEqual(source.loadTasks('2026-08-16'))
+    expect(target.loadTasks('2026-08-17')).toEqual(source.loadTasks('2026-08-17'))
+  })
+})
diff --git a/src/main.js b/src/main.js
index 4d64ddb..fbf83f5 100644
--- a/src/main.js
+++ b/src/main.js
@@ -1,6 +1,15 @@
 import { mount } from 'svelte';
 import App from './App.svelte';
 
+// Production only. A service worker in dev caches your own edits back at you.
+if (import.meta.env.PROD && 'serviceWorker' in navigator) {
+  window.addEventListener('load', () => {
+    navigator.serviceWorker.register('/sw.js').catch(() => {
+      // Offline support is a bonus; the app works without it.
+    });
+  });
+}
+
 export default mount(App, {
   target: document.getElementById('app'),
 });
diff --git a/src/style.css b/src/style.css
index 0b83913..32a8270 100644
--- a/src/style.css
+++ b/src/style.css
@@ -46,7 +46,9 @@ body {
 .header {
   background-color: var(--bg-surface);
   border-bottom: 1px solid var(--border);
-  padding: 24px 48px;
+  /* The extra top padding is the iOS status bar when the app is installed to
+     the home screen. Without it the header sits underneath the clock. */
+  padding: calc(24px + env(safe-area-inset-top)) 48px 24px;
   position: sticky;
   top: 0;
   z-index: 100;
@@ -149,7 +151,7 @@ body {
 }
 
 .main {
-  padding: 40px 0;
+  padding: 40px 0 calc(40px + env(safe-area-inset-bottom));
 }
 
 .container {
@@ -471,9 +473,76 @@ html.dark .task-item.dragging {
   margin: 0;
 }
 
+/* Deliberately quiet. Export and import get reached for once in a blue moon,
+   so they sit below the list in secondary text rather than taking a slot in
+   the header next to things you use constantly. */
+.data-footer {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  margin-top: 32px;
+  padding-top: 16px;
+  border-top: 1px solid var(--border);
+  font-size: 13px;
+  color: var(--text-secondary);
+  flex-wrap: wrap;
+}
+
+.data-link {
+  background: transparent;
+  border: none;
+  padding: 4px 6px;
+  margin: 0;
+  border-radius: 4px;
+  font-family: var(--font-family);
+  font-size: 13px;
+  color: var(--text-secondary);
+  cursor: pointer;
+  transition: color 200ms ease, background-color 200ms ease;
+}
+
+.data-link:hover {
+  color: var(--accent);
+  background-color: var(--hover);
+}
+
+.data-sep {
+  color: var(--border);
+}
+
+.data-status {
+  margin-left: 4px;
+  opacity: 0;
+  transition: opacity 200ms ease;
+}
+
+.data-status:not(:empty) {
+  opacity: 1;
+}
+
+.data-status.error {
+  color: #d14343;
+}
+
+html.dark .data-status.error {
+  color: #ff8a8a;
+}
+
+.visually-hidden {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border: 0;
+}
+
 @media (max-width: 768px) {
   .header {
-    padding: 16px 24px;
+    padding: calc(16px + env(safe-area-inset-top)) 24px 16px;
   }
 
   .header-content {
@@ -514,7 +583,7 @@ html.dark .task-item.dragging {
 
 @media (max-width: 480px) {
   .header {
-    padding: 12px 16px;
+    padding: calc(12px + env(safe-area-inset-top)) 16px 12px;
   }
 
   .container {
