diff --git a/app/app.vue b/app/app.vue
index 32129f5..c08ea3f 100644
--- a/app/app.vue
+++ b/app/app.vue
@@ -154,11 +154,11 @@ onMounted(() => {
 </script>
 
 <template>
-  <div class="relative h-screen w-screen overflow-hidden bg-gradient-to-br from-slate-950 via-indigo-950 to-slate-900 text-slate-100">
+  <div class="relative h-screen w-screen overflow-hidden bg-gradient-to-br from-slate-950 via-indigo-950 to-slate-900 text-slate-100 max-md:overflow-y-auto max-md:overscroll-contain max-md:pb-16">
     <div class="pointer-events-none absolute inset-0 flex items-center justify-center">
       <div class="text-center opacity-25">
-        <h1 class="text-5xl font-bold tracking-tight">DOMinic</h1>
-        <p class="mt-3 text-slate-400">An AI agent is the primary app author.</p>
+        <h1 class="text-5xl font-bold tracking-tight max-md:text-4xl">DOMinic</h1>
+        <p class="mt-3 text-slate-400 max-md:px-6">An AI agent is the primary app author.</p>
       </div>
     </div>
 
@@ -187,7 +187,7 @@ onMounted(() => {
       :on-uninstall-app="uninstallApp"
     />
 
-    <div class="absolute right-4 top-4 z-50 flex flex-col gap-2 rounded-lg border border-white/10 bg-slate-900/90 p-3 backdrop-blur">
+    <div class="absolute right-4 top-4 z-50 flex flex-col gap-2 rounded-lg border border-white/10 bg-slate-900/90 p-3 backdrop-blur max-md:right-3 max-md:top-3">
       <span class="text-xs font-semibold uppercase tracking-wide text-slate-400">System</span>
       <button
         class="rounded border border-dashed border-white/20 px-3 py-1.5 text-left text-xs text-slate-400 hover:text-slate-100"
@@ -197,6 +197,6 @@ onMounted(() => {
       </button>
     </div>
 
-    <span class="absolute right-4 bottom-16 z-50 text-xs text-slate-400">{{ now ?? "" }}</span>
+    <span class="absolute right-4 bottom-16 z-50 text-xs text-slate-400 max-md:hidden">{{ now ?? "" }}</span>
   </div>
 </template>
diff --git a/app/features/os/components/Taskbar.vue b/app/features/os/components/Taskbar.vue
index db4d1b9..d1ca788 100644
--- a/app/features/os/components/Taskbar.vue
+++ b/app/features/os/components/Taskbar.vue
@@ -26,59 +26,61 @@ function onTaskbarClick(id: string): void {
 </script>
 
 <template>
-  <footer class="absolute bottom-0 left-0 right-0 z-40 flex h-12 items-center gap-2 border-t border-white/10 bg-slate-950/90 px-3 backdrop-blur">
-    <span class="text-sm font-bold tracking-tight text-indigo-300">DOMinic</span>
-    <span class="mx-2 h-6 w-px bg-white/10" />
-    <div
-      v-for="app in props.apps"
-      :key="app.id"
-      class="flex h-8 items-stretch overflow-hidden rounded border border-white/10 bg-slate-800"
-    >
-      <button
-        class="flex min-w-0 items-center gap-1.5 px-3 text-xs text-slate-200 hover:bg-slate-700"
-        :aria-label="`Open ${app.title}`"
-        @click="props.onOpenApp(app.id)"
+  <footer class="absolute bottom-0 left-0 right-0 z-40 flex h-12 max-md:h-14 max-md:fixed items-center gap-2 max-md:gap-1 border-t border-white/10 bg-slate-950/90 px-3 max-md:px-2 backdrop-blur max-md:pb-[max(env(safe-area-inset-bottom),0.25rem)]">
+    <div class="flex min-w-0 flex-1 max-md:flex-none items-center gap-2 max-md:gap-1 overflow-x-auto">
+      <span class="text-sm font-bold tracking-tight text-indigo-300 max-md:hidden">DOMinic</span>
+      <span class="mx-2 h-6 w-px bg-white/10 max-md:hidden" />
+      <div
+        v-for="app in props.apps"
+        :key="app.id"
+        class="flex h-8 max-md:h-11 items-stretch overflow-hidden rounded border border-white/10 bg-slate-800 shrink-0"
       >
-        <span aria-hidden="true">{{ app.icon }}</span>
-        <span class="max-w-28 truncate">{{ app.title }}</span>
-        <span
-          class="h-1.5 w-1.5 shrink-0 rounded-full"
-          :class="isRunning(app.id) ? 'bg-emerald-400' : 'bg-slate-600'"
-          :aria-label="isRunning(app.id) ? 'Running' : 'Not running'"
-        />
-      </button>
-      <button
-        class="flex w-8 items-center justify-center border-l border-white/10 text-slate-400 hover:bg-slate-700 hover:text-slate-100"
-        :aria-label="`View source for ${app.title}`"
-        title="View source"
-        @click="props.onViewSource(app.id)"
-      >
-        <Code2 :size="14" aria-hidden="true" />
-      </button>
+        <button
+          class="flex min-w-0 items-center gap-1.5 px-3 max-md:px-4 text-xs max-md:text-sm text-slate-200 hover:bg-slate-700 max-md:py-[10px]"
+          :aria-label="`Open ${app.title}`"
+          @click="props.onOpenApp(app.id)"
+        >
+          <span aria-hidden="true">{{ app.icon }}</span>
+          <span class="max-w-28 max-md:max-w-20 truncate">{{ app.title }}</span>
+          <span
+            class="h-1.5 w-1.5 shrink-0 rounded-full"
+            :class="isRunning(app.id) ? 'bg-emerald-400' : 'bg-slate-600'"
+            :aria-label="isRunning(app.id) ? 'Running' : 'Not running'"
+          />
+        </button>
+        <button
+          class="flex w-8 max-md:w-11 items-center justify-center border-l border-white/10 text-slate-400 hover:bg-slate-700 hover:text-slate-100"
+          :aria-label="`View source for ${app.title}`"
+          title="View source"
+          @click="props.onViewSource(app.id)"
+        >
+          <Code2 :size="14" aria-hidden="true" />
+        </button>
+        <button
+          class="flex w-8 max-md:w-11 items-center justify-center border-l border-white/10 text-slate-400 hover:bg-red-500/80 hover:text-white"
+          :aria-label="`Uninstall ${app.title}`"
+          title="Uninstall"
+          @click="props.onUninstallApp(app.id)"
+        >
+          <Trash2 :size="14" aria-hidden="true" />
+        </button>
+      </div>
+      <span v-if="props.apps.length" class="h-6 w-px bg-white/10 max-md:hidden" />
       <button
-        class="flex w-8 items-center justify-center border-l border-white/10 text-slate-400 hover:bg-red-500/80 hover:text-white"
-        :aria-label="`Uninstall ${app.title}`"
-        title="Uninstall"
-        @click="props.onUninstallApp(app.id)"
+        v-for="win in store.windows"
+        :key="win.id"
+        class="max-w-48 truncate rounded border px-3 max-md:px-4 py-1 max-md:py-2.5 text-xs max-md:text-sm transition-colors shrink-0"
+        :class="
+          win.minimized
+            ? 'border-white/10 bg-slate-900 text-slate-400 hover:text-slate-100'
+            : store.focusedId === win.id
+              ? 'border-indigo-400/60 bg-indigo-500/20 text-indigo-100'
+              : 'border-white/10 bg-slate-800 text-slate-200 hover:bg-slate-700'
+        "
+        @click="onTaskbarClick(win.id)"
       >
-        <Trash2 :size="14" aria-hidden="true" />
+        {{ win.title }}
       </button>
     </div>
-    <span v-if="props.apps.length" class="h-6 w-px bg-white/10" />
-    <button
-      v-for="win in store.windows"
-      :key="win.id"
-      class="max-w-48 truncate rounded border px-3 py-1 text-xs transition-colors"
-      :class="
-        win.minimized
-          ? 'border-white/10 bg-slate-900 text-slate-400 hover:text-slate-100'
-          : store.focusedId === win.id
-            ? 'border-indigo-400/60 bg-indigo-500/20 text-indigo-100'
-            : 'border-white/10 bg-slate-800 text-slate-200 hover:bg-slate-700'
-      "
-      @click="onTaskbarClick(win.id)"
-    >
-      {{ win.title }}
-    </button>
   </footer>
 </template>
diff --git a/app/features/os/components/WindowFrame.vue b/app/features/os/components/WindowFrame.vue
index 30b9647..47acab6 100644
--- a/app/features/os/components/WindowFrame.vue
+++ b/app/features/os/components/WindowFrame.vue
@@ -1,13 +1,31 @@
 <script setup lang="ts">
-import { computed, ref } from "vue";
+import { computed, ref, watch } from "vue";
+import { useMediaQuery } from "@vueuse/core";
 import { useOsStore, type OsWindow } from "../stores/os";
 
 const props = defineProps<{ win: OsWindow }>();
 
 const store = useOsStore();
 
+// Below the md breakpoint the shell degrades to stacked full-width cards
+// (ADR 0004, NEXT.md 3.1): the stored geometry is ignored, so dragging is
+// a no-op at phone widths.
+const isPhone = useMediaQuery("(max-width: 767px)");
+
 const dragHandle = ref<HTMLElement | null>(null);
 const dragging = ref(false);
+const el = ref<HTMLElement | null>(null);
+
+// A phone card has no visible neighbors; focusing a window scrolls it into
+// view the way raising it does on desktop.
+watch(
+  () => store.focusedId === props.win.id,
+  (focused) => {
+    if (isPhone.value && focused) {
+      el.value?.scrollIntoView({ behavior: "smooth", block: "start" });
+    }
+  },
+);
 
 const style = computed(() => {
   if (props.win.state === "maximized") {
@@ -34,6 +52,7 @@ function clamp(x: number, min: number, max: number): number {
 
 function onPointerDown(event: PointerEvent): void {
   if (props.win.state === "maximized") return;
+  if (isPhone.value) return;
   store.focusWindow(props.win.id);
   dragging.value = true;
   (event.currentTarget as HTMLElement).setPointerCapture(event.pointerId);
@@ -57,15 +76,16 @@ function onPointerUp(event: PointerEvent): void {
 
 <template>
   <section
+    ref="el"
     v-show="!win.minimized"
-    class="absolute flex flex-col overflow-hidden rounded-lg border border-white/10 bg-slate-900/95 shadow-2xl backdrop-blur"
+    class="absolute flex flex-col overflow-hidden rounded-lg border border-white/10 bg-slate-900/95 shadow-2xl backdrop-blur max-md:!static max-md:!mx-2 max-md:!mb-3 max-md:!mt-4 first:max-md:!mt-0 max-md:!h-[70vh] max-md:!w-auto"
     :class="store.focusedId === win.id ? 'ring-2 ring-indigo-400' : ''"
     :style="style"
     @pointerdown="store.focusWindow(win.id)"
   >
     <header
       ref="dragHandle"
-      class="flex h-9 shrink-0 cursor-grab items-center justify-between border-b border-white/10 bg-slate-800/80 px-3 select-none active:cursor-grabbing"
+      class="flex h-9 shrink-0 cursor-grab items-center justify-between border-b border-white/10 bg-slate-800/80 px-3 select-none active:cursor-grabbing max-md:cursor-default"
       @pointerdown="onPointerDown"
       @pointermove="onPointerMove"
       @pointerup="onPointerUp"
diff --git a/tests/e2e/mobile-shell.spec.ts b/tests/e2e/mobile-shell.spec.ts
new file mode 100644
index 0000000..a942af6
--- /dev/null
+++ b/tests/e2e/mobile-shell.spec.ts
@@ -0,0 +1,119 @@
+import { expect, test } from '@playwright/test'
+import {
+  appWindow,
+  dominicHooks,
+  keepRequestsLocal,
+  openDesktop,
+  waitForDesktop,
+} from './support/desktop'
+
+// NEXT.md step 3.1: below 768px the shell degrades to stacked full-width
+// cards, dragging is disabled, and the taskbar becomes a touch-sized
+// bottom sheet. Every assertion here runs at a phone viewport.
+
+test.use({ viewport: { width: 390, height: 844 } })
+
+test.beforeEach(async ({ page, baseURL }) => {
+  await keepRequestsLocal(page, baseURL)
+})
+
+test('phone viewport: cards stack, drag is off, the taskbar sheet works', async ({ page }) => {
+  const dominic = dominicHooks(page)
+  await openDesktop(page)
+
+  await test.step('the installed app renders as a stacked card', async () => {
+    expect(await dominic.installFixture('pomodoro-timer')).toBe(true)
+    const pomodoro = appWindow(page, 'Pomodoro Timer')
+    await expect(pomodoro.getByText('25:00')).toBeVisible()
+
+    const card = await pomodoro.boundingBox()
+    expect(card).toBeTruthy()
+    expect(card!.width).toBeGreaterThan(340) // full width minus insets
+    expect(card!.width).toBeLessThanOrEqual(390)
+  })
+
+  await test.step('dragging the title bar does not move the card', async () => {
+    const pomodoro = appWindow(page, 'Pomodoro Timer')
+    const before = await pomodoro.boundingBox()
+
+    const handle = pomodoro.locator('header')
+    const box = await handle.boundingBox()
+    expect(box).toBeTruthy()
+    await page.mouse.move(box!.x + box!.width / 2, box!.y + box!.height / 2)
+    await page.mouse.down()
+    await page.mouse.move(box!.x + 120, box!.y + 80, { steps: 4 })
+    await page.mouse.up()
+
+    const after = await pomodoro.boundingBox()
+    expect(after!.x).toBeCloseTo(before!.x, 1)
+    expect(after!.y).toBeCloseTo(before!.y, 1)
+  })
+
+  await test.step('the agent chat stacks as its own card (insertion order)', async () => {
+    const chat = appWindow(page, 'Agent Chat')
+    await expect(
+      chat.getByPlaceholder("Ask DOMinic to build an app"),
+    ).toBeVisible()
+    const chatBox = await chat.boundingBox()
+    const pomodoroBox = await appWindow(page, 'Pomodoro Timer').boundingBox()
+    expect(chatBox).toBeTruthy()
+    expect(pomodoroBox).toBeTruthy()
+    // Chat mounted first, so it is the top card; cards never overlap.
+    expect(chatBox!.y + chatBox!.height).toBeLessThanOrEqual(pomodoroBox!.y)
+  })
+
+  await test.step('the sheet stays pinned to the viewport bottom while cards scroll', async () => {
+    await page.locator('footer').evaluate((f) => {
+      const root = f.closest('.h-screen') as HTMLElement
+      root.scrollTop = root.scrollHeight
+    })
+    const sheet = await page.locator('footer').boundingBox()
+    expect(sheet!.y + sheet!.height).toBeCloseTo(844, 0)
+  })
+
+  await test.step('the focused card scrolls into view above the sheet', async () => {
+    // Pomodoro was already focused since install; move focus away and back.
+    await page.locator('footer button').filter({ hasText: 'Agent Chat' }).click()
+    await page.getByRole('button', { name: 'Open Pomodoro Timer' }).click()
+    await expect
+      .poll(async () => (await appWindow(page, 'Pomodoro Timer').boundingBox())!.y)
+      .toBeLessThanOrEqual(300)
+  })
+
+  await test.step('the taskbar sheet has touch-sized controls', async () => {
+    const sheet = page.locator('footer')
+    await expect(sheet).toBeVisible()
+    const box = await sheet.boundingBox()
+    expect(box).toBeTruthy()
+    expect(box!.height).toBeGreaterThanOrEqual(52) // h-14 = 56px, allow scroll rounding
+    // Viewport-relative: pinned by max-md:fixed, bottom edge sits at 844.
+    expect(box!.width).toBeGreaterThan(380)
+    // h-11 targets 44px touch targets on the sheet's own controls.
+    const buttons = sheet.locator('button')
+    const count = await buttons.count()
+    expect(count).toBeGreaterThan(0)
+    for (let i = 0; i < count; i++) {
+      const bb = await buttons.nth(i).boundingBox()
+      expect(bb!.height).toBeGreaterThanOrEqual(38)
+    }
+  })
+
+  await test.step('tapping the window button minimizes and restores', async () => {
+    // Exact match: the launcher button also contains the title but with an
+    // icon span and status dot around it.
+    const winButton = page
+      .locator('footer button')
+      .filter({ hasText: /^Pomodoro Timer$/ })
+    await winButton.click()
+    await expect(appWindow(page, 'Pomodoro Timer')).toBeHidden()
+    await winButton.click()
+    await expect(appWindow(page, 'Pomodoro Timer')).toBeVisible()
+  })
+
+  await test.step('the fixture persists across reload in card mode', async () => {
+    await page.reload()
+    await waitForDesktop(page)
+    await page.getByRole('button', { name: 'Open Pomodoro Timer' }).click()
+    await expect(appWindow(page, 'Pomodoro Timer').getByText('25:00')).toBeVisible()
+  })
+})
\ No newline at end of file