diff --git a/packages/scenarios-stage-tamagotchi-browser/src/scenes/intro-manual-scene.vue b/packages/scenarios-stage-tamagotchi-browser/src/scenes/intro-manual-scene.vue
index 7c65ed116..43c9d396b 100644
--- a/packages/scenarios-stage-tamagotchi-browser/src/scenes/intro-manual-scene.vue
+++ b/packages/scenarios-stage-tamagotchi-browser/src/scenes/intro-manual-scene.vue
@@ -11,6 +11,24 @@ import { PlatformRoot } from '../components/platforms/macos-26'
 import { Application } from '../components/platforms/macos-26/containers/dock'
 import { WindowRoot } from '../components/platforms/macos-26/containers/window'
 
+/**
+ * These coordinates are expressed in the logical `1920x1080` canvas provided by
+ * `ScenarioCanvas`, not in the browser's live viewport.
+ *
+ * That is why the windows keep their relative placement when the viewport size
+ * changes: the browser scales the entire fixed scene surface after layout rather
+ * than reinterpreting each translate against a resized responsive container.
+ */
+const stageWindowStyle = {
+  left: '1200px',
+  top: '400px',
+}
+
+const websocketWindowStyle = {
+  left: '480px',
+  top: '120px',
+}
+
 async function waitForImageSource(source: string): Promise<void> {
   await new Promise<void>((resolve, reject) => {
     const image = new Image()
@@ -38,14 +56,14 @@ onMounted(async () => {
 </script>
 
 <template>
-  <ScenarioCanvas>
+  <ScenarioCanvas :width="1920" :height="1080">
     <ScenarioCaptureRoot name="intro-chat-window">
       <PlatformRoot :dock-size="1.5">
         <template #windows>
-          <WindowRoot class="translate-x-300 translate-y-100" :frame="false" :has-shadow="false">
+          <WindowRoot :style="stageWindowStyle" :frame="false" :has-shadow="false">
             <img :src="stageShot" class="w-95">
           </WindowRoot>
-          <WindowRoot class="translate-x-120 translate-y-30">
+          <WindowRoot :style="websocketWindowStyle">
             <img :src="websocketSettingsShot" class="w-120">
           </WindowRoot>
         </template>
diff --git a/packages/vishot-runtime/src/components/scenario-canvas.vue b/packages/vishot-runtime/src/components/scenario-canvas.vue
index fefbae9fe..40363c6b3 100644
--- a/packages/vishot-runtime/src/components/scenario-canvas.vue
+++ b/packages/vishot-runtime/src/components/scenario-canvas.vue
@@ -1,9 +1,109 @@
+<script setup lang="ts">
+import { computed, onMounted, onUnmounted, ref } from 'vue'
+
+import { computeScenarioCanvasScale } from '../runtime/scene-canvas'
+
+const props = withDefaults(defineProps<{
+  width?: number
+  height?: number
+}>(), {
+  width: 1920,
+  height: 1080,
+})
+
+const canvasRoot = ref<HTMLElement | null>(null)
+const viewportWidth = ref(0)
+const viewportHeight = ref(0)
+
+let resizeObserver: ResizeObserver | null = null
+
+/**
+ * Tracks the actual viewport available to the scenario host.
+ *
+ * The important part is that child content does not use these dimensions
+ * directly for layout. They are only used to compute a single scale factor for
+ * the fixed logical surface below.
+ */
+function updateViewportSize(): void {
+  viewportWidth.value = canvasRoot.value?.clientWidth ?? window.innerWidth
+  viewportHeight.value = canvasRoot.value?.clientHeight ?? window.innerHeight
+}
+
+onMounted(() => {
+  updateViewportSize()
+  window.addEventListener('resize', updateViewportSize)
+
+  if ('ResizeObserver' in window && canvasRoot.value) {
+    resizeObserver = new ResizeObserver(() => updateViewportSize())
+    resizeObserver.observe(canvasRoot.value)
+  }
+})
+
+onUnmounted(() => {
+  window.removeEventListener('resize', updateViewportSize)
+  resizeObserver?.disconnect()
+})
+
+const scale = computed(() => computeScenarioCanvasScale({
+  viewportWidth: viewportWidth.value,
+  viewportHeight: viewportHeight.value,
+  canvasWidth: props.width,
+  canvasHeight: props.height,
+}))
+
+/**
+ * The outer wrapper owns centering in real viewport pixels. It uses the scaled
+ * dimensions so layout centering is based on the final visible box, not the
+ * unscaled logical canvas size.
+ */
+const wrapperStyle = computed(() => ({
+  width: `${props.width * scale.value}px`,
+  height: `${props.height * scale.value}px`,
+  transform: 'translate(-50%, -50%)',
+}))
+
+/**
+ * The inner surface always keeps its logical pixel size. Absolute-positioned
+ * children are laid out against this stable coordinate system, while scaling is
+ * applied inside the already-centered wrapper.
+ *
+ * This avoids the "drifting translate" problem that happens when windows are
+ * positioned inside a naturally responsive container whose width/height changes
+ * with the browser viewport.
+ *
+ * Slidev uses the same pattern in:
+ * - `slidev/packages/client/internals/SlideContainer.vue`
+ * - `slidev/packages/client/internals/SlideWrapper.vue`
+ */
+const surfaceStyle = computed(() => ({
+  width: `${props.width}px`,
+  height: `${props.height}px`,
+  transform: `scale(${scale.value})`,
+}))
+</script>
+
 <template>
   <main
+    ref="canvasRoot"
     :class="[
-      'relative min-h-screen w-full overflow-hidden',
+      'relative h-screen w-full overflow-hidden',
     ]"
   >
-    <slot />
+    <div
+      :class="[
+        'absolute left-1/2 top-1/2',
+      ]"
+      :style="wrapperStyle"
+    >
+      <div
+        data-scenario-canvas-surface
+        :class="[
+          'origin-top-left',
+        ]"
+        :style="surfaceStyle"
+      >
+        <slot />
+      </div>
+    </div>
   </main>
 </template>
diff --git a/packages/vishot-runtime/src/runtime/scene-canvas.ts b/packages/vishot-runtime/src/runtime/scene-canvas.ts
new file mode 100644
index 000000000..a52b2565f
--- /dev/null
+++ b/packages/vishot-runtime/src/runtime/scene-canvas.ts
@@ -0,0 +1,31 @@
+export interface ScenarioCanvasScaleOptions {
+  viewportWidth: number
+  viewportHeight: number
+  canvasWidth: number
+  canvasHeight: number
+}
+
+/**
+ * Computes the single scale factor used to fit a fixed logical scene surface into
+ * the current viewport.
+ *
+ * This mirrors the core idea used by Slidev: keep scene coordinates stable by
+ * defining a fixed inner canvas size, then scale that whole surface as one unit
+ * instead of positioning content directly in a responsive box.
+ *
+ * Slidev references:
+ * - `slidev/packages/client/internals/SlideContainer.vue`
+ * - `slidev/packages/client/internals/SlideWrapper.vue`
+ * - `slidev/packages/client/env.ts`
+ */
+export function computeScenarioCanvasScale(options: ScenarioCanvasScaleOptions): number {
+  const { viewportWidth, viewportHeight, canvasWidth, canvasHeight } = options
+
+  if (viewportWidth <= 0 || viewportHeight <= 0 || canvasWidth <= 0 || canvasHeight <= 0)
+    return 1
+
+  return Math.min(
+    viewportWidth / canvasWidth,
+    viewportHeight / canvasHeight,
+  )
+}
diff --git a/packages/vishot-runtime/src/__tests__/exports.test.ts b/packages/vishot-runtime/src/test/exports.test.ts
similarity index 100%
rename from packages/vishot-runtime/src/__tests__/exports.test.ts
rename to packages/vishot-runtime/src/test/exports.test.ts
diff --git a/packages/vishot-runtime/src/__tests__/ready.test.ts b/packages/vishot-runtime/src/test/ready.test.ts
similarity index 100%
rename from packages/vishot-runtime/src/__tests__/ready.test.ts
rename to packages/vishot-runtime/src/test/ready.test.ts
diff --git a/packages/vishot-runtime/src/test/scene-canvas.test.ts b/packages/vishot-runtime/src/test/scene-canvas.test.ts
new file mode 100644
index 000000000..f7cd0e777
--- /dev/null
+++ b/packages/vishot-runtime/src/test/scene-canvas.test.ts
@@ -0,0 +1,53 @@
+// @vitest-environment jsdom
+import { describe, expect, it } from 'vitest'
+import { createApp, h, nextTick } from 'vue'
+
+import ScenarioCanvas from '../components/scenario-canvas.vue'
+
+import { computeScenarioCanvasScale } from '../runtime/scene-canvas'
+
+describe('computeScenarioCanvasScale', () => {
+  it('fits the canvas to the smallest viewport ratio', () => {
+    expect(computeScenarioCanvasScale({
+      viewportWidth: 1440,
+      viewportHeight: 900,
+      canvasWidth: 1920,
+      canvasHeight: 1080,
+    })).toBe(0.75)
+  })
+
+  it('falls back to 1 when dimensions are missing', () => {
+    expect(computeScenarioCanvasScale({
+      viewportWidth: 0,
+      viewportHeight: 900,
+      canvasWidth: 1920,
+      canvasHeight: 1080,
+    })).toBe(1)
+  })
+
+  it('renders a fixed logical surface for absolute-positioned scene content', async () => {
+    const host = document.createElement('div')
+    document.body.appendChild(host)
+
+    createApp({
+      render: () => h(
+        ScenarioCanvas,
+        {
+          width: 1920,
+          height: 1080,
+        },
+        {
+          default: () => h('div', { id: 'scene-content' }),
+        },
+      ),
+    }).mount(host)
+
+    await nextTick()
+
+    const surface = host.querySelector<HTMLElement>('[data-scenario-canvas-surface]')
+
+    expect(surface).not.toBeNull()
+    expect(surface?.style.width).toBe('1920px')
+    expect(surface?.style.height).toBe('1080px')
+  })
+})