diff --git a/src/components/game/CodSkeleton/CodSkeleton.accessibility.test.tsx b/src/components/game/CodSkeleton/CodSkeleton.accessibility.test.tsx
index c3fb833e..dc0170b4 100644
--- a/src/components/game/CodSkeleton/CodSkeleton.accessibility.test.tsx
+++ b/src/components/game/CodSkeleton/CodSkeleton.accessibility.test.tsx
@@ -8,7 +8,7 @@
  */
 
 import { describe, it, expect, vi } from 'vitest';
-import { render } from '@testing-library/react';
+import { render, fireEvent } from '@testing-library/react';
 import { axe, toHaveNoViolations } from 'jest-axe';
 import React from 'react';
 
@@ -38,15 +38,43 @@ vi.mock('@react-three/fiber', () => ({
 
 import CodSkeleton from './CodSkeleton';
 
+/** Render, then press the start control — the scene is gated behind it (#757). */
+function renderStarted(): ReturnType<typeof render> {
+  const utils = render(<CodSkeleton />);
+  fireEvent.click(utils.getByRole('button', { name: /start the scene/i }));
+  return utils;
+}
+
 describe('CodSkeleton Accessibility', () => {
-  it('should have no accessibility violations on the DOM chrome', async () => {
+  // The gate (#757) means there are now TWO states a visitor can be looking at,
+  // and the one they see FIRST is the placeholder. Auditing only the started
+  // scene would leave the default state unmeasured — the shape of #411.
+  it('should have no accessibility violations before the scene is started', async () => {
     const { container } = render(<CodSkeleton />);
     const results = await axe(container);
     expect(results).toHaveNoViolations();
   });
 
+  it('should have no accessibility violations on the DOM chrome', async () => {
+    const { container } = renderStarted();
+    const results = await axe(container);
+    expect(results).toHaveNoViolations();
+  });
+
   it('canvas mock has an aria-label for screen-reader users', () => {
-    const { getByTestId } = render(<CodSkeleton />);
+    const { getByTestId } = renderStarted();
     expect(getByTestId('canvas-mock').getAttribute('aria-label')).toBeTruthy();
   });
+
+  it('the start control is reachable by name and meets the 44px touch floor', () => {
+    // `min-h-11 min-w-11` is the repo's mobile-first touch target. It is asserted
+    // here because jsdom has no layout: the class IS the contract, and the
+    // mobile-touch-targets sweep cannot see a control that only exists after a
+    // click it never performs.
+    const { getByRole } = render(<CodSkeleton />);
+    const start = getByRole('button', { name: /start the scene/i });
+
+    expect(start.className).toContain('min-h-11');
+    expect(start.className).toContain('min-w-11');
+  });
 });
diff --git a/src/components/game/CodSkeleton/CodSkeleton.stories.tsx b/src/components/game/CodSkeleton/CodSkeleton.stories.tsx
index b46e907a..51ccca21 100644
--- a/src/components/game/CodSkeleton/CodSkeleton.stories.tsx
+++ b/src/components/game/CodSkeleton/CodSkeleton.stories.tsx
@@ -9,7 +9,7 @@ const meta = {
     docs: {
       description: {
         component:
-          'First-person "walking skeleton" for the Claude-of-Duty extraction spike. R3F owns the render loop; the vendored CoD BVH + swept-capsule character controller run a fixed 120 Hz tick in useFrame and drive the camera. WASD + pointer-lock mouselook, collide-and-slide against a small procedural level (floor, a 0.40 m step-up, a wall, a crate) skinned with zero-asset procedural DataTexture surfaces. Falls back to FallbackPanel when WebGL is unavailable.',
+          'First-person "walking skeleton" for the Claude-of-Duty extraction spike. R3F owns the render loop; the vendored CoD BVH + swept-capsule character controller run a fixed 120 Hz tick in useFrame and drive the camera. WASD + pointer-lock mouselook, collide-and-slide against a small procedural level (floor, a 0.40 m step-up, a wall, a crate) skinned with zero-asset procedural DataTexture surfaces. Falls back to FallbackPanel when WebGL is unavailable. **Every story opens on the start placeholder, not the scene** — mounting the canvas bakes 1K textures synchronously, which cost 22.6-30.2s on a GPU-less runner and timed the mobile-layout sweep out three times (#757), so it now waits to be asked. Press "Start the scene".',
       },
     },
   },
diff --git a/src/components/game/CodSkeleton/CodSkeleton.test.tsx b/src/components/game/CodSkeleton/CodSkeleton.test.tsx
index f4c9c398..0313c28f 100644
--- a/src/components/game/CodSkeleton/CodSkeleton.test.tsx
+++ b/src/components/game/CodSkeleton/CodSkeleton.test.tsx
@@ -9,10 +9,16 @@
  * under the mocked Canvas — these tests assert the DOM contract + the WebGL
  * fallback path. Physics correctness is proven separately by the standalone
  * r184 smoke test; canvas rendering is a Playwright concern.
+ *
+ * THE SCENE IS GATED BEHIND A START (#757), so every test that wants the canvas
+ * has to ask for it. That gate is the fix for a route which took 22.6-30.2s on a
+ * GPU-less chromium runner and 12.7-41.7s on webkit before its layout could be
+ * measured, timing out `mobile-horizontal-scroll` three times and blocking two
+ * merges. The guards below are what stop it coming back a fourth time.
  */
 
 import { describe, it, expect, vi } from 'vitest';
-import { render } from '@testing-library/react';
+import { render, fireEvent } from '@testing-library/react';
 import React from 'react';
 
 // Mock @react-three/fiber: Canvas -> div (renders children), hooks -> no-ops.
@@ -28,9 +34,16 @@ vi.mock('@react-three/fiber', () => ({
 
 import CodSkeleton from './CodSkeleton';
 
+/** Render, then press the start control — for tests that need the live scene. */
+function renderStarted(): ReturnType<typeof render> {
+  const utils = render(<CodSkeleton />);
+  fireEvent.click(utils.getByRole('button', { name: /start the scene/i }));
+  return utils;
+}
+
 describe('CodSkeleton', () => {
-  it('renders the canvas mock (physics world mounts without WebGL)', () => {
-    const { getByTestId } = render(<CodSkeleton />);
+  it('renders the canvas mock once started (physics world mounts without WebGL)', () => {
+    const { getByTestId } = renderStarted();
     expect(getByTestId('canvas-mock')).toBeInTheDocument();
   });
 
@@ -40,7 +53,7 @@ describe('CodSkeleton', () => {
   });
 
   it('passes a quality-driven dpr (0 < dpr <= 2) to the canvas', () => {
-    const { getByTestId } = render(<CodSkeleton />);
+    const { getByTestId } = renderStarted();
     const props = JSON.parse(
       getByTestId('canvas-mock').getAttribute('data-props') ?? '{}'
     );
@@ -50,6 +63,56 @@ describe('CodSkeleton', () => {
   });
 });
 
+describe('CodSkeleton — the scene is gated behind a start (#757)', () => {
+  it('mounts NO canvas until the visitor asks for one', () => {
+    // The whole point. If this regresses, `/game/cod-skeleton` goes back to
+    // spending ~28s of a 30s test budget on a mount nobody requested, and the
+    // mobile-layout sweep starts timing out again on branches that never touched
+    // this route.
+    const { queryByTestId, container } = render(<CodSkeleton />);
+
+    expect(queryByTestId('canvas-mock')).not.toBeInTheDocument();
+    expect(
+      container.querySelector('[data-scene-started="false"]')
+    ).toBeInTheDocument();
+  });
+
+  it('mounts the canvas after the start control is pressed', () => {
+    // The other half: a gate that never opens would pass the test above while
+    // shipping a dead route.
+    const { getByTestId, container } = renderStarted();
+
+    expect(getByTestId('canvas-mock')).toBeInTheDocument();
+    expect(
+      container.querySelector('[data-scene-started="true"]')
+    ).toBeInTheDocument();
+  });
+
+  it('gives the placeholder the SAME box as the started scene', () => {
+    // The coverage floor (#396). `mobile-horizontal-scroll` measures this route's
+    // geometry; if the placeholder sized itself differently from the canvas
+    // wrapper, the sweep would quietly start measuring something else and its
+    // green would stop meaning what it used to mean. jsdom has no layout, so the
+    // decidable invariant is that both branches carry the identical wrapper class
+    // — which is why the sizing lives on the wrapper and not on either branch.
+    // Unmount between the two renders: both mount into the same document, so
+    // leaving the first up makes `getByRole('button')` ambiguous rather than wrong
+    // — a failure that looks like a component bug and is not one.
+    const first = render(<CodSkeleton />);
+    const before = first.container
+      .querySelector('[data-scene-started]')
+      ?.getAttribute('class');
+    first.unmount();
+
+    const after = renderStarted()
+      .container.querySelector('[data-scene-started]')
+      ?.getAttribute('class');
+
+    expect(before).toBeTruthy();
+    expect(after).toBe(before);
+  });
+});
+
 describe('CodSkeleton — WebGL fallback', () => {
   it('renders FallbackPanel instead of Canvas when WebGL is unavailable', () => {
     const original = HTMLCanvasElement.prototype.getContext;
@@ -67,13 +130,13 @@ describe('CodSkeleton — WebGL fallback', () => {
     HTMLCanvasElement.prototype.getContext = original;
   });
 
-  it('renders Canvas when WebGL is available', () => {
+  it('renders Canvas when WebGL is available and the scene is started', () => {
     const original = HTMLCanvasElement.prototype.getContext;
     HTMLCanvasElement.prototype.getContext = vi.fn(
       () => ({}) as unknown as RenderingContext
     ) as unknown as typeof HTMLCanvasElement.prototype.getContext;
 
-    const { container, getByTestId } = render(<CodSkeleton />);
+    const { container, getByTestId } = renderStarted();
     expect(getByTestId('canvas-mock')).toBeInTheDocument();
     expect(
       container.querySelector('[data-webgl-ok="true"]')
diff --git a/src/components/game/CodSkeleton/CodSkeleton.tsx b/src/components/game/CodSkeleton/CodSkeleton.tsx
index 5bb1abc6..8c0e893d 100644
--- a/src/components/game/CodSkeleton/CodSkeleton.tsx
+++ b/src/components/game/CodSkeleton/CodSkeleton.tsx
@@ -428,6 +428,7 @@ export default function CodSkeleton({
   speed = 4.5,
 }: CodSkeletonProps = {}): React.ReactElement {
   const [webglOk, setWebglOk] = useState<boolean>(() => isWebGLAvailable());
+  const [started, setStarted] = useState<boolean>(false);
   const [stance, setStance] = useState<Stance>('stand');
   const { tier, preset, setTier } = useQuality();
   const handleRetry = useCallback(() => setWebglOk(isWebGLAvailable()), []);
@@ -462,8 +463,58 @@ export default function CodSkeleton({
     );
   }
 
+  // THE SCENE DOES NOT MOUNT UNTIL THE VISITOR ASKS FOR IT (#757).
+  //
+  // Mounting <Canvas> during page load builds a MaterialSystem and bakes its 1K
+  // texture sets synchronously before the page is usable. On a GPU-less runner that
+  // measured 22.6-30.2s on chromium and 12.7-41.7s on webkit, against the 30s
+  // per-test budget — so `mobile-horizontal-scroll` timed out on this route three
+  // times and blocked two merges. Firefox, which has no WebGL and never mounts the
+  // canvas, finished the identical layout measurement in 2.8-3.3s: the whole gap is
+  // this mount.
+  //
+  // That is a property of the PAGE, not of the test. A software rasteriser stands in
+  // for a low-end visitor, and they pay the same cost on a route that has not yet
+  // been asked to do anything. Games gate their scene behind a start for exactly this
+  // reason, and this one already tells you to click.
+  //
+  // The placeholder lives inside the SAME wrapper, so `aspect-video w-full` gives it
+  // the identical box and the layout sweep measures the geometry it always measured.
+  // `CodSkeleton.test.tsx` asserts that; do not move the sizing onto either branch.
+  if (!started) {
+    return (
+      <div
+        className={wrapperClass}
+        data-webgl-ok="true"
+        data-scene-started="false"
+      >
+        <div className="bg-base-200 border-base-300 absolute inset-0 flex flex-col items-center justify-center gap-3 rounded border p-4 text-center">
+          <p className="text-base-content max-w-md text-sm">
+            The 3D scene is not running yet. Starting it compiles shaders and
+            bakes textures, so it waits until you ask.
+          </p>
+          <button
+            type="button"
+            onClick={() => setStarted(true)}
+            className="btn btn-primary min-h-11 min-w-11"
+          >
+            Start the scene
+          </button>
+          <p className="text-base-content/85 text-xs">
+            Then: click to capture · WASD move · Shift sprint · C crouch · X
+            prone · Space jump
+          </p>
+        </div>
+      </div>
+    );
+  }
+
   return (
-    <div className={wrapperClass} data-webgl-ok="true">
+    <div
+      className={wrapperClass}
+      data-webgl-ok="true"
+      data-scene-started="true"
+    >
       <Canvas
         dpr={Math.max(
           0.5,