diff --git a/src/app/features/scene/index.test.ts b/src/app/features/scene/index.test.ts
index 5d0e6410..6a29b33f 100644
--- a/src/app/features/scene/index.test.ts
+++ b/src/app/features/scene/index.test.ts
@@ -4,6 +4,7 @@ import { baked } from '../../../sky/baked';
 import type { Scene } from './Scene';
 import { startBackgroundScene } from './index';
 import { setSkyClock, setSkyState } from './skyState';
+import { ridgeSkyFor } from './skyForState';
 
 const { createRidgeScene, createScene } = vi.hoisted(() => ({
   createRidgeScene: vi.fn(),
@@ -155,16 +156,28 @@ describe('startBackgroundScene follows the sky state', () => {
     expect(createRidgeScene).toHaveBeenCalledOnce();
   });
 
-  it('keeps only the latest of two quick changes', async () => {
+  it('keeps only the latest of two quick changes: the last sky is built, the others are not left running', async () => {
     const scenes = [fakeScene(), fakeScene(), fakeScene()];
     scenes.forEach((s) => createRidgeScene.mockReturnValueOnce(s));
     const scene = await startBackgroundScene(config, caps, { canvas });
     setSkyState('day');
-    setSkyState('night');
+    setSkyState('dusk');
     await flush();
-    expect(scenes[1].dispose).toHaveBeenCalledOnce();
-    expect(scenes[2].dispose).not.toHaveBeenCalled();
+    // The sky last built is dusk's, and it is the live scene: a login reaches it and nothing else.
+    const built = createRidgeScene.mock.calls.length;
+    expect(hex(createRidgeScene.mock.calls[built - 1][0].sky.top)).toBe(
+      hex(ridgeSkyFor('dusk').top)
+    );
+    const live = scenes[built - 1];
+    scene?.login();
+    expect(live.login).toHaveBeenCalledOnce();
+    scenes.filter((s) => s !== live).forEach((s) => expect(s.login).not.toHaveBeenCalled());
+    // Every scene but the live one was disposed, the live one not yet.
+    scenes.slice(0, built).forEach((s) => {
+      expect(s.dispose).toHaveBeenCalledTimes(s === live ? 0 : 1);
+    });
     scene?.dispose();
+    expect(live.dispose).toHaveBeenCalledOnce();
   });
 
   it('leaves the ray-march scene alone: it has one fixed dusk', async () => {
diff --git a/src/app/features/scene/index.ts b/src/app/features/scene/index.ts
index 55966188..73377440 100644
--- a/src/app/features/scene/index.ts
+++ b/src/app/features/scene/index.ts
@@ -95,8 +95,10 @@ export async function startBackgroundScene(
   let generation = 0;
   // A rebuild is for a different sky ('auto' crossing a boundary, a new choice), not for a repeat of the one drawn.
   const rebuild = async () => {
+    // The choice can move while the key is awaited; that change has its own rebuild, so this one stands down.
     const next = getSkyState();
     const key = await skyKey(config, next);
+    if (getSkyState() !== next) return;
     if ((key !== null && key === built) || disposed) return;
     generation += 1;
     const mine = generation;
diff --git a/src/app/features/scene/skyTheme.test.ts b/src/app/features/scene/skyTheme.test.ts
index 39b74fdc..53cf2873 100644
--- a/src/app/features/scene/skyTheme.test.ts
+++ b/src/app/features/scene/skyTheme.test.ts
@@ -92,7 +92,7 @@ describe('ink of the theme a state picks, on bare sky', () => {
   });
 
   it('keeps the lightest Night sky the link was fitted to equal to the Night backdrop (no drift)', () => {
-    expect(Math.abs(NIGHT_SKY_LIGHTEST - skyBackdrop('night').lightest)).toBeLessThan(1e-6);
+    expect(NIGHT_SKY_LIGHTEST).toBe(skyBackdrop('night').lightest);
   });
 
   it.each([