diff --git a/tests/unit/quantized-environment-blend-cache.test.ts b/tests/unit/quantized-environment-blend-cache.test.ts
new file mode 100644
index 00000000..ab3a5649
--- /dev/null
+++ b/tests/unit/quantized-environment-blend-cache.test.ts
@@ -0,0 +1,135 @@
+import { Texture } from "three";
+import { describe, expect, it, vi } from "vitest";
+
+import {
+  createQuantizedEnvironmentBlendCacheKey,
+  getQuantizedEnvironmentBlendAmount,
+  QuantizedEnvironmentBlendCache,
+  quantizeEnvironmentBlendBucket
+} from "../../src/rendering/quantized-environment-blend-cache";
+
+describe("quantized environment blend cache helpers", () => {
+  it("quantizes twilight blend amounts into fixed buckets", () => {
+    expect(quantizeEnvironmentBlendBucket(0, 8)).toBe(0);
+    expect(quantizeEnvironmentBlendBucket(0.24, 8)).toBe(2);
+    expect(quantizeEnvironmentBlendBucket(0.51, 8)).toBe(4);
+    expect(quantizeEnvironmentBlendBucket(1, 8)).toBe(8);
+    expect(getQuantizedEnvironmentBlendAmount(5, 8)).toBeCloseTo(0.625);
+  });
+
+  it("keys cached blends by ordered source pair and bucket", () => {
+    const dayTexture = new Texture();
+    const nightTexture = new Texture();
+
+    expect(
+      createQuantizedEnvironmentBlendCacheKey(dayTexture, nightTexture, 3)
+    ).not.toBe(
+      createQuantizedEnvironmentBlendCacheKey(nightTexture, dayTexture, 3)
+    );
+    expect(
+      createQuantizedEnvironmentBlendCacheKey(dayTexture, nightTexture, 2)
+    ).not.toBe(
+      createQuantizedEnvironmentBlendCacheKey(dayTexture, nightTexture, 3)
+    );
+  });
+});
+
+describe("QuantizedEnvironmentBlendCache", () => {
+  it("queues exact bucket builds, reuses the nearest cached bucket while pending, and disposes cached entries", () => {
+    const scheduledBuilds: Array<() => void> = [];
+    const disposeSpies: Array<ReturnType<typeof vi.fn>> = [];
+    const buildBlendTexture = vi.fn(
+      (
+        _baseTexture: Texture,
+        _overlayTexture: Texture,
+        _blendAmount: number
+      ) => {
+        const dispose = vi.fn();
+        disposeSpies.push(dispose);
+
+        return {
+          texture: new Texture(),
+          dispose
+        };
+      }
+    );
+    const onTextureReady = vi.fn();
+    const cache = new QuantizedEnvironmentBlendCache({
+      bucketCount: 8,
+      buildBlendTexture,
+      onTextureReady,
+      scheduleBuild: (callback) => {
+        scheduledBuilds.push(callback);
+      }
+    });
+    const dayTexture = new Texture();
+    const nightTexture = new Texture();
+
+    expect(cache.resolveBlendTexture(dayTexture, nightTexture, 0.26)).toBeNull();
+    expect(buildBlendTexture).not.toHaveBeenCalled();
+    expect(scheduledBuilds).toHaveLength(1);
+
+    scheduledBuilds.shift()?.();
+
+    expect(buildBlendTexture).toHaveBeenCalledWith(
+      dayTexture,
+      nightTexture,
+      0.25
+    );
+    expect(onTextureReady).toHaveBeenCalledTimes(1);
+
+    const firstBlendTexture = cache.resolveBlendTexture(
+      dayTexture,
+      nightTexture,
+      0.24
+    );
+
+    expect(firstBlendTexture).not.toBeNull();
+    expect(
+      cache.resolveBlendTexture(dayTexture, nightTexture, 0.62)
+    ).toBe(firstBlendTexture);
+    expect(scheduledBuilds).toHaveLength(1);
+
+    scheduledBuilds.shift()?.();
+
+    const laterBlendTexture = cache.resolveBlendTexture(
+      dayTexture,
+      nightTexture,
+      0.62
+    );
+
+    expect(laterBlendTexture).not.toBe(firstBlendTexture);
+    expect(onTextureReady).toHaveBeenCalledTimes(2);
+
+    cache.clear();
+
+    expect(disposeSpies).toHaveLength(2);
+    expect(disposeSpies[0]).toHaveBeenCalledTimes(1);
+    expect(disposeSpies[1]).toHaveBeenCalledTimes(1);
+  });
+
+  it("returns the authored single-image environment at the quantized endpoints and disposes builder resources", () => {
+    const disposeBuildResources = vi.fn();
+    const buildBlendTexture = vi.fn();
+    const cache = new QuantizedEnvironmentBlendCache({
+      bucketCount: 8,
+      buildBlendTexture,
+      disposeBuildResources,
+      scheduleBuild: () => undefined
+    });
+    const dayTexture = new Texture();
+    const nightTexture = new Texture();
+
+    expect(cache.resolveBlendTexture(dayTexture, nightTexture, 0.01)).toBe(
+      dayTexture
+    );
+    expect(cache.resolveBlendTexture(dayTexture, nightTexture, 0.99)).toBe(
+      nightTexture
+    );
+    expect(buildBlendTexture).not.toHaveBeenCalled();
+
+    cache.dispose();
+
+    expect(disposeBuildResources).toHaveBeenCalledTimes(1);
+  });
+});