diff --git a/tests/domain/scene-document-validation.test.ts b/tests/domain/scene-document-validation.test.ts
index 55f1ae3f..01f72f1f 100644
--- a/tests/domain/scene-document-validation.test.ts
+++ b/tests/domain/scene-document-validation.test.ts
@@ -1172,6 +1172,7 @@ describe("validateSceneDocument", () => {
     };
     document.world.shaderSky.dayTopColorHex = "bad-color" as `#${string}`;
     document.world.shaderSky.horizonHeight = 0.75;
+    document.world.shaderSky.stars.horizonFadeOffset = 0.75;
     document.world.shaderSky.celestial.sunDiscSizeDegrees = 0;
     document.world.shaderSky.clouds.coverage = 2;
     document.world.timeOfDay.dawn.background = {
@@ -1190,6 +1191,10 @@ describe("validateSceneDocument", () => {
           code: "invalid-world-shader-sky-horizon-height",
           path: "world.shaderSky.horizonHeight"
         }),
+        expect.objectContaining({
+          code: "invalid-world-shader-sky-star-horizon-fade-offset",
+          path: "world.shaderSky.stars.horizonFadeOffset"
+        }),
         expect.objectContaining({
           code: "invalid-world-shader-sky-sun-disc-size",
           path: "world.shaderSky.celestial.sunDiscSizeDegrees"
diff --git a/tests/domain/world-settings.test.ts b/tests/domain/world-settings.test.ts
index a96fd0c0..0cc24c79 100644
--- a/tests/domain/world-settings.test.ts
+++ b/tests/domain/world-settings.test.ts
@@ -177,4 +177,13 @@ describe("world settings helpers", () => {
 
     expect(areWorldSettingsEqual(left, right)).toBe(false);
   });
+
+  it("treats shader sky star horizon offset as part of authored world equality", () => {
+    const left = createDefaultWorldSettings();
+    const right = cloneWorldSettings(left);
+
+    right.shaderSky.stars.horizonFadeOffset = 0.08;
+
+    expect(areWorldSettingsEqual(left, right)).toBe(false);
+  });
 });
diff --git a/tests/serialization/project-document-json.test.ts b/tests/serialization/project-document-json.test.ts
index e5dfc528..83ac56bb 100644
--- a/tests/serialization/project-document-json.test.ts
+++ b/tests/serialization/project-document-json.test.ts
@@ -69,6 +69,7 @@ describe("project document JSON", () => {
     activeScene.world.shaderSky.dayBottomColorHex = "#d6efff";
     activeScene.world.shaderSky.horizonHeight = -0.06;
     activeScene.world.shaderSky.stars.density = 0.72;
+    activeScene.world.shaderSky.stars.horizonFadeOffset = 0.09;
     activeScene.world.shaderSky.clouds.coverage = 0.63;
     activeScene.world.shaderSky.clouds.tintHex = "#ece7df";