diff --git a/tests/domain/scene-document-validation.test.ts b/tests/domain/scene-document-validation.test.ts
index 5fcd479f..55f1ae3f 100644
--- a/tests/domain/scene-document-validation.test.ts
+++ b/tests/domain/scene-document-validation.test.ts
@@ -1171,6 +1171,7 @@ describe("validateSceneDocument", () => {
       mode: "shader"
     };
     document.world.shaderSky.dayTopColorHex = "bad-color" as `#${string}`;
+    document.world.shaderSky.horizonHeight = 0.75;
     document.world.shaderSky.celestial.sunDiscSizeDegrees = 0;
     document.world.shaderSky.clouds.coverage = 2;
     document.world.timeOfDay.dawn.background = {
@@ -1185,6 +1186,10 @@ describe("validateSceneDocument", () => {
           code: "invalid-world-shader-sky-day-top-color",
           path: "world.shaderSky.dayTopColorHex"
         }),
+        expect.objectContaining({
+          code: "invalid-world-shader-sky-horizon-height",
+          path: "world.shaderSky.horizonHeight"
+        }),
         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 8f7dc533..a96fd0c0 100644
--- a/tests/domain/world-settings.test.ts
+++ b/tests/domain/world-settings.test.ts
@@ -168,4 +168,13 @@ describe("world settings helpers", () => {
 
     expect(areWorldSettingsEqual(left, right)).toBe(false);
   });
+
+  it("treats shader sky horizon height as part of authored world equality", () => {
+    const left = createDefaultWorldSettings();
+    const right = cloneWorldSettings(left);
+
+    right.shaderSky.horizonHeight = 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 4a39c4e3..e5dfc528 100644
--- a/tests/serialization/project-document-json.test.ts
+++ b/tests/serialization/project-document-json.test.ts
@@ -67,6 +67,7 @@ describe("project document JSON", () => {
     activeScene.world.showCelestialBodies = true;
     activeScene.world.shaderSky.dayTopColorHex = "#4a76bb";
     activeScene.world.shaderSky.dayBottomColorHex = "#d6efff";
+    activeScene.world.shaderSky.horizonHeight = -0.06;
     activeScene.world.shaderSky.stars.density = 0.72;
     activeScene.world.shaderSky.clouds.coverage = 0.63;
     activeScene.world.shaderSky.clouds.tintHex = "#ece7df";
diff --git a/tests/unit/world-shader-sky.test.ts b/tests/unit/world-shader-sky.test.ts
index 46abef58..828080e8 100644
--- a/tests/unit/world-shader-sky.test.ts
+++ b/tests/unit/world-shader-sky.test.ts
@@ -18,6 +18,7 @@ describe("resolveWorldShaderSkyRenderState", () => {
     world.showCelestialBodies = true;
     world.shaderSky.dayTopColorHex = "#88ccff";
     world.shaderSky.dayBottomColorHex = "#dff3ff";
+    world.shaderSky.horizonHeight = -0.08;
     world.timeOfDay.dawn.background = {
       mode: "verticalGradient",
       topColorHex: "#ff8855",
@@ -106,6 +107,7 @@ describe("resolveWorldShaderSkyRenderState", () => {
     expect(dawnSky).not.toBeNull();
     expect(noonSky?.sky.topColorHex).toBe("#88ccff");
     expect(noonSky?.sky.bottomColorHex).toBe("#dff3ff");
+    expect(noonSky?.sky.horizonHeight).toBe(-0.08);
     expect(dawnSky?.sky.topColorHex).not.toBe(noonSky?.sky.topColorHex);
     expect(dawnSky?.sky.topColorHex).not.toBe(midnightSky?.sky.topColorHex);
     expect(midnightSky?.stars.visibility ?? 0).toBeGreaterThan(