Keep the review card’s fallback color on the draft so a reload does not pick a new one.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/unit/previewSurfaceColor.test.ts

@@ -1,5 +1,6 @@
 import { describe, expect, it } from "vitest";
 import {
+  isPreviewSurfaceColor,
   mostCommonOpaqueColor,
   randomPreviewSurfaceColor,
   readableCardFill,
@@ -75,3 +76,15 @@ describe("randomPreviewSurfaceColor", () => {
     );
   });
 });
+
+describe("isPreviewSurfaceColor", () => {
+  it("accepts the hsl strings this module writes", () => {
+    expect(isPreviewSurfaceColor("hsl(12, 50%, 80%)")).toBe(true);
+    expect(isPreviewSurfaceColor("hsl(359, 84%, 87%)")).toBe(true);
+  });
+
+  it("rejects other CSS colors", () => {
+    expect(isPreviewSurfaceColor("rgb(12, 80, 40)")).toBe(false);
+    expect(isPreviewSurfaceColor("red")).toBe(false);
+  });
+});