chore: import upstream snapshot with attribution

showcase/scripts/__tests__/baseline-sync.test.ts

@@ -0,0 +1,35 @@
+/**
+ * Sync contract: validate-parity.ts's BASELINE_DEMO_COUNT constant and
+ * fail-baseline.json's `baselineDemoCount` field are two declarations of
+ * the same number — the per-package e2e-spec-count floor. The workflow
+ * .github/workflows/showcase_validate.yml reads the JSON; validate-parity.ts
+ * uses the TS constant as its default. A divergence means the validator
+ * and the CI gate disagree silently, so we lock them together here.
+ *
+ * Prior to this test the contract was enforced only by a comment ("keep
+ * in sync"), which is trivially violated without any CI signal. R29-7
+ * finding #4 / R29-5.
+ */
+
+import { describe, it, expect } from "vitest";
+import fs from "fs";
+import path from "path";
+import { fileURLToPath } from "url";
+import { BASELINE_DEMO_COUNT } from "../validate-parity.js";
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+
+describe("baselineDemoCount sync contract", () => {
+  it("fail-baseline.json `baselineDemoCount` equals validate-parity.ts BASELINE_DEMO_COUNT", () => {
+    const baselinePath = path.resolve(__dirname, "..", "fail-baseline.json");
+    const raw = fs.readFileSync(baselinePath, "utf8");
+    const parsed = JSON.parse(raw) as { baselineDemoCount?: unknown };
+    // Explicit type guard rather than a blind cast — if the field ever
+    // disappears or its type flips, we want a clear failure, not
+    // `undefined === <n>` silently passing as false.
+    expect(typeof parsed.baselineDemoCount).toBe("number");
+    expect(Number.isInteger(parsed.baselineDemoCount)).toBe(true);
+    expect(parsed.baselineDemoCount).toBe(BASELINE_DEMO_COUNT);
+  });
+});