chore: import upstream snapshot with attribution

packages/react-core/scripts/__tests__/fixtures/tiny-entry.js

@@ -0,0 +1,5 @@
+// Minimal fixture used by measure-copilotchat.test.mjs. The function under test
+// bundles `export { CopilotChat } from "<entryModule>"`, so this exports a
+// trivial CopilotChat symbol to validate the script's bundling pipeline without
+// depending on react-core's built dist.
+export const CopilotChat = () => null;

packages/react-core/scripts/__tests__/measure-copilotchat.test.mjs

@@ -0,0 +1,43 @@
+// Standalone Node test (not vitest) — the script under test calls esbuild,
+// which trips vitest's jsdom env probe, and the package-wide vitest setup uses
+// jsdom-only globals. Running with `node --test` keeps this isolated.
+//
+// Invoked from package.json `test:scripts` and the chained `test` command.
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import { fileURLToPath } from "node:url";
+import path from "node:path";
+import { measureBundle } from "../measure-copilotchat.mjs";
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const fixtureDir = path.join(here, "fixtures");
+const fixtureEntry = path.join(fixtureDir, "tiny-entry.js");
+
+describe("measureBundle", () => {
+  it("bundles a tiny CopilotChat fixture and returns a positive gzip total", async () => {
+    const result = await measureBundle({
+      entryModule: fixtureEntry,
+      pkgRoot: fixtureDir,
+    });
+    assert.ok(result.totalBytes > 0, "totalBytes should be > 0");
+    // Trivial fixture; a sane upper bound guards against accidental inclusion
+    // of huge externals or the loader stubs regressing.
+    assert.ok(
+      result.totalBytes < 50_000,
+      `totalBytes should be < 50_000, got ${result.totalBytes}`,
+    );
+    assert.ok(result.outputCount >= 1, "outputCount should be >= 1");
+  });
+
+  it("returns a deterministic gzip total across two runs", async () => {
+    const a = await measureBundle({
+      entryModule: fixtureEntry,
+      pkgRoot: fixtureDir,
+    });
+    const b = await measureBundle({
+      entryModule: fixtureEntry,
+      pkgRoot: fixtureDir,
+    });
+    assert.equal(b.totalBytes, a.totalBytes);
+  });
+});