feat(audience): guard CDN bundle against double-import

- Preserves the first window.ImmutableAudience if the bundle runs twice.
- Emits a console.warn instead of silently overwriting a live instance.
- Prevents session loss if a studio accidentally loads the script twice.

Refs SDK-115

Author: ImmutableJeffrey

packages/audience/sdk/src/cdn.test.ts

@@ -42,4 +42,18 @@ describe('cdn entry point', () => {
     });
     expect(err).toBeInstanceOf(Error);
   });
+
+  it('does not overwrite a pre-existing global', async () => {
+    const sentinel = { Audience: 'FAKE' };
+    (globalThis as unknown as { ImmutableAudience?: unknown }).ImmutableAudience = sentinel;
+
+    const warn = jest.spyOn(console, 'warn').mockImplementation(() => {});
+    await import('./cdn');
+
+    expect(
+      (globalThis as unknown as { ImmutableAudience?: unknown }).ImmutableAudience,
+    ).toBe(sentinel);
+    expect(warn).toHaveBeenCalledWith(expect.stringContaining('loaded twice'));
+    warn.mockRestore();
+  });
 });

packages/audience/sdk/src/cdn.ts

@@ -36,9 +36,16 @@ const globalObj = (
   typeof globalThis !== 'undefined' ? globalThis : window
 ) as unknown as { ImmutableAudience?: ImmutableAudienceGlobal };
 
-globalObj.ImmutableAudience = {
-  Audience,
-  AudienceError,
-  IdentityType,
-  version: LIBRARY_VERSION,
-};
+if (globalObj.ImmutableAudience) {
+  // eslint-disable-next-line no-console
+  console.warn(
+    '[@imtbl/audience] CDN bundle loaded twice; keeping the first instance.',
+  );
+} else {
+  globalObj.ImmutableAudience = {
+    Audience,
+    AudienceError,
+    IdentityType,
+    version: LIBRARY_VERSION,
+  };
+}