test(frontend): harden reveal fooled-player normalization

frontend/tests/angular-api-client.test.ts

@@ -1,6 +1,7 @@
 import { describe, expect, it, vi } from 'vitest';
 
 import { createAngularApiClient, type AngularHttpClientLike } from '../src/api/angular-client';
+import { mapSubmitGuessResponse } from '../src/api/mappers';
 
 describe('createAngularApiClient', () => {
   it('reads health and session detail using Django-compatible endpoints', async () => {
@@ -384,6 +385,22 @@ describe('createAngularApiClient', () => {
     }
   });
 
+  it('maps omitted fooled_player_id to null in submit guess mapper payloads', () => {
+    const mapped = mapSubmitGuessResponse({
+      guess: {
+        id: 200,
+        player_id: 9,
+        round_question_id: 77,
+        selected_text: 'A',
+        is_correct: false,
+        created_at: '2026-03-01T16:01:00Z'
+      },
+      window: { guess_deadline_at: '2026-03-01T16:01:30Z' }
+    });
+
+    expect(mapped.guess.fooled_player_id).toBeNull();
+  });
+
   it('maps host/player gameplay endpoints through typed response mappers', async () => {
     const get = vi.fn<AngularHttpClientLike['get']>(async <T>(url: string) => {
       if (url === '/lobby/sessions/ABCD12/scoreboard') {