fix(frontend): normalize omitted reveal fooled-player ids

frontend/src/api/mappers.ts

@@ -135,7 +135,7 @@ function mapSessionDetail(payload: unknown): SessionDetailResponse {
         if (fooledPlayerIdRaw !== undefined && fooledPlayerIdRaw !== null && !isNumber(fooledPlayerIdRaw)) {
           throw new Error(`Invalid API contract: expected number|null at session_detail.reveal.guesses[${index}].fooled_player_id`);
         }
-        const fooledPlayerId = fooledPlayerIdRaw === undefined ? null : fooledPlayerIdRaw;
+        const fooledPlayerId = fooledPlayerIdRaw ?? null;
         const fooledPlayerNickname = record.fooled_player_nickname;
         if (fooledPlayerNickname !== undefined && !isString(fooledPlayerNickname)) {
           throw new Error(`Invalid API contract: expected string at session_detail.reveal.guesses[${index}].fooled_player_nickname`);
@@ -389,10 +389,11 @@ export function mapSubmitGuessResponse(payload: unknown): SubmitGuessResponse {
   const root = asRecord(payload, 'submit_guess');
   const guess = asRecord(root.guess, 'submit_guess.guess');
   const window = asRecord(root.window, 'submit_guess.window');
-  const fooledPlayerId = guess.fooled_player_id;
-  if (fooledPlayerId !== null && !isNumber(fooledPlayerId)) {
+  const fooledPlayerIdRaw = guess.fooled_player_id;
+  if (fooledPlayerIdRaw !== undefined && fooledPlayerIdRaw !== null && !isNumber(fooledPlayerIdRaw)) {
     throw new Error('Invalid API contract: expected number|null at submit_guess.guess.fooled_player_id');
   }
+  const fooledPlayerId = fooledPlayerIdRaw ?? null;
 
   return {
     guess: {

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

@@ -283,7 +283,7 @@ describe('createAngularApiClient', () => {
     }
   });
 
-  it('normalizes omitted fooled_player_id to null in canonical reveal payload guesses', async () => {
+  it('normalizes omitted fooled_player_id to null in canonical reveal payloads', async () => {
     const get = vi.fn<AngularHttpClientLike['get']>(async <T>(url: string) => {
       if (url === '/lobby/sessions/ABCD12') {
         return {
@@ -346,7 +346,25 @@ describe('createAngularApiClient', () => {
       throw { status: 404, error: { error: 'Not found' } };
     });
 
-    const client = createAngularApiClient({ get, post: vi.fn() } as unknown as AngularHttpClientLike);
+    const post = vi.fn<AngularHttpClientLike['post']>(async <T>(url: string, body: unknown) => {
+      if (url === '/lobby/sessions/ABCD12/questions/77/guesses/submit') {
+        expect(body).toEqual({ player_id: 9, session_token: 'tok', selected_text: 'A' });
+        return {
+          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' }
+        } as T;
+      }
+      throw { status: 404, error: { error: 'Not found' } };
+    });
+
+    const client = createAngularApiClient({ get, post } as AngularHttpClientLike);
     const session = await client.getSession('abcd12');
 
     expect(session.ok).toBe(true);
@@ -354,6 +372,16 @@ describe('createAngularApiClient', () => {
       expect(session.data.reveal?.guesses[0].fooled_player_id).toBeNull();
       expect(session.data.reveal?.guesses[0]).not.toHaveProperty('fooled_player_nickname');
     }
+
+    const submitGuess = await client.submitGuess('ABCD12', 77, {
+      player_id: 9,
+      session_token: 'tok',
+      selected_text: 'A'
+    });
+    expect(submitGuess.ok).toBe(true);
+    if (submitGuess.ok) {
+      expect(submitGuess.data.guess.fooled_player_id).toBeNull();
+    }
   });
 
   it('maps host/player gameplay endpoints through typed response mappers', async () => {