export async function GET(req: NextRequest) {
  try {
    await requireSession();
    const { searchParams } = new URL(req.url);
    const email = (searchParams.get('email') ?? '').trim().toLowerCase();
    const uid = (searchParams.get('uid') ?? '').trim();

    if (!email && !uid) {
      return NextResponse.json(
        { error: 'Informe ?email=... ou ?uid=...' },
        { status: 400 },
      );
    }

    // 1) Auth: user-not-found NO es 500, es resultado vacío
    let authUser;
    try {
      authUser = uid
        ? await adminAuth().getUser(uid)
        : await adminAuth().getUserByEmail(email);
    } catch (e: unknown) {
      const code = (e as { code?: string } | null)?.code;
      if (code === 'auth/user-not-found') {
        return NextResponse.json({ found: false, query: email || uid });
      }
      throw e;
    }

    // 2) Firestore: 2 reads en paralelo
    const [trainerSnap, alunoSnap] = await Promise.all([
      adminDb().collection('trainers').doc(authUser.uid).get(),
      adminDb().collection('alunos').doc(authUser.uid).get(),
    ]);

    const trainer = trainerSnap.exists ? trainerSnap.data() : null;
    const aluno = alunoSnap.exists ? alunoSnap.data() : null;

    // 3) Tipo principal: trainer / aluno / both / solo-auth
    let userType: 'trainer' | 'aluno' | 'both' | 'auth-only' = 'auth-only';
    if (trainer && aluno) userType = 'both';
    else if (trainer) userType = 'trainer';
    else if (aluno) userType = 'aluno';

    return NextResponse.json({ found: true, query: email || uid, userType /* ... */ });
  } catch (e) {
    return errResponse(e);
  }
}

En entrevista se nota: diferenciar «no encontrado» de un error real, poner llamadas independientes en paralelo, tratar errores del SDK como unknown con narrowing y normalizar timestamps propietarios — todo en ~60 líneas.