diff --git a/api/tests/test_api_admin.py b/api/tests/test_api_admin.py
index 7fb4c93..18356d3 100644
--- a/api/tests/test_api_admin.py
+++ b/api/tests/test_api_admin.py
@@ -183,14 +183,15 @@ async def test_list_users_search_filter_and_page(auth_client: AuthClientFactory,
     office = await _office(seeded, ROSTOV)
     await make_user(seeded, email="Zoya_Search@example.com", office=office, roles=["KA_RF", "EXPERT"], full_name="Зоя")
     await make_user(seeded, email="off@example.com", office=office, full_name="Зоя Отключённая", is_active=False)
+    await make_user(seeded, email="zoyaXs@example.com", office=office)  # совпал бы с `zoya_s`, если `_` — шаблон LIKE
     admin = await auth_client(ADMIN)
 
     everyone = (await admin.get(USERS)).json()
     assert set(everyone) == {"items", "total", "limit", "offset"}
-    assert everyone["total"] == len(everyone["items"]) >= 9  # noqa: PLR2004 - 7 dev-пользователей + 2 новых
+    assert everyone["total"] == len(everyone["items"]) >= 10  # noqa: PLR2004 - 7 dev-пользователей + 3 новых
 
     by_email = (await admin.get(USERS, params={"q": "zoya_s"})).json()  # `_` ищется буквально, без регистра
-    assert [item["email"] for item in by_email["items"]] == ["Zoya_Search@example.com"]
+    assert [item["email"] for item in by_email["items"]] == ["Zoya_Search@example.com"]  # `zoyaXs@…` не найден
     assert by_email["items"][0]["roles"] == ["EXPERT", "KA_RF"]
     assert by_email["items"][0]["regional_office"]["name"] == ROSTOV
 
@@ -364,6 +365,57 @@ async def test_second_admin_allows_dropping_own_admin_role(
     assert (await admin.get("/admin/roles")).status_code == HTTP_FORBIDDEN  # права пересчитаны на следующем запросе
 
 
+async def _grant_users_admin(session: AsyncSession, role_code: str, *, is_active: bool = True) -> None:
+    """Даёт роли право `USERS_ADMIN` напрямую в БД (и задаёт `is_active` роли) — как после правки матрицы прав."""
+    role = (await session.execute(select(Role).where(Role.code == role_code))).scalar_one()
+    permission_id = (await session.execute(select(Permission.id).where(Permission.code == "USERS_ADMIN"))).scalar_one()
+    session.add(RolePermission(role_id=role.id, permission_id=permission_id))
+    role.is_active = is_active
+    await session.flush()
+
+
+@pytest.mark.integration
+async def test_sole_admin_moved_to_active_role_with_users_admin_stays_admin(
+    auth_client: AuthClientFactory, seeded: AsyncSession
+) -> None:
+    """Ветка `kept_roles`: оставшаяся активная роль даёт `USERS_ADMIN` — другого администратора не требуется (T12.1)."""
+    await _grant_users_admin(seeded, "EXPERT")
+    admin_id = await _user_id(seeded, ADMIN)
+    admin = await auth_client(ADMIN)
+    response = await admin.put(f"{USERS}/{admin_id}/roles", json={"roles": ["EXPERT"]})
+    assert response.status_code == HTTP_OK, response.text
+    assert await _role_codes(seeded, admin_id) == ["EXPERT"]
+    assert (await admin.get(USERS)).status_code == HTTP_OK  # право USERS_ADMIN сохранено через EXPERT
+    assert len(await _events(seeded, AuditAction.USER_ROLE_CHANGE)) == 1
+
+
+@pytest.mark.integration
+async def test_sole_admin_cannot_be_moved_to_inactive_role_with_users_admin(
+    auth_client: AuthClientFactory, seeded: AsyncSession
+) -> None:
+    """Неактивная роль с `USERS_ADMIN` не даёт права и не назначается: набор ролей и администратор не меняются (T12.1).
+
+    Сервис отсекает её раньше проверки `LAST_ADMIN` — 422 `UNKNOWN_ROLE`; сам фильтр `is_active` в `kept_roles`-проверке
+    (`roles_grant_permission`) защитный и до неё через API недостижим, поэтому проверяется отдельно.
+    """
+    await _grant_users_admin(seeded, "EXPERT", is_active=False)
+    admin_id = await _user_id(seeded, ADMIN)
+    admin = await auth_client(ADMIN)
+    response = await admin.put(f"{USERS}/{admin_id}/roles", json={"roles": ["EXPERT"]})
+    assert response.status_code == HTTP_UNPROCESSABLE, response.text
+    assert _detail_code(response) == "UNKNOWN_ROLE"
+    assert await _role_codes(seeded, admin_id) == ["ADMIN"]
+    assert await _events(seeded, AuditAction.USER_ROLE_CHANGE) == []
+    assert (await admin.get(USERS)).status_code == HTTP_OK
+
+    roles = {
+        role.code: role.id
+        for role in (await seeded.execute(select(Role).where(Role.code.in_(["ADMIN", "EXPERT"])))).scalars()
+    }
+    assert await users_repo.roles_grant_permission(seeded, {roles["ADMIN"]}, "USERS_ADMIN") is True
+    assert await users_repo.roles_grant_permission(seeded, {roles["EXPERT"]}, "USERS_ADMIN") is False  # неактивная роль
+
+
 @pytest.mark.integration
 async def test_last_admin_cannot_deactivate_self(auth_client: AuthClientFactory, seeded: AsyncSession) -> None:
     """Review Focus 5: последний активный с `USERS_ADMIN` не может деактивировать себя; при втором — может."""
@@ -401,6 +453,7 @@ async def test_deactivating_other_admin_respects_last_admin(
     admin_id = await _user_id(seeded, ADMIN)
     response = await admin.patch(f"{USERS}/{admin_id}", json={"is_active": False})
     assert response.status_code == HTTP_CONFLICT
+    assert _detail_code(response) == "LAST_ADMIN"
     assert (await second_client.get(USERS)).status_code == HTTP_FORBIDDEN