test(email): контактный адрес, Reply-To и тестовая отправка письма

Покрытие валидации/сохранения contact_email, простановки Reply-To в
письмах регистрации/приглашений/саммари при включённом и выключенном
контактном адресе, и эндпоинта тестовой отправки (успех, дефолтный
получатель, сбой транспорта без утечки логина/пароля).

backend/tests/test_instance_settings.py

@@ -48,6 +48,7 @@ from services.instance_settings import (
     BootstrapOverrides,
     InstanceSettingsService,
     InvalidAiLevelError,
+    InvalidContactEmailError,
     InvalidEmailDomainError,
     InvalidTimezoneError,
     SettingsUpdateIn,
@@ -69,6 +70,7 @@ _MANAGED_KEYS = (
     "display_timezone",
     "registration_team_choice",
     "registration_email_domain",
+    "contact_email",
 )
 
 
@@ -123,6 +125,7 @@ async def test_ensure_bootstrapped_imports_yaml_defaults(
         "display_timezone",
         "registration_team_choice",
         "registration_email_domain",
+        "contact_email",
     }
     cfg = await service.get()
     assert cfg.transcriber.provider == "faster_whisper_cpu"
@@ -132,6 +135,8 @@ async def test_ensure_bootstrapped_imports_yaml_defaults(
     assert cfg.registration_team_choice is False
     assert cfg.registration_email_domain_enabled is False
     assert cfg.registration_email_domain is None
+    assert cfg.contact_email_enabled is False
+    assert cfg.contact_email is None
 
 
 async def test_ensure_bootstrapped_is_idempotent_and_keeps_admin_edits(
@@ -384,6 +389,68 @@ async def test_registration_email_domain_can_be_disabled_keeping_stored_domain(
     assert cfg.registration_email_domain == "acme.io"
 
 
+async def test_contact_email_enable_without_email_rejected(
+    db_session: AsyncSession, clean_instance_settings: None
+) -> None:
+    """Включение контактного адреса без email (ни в патче, ни ранее сохранённого) → 400."""
+    service = InstanceSettingsService(db_session)
+    await service.ensure_bootstrapped(PLUGINS_YAML)
+
+    with pytest.raises(InvalidContactEmailError):
+        await service.update(SettingsUpdateIn(contact_email_enabled=True))
+
+    cfg = await service.get()
+    assert cfg.contact_email_enabled is False
+    assert cfg.contact_email is None
+
+
+async def test_contact_email_rejects_invalid_format(
+    db_session: AsyncSession, clean_instance_settings: None
+) -> None:
+    service = InstanceSettingsService(db_session)
+    await service.ensure_bootstrapped(PLUGINS_YAML)
+
+    with pytest.raises(InvalidContactEmailError):
+        await service.update(SettingsUpdateIn(contact_email="not an email"))
+
+    cfg = await service.get()
+    assert cfg.contact_email is None
+
+
+async def test_contact_email_normalizes_input(
+    db_session: AsyncSession, clean_instance_settings: None
+) -> None:
+    """` Contact@VidConf.RU ` нормализуется в `contact@vidconf.ru` (strip, lower)."""
+    service = InstanceSettingsService(db_session)
+    await service.ensure_bootstrapped(PLUGINS_YAML)
+
+    cfg = await service.update(
+        SettingsUpdateIn(contact_email_enabled=True, contact_email=" Contact@VidConf.RU ")
+    )
+
+    assert cfg.contact_email_enabled is True
+    assert cfg.contact_email == "contact@vidconf.ru"
+
+    reloaded = await service.get()
+    assert reloaded.contact_email == "contact@vidconf.ru"
+
+
+async def test_contact_email_can_be_disabled_keeping_stored_email(
+    db_session: AsyncSession, clean_instance_settings: None
+) -> None:
+    """Выключение контактного адреса без передачи email не требует его и не роняет валидацию."""
+    service = InstanceSettingsService(db_session)
+    await service.ensure_bootstrapped(PLUGINS_YAML)
+    await service.update(
+        SettingsUpdateIn(contact_email_enabled=True, contact_email="contact@acme.io")
+    )
+
+    cfg = await service.update(SettingsUpdateIn(contact_email_enabled=False))
+
+    assert cfg.contact_email_enabled is False
+    assert cfg.contact_email == "contact@acme.io"
+
+
 async def test_transcription_enabled_flag_toggles_both_transcriber_and_summarizer(
     db_session: AsyncSession, clean_instance_settings: None
 ) -> None: