Email Notification Delivery

In-app notifications are the canonical notification channel. They remain available when no email implementation is installed.

Production email delivery is an optional integration with the mail.notificationDelivery capability:

Notifications owns recipient intent, notification preferences, content, and notification status.
Mail owns server profiles, credentials, queue persistence, retry policy, and transport outcomes.
An accepted handoff is recorded as accepted; it does not claim that the remote SMTP server has delivered the message.
If Mail or a usable profile is unavailable, delivery is recorded as paused. The notification is retained and can be retried after the capability becomes available.
Transport failures are recorded as failed with an attempt record and do not remove the in-app notification.
File-based EML delivery is development-only and must not be used as a production fallback.

The capability contract deliberately passes references to recipient, tenant, and profile context without exposing or duplicating Mail credentials.