//! [`DomainEvent`] — a fact about something that happened in the domain.
/// A persisted fact. Supplies optional metadata the read side needs:
///
/// * [`DomainEvent::tags`] — categorization keys for `events_by_tag`
/// subscriptions in [`atomr_persistence_query::ReadJournal`].
/// * [`DomainEvent::correlation_id`] — threads related events across
/// aggregates so a [`crate::saga::Saga`] can correlate them.