Glossary

Domain and persistence

Term	Meaning
Aggregate	An application-owned consistency boundary that changes state only by applying domain events.
Domain event	An immutable application-owned fact that implements IDomainEvent<TAggregate> and has a stable [EventType] name and version.
Event envelope	The stored event plus persistence metadata: tenant, stream, versions, event ID, occurrence time, and metadata.
Stream	The ordered event history for one aggregate identity and aggregate type within a tenant.
Stream version	A consecutive number that orders events within one stream and supports optimistic concurrency.
Expected version	The stream state an append requires: no stream, an exact version, an existing stream, or any version.
Append ID	A caller-owned, tenant-scoped identifier used to safely retry the same command after an ambiguous failure.
Tenant offset	A consecutive, committed position that orders all events for one tenant. It is the checkpoint position for asynchronous processing.
Snapshot	A versioned aggregate-owned state cache, declared as IAggregateSnapshot<TAggregate>, that shortens replay. Event history remains authoritative.

Processing and delivery

Term	Meaning
Projection	Code that consumes committed events to produce a read model or perform a side effect.
Projection key	A projection’s durable identity: a stable name and positive version. Each version has independent checkpoints and failures.
Checkpoint	The tenant offset through which a projection has durably completed processing.
Transactional EF projection	A projection whose EventLoom-context read-model changes and checkpoint commit in one transaction.
Asynchronous projection	A background projection that is delivered at least once and must therefore be idempotent.
Inline projection	A handler that runs inside the event append transaction and can veto the append. It may perform transactional database work only.
Outbox message	A durable integration message written atomically with an event append when an outbox publisher is configured.
Outbox publisher	A background worker that delivers pending outbox messages. Delivery is at least once.
Lease	Time-limited worker ownership for a tenant and processing responsibility. PostgreSQL uses fenced leases to reject stale worker commits.

Operational outcomes

Term	Meaning
At least once	A handler or publisher can receive the same event or message more than once. Effects must be idempotent.
Effectively once	Transactional EF projection changes and their checkpoint commit together, preventing duplicate database effects at that boundary.
Idempotency	Repeating an operation yields the same externally visible result as running it once.
Paused projection	A projection version that stopped for a tenant after exhausting retry attempts. An operator must resume, skip, or rebuild it.
Replay	Resetting a projection checkpoint so a projection version processes tenant history again. Replay does not clear a read model.