Change Data Capture: durable record of every committed write, ordered, addressable, and consumable by external systems. The transaction layer hands committed deltas here at commit time; this crate persists them, exposes the consumer-side cursor APIs that downstream replication, subscriptions, and external sinks read from, and runs the background compactor that prunes records past retention.
Producers and consumers are decoupled - a write only needs to be persisted before the transaction returns; the consumer side can fall arbitrarily far behind and catch up later. Storage is pluggable so the same protocol can be backed by SQLite for embedded deployments and by a horizontally scaled log for production.
Invariant: a CDC record published for a transaction reflects exactly the deltas that were committed under that transaction id, in the order the engine produced them. Reordering or dropping deltas inside CDC desynchronises replicas and subscriptions from the source of truth.