Transactional layer over the storage tier: opens a read or read-write transaction, accumulates deltas, validates
conflicts, and commits atomically. The crate offers two flavours - a multi-version path for OLTP traffic that needs
snapshot isolation, and a single-version path for workloads where versioning would only add overhead - and exposes
both behind a uniform Transaction handle that the engine threads through every request.
Every change recorded inside a transaction is captured as a delta, surfaced through the change accumulator, and published downstream so CDC consumers, replication, and subscriptions observe the same write set the engine just committed. Interceptors hook the commit boundary and let policy, audit, and consistency checks run with full visibility into what is about to be written.
Invariant: a TransactionId is unique system-wide and monotonic via Uuid7; downstream consumers (CDC, replication,
subscriptions) order events by transaction id, so reusing or back-dating an id silently breaks consumer
consistency.