Module callback 

Pipeline callback trait and source registration types.

Decouples the pipeline coordinator from db.rs internals so the TPC coordinator can drive SQL cycles, sink writes, and checkpoints through a narrow interface.

Structs

SourceRegistration

A registered source with its name and config.

Enums

BarrierOutcome

Outcome of a barrier-aligned checkpoint attempt. Skipped is logged at debug; Failed keeps the retry warning.

SkipReason

Why a barrier checkpoint was deliberately skipped, as opposed to attempted-and-failed.

Traits

PipelineCallback

Callback trait for the coordinator to interact with the rest of the DB. Trait exists for test seam; production impl is ConnectorPipelineCallback.