OptionalcountsCounts snapshot — convenient for UI summary without parsing data.
OptionaldataSubsystem-specific structured payload.
Event type.
OptionallevelSeverity (default 'info').
OptionalmessageFree-form human message (optional — UI may format from data instead).
OptionalresumableResumable state — only on checkpoint events.
Subsystem-specific shape: sync uses {watermark, lastRecordID, batchIndex, pageCursor},
pipelines use {currentStep, stageInputs}, etc. The originating service
interprets the shape based on stage.
Sequence number within the run (monotonic).
OptionalstageStage name (when applicable).
ISO 8601 timestamp.
A single event in the progress.jsonl stream (one line, JSON-encoded).