Find all in-flight (non-terminated) runs — for restart-resumption discovery.
Read snapshot of a single run. Returns undefined if runID not found.
Find the latest checkpoint for a run (for resumption).
List runs, newest-first by mtime.
Tail events since a given sequence.
Read API for the progress artifacts. Frontend / health-check / resumption code uses this to inspect ongoing or completed runs without touching the emitter.
Implementation is purely file-system reads; no shared state with the emitter (an emitter in another process can write while this reader tails).