Pure-function module that derives per-stage StageState (one of
pending / in_progress / done / skipped) from the existing ScanStatus
payload. No new query, no new endpoint — reuses what
createScanStatusQuery already polls.
Truth table covered by tests: scan undefined → skipped; in-flight
with no tallies → all pending; in-flight with library tally only →
library in_progress, rest pending; in-flight with library +
mbid_backfill → library done, mbid in_progress; finished with all
tallies → all done; finished with missing library tally → library
skipped, others done; in-flight with last stage tally → only last
stage in_progress (all earlier done).
bvandeusen
a368c74a9a