A DICOM file's tags, or null when it is not one.
A folder's first entries; null when it is not there,
refused when the store will not show it to this identity (a shared
feed's data in someone else's uploads).
A job's output folder, or null when it has none.
OptionalseriesWhat CUBE's own series record says of a series in its PACS store (modality, description), or null: asked before a header is read, since a record costs no file.
How the sweep reads: injected, so it is testable without a daemon, and so the provider that owns output paths can hand its reader in.