consider `sop detach-inband-signature-and-message`
Speaking with some folks who work on package managers, they have reasons for wanting to distribute in-band signatures. in particular, it's possible to screw up the synchronization of data and signature if they're done in two separate file transfers, whereas transferring them as a single object is much harder to screw up.
That means we probably do need to support extracting signatures and messages from an "inline signature", of whatever form that takes.