The db.destroy callback receives two arguments, body and headers; body looks like this:

{ ok: true,
  id: '123',
  rev: '6-df512f26f0e5342855867591c2770ed5' }

...which propagates through ImageRecord.delete to purge.

So, to echo the id / revision of records as they are deleted, we need only remove the _. Sheesh.

(Mildly annoying that CouchDB expects id / rev to have an underscore in some places, but not in others.)