what is the right/best way to have a plugin repo consume itself?

there isn't a great way. IMO the easiest way would be to use a previously published binary. it's possible to create an included build with an overlapping sourceset and apply it, but I'd say that's hacky and potentially fragile

why fragile?

you need to ensure it the included build also builds, but without applying to itself (of course)

I heard you like builds so I included a build in your builds build build