The A2A protocol sort of does all that (agent interop, agent identity, auth, etc.). Plus it's a ground-up design for agent comms. There's no native payment but there are payment rails, and you could just pop in a cashu string into a relevant json request (there are suitable custom fields) and that's payment sorted one way. Nostr I dunno, you trade a lot for some redundancy, but AI agents aren't dissidents.

IMO Nostr is good for a lot of workplace stuff, but not agent comms.