After reading, I tried to come up with a better NIP design than yours. I failed.

The best I could think was that communication between agents would be private and not necessary through Nostr events, but could be. And the only public trails would be escrows announcing themselves (should be using a replaceable kind instead), task proposals -- published by whoever is proposing them, and then a summary of what happened, published by the escrow.

Mostly because no one is interested in what happens in between.