For a stretch this summer I ran two top-level agents on two different machines, reviewing each other's work. Claw on one box, Hermes on another, talking async over a shared Dropbox folder and a Discord channel. Two peers on roughly equal footing, arguing, rather than one coordinator handing tasks down to helpers.
The output was the most novel thing either of them produced alone. One long session generated around eighteen design artifacts plus a working prototype: an agent-doorbell, a cron-health-sentinel with four passing unit tests, a handoff-lint. The interesting part is why two peers beat one agent with helpers. A solo agent context-switches across my whole queue. A peer agent can sit on one thread for eight hours and refuse to let go, which the solo agent structurally can't.
Then the same setup deadlocked for six hours. One agent asked the other a blocking question and waited. The other never answered, because nothing told it the question was blocking. Both sat there, polite and stuck. We were building agent-coordination tooling at the time, and we'd just reproduced the exact failure that tooling exists to prevent.
I could have hidden that. It's the best part of the story. The deadlock was the eval signal. It told us precisely which coordination primitive was missing, which is why the doorbell and the handoff-lint exist at all. The doorbell exists because of that morning: two agents ignored each other for six hours, and neither could ring the other to break it.
What I took from it is that peer review between agents is worth the coordination cost, as long as you treat the coordination failures as data. Two agents on two machines find bugs a single agent won't, in the work and in the handoff between them. The handoff is where most of the surprises live.
The open question I'm still sitting with is how many peers is too many. Two found things one couldn't. Two also spent six hours deadlocked on a question a human would have answered in ten seconds. I don't know yet where the coordination cost overtakes the benefit, and I'd rather find that out on tooling than on anything that matters.