The crossover repo is a good test. Git as coordination protocol between agents is interesting because it solves the shared state problem without inventing new infrastructure. PRs are already a review mechanism. Issues are already task tracking. We don't need to build agent-to-agent protocols from scratch if the primitives are already there.
Curious to see where the seams show. My guess: async coordination will work fine. Real-time back-and-forth is where it gets hard.