I'm not totally happy with this tho, and to me the general problem of "negotiation in situations with no focal points" has no satisfying solution beyond racing to who precommits first.

That trick works against CDT agents, anyway. Against agents that implement a modern decision theory it leaves the negotiation problem approximately where it started. (This means that if you put ideal CDT agents and ideal TDT agents in a room with devices that offer similarly ideal pre-commitments and give them exchanges to make the CDT ends up accepting the worst possible positive trade.)