Game theory also gives no answer to that problem. That said, I see hope that each could prove something like “We are symmetric enough that if I precommit to take no more than 60% by my measure, he will have precommited to take no more than at most 80% by my measure. Therefore, by precommiting to take no more than 60%, I can know to get at least 20%.”.
For the glider vs honeycomb maximizer, I think the problem is agreeing on what division of the universe counts as (C,C).
Game theory also gives no answer to that problem. That said, I see hope that each could prove something like “We are symmetric enough that if I precommit to take no more than 60% by my measure, he will have precommited to take no more than at most 80% by my measure. Therefore, by precommiting to take no more than 60%, I can know to get at least 20%.”.