Function decide 

pub fn decide(
    proposal: &SplitProposal,
    check: &SplitCheck,
    cap: usize,
) -> Decision

Rule on a proposal, given the check and the cap.

Every path out of disagreement is “do not split”. The proposing agent declining, the checking agent rejecting, and the checking agent striking enough parts that one is left all mean the same thing here, because a split into one part is not a split.