// For the sibling pair (l, i) and (l, i+1), due is (T - last) / 2^l, with T the
// number of messages and last the ID of the last message of the pair. That is
// how long ago the pair ended, measured in its own line size. With a budget of
// For the sibling pair (l, i) and (l, i+1), due is (T - last) / 2^l, with T the
// number of messages and last the ID of the last message of the pair. That is
// how long ago the pair ended, measured in its own line size. With a budget of