[core] Correcting discrepancies between `current_transform()` and `matches`

Jess has been working on a new match display. Thanks to her work, we've discovered a number of bugs in how matches work right now. Due to the way `iterate` works, `matches` is usually one iteration behind `current_transform()` (except right after `begin()`) and thus functions like `calculate_cost()` are technically wrong. I don't know the best way to correct this right now, but it needs to happen.