Donald has already taken care of creating a card that can gloriously counter handsize reduction attacks, and that is no other than Horse Traders, one of the best cards in Dominion (in my opinion).
Horse Traders has a lot of uses. It's good for Engines, Slogs, counters handsize-reducers and top-deck junkers, and even if the attack played is not countered by Horse Traders, the +1 Card bonus is always nice.