At the start of the game, qRook - king - kRook all store the location e1. If the king moves (say we're playing the Bongcloud), qR and kR get set back to their

At the start of the game, qRook - king - kRook all store the location e1. If the king moves (say we're playing the Bongcloud), qR and kR get set back to their original squares, a1 and h1. Now if the King slides back, castling is off the board.