Ah yeah, I noticed there was no reset after I tried cramming two sheep(?) into a corner :P
But there are probably work-arounds, like, I think there's a hack that can transform/swap tiles. So perhaps that could be used to reset some things. Or just having small one-off puzzles as I think you implied. Or puzzles that can't put you in a lose state.
Hm, though, I guess if it had a reset and undo it would basically be puzzlescript? Gosh, with all these hacks bitsy can be almost ANYTHING! Soon bitsy will consume all games, MWA HA HA HA HA!!! :P