Magic Sheet undo

Please add "undo" to the magic sheet. 

At least esc key should disconnect any movement I have begun.  If I start to drag something and realize I don't want to, currently I'm stuck with what I started and have to undo it by hand, sometimes by recreating a lot of work that accidentally got messed up. 

If that's too hard, how about saving state every time I pause inputting for more than a few seconds instead of having to remember to do it by hand.