Extremely valid feedback! The reason the undo is so limited is because I wanted to avoid having to keep track object existence - if you intentionally walked a mech into a pool of water, the game would need to be able to recreate the mech object on undo, and while not very difficult to implement, I was in a bit of a hurry at the time and thus opted for a simpler-but-less-useful undo. Apologies about that.
I guess I could implement the suggested feature for the extra turns in a future update. Thanks for the suggestion!