This was fun, very polished and satisfying. Seconded wanting an undo button, and I wish some of the levels got harder by requiring more thinking instead of just needing lots of lasers to be placed. For me in puzzle games I think about the delay between knowing how to solve something and actually being able to do it, and when that delay is long (like having to move 12 mirrors around even though you know where they should go), I feel less engaged. Nice work!