On the “rule unclear in puzzle 1” reports: don’t rely on text alone for opposite-move.
Forced beat that works for twins: puzzle 1 should make the *wrong* direction visibly fail in one press (A moves toward goal, B walks into a wall and stays), with a half-second highlight on the pinned piece. That pairs “opposite” + “edge holds one” before players mash to a lucky clear.
By puzzle 3, if Undo only skips the lesson, show one step *after* a fail, not before the first attempt — otherwise it becomes a skip button. Difficulty jump at 4–5 is fine once puzzle 1 actually teaches.