3 × N board · drag with the mouse to swap · each drag = 1 move
idle
How to move: press the mouse on a cell, drag across cells that share a
corner (8 directions) and release. Every cell you cross is one swap.
The whole drag counts as a single move.
Goal: every column must contain three identical gems.
Ctrl+Z undo · Esc cancel current drag.
Edge‑safe drag keeps you from accidentally clipping a side cell while
flicking diagonally — you must push a little past the edge before the swap
commits. Tune the margin slider to taste.