Yeah, I wasn't sure if just the first level with a stone and the border would be enough, or if I should have forced it to move on the earlier level with the first stones. I figured it was probably better to not introduce two ideas at once.
I'm slowly working on my own basic C engine for another game, but like 80% of the annoying parts that both would need to do are shared, so I'll probably wind up just incidentally making this a real game on my path to something more ambitious!