Note that the implementation described above uses the Arc Consistency 3 algorithm for the propagate step. It's often an order of magnitude faster to use AC4, as is done in the original WFC repo and in my implementation (https://github.com/BorisTheBrave/DeBroglie).
I broke it. (In a good way) I managed to embed a pattern in the feed that is not repeated in the output. Well, at least some of the time is not repeated-haven’t done very many iterations.
That might be due to the blue rect and the green rect must be separated with a straight line, and straight lines are hard to come by: https://imgur.com/85W15eI