[sumul]

This is excellent, thanks for sharing. My solver is designed to find every possible solution so that I can evaluate the ratio of "best" solutions to all solutions. A lot of these optimizations are super interesting, but since I'm intentionally going for comprehensive brute force (rather than finding any winning solution as quickly as possible), they're mostly off the table, at least as long as puzzles are randomly generated and I need to filter them based on solution space characteristics like this.

I did realize while reading this that I could get a little more sophisticated by finding out the number of moves in a best solution using an aggressively optimized fast solver. If that number is within a range that's fun to play, say 8-11 moves, then go ahead and find all the rest of the solutions with the maximum brute force. If not, then just scrub the whole thing since I wouldn't use that puzzle anyway.