I haven't solved it, but from what I've read, puzzle 12 requires a master builder. Now I had some, of course, but having completed my tech, built everything, and waited several generations for the gc to appear, they've all long since died off. And I don't see any way to train up any new ones. Even the debris event doesn't provide enough experience to create a master, supposing I had enough food to keep everyone feed for a single person to clear it.

So how does one solve puzzle 12?