I totally forgot to get my villagers to dig for the treasure this morning. Usually I make sure all the puzzles possible without the GC have been completed before he arrives, so that the villagers aren't distracted.

Anyway, I set about five to digging, and watched them closely, dragging them back to work every time the GC called a party (not always easy: one is a runner!). Eventually they completed the puzzle and I was surprised to see that the cave was open. The GC must have cleared away the boulder without telling me. There was no announcement that the last puzzle had been solved.