+
+ Note: The sort_key is a modified version of the puzzle_id, (used
+ to make metapuzzles appear in the ordering before non-metapuzzles).
+ If you've been handed a sort_key, then looking up a puzzle by
+ sort_key is the right thing to do. But if you instead have just
+ a puzzle_id, see find_puzzle_for_puzzle_id rather than trying
+ to convert the puzzle_id into a sort_key to use this function.