Thanks! "Solvability" check is indeed missing from the game. To avoid having to implement it here (perhaps next year if that game uses keys!), my strategy to counter it was to be quite liberal with giving keys and hope players will learn to save them when they are low. There is also two entrances to the enemy ship which sometimes gives new paths. I was kinda thinking of adding a "restart level" option to the ship computer to allow players to get out of the soft lock without fully restarting the game, but it's not that fun or discoverable option (and I ran out of time anyway).