qwertyuiopasdfghjkl;'zxcvbnm,. large/high
I'm almost certain this one is impossible - you can't pick up any gems fast enough to wall up the middle, and there's nowhere to build up enough reactors to really get anywhere - you might be able to set up a wall of repulsors in time, but I can't see how you could advance afterwards so it wouldn't really matter. Experimental map with a 303M (!) intensity surface emitter, and drones, and even more drones + phantoms past decaying terrain just for the fun of it. Probably impossible on small and medium size too.