Standing room for a pool

Keep room for a pool of sandboxes until you cancel it: name the snapshots it forks from and the room is held on the servers holding them, so a sandbox replaced after each use is never refused for room or limits. forKey keeps it for one key's sandboxes, and inUse says how much of it runs now. Room none of them uses costs a quarter of the memory rate, $0.001875 per GiB-hour. See standing room.