LegendQuest: CrawlSpace

For Forge 1.20.1 and NeoForge 1.21.11, 26.1.2, 26.2 and 26.3. Dungeons already in your world keep their layout.

Dungeon types, and themes of your own, from datapacks. Asked for by Sable for a zombie-apocalypse world: research bases, old mansions and bunkers instead of crypts. Dungeons with no pack installed are as before, apart from the stair-well railing fix below.

• Dungeon types. A datapack can add kinds of dungeon (crawlspace/dungeon/<id>.json), each with its themes by depth, a weight, the biomes it is found in (optionally the only kind found there), its entrance style and its depth. Each dungeon picks its type from its own seed. The fantasy dungeons are the classic type, and a pack can switch them off.
• New themes. A theme file with a new name makes a new theme, starting from a base (any other theme). Besides its blocks, monsters and boss, a theme now sets its layout (room shapes, corridor styles, narrow corridors, floor heights, pools, room size), its furnishing (what fills a room, clutter, cobwebs, bookshelves, overgrowth, columns, beams, panelling, statues), several bosses with every stat (health, damage, speed, size, powers, minions, followers), and its loot tables.
• A dungeon keeps the layout it was born with. It saves a copy of its themes' layout and furnishing, so editing or removing a pack later changes its blocks, monsters and loot, never its walls.
• /crawlspace types lists the types in force, /crawlspace build and showcase take a type, /crawlspace here tells you which dungeon you are standing in, and /crawlspace export now writes types, layouts, furnishing, bosses and loot too.
• docs/DATAPACKS.md is the full reference, and examples/apocalypse is a worked pack: Research Base, Old Mansion and Fallout Bunker, eight themes, with the classic dungeons off.
• A datapack theme that no level can be planned with now leaves no dungeon there, rather than failing the chunk.
• A stair well's railing no longer cuts off a doorway. The railing round a hole down to the next level could rail off a door on the room side when the corridor beyond happened to lead round to it.
• A second world in the same game starts clean. In single player, quitting to the title and opening another world kept a little of the first: level titles already seen, a trap noticed, the safe spot a fall puts you back to, dig protection and mimic warnings. They are now forgotten when a world closes.