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Clean-room (spec-yungsapi.md §2, §3, §5; no mod source read; the legacy files were deleted unread). horizon-port-pack's new `yung` module carries `yungsapi:yung_jigsaw` structures and `yungsapi:yung_single_element` pool elements as the mods write them, so players' packs reach the YUNG draws of the jigsaw assembler. Fields whose behaviour the specification leaves open (adapt_noise, max_y/min_y, enhanced terrain, element conditions, modifiers, priorities, depths, ignore_bounds) are counted as lost by name. YUNG's other structure, placement and processor types go to the general code (unsupported or dropped) until the specification covers them. Deleted: legacy_structure_mods/yung.rs, horizon-world's structure/yung.rs, the `horizon:yungsapi` keys and `horizon:disables`, which nothing writes now. Two test initializers of the removed field (enhanced_terrain.rs, piece_limited.rs) were removed by line from the compiler's error positions. The layout harness now carries the mods through `horizon-port-pack carry`: 82 of 84 Better Dungeons starts match the oracle piece for piece, as before. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>