`ProtoChunk::new` took its height from the noise settings while
`Chunk::build_level_sections` builds and reads back `dimension.height / 16`
sections. The End and the Nether are the two dimensions taller than their noise
settings (256 vs 128), so their proto chunks held 8 sections for the 16 the
level chunk asks for and `get_block_state_raw` indexed past the end of
`flat_block_map`, panicking on every generation thread. The same mismatch left
light data covering half the column and dropped features placed above y = 128.
A chunk spans its dimension, as in vanilla's `LevelHeightAccessor`; the noise
settings only bound the vertical window the generator writes into. `ProtoChunk`
now carries both, storage sized by the dimension plus a generation window built
with `GenerationShapeConfig::trim_height`, so surface rules, carver height
providers and feature placement keep resolving against y < 128 there.
The panic quoted in the issue (`chunk_density_function.rs`, len 99 index 129)
was the same conflation in `populate_noise` and is already fixed by 3c43f971.
`AnvilLevelInfo::read_world_info` validated the version tags and then returned
`LevelData::default(Seed(0))`, so level name, difficulty, spawn, world border
and data packs were discarded on every start, and the writer emitted only
`DataVersion`, `version` and `LastPlayed`, truncating the rest on save. A world
whose seed lives in level.dat's legacy `Data.WorldGenSettings` compound, as
converters such as Chunker emit, therefore loaded with seed 0 and generated
foreign terrain into its existing region files.
level.dat is now read and written tag by tag through pumpkin-nbt, every field
falling back to its vanilla default, so a missing optional tag such as
`Version.Series` no longer costs the whole file. Saving merges into the existing
`Data` compound, so tags Pumpkin does not model survive. A world with no seed
in either file aborts startup instead of silently regenerating, and the seed is
mirrored into level.dat, the only world file that is backed up. Version tags are
re-stamped with the current constants on save so level.dat stays consistent with
the chunks Pumpkin writes.
