The world now survives restarts: chunks load from disk (read-through
cache) and player edits persist via async autosave + a final SaveAll on
shutdown. RegionIO finally does region I/O.
- world/regionfile.go: Anvil .mca container — 8192-byte header
(offset + timestamp tables), 4096-byte sectors, zlib chunk records.
- world/compress.go: zlib deflate/inflate for chunk payloads.
- world/store.go: chunk <-> Level-nested NBT (per-section
block_states/biomes palettes, WORLD_SURFACE heightmap, DataVersion
4790, yPos -4) via the existing nbt package; Store opens one
RegionFile per region with proper floor-division coords.
- world/state_names.go: id->name bridge from the embedded blocks.json
report so network int-IDs round-trip through the disk named palette.
- world/encode.go: GetBiome read accessor for serialization.
- world/cache.go: read-through (disk then generation), dirty tracking,
StartAutosave (returns a done channel so the saver exits before
Close), SaveAll, NewCacheWithStore.
- server.go + main.go: Config.WorldDir (default "world"), -world flag,
autosave loop every 30s, SaveAll + store Close on signal.
- Tests: region round-trip/absent/overwrite, chunk NBT round-trip,
end-to-end save-reload, negative chunk coords, autosave persistence.
