Pier 26.32.2

Terrain packs replace the declarative layers and noise terrains, and the ABI moves
to v2. Nothing in this section had shipped in a tagged release, which is why the
removals below are removals and not deprecations.

Changed

• ABI v2. PIER_ABI_VERSION and PIER_ABI_MIN_SUPPORTED are both 2. The four slots
  retired in 26.20.3, md_add_simple_dimension, md_add_plot_dimension,
  md_set_plot_grid and md_clear_plot_grid, are deleted from PierApi; every slot
  after them moves, so a mod built against v1 is refused at load with the version range
  in the message. tools/abi-v1.slots was re-blessed for v2.
• Three terrain kinds. md_add_dimension serves terrain:{kind:"native"} only, now
  with generator:"flat" and "void" beside the three vanilla worlds and a biome for
  the void. A layers or noise terrain is refused with a pointer to the pack tool;
  pier-pack from-layers converts an old layers spec into a template source.
• Dimension spec. The stored form of a pack terrain is
  terrain:{kind, pack, sha256, params, roles}: the config path, the binary's hash at
  registration, every bound parameter and the role overrides, so the terrain is
  regenerable from the save alone and a changed binary is refused rather than mixed in.

Added

• md_add_dimension_pack(name, config_path, spec_snbt). Registers a dimension from a
  terrain pack: a directory with a config file and a binary. The host reads four keys of
  the config (pier_terrain, type, binary, sha256), compares the spec's terrain
  kind with the config's type and the binary's magic, hashes the binary against the
  config, binds the parameters by kind (free, fixed, choice, derived), checks the pack's
  constraints, and only then stores the spec. Refusals return one of the PIER_PACK_*
  codes, all negative; a dimension id is never negative.

• md_pack_inspect(config_path, ctx, sink). What a pack asks for as one JSON
  document, the same shape pier-pack inspect prints, so a mod builds its form from the
  pack's own parameter list without a parser of the binary.

• Template packs (PIERTPL). A fixed range with parameters and cells whose data is
  the same: zones along each axis with expression lengths, a block stack per combined
  zone, constraints, and 3D structures as a CSG graph (box, cylinder, wedge, translate,
  rotate, mirror, repeat, union, difference, intersect, shell, paint, choose by parameter
  or cell hash, voxel blobs with keep and air cells) picked per cell with weights and
  turns. A CONF section registers the cell grid for the confinement rules from the same
  mount that produced the terrain. The plot world is the acceptance fixture and is
  compared cell by cell with a line-for-line port of the 26.20.2 PlotGenerator.

• Volume packs (PIERVOL). Java's density function graph: 31 operators including
  splines, shifted noise, the caches, interpolation, end islands, the 1.18 blended
  noise and the weird scaled sampler; the multi-noise biome parameter list; and the
  surface rule subset (block, sequence, condition, biome, noise_threshold,
  vertical_gradient, y_above, water, temperature, steep, not, hole,
  above_preliminary_surface, stone_depth). A pack stores noise parameters, never tables:
  the host builds the tables from the world seed with Java's Xoroshiro128++ or legacy
  random source, so one pack serves any seed. pier-pack from-datapack assembles a
  source from a Java datapack directory.

• tools/pier-pack. build, inspect, hash, from-layers, from-datapack, a
  Python reference generator for each pack kind, and tests that compile the engine-free
  pack layer under g++ and compare it with the reference cell by cell.

• Rust SDK. dimensions::add_dimension_pack, dimensions::pack_inspect, PackStatus
  and PackError; GeneratorType::spec_name for the spelling a spec uses. The crate is
  2.0.0, since the four removed functions are a breaking change.

• tools/migrate_dimension_config.py no longer writes a layers terrain. A void or a
  vanilla generator migrates in place as before; a pre-26.20.3 plot entry is left alone and
  the three steps to rebuild it as a template pack are printed, since the terrain of a plot
  world is a binary the host verifies by hash and cannot be written into the config file.

Removed

• spec::Layers, spec::Noise, LayersGenerator and NoiseGenerator, superseded by
  the two pack kinds; the Rust SDK's add_simple, add_plot, set_plot_grid,
  clear_plot_grid and PlotLayout, superseded by add_dimension_pack and
  pack_inspect.

Known limits

• The liquid layer of a voxel blob is decoded but not yet written into the chunk's
  second block layer, so waterlogged blocks in a blob come out dry.
• A volume pack has no aquifers, ore veins or bandlands, and the biome of a column is the
  one at its surface rather than a 3D field; temperature uses the biome's base
  temperature without the vanilla noise term; sea_level of the pack is used for the
  fluid fill but the dimension's own sea level stays at the sky's default.