Replaces the single-DistrictProfile walking-skeleton restriction so
continuous terrain parameters no longer step at the 2 km district pitch
(D-239 §4/§7/§8). ChunkContext gains secondary: Option<DistrictProfile> +
blend_weight: u8; derive_chunk_context detects a chunk within one chunk of
a district border, looks up the adjacent profile, and integer-blends
meander/channel params on the context. derive_voxel_column integer-blends
elev_q/moisture_q before material selection, reusing the same warp offset so
the seam cannot align with the chunk edge (Cow fast-path keeps interior
chunks bit-identical — golden seed unchanged).
Morphology FAMILY selection is never blended — stays sharp per D-239 §7
(family dispatch reads the primary district only). Climate feathering is the
separate T-1078 path. Adds cross_district_elevation_blend_reduces_seam_step
and cross_district_morphology_family_seams_stay_sharp to the derivation
harness.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
jpmschweitzerandClaude Opus 4.8
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