fine_block=(by, bx) partitions the ENTIRE fine_shape (incl. the four-cell
patch ghost band) with a non-periodic one-cell-halo BlockLayout2D; body-
free only (fine_objects rejected in blocked mode; dense fine-body and
actuation path unchanged). Per coarse step on the same stream:
BlockExplode into ghost owner cores -> gather -> BlockStep(kind) ->
gather -> BlockStep(kind) -> unchanged PatchCoarseStep reading remapped
owner-core child slots in the original row/child order. Public arrays
keep the dense fine shape; only the private allocation is blocked.
blocks.cu: explicit BlockExplode; BlockStep gains nullable kind
(OUTER skip pull + NaN, INNER pull only, ACTIVE pull + SRT).
PeriodicBlockStepper passes an explicit null kind (raw launch ABI).
refinement.cu/refinement.py and coarse numerics unchanged.
Tests: CPU rejections and table remap (dense (q,cell) and child order
preserved, owner cores, kinds); GPU gate: periodic and slot_reservoir,
8 coarse steps, dense vs 1x1/2x2/4x2 fine blocks bit-identical in
masked downloads and raw coarse/unpacked fine incl. ghost NaN masks.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
