blocks.cu: BlockCurvedBoundary passes the receiver-local core cell and the
block-offset fi to the unchanged apply_bouzidi_link (Uw=Vw=0, obs=nullptr),
so k_s and the q<1/2 donor follow the window image the next pull reads.
BlockStep takes nullable block-cell flags; solid cores store NaN each step.
Adds core/flags.cuh, core/obs.cuh and boundary/curved_boundary.cuh.
block_stepper.py: objects=() accepts stationary passive circles only; host
preparation rejects before CUDA: non-circle/moving/actuated/sensor roles,
overlap, domain-edge contact, and any fluid core (all rows/columns, periodic
neighbors) whose pull from a solid lacks exactly one cut link. Uses
map_cut_links for unique receiver owner/local writer. Order per step:
halo copy -> BFL -> pull/collide, no copy in between. Fluid-only
initialize validation; solids NaN.
Tests: CPU rejections/tables; GPU 32x24, nu .1, 8 steps, circle
(15.5,11.5) R4.3 with halo-write and halo-donor presence asserted,
1x1/2x2/4x2 bit-identical, finite fluid/NaN solid, FP64 BFL+pull/SRT
<= 3e-6 on fluid; drift reported. Body-free gate unchanged.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
