- GPU test: after hop 2 some INNER_GHOST populations are NaN (pulled from
OUTER poisoned on hop 1; 236 slots in pinned CPUREF); assert ACTIVE
finite and OUTER NaN, keep the full dense-vs-blocked raw value/NaN-mask
comparison.
- A 1x1 non-periodic fine layout has zero halo pairs: skip the halo table
uploads (CUDA rejects mem_alloc(0)); _fine_halo already skips launch.
CPU guard test with driver doubles.
- Drop the class-level fine_layout default; the followup fake backend now
sets fine_layout = None explicitly.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Frank14f