Every FixedPatchStepper in test_refinement_followup passes explicit tiles
(whole-level tiles on the GPU cases, (1, 1) in the pre-CUDA margin
contract). Assertions kept; dense-specific probes rewritten:
- fault fakes use a blocked BlockLayout2D instead of _layouts [None, None];
- slot/reservoir: the fine module sees its tile window incl. halo
(fx+2, fy+2) with slot fields zeroed; the root's walls are
block_root_bc 1 (fine 0) instead of dense Y_WALL_BC/TOP_WALL_BC macros;
- raw owner storage is read through each level's layout (to_dense);
- the off-centre allocation bound counts blocked buffers.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
