Preserve bounded validation evidence and historical failures

research/fine_surface_joint_20261014/incremental.diff

@@ -0,0 +1,10 @@
+--- a/src/CelerisLab/lbm/refinement_stepper.py
++++ b/src/CelerisLab/lbm/refinement_stepper.py
+@@ -39,6 +39,7 @@
+     velocities are in coarse lattice units (dx=dt=1). Independent local copies
+     are projected at fine cell centers. Their complete stencil must be active
+     and disjoint from the actual two-hop transfer footprint.
++    These use the edge/cell-center frame (coarse centers I+.5), whereas ordinary Simulation objects use the integer-node frame.
+ 
+     ``initialize(coarse_g, fine_g)`` accepts physical Q-major (9,ny,nx) arrays
+     already in postcollision phase. It does not collide or build channel flags.