Two changes that work together:
1. terrain_mesh.cpp: bump texture-coord scale from 1× to 4× per
chunk so the texture's own pattern repeats every ~8 yards
instead of every ~33 yards. At 1×, the texture's repeat
frequency syncs with the chunk grid and any per-chunk alpha
difference reads as a hard 33-yard square. At 4× the pattern
noise breaks up the boundary line and the eye stops locking
onto the grid.
2. terrain.frag.glsl: widen the alpha-edge feather from 3 to 8
texels and use 9 taps instead of 5 so per-chunk alpha values
bleed across the chunk boundary instead of stepping. Hard
alpha steps were the second contributor to visible chunk
tiles in painted regions.
Reported by user via screenshot showing obvious chunk-grid
artifacts in painted areas of the texture-paint editor.
WHM load already scrubs, but mid-edit terrain can briefly carry
NaN before stitchEdges runs. A single NaN vertex propagates into
normal computations and the chunk's frustum cull, crashing both.
