== BEFORE (phase-08 CSS) ==
FULL   before, 5s apart: 1.436% px>12, mean|d|=1.9793, max=54
   top-left: mean|d|=3.0659
   top-right: mean|d|=1.2274
   bottom-left: mean|d|=0.7014
   bottom-right: mean|d|=2.9225
GRIDONLY before, 5s apart (glow hidden): 1.526% px>12, mean|d|=0.4778, max=60
   top-left: mean|d|=0.8985
   top-right: mean|d|=0.8776
   bottom-left: mean|d|=0.0681
   bottom-right: mean|d|=0.0671
OCCLUSION PROBE: 3127 red-line px (x 132..1276, y 64..254) -> grid layer IS painted (no occlusion); earlier 0-pixel reading was a too-strict absolute-threshold detector (blended red ≈ rgb(78,27,35))

== AFTER (phase-22 CSS: grid lines 0.6 alpha, mask 140% 110% / 40% / 90%, glow 0.85..1) ==
FULL   after, 5s apart: 4.159% px>12, mean|d|=2.3007, max=87
   top-left: mean|d|=2.9225
   top-right: mean|d|=2.1081
   bottom-left: mean|d|=1.6897
   bottom-right: mean|d|=2.4826
GRIDONLY after, 5s apart (glow hidden): 6.094% px>12, mean|d|=1.8162, max=74
   top-left: mean|d|=2.2062
   top-right: mean|d|=2.1563
   bottom-left: mean|d|=1.4749
   bottom-right: mean|d|=1.4275