Pass 2 magnifies the object sheet where the surface steepens at the cracks,
so a one-pixel silhouette showed up as hard blocks. Nine jittered rays per
pixel give the edge a soft ramp instead.
Pass 1 draws one raymarched gem on sheet 1 instead of plasma; its alpha
carries coverage rather than depth, so pass 2 can light it as a solid
while every other sheet still absorbs by path length.
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