Since the model's mesh went back to the reference mesher (#940), the GPU viewport drew
opaque bodies from their display plans while hover and selection lit faces with the
reference mesh's triangles. Two triangulations of the same face at equal depth fought, so
a hovered face shimmered in wedges instead of lighting whole.
Faces lit over a body drawn from its plan now use the plan's own triangles
(ModelBody::plan_mesh, evaluated once on the CPU), and the highlight pass gets a small
depth bias toward the eye so f32 rounding between the GPU and CPU evaluations of the same
triangles cannot speckle it either.
Test: every face of a box with a pocket and a round boss, hovered and rendered offscreen
through the viewport's real pipelines on the GPU path, lights the same pixels as on the
CPU path (skipped without a GPU adapter).
Co-authored-by: Claude Opus 5.5 <[email protected]>
