Verifying the GLBs in three.js (not just Blender) showed four assets reporting
inflated bounds: tramp_01 came back 3.29 x 1.27 m against a true 2.96 x 0.78.
Box3.setFromObject expands each mesh's LOCAL box by the world matrix, so a node
carrying a rotation over-reports — the same trap Blender's obj.bound_box sets,
and what three uses for frustum culling. Joined nodes inherited parts[0]'s
rotation, which for an arc is half a segment step off-axis.
Applying rotation at join time makes every local box axis-aligned, so the
default Box3 path is now correct for consumers and culling is tight. World
geometry is unchanged; the exported dims are identical.
Adds tools/assetcheck/, the three.js harness that caught this. It's the only
check that can: a Blender round-trip exports Z-up->Y-up and imports Y-up->Z-up,
so a broken export_yup flips back and passes green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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