Pointmap: drop PBR material + doubleSided hack + process=True; just plain vertex colors

app.py

@@ -321,15 +321,13 @@ def _make_glb(image_pil_texture: Image.Image, pointmap_hwc: np.ndarray,
     vc[..., 3] = 255
     vertex_colors = vc.reshape(-1, 4)
 
+    # Plain vertex colors only — no PBR material customization, no normals,
+    # nothing that would inject lighting variation between surfels.
     mesh = trimesh.Trimesh(
         vertices=verts, faces=faces,
         vertex_colors=vertex_colors,
-        process=True,
+        process=False,
     )
-    # Force double-sided so surfels are visible regardless of normal flip after the Y-flip.
-    if hasattr(mesh.visual, "material") and hasattr(mesh.visual.material, "doubleSided"):
-        mesh.visual.material.doubleSided = True
-
     out_path = tempfile.NamedTemporaryFile(delete=False, suffix=".glb").name
     mesh.export(out_path)
     return out_path