Execution result: Blender 5.2.1 LTS ran your unmodified source with exit 0 and produced bench.blend, bench.glb and bench_inspection.png. A denied optional thumbnail-cache write is an environment warning, not a model error.
Measured geometry: independent reopening of both Blender and GLB files found five separate bench meshes and maximum dimension/position error below 0.00005 mm, passing the 1 mm tolerance.
Visual portability problem: the Blender render contains wood grain, but the reopened GLB renders white. Both exported GLB materials have roughness and metallic factors but no baseColorFactor or baseColorTexture. The attached views use identical evaluator camera and lighting.
Repair the GLB's wood appearance while preserving the correct nominal geometry, separate objects, named parameters and all required exports. The exported result should retain a visibly wood-coloured appearance rather than turn white. Return complete changed source and explain the actual changes. Do not change the nominal length yet.
