Extract the GLB build (prepare + GLTFExporter + WebGPUTextureUtils) out of ExportManager into exportSceneToGlb so it can run outside the editor download flow. Add a BakeExporter R3F component that fires the export once a host viewer signals scene-ready and hands back the ArrayBuffer. Both exported for the headless bake route (baked-glb-export phase 3, headless de-risk). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>