Function export_gltf_streaming_with_index 

pub fn export_gltf_streaming_with_index(
    content: &[u8],
    opts: &GltfOptions,
    index: Arc<EntityIndex>,
    chunk_cap: usize,
    sink: impl FnMut(GltfBuffer),
) -> Vec<u8> 

Like export_gltf_streaming but reuses a pre-built entity index instead of scanning content again on EACH of its two passes. A caller that already built the index — e.g. to share with the attribute pass (crate::stream_export_model_with_index) — passes it here to remove the redundant SIMD scans on the large models this path targets (#1516). index MUST come from build_entity_index over the same content; output is byte-identical to export_gltf_streaming.