Function assemble_optimized_output 

fn assemble_optimized_output(
    version: u8,
    include_normals: bool,
    instance_parquet: &[u8],
    mesh_parquet: &[u8],
    material_parquet: &[u8],
    vertex_parquet: &[u8],
    index_parquet: &[u8],
) -> Result<Bytes, ParquetError>

Header: [version:u8][flags:u8][instance_len:u32][mesh_len:u32][material_len:u32][vertex_len:u32][index_len:u32] Then: [instance_parquet][mesh_parquet][material_parquet][vertex_parquet][index_parquet]

Each section length is a wire-format u32: fail loud via check_optimized_section_lengths instead of silently truncating a >4 GiB section into a corrupt length prefix that disagrees with the bytes appended below. Mirrors the guard parquet::frame_sections/ frame_combined_sections apply to the non-optimized writer’s sections.