Function frame_combined_sections 

fn frame_combined_sections(
    mesh: &[u8],
    vertex: &[u8],
    index: &[u8],
) -> Result<Bytes, ParquetError>

Assemble the three Parquet buffers directly into the OUTER combined framing the parse endpoints wrap the geometry blob in: [geo_len:u32][geo_bytes][data_model_len=0:u32], where geo_bytes is exactly frame_sections’s [mesh_len][mesh][vertex_len][vertex][index_len][index] layout. Endpoints that don’t attach a data model inline (the streamed cache fill) previously called frame_sections for the inner blob and then copied that whole blob a second time into an outer Vec to add the [geo_len]...[dm_len=0] wrapper. Writing both frames into one pre-sized allocation skips that second copy; the resulting bytes are identical to the old two-copy path.