Function parse_planes 

pub fn parse_planes(
    buf: &[u8],
    count: u32,
) -> Result<Vec<BlobPlane<'_>>, BlobError>

Parse count plane records from a planes region.

buf is exactly the region — blob[regions.planes..regions.end]. count has already been bounded by region_offsets against the bytes present, but every per-record length is re-checked here because those live inside the region rather than in the header.