Function fpfh_descriptors_gpu 

pub fn fpfh_descriptors_gpu(
    runtime: &WgpuRuntime,
    cloud: &PointCloud,
    feature_radius: f32,
    neighbor_capacity: u32,
) -> SpatialResult<GpuFpfhResult>

Explicitly uploads a cloud, runs GPU radius search, SPFH and weighted FPFH, then downloads descriptors/status. No automatic CPU fallback occurs. neighbor_capacity includes self and must fit ALL radius matches; overflow returns an error rather than descriptors computed from truncated rows. Input validation matches CPU FPFH; GPU angular/bin rounding may differ near boundaries. Descriptor matching and RANSAC registration remain CPU.