Function lower_reduction_to_cuda 

pub fn lower_reduction_to_cuda(spec: &ReductionSpec, eps: Epsilon) -> String

Lower a recognized reduction (rmsnorm/softmax, from crate::tensor_recognize::recognize_reduction) with the program’s epsilon to a self-contained float CUDA program — the reduction analog of lower_matmul_to_cuda. Deterministic float fill, one thread per element, and a Σ Y checksum printed with fixed precision so it compiles + runs on the GPU.