Function lower_matmul_to_cuda_with 

pub fn lower_matmul_to_cuda_with(spec: &MatmulSpec, knobs: &CudaKnobs) -> String

Lower a recognized matmul under an explicit CudaKnobs point. The precision knob selects the kernel: ResolvedPrecision::Int64 (always-correct i64 accumulation, the general default) or ResolvedPrecision::Int8Dp4a (__dp4a int8 fast path — valid only when operands fit int8, which is why it is opt-in). Both reproduce the LOGOS program’s fill + checksum, so both equal the VM byte-for-byte on any int8-safe program; they differ only in how the contraction is computed on the GPU.