baracuda-optim

Optimizer kernels (Adam / LAMB / SGD) for the baracuda CUDA stack, built on the multi_tensor_apply idiom vendored from NVIDIA Apex (BSD-3-Clause). One launch over thousands of parameter tensors — critical for the optimizer step on large-model training stacks. NEW in Phase 49; deliberate scope expansion (training-framework-adjacent). Off-by-default in baracuda-kernels via the `optim` cargo feature so inference-only consumers don't pay the FFI surface cost.