Route with σ(W_r x), Top-k(s+b), then L1-normalize over the selected set. Add Switch/GShard aux and router z-loss into train_k3 and train_sft. Wiki parquet URLs honor HF_ENDPOINT for mirrored downloads.
Standalone tree split from LLMRL/projects/kda. Includes Triton dt_bias backward fix, train_k3 --preset 0.5b, SFT, Docker runtime, and tests.