- Fix LSE output: all 128 rows now write (mLSE[sfw_idx, 0, 0]) instead of only row 0 (mLSE[0]) - Each softmax thread (sfw_idx 0..127) independently writes its LSE - This enables accurate Python-side KV merge for multi-KV-tile - New test: test_d5b_perrow_lse.py with LSE verification + KV merge