Fuses GEMM + bias-add + ReLU into a single cublasLtMatmul kernel via
CUBLASLT_EPILOGUE_RELU_BIAS. Eliminates 7 separate add_bias_relu
kernel launches per forward pass (3 trunk + 4 branch hidden layers).
Creates separate cached descriptors with epilogue enabled at init time.
Falls back to separate kernels if the epilogue heuristic isn't available.
Bias pointer set dynamically per-call via set_matmul_desc_attribute.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>