param_sizes[12] grows by 3*adv_h for direction conditioning.
mag_concat_buf [B, SH2+3] and d_mag_concat_buf allocated.
mag_concat_qdir and strided_accumulate kernels loaded.
launch_mag_concat and accumulate_d_h_s2_from_concat methods added.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>