Function cycle4_kernel_output_cols 

pub fn cycle4_kernel_output_cols(leader_idx: u8) -> Vec<ProjectExpr>

Promoter helper: 4-cycle canonical head-projection table.

Maps the kernel-direct output (in leader’s rotated cycle order) back to the canonical head order (W, X, Y, Z). All 4 entries are pure permutations; no col-swap is involved.