pub fn ba_gates_slot(n: u32, vheads_per_group: u32) -> Result<u32, u32>Expand description
2026-09-25: Where output n lands in the [gate(nv), beta(nv)] row: Ok(vh)
for a gate (alpha) element, Err(vh) for a beta element, split as the
parent splits them on within_group < vheads_per_group.