$ρ_k(S∘T) ≤ ‖S‖ ρ_k(T)$, the companion of $bernsteinNumber_comp_le_mul_norm$ with the norm on the outer factor. This is the direction that propagates degeneracy forwards: once $ρ_k(𝓛^{(n₀)}_ω) = 0$, every later iterate has $ρ_k = 0$ as well.