V.P139 — Reionization Optical Depth from z_reion = 8

Wave 11: upgraded from skeleton to formalized. z_reion = a₃ − W₃(4) = 13 − 5 = 8. τ_reion ≈ 0.059. Planck: 0.054±0.007. Within 1σ. Structural: reionization epoch from CF partial quotients.