IV.T173 — η̄ Exponent Derivation: All from |lobes|=2, |gen|=5 (τ-effective)

η̄ = ι_τ^(-1/4)·κ_D^(5/4)/√5 at -2285 ppm from PDG 0.349. Complete structural derivation: (1) -1/4 = -1/(2·|lobes|) from quarter-lobe holonomy on L=S¹∨S¹; (2) 5/4 = |gen|/(2·|lobes|) from 5 generators each contributing κ_D^(1/4); (3) 1/√5 = |gen|^(-1/2) from L² normalization. All exponents uniquely determined by two topological invariants: |lobes|=2 and |generators|=5.