IV.D360 — m_μ/m_e NNLO k=23/3: W₃(4)+W₃(3)+1 Window-Algebra Exponent

m_μ/m_e NNLO correction: ×(1-ι_τ^k) with k=23/3. Structural ID: 23=W₃(4)+W₃(3)+1=5+17+1 (first Window-algebra derivation of NNLO exponent). Also: k=23/3=7+2/3, factor 2/3=2/|sectors|. Best rational: k=45/6=7.5=(3×W₃(4))/2 at -8.2 ppm.