The Neutral Matching Unit in QDL Closure Grammar: A Uniqueness Theorem for 1/18 from Binary–Ternary Sector Coupling, Z 6 Operator Grading, and Electroweak Residual Preservation

The Quantized Dimensional Ledger (QDL) closure sequence identified a compact recurring grammar across several sectors of known physics, including the objects 1/8, 1, 1/4, 1/18, 49/72, 53/18, 9 + 1/27, and rho_QDL. Among these, the unit 1/18 is the most important unresolved residue because it appears in the scalar residual coefficient, the weak-angle residual coefficient, electromagnetic residual structure, and the cosmological horizon-screening ansatz. This paper formulates a neutral matching uniqueness theorem. Under declared QDL admissibility conditions — binary weak-residual closure, ternary sector exposure, source-target neutral interface matching, minimal positive inverse exposure, Z6-compatible sector grading, and simultaneous recovery of the scalar and weak residual coefficients — the unique neutral matching unit is derived as epsilon_N = 1/(2*3^2) = 1/18. Once this unit is admitted, the scalar residual coefficient and weak-angle residual coefficient are no longer independent: C_lambda = 1 - 1/4 - 1/8 + 1/18 = 49/72, and C_W = 3 - 1/18 = 53/18. The electromagnetic threshold ledger is identified as T_alpha = 3^2 + 3^-3 = 9 + 1/27, while the electroweak-flavor leakage parameter is rho_QDL = alpha / sin^2(theta_W). The paper includes no-go lemmas for alternative residues, a residual-coefficient inversion check, a “Why This Is Not Numerology” section, links to EFT/RG/SMEFT reasoning, audit-level predictions, falsification tests, and executable Python workbooks for exact rational verification.