GW231123, the most massive binary black hole merger observed by LIGO- Virgo-KAGRA, has component masses M1 = 137 M⊙and M2 = 103 M⊙—both inside the pair-instability mass gap—and near-extremal spins χ1 ≃0.9, χ2 ≃0.8. We interpret this event within the One-Octonion Brane-Bulk Framework as the merger of two coupled sump infundibula: focal-deceleration standing waves whose coherence radii rT ∗ 2 (M) = p GM/a0 overlap throughout the binary inspiral. For each BH, rT ∗ 2 (M1) = 1.32 × 1016 m = 0.43 pc and rT ∗ 2 (M2) = 1.15 × 1016 m = 0.37 pc, while the binary separation at chemically homogeneous evolution (CHE) orbital periods (Porb ∼2 d) is rbin ≃0.19 AU, giving rbin/rT ∗ 2 (M1) ≃2×10−6— a strongly coupled regime. The Klein ladder of the G2 automorphism group predicts a mass ratio q = λ4/λ6 = 3/4 = 0.7500, matching the observed q = 103/137 = 0.7518 at the 0.24% level. Within the coupled infundibulum, the pair-instability gap mass range (Mlow, Mup) ≃(69, 139) M⊙corresponds to rT ∗ 2 () ∈(0.30, 0.43) pc: masses where a single isolated focal zone is resonantly unstable but a coupled binary is stabilised by the brane current exchange between the two focal zones. High spins χ ≲1 arise naturally because each BH draws angular momentum from the combined coherence volume of both infundibula. Three testable predictions follow.Part of the One-Octonion Brane-Bulk Framework series. Anchor DOI: 10.5281/zenodo.19120873. Community: one-octonion-brane-bulk. Author: Bharathi Dasan Jagadeesan, M.D., University of Minnesota. ORCID: 0000-0002-1143-941X.