Leading-Order Bessel Reduction and the Asymptotic Transport Ratio for the Open Chiral SCT Connection Matrix

Paper 43 in the "Geometry of the Critical Line" programme. Paper 42 established the numerical asymptotic law R(λ,m) = M₂₁/M₁₁ → ρ(m) for the SCT connection matrix as λ → +∞. This paper explains the mechanism behind that stabilisation. The leading endpoint rescaling ε = x/√λ reduces the singular transport problem to a complex-order Bessel equation of order ν(m). In that leading model, the normalised transport ratio is asymptotically independent of the interior oscillatory phase, with exponentially small phase dependence, explaining the observed high-energy stabilisation. The model does not recover the numerically observed value of ρ(m), indicating that subleading endpoint terms remain essential for the full matching problem. No arithmetic interpretation is claimed. Part of a 46-paper open-access programme. The programme does not claim to prove the Riemann Hypothesis.