The Constant D as a Natural Stability Threshold for Friedmann Spacetimes

We conjecture that the mathematical constant D = Sum 1/(2*n!+1) approximately 0.96895 (OEIS A396384) may serve as a natural stability threshold for Friedmann spacetimes in the context of Temple et al. (2026). We establish the complete chain QFT→D→STV→observables: the QFT mechanism at w=1/3 gives g(n)=2n!+1 and D as total vacuum amplitude; numerical STV integration through the transition w:1/3→0 gives the first quantitative measurement of Friedmann symmetry breaking (|C-/C+|→2); and the trajectory k_Temple=-(1-D)=-0.031046 gives H0=68.44 km/s/Mpc consistent with DESI 2024 to 0.1 sigma. The CMB shift parameter R=1.749 is identified as the target for Temple's nonlinear STV solution.