Quantum Resonance Gravity: Paper II — Lagrangian Foundation

This paper establishes Quantum Resonance Gravity on a covariant Lagrangian foundation. Starting from a scalar-tensor action with nonminimal coupling between the strain field D and spacetime curvature, I derive the modified Einstein equations and strain field equation without approximation. General Relativity is recovered exactly on the trivial branch. The PPN parameters γ = β = 1 are derived to Cassini precision from the large Brans-Dicke parameter of the theory (not assumed). The microscopic source nonlinearity — the (ρ/ρ₀)² coherence factor — is derived from pairwise phase-locking of spin oscillators, fixing the source exponent α = 2 from first principles. Additional topics include linear stability analysis, strong-field branch structure, microscopic toy model, and observable consequences of the nontrivial branch. Part 2 of a 5-paper series on Quantum Resonance Gravity.