Providing a testable phenomenological bridge between general relativity and quantum mechanics remains a central unsolved problem in theoretical physics. We propose that this impasse may reflect less a limitation of mathematical technique than the absence of a shared dynamical structure connecting spacetime geometry and quantum fields. Structural Quantum Gravity (SQG) introduces the breathing field ψ = √ρ exp(iφ), a complex scalar that mediates between quantum amplitude and spacetime curvature through a master action that provides a testable phenomenological bridge. This action incorporates three innovations: (1) curvature-density coupling (α_SQG R ρ) implementing "gravity as breathing asymmetry," (2) structural potential U_Ξ(ρ) encoding fluctuation as "creative margin," and (3) phase as temporal beat (∂_t φ) defining time through structural rhythm. The master action is designed to recover the Schrödinger equation in the flat-space non-relativistic limit and Einstein field equations in the classical limit, satisfying the correspondence principle under specified limits. Variational analysis yields two coupled equations: a breathing equation (curved-space wave equation) and modified Einstein equations with quantum stress-energy. Two laboratory-facing observables are emphasized: (1) interference-pattern sidebands sourced by U_Ξ (a direct FFT-resolvable signature), and (2) a curvature-proxy dependence of the coherence length ξ(R_eff) formulated as a differential null test. This is a preprint of a work in progress. Correspondence and feedback are welcome at info@kenzo-clinic.com