The prevention of catastrophic structural failure in aerospace, civil, and mechanical engineering relies heavily on empirical fatigue models, such as S-N curves, and the probabilistic application of the Stress Intensity Factor (KIc). These classical fracture mechanics treat material fatigue as a statistical degradation over time rather than a deterministic spatial boundary. This paper introduces a strict non-local continuum damage framework for microstructural yield scaling. By modeling the material matrix as a thermodynamic balance between the elastic delocalization of strain energy and the localized cavitation of micro-voids, we derive a universal critical yield radius (rcrit). We demonstrate that structural yield is not a random statistical event, but an exact deterministic limit where localized defect cavitation strictly overpowers the elastic dissipation capacity of the atomic lattice. We contrast this geometric invariant with traditional Griffith crack theory and present a blueprint for Active Microstructural Monitoring (AMM) using real-time ultrasonic tracking.