This work develops a measure-theoretic diagnostic framework for detecting stability loss in complex operational systems. The central quantity is the generative velocity, defined as the proportion of non-absorbed structure in a Radon–Nikodym decomposition. Stability degradation is interpreted as the progressive loss of local absolute continuity across operational scales, allowing structural transitions to be detected before catastrophic divergence of observable indicators. The paper develops a unified diagnostic structure including: - generative velocity monitoring- time-to-threshold estimation- multi-scale overlap geometry- polymetric instability indicators A spacecraft vibration case study illustrates how heavy-tailed excitation compresses intervention horizons even when nominal energy levels remain within bounds. The main text is written for applied mathematicians and control engineers, while the technical appendices provide rigorous measure-theoretic foundations, overlap geometry, and scale-differential diagnostics. In particular, stability loss is shown to correspond structurally to the emergence of singular components in evolving measures, making technically describable the critical structures that classical Lebesgue integration treats as measure-zero and therefore excludes from analysis. This work builds on three complementary layers of prior development: Observer-dependent measure structure TI03: Trans–Integral: Observer–Dependent Measure and the Emergence of Time — Lebesgue Theory as a Dirac–Limit of Assembler Density https://doi.org/10.5281/zenodo.17671551 Structural limits of integration-based diagnosis TI_e_01: On the Limits of Modern Integration as an Analytical Tool and a Constructive Resolution via the Trans–Integral Framework — The Economy under Frontier Loss as a Case https://doi.org/10.5281/zenodo.17933860 Measure-theoretic invariant of singular persistence Generative Velocity: A Measure-Theoretic Invariant of Singular Persistence and Regime Transition Geometry https://doi.org/10.5281/zenodo.18825445 While TI03 establishes the observer-dependent foundation and TI_e_01 identifies the diagnosability limits of classical integration, the Generative Velocity paper introduces the invariant that makes structural regime transitions quantitatively measurable. The present work develops the applied diagnostic consequences of this invariant in stability-critical systems. A minimal operational prototype implementing these principles is presented in: A Toy Model for Generative Velocity and the Geometry of Stability Loss https://doi.org/10.5281/zenodo.18896917