A Reproducible Kinematic Relaxation Discriminator for Galactic Disks

We present a reproducible kinematic relaxation discriminator constructed from age-stratified stellar velocity dispersion in galactic disks. The method defines a dimensionless regime metric D (R) that quantifies departures from quasi-steady kinematic behaviour using publicly accessible Gaia DR3 data and an explicitly documented ADQL query. Applied to a restricted Milky Way sample of 2292 disk stars across five radial bins (7. 25–9. 25 kpc), the discriminator yields D (R) values of order 10⁻². Given per-bin statistical uncertainties and power thresholds, this constitutes a non-detection of non–quasi-steady behaviour above D ≈ 0. 03–0. 09 at 95 percent power, depending on radial bin. The best-constrained bin (R ≈ 8. 75 kpc, N⋆ = 772) yields D = 0. 023 ± 0. 009 with Dₘin, power = 0. 031. Smaller deviations cannot be excluded at current resolution. A phenomenological scaling ansatz is evaluated against independent SPARC rotation-curve data as a gradient-sign consistency test. For NGC 3198, the full radial sample shows significant rank monotonicity (Spearman ρ = 0. 70, p < 10⁻⁴), while the quasi-steady-restricted outer regression is not statistically significant at present resolution and is therefore reported as a null result. This work does not propose a modification of gravity. It provides a documented kinematic pipeline with fixed parameter governance, quantified detection floors, and explicit falsifiability criteria. All intermediate tables, data products, and regression summaries are included to enable independent verification.