A Universal Perturbation Boundary at χ = 0.15 in Collisionless Plasmas: Empirical Evidence from 1. 5 Million Observations

We report a universal cap on normalized plasma perturbations, χ ≡ max(|δB/B|, |δn/n|, |δV/V|) = 0.15, validated across 1.48 million observations from Earth's solar wind (DSCOVR, 2016–2026), ground magnetospheres (USGS, 2025), and Mars' induced field (MAVEN, 2019–2025). Zero violations observed over 10,000× field range (5 nT to 50 kN). Transient shocks (CMEs, CIRs) exceed χ = 0.15 as expected for unbounded MHD structures; quasi-steady boundary regions respect the cap. The bound corresponds to maximum interfacial steepness in collisionless shock theory and aligns numerically with (m_e/m_p)^(1/4) ≈ 0.153 (1.3% error). A real-time validation portal (LUFT) deployed at GitHub confirms ongoing adherence through January 2026. Predictions: χ ≤ 0.15 in Parker Solar Probe data at 0.046 AU, outer-planet magnetospheres, and lab plasmas. Full data, code, and validation portal at OSF: https://doi.org/10.17605/OSF.IO/X5M2T