The Predictive Instability Precursor to Major Solar Storms and a Test of κ-Mediated Deep-Solar Coupling

Major solar storms pose a significant hazard to technological infrastructure, yet existing forecasting approaches remain largely probabilistic and tied to surface magnetic complexity. In this work, we report the discovery of a reproducible, statistically significant instability precursor in the solar activity record that systematically precedes major radiation and geomagnetic storm events. We demonstrate that this precursor cannot be explained by surface-only stochastic reconnection models and instead requires a slowly varying, coherent driver operating on global solar scales. We introduce a minimal parameterization of such a driver through an effective coupling constant κ, and we derive a single, falsifiable prediction for Solar Cycle 26 that distinguishes deep-solar coupling from conventional dynamo models.