Stability Engine v4.2: Integrity Unit Holonomic Drift Correction Prototype

Stability Engine v4.2 is a focused implementation increment that begins operationalizing the Integrity Unit through a bounded, runnable holonomic drift correction prototype. Built on the structurally tightened v4.1 scaffold, this release adds metric-aware residual evaluation, bounded iterative correction, domain admissibility checks, Jacobian and metric validation, explicit convergence and failure states, and deterministic correction limits. The canonical implementation consists of integrity_unit_v4_2.py and test_integrity_unit_v4_2.py, with all 7 tests passing. v4.2 also formalizes the integration boundary between the Stability Engine and URIEL-3b: Integrity Unit owns the interface. URIEL owns the internal holonomy. Adapter mediates. Nothing crosses raw. This release does not claim completed URIEL-3b integration, full Integrity Unit implementation, adversarial hardening, or production readiness. It remains a structurally consistent implementation scaffold with cooperative enforcement boundaries, now including a demonstrable Integrity Unit holonomic drift correction surface.