No Drift in Functor Models for Under Governed Semantic Updates

This document formalizes and proves a no-drift property for systems evolving under governed updates. Artifacts are modeled as parameterized functions with observable behavior, and updates are required to preserve semantics unless explicitly declared contract changing. This shows that, under these assumptions, semantic equivalence is preserved and reflected by all non-contract-changing updates, and that any change in observable behavior must occur through an explicitly governed update. The result establishes a formal guarantee of behavioral stability in a controlled deployment model and is mechanized in the Lean theorem prover. See https://github.com/AutonomicAI/equivalence-leanPatent pending.