EGC: Electromagnetism–Gravity Consistency Gates

EGC (Electromagnetism–Gravity Consistency Gates) is a constraint framework for auditing proposed GR–EM effective-action extensions. It enforces necessary consistency gates: diffeomorphism invariance, U(1) gauge invariance (or explicitly controlled breaking), conservation closure via the Bianchi identity, correct limit recovery (Einstein–Maxwell and flat-space Maxwell), and DOF/constraint sanity.This release includes a worked screening example for the curvature-activated operator family RFμνFμνR F_{\mu\nu}F^{\mu\nu}RFμνFμν, demonstrating why Minkowski limit checks are insufficient when operators activate in weak curvature. Optional CST screening is integrated as a stability/causality back-end. EGC outputs PASS/FAIL with explicit failure mode localization and is intended as a “consistency compiler” for gravity–electromagnetism EFT model building.