ImpactGate: A merge gate that scores the structural decay AI adds

ImpactGate is a merge gate tool that measures and quantifies structural decay introduced by code changes using a complexity-based scoring formula that penalizes additions to already-complex code structures. The tool can be deployed as a standalone CLI, git pre-commit hook, or CI/CD plugin (GitHub, GitLab, Jenkins) to either warn developers or block builds when code changes exceed acceptable decay thresholds. It scores changes by calculating impact based on files modified, existing complexity in affected containers, cyclomatic complexity, and line changes, making it expensive to pile onto already-heavy classes while keeping new imports cheap.