California just announced it'll start ticketing driverless cars that break traffic laws. That got me thinking — not about self-driving cars specifically, but about a problem I've hit on three different projects: how do you make an automated system respect a set of rules that change over time? Whether you're building a CI/CD pipeline that enforces deployment policies, an API gateway with rate-limiting rules, or a workflow engine that needs to comply with business regulations, you eventually need a rule engine. And if you reach for a massive enterprise framework on day one, you'll regret it. Here's how I build lightweight rule engines that actually hold up in production. The Problem: Hardcoded Rules Rot Fast Every project starts the same way. Someone says "just add an if-statement." So you do. # This is fine... for now def check_deployment ( deploy_request ): if deploy_request . target == " production " and not deploy_request .…