As a Security Engineer with over 10+ years in industry, I kept running into the same problem with coding agents: Instructions are not guarantees.I put guidance in `CLAUDE.md`, `AGENTS.md`, memory files, MCP descriptions, and tool documentation. I explicitly told the agent things like:* Use the code graph for architecture questions instead of grepping the repository. * Do not use deprecated APIs or Unsafe code. * Prefer specific tools for specific tasks.The agent would still ignore those instructions surprisingly often. It would grep the entire repo, use deprecated APIs, or choose a slower tool even when a better one was available.That made me realize prompts and rules solve different problems.A prompt is a probabilistic influence on model behavior. A rule is an enforcement mechanism.So I built SSG (SigmaShake Governance), which sits between the agent and its tools. Instead of asking the model to remember a policy, SSG evaluates every tool call before it executes.For example, this rule ...