Architecture diagrams are where design intentions go to die, especially when AI writes your code. 💀 AI agents optimize for immediate features, not structural boundaries. They’ll happily bypass layers and inject a repository straight into a controller for a fast path to a green test. They aren't careless; they just lack structural feedback. To protect your codebase from rotting, you must treat architecture rules exactly like unit tests. Enter ArchUnit for Java & Spring Boot. 🛠️ Learn how to build automated "architecture fitness functions" to enforce layer boundaries, block leaked database entities, and safely baseline legacy debt. Stop trusting your diagram. Start testing it.