# Stop Fixing Broken Architecture: Auto-Enforce Package Boundaries with Cursor Composer and ArchUnit > Source: > Published: 2026-06-16 08:30:56+00:00 ## Stop Fixing Broken Architecture: Auto-Enforce Package Boundaries with Cursor Composer and ArchUnit In 2026, we aren't writing boilerplate anymore; we are directing AI agents to refactor entire modules at once. But if you don't establish automated architectural guardrails, Cursor Composer will happily turn your clean hexagonal architecture into a giant ball of mud in under thirty seconds. ## Why Most Developers Get This Wrong - **Passive PR reviews:** Relying on human reviewers to catch illegal package imports (e.g., `domain` importing `infrastructure` ) during fast-paced AI code generation is a losing battle. - **Static documentation:** Writing "architectural guidelines" in Notion that nobody reads, instead of writing executable fitness functions that run in your build pipeline. - **Manual untangling:** Spending hours manually untangling cyclical dependencies after Cursor Composer applies a massive multi-file refactoring across five packages with a single prompt. ## The Right Way The only way to scale AI-driven development is to treat your architecture as unit tests, using Cursor Composer to generate the ArchUnit rules that govern its own output. - **Automated Fitness Functions:** Use ArchUnit 1.3.x to write JUnit 5 tests that assert package isolation, ensuring your hexagonal boundaries are strictly defined in code. - **Cursor Contextualization:** Feed your `.cursorrules` file with your ArchUnit definitions so the LLM (like Claude 3.7 Sonnet) knows it cannot violate boundaries before it even attempts a multi-file edit. - **CI-Gated Enforcement:** Run these architectural tests on every single commit; if Cursor breaches a boundary, the build fails instantly, forcing the AI to refactor its own mistake. If you're prepping for interviews, I've been building [javalld.com](https://javalld.com) — real machine coding problems with full execution traces. ## Show Me The Code (or Example) Here is the exact ArchUnit 1.3.0 test you need to prevent Cursor from leaking infrastructure details into your pure domain layer: ## Key Takeaways - **AI needs guardrails:** Multi-file code generators like Cursor Composer are incredibly powerful but blind to architectural intent without executable tests. - **Shift-left architecture:** Write your ArchUnit rules *before* prompting the AI to build new features to ensure it adheres to your domain boundaries. - **Zero-tolerance drift:** Treat architectural violations exactly like broken unit tests—red means stop, no exceptions.