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.

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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:

@AnalyzeClasses(packages = "com.faang.billing")
class ArchitectureTest {
    @ArchTest
    static final ArchRule no_infrastructure_in_domain = noClasses()
        .that().resideInAPackage("..domain..")
        .should().dependOnClassesThat().resideInAPackage("..infrastructure..")
        .because("Domain layer must remain pure and infrastructure-agnostic");
}

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.