How I Prevented Claude Code from Breaking My Architecture with 18 Tests That Run in 0.4 Seconds

I spent the last few weeks building a production boilerplate for AI Agent and IoT systems. FastAPI, asyncpg, LangGraph, MQTT, pgvector — a complex stack with very specific architectural boundaries that cannot be violated.

The problem: I was using Claude Code and Cursor to accelerate development. And they are brilliant. But they are also completely agnostic to the architecture you have in your head.

Let me show you the kind of thing that happens without protection.

The Problem

My system has one critical rule: the IngestionService must never import SQLModel or SQLAlchemy. It's the hot path for IoT telemetry ingestion — asyncpg raw SQL only, zero ORM overhead. This separation is intentional and documented in 20 pages of ARCHITECTURE.md.