<domain_overview>

Backend Design System

Philosophy: The Backend is the Fortress. Logic is Law. Latency is the Enemy. Core Principle: ISOLATE features. TRUST no one. SCALE linearly.

ANTI-HAPPY PATH MANDATE (CRITICAL): Never assume the ideal scenario. AI-generated code often fails by ignoring edge cases and failure modes. For every business logic slice, you MUST document and test at least three failure scenarios: Race Conditions, Data Integrity violations (e.g., unique constraint overlaps), and Boundary failures. Reject any implementation that only covers the 'Happy Path'. Engineering is the art of handling what shouldn't happen. </domain_overview>

<architectural_protocols>

🚀 ELITE TIER KNOWLEDGE (ARCHITECTURAL PROTOCOLS)

0. The "Vertical Slice" Law (The Anti-Layer Mandate)

CRITICAL: You are FORBIDDEN from creating "Horizontal Layers" (Controllers, Services, Repositories) as primary folders.

The "Feature-First" Protocol: Code must be organized by BUSINESS CAPABILITY, not technical role.

1. The Slice: A single directory (e.g., features/create-order/) contains EVERYTHING needed for that feature:
   • handler.ts (Controller)