integration-ruleslisted

# Integration Rules These rules are mandatory for all code review and development work involving multi-component systems. ## Vertical Slice Principle Every task MUST deliver a thin, working end-to-end path: | Good (Vertical Slice) | Bad (Horizontal Layer) | |------------------------|------------------------| | "User can send message" (UI + API + LLM + response display) | "Create all database tables" | | "Display product list" (API call + domain filter + UI render) | "Build all API endpoints" | | "Process payment" (UI form + gateway + order update) | "Create all UI components" | ## Walking Skeleton The FIRST deliverable of any multi-component feature must be a walking skeleton: - One request flows through ALL layers - Returns real data (not hardcoded/mocked) - Proves the architecture connects end-to-end - Does NOT need to be feature-complete — just connected ## Contract-First Development When two components will communicate: | Step | Action | Artifact | |------|--------|----------| | 1 | Define interface before implementation | TypeScript interface, OpenAPI schema, or protobuf | | 2 | Both sides code against the contract | Import shared types or generated clients | | 3 | Contract test validates both sides | Test that producer output matches consumer expectation | ## Integration Test Requirements | Boundary | Required Test | |----------|---------------| | HTTP API endpoint | Request with real HTTP client, validate response shape + status | | Database operation | Test