Custom Fullstack Development

# Technical Manual: Fullstack Engineering Playbook

This playbook outlines the strict operational specs, security standards, and SLA guarantees applied across all custom fullstack systems developed under this framework.

1. Architectural Blueprint: The Modular Monolith

All custom systems are engineered as modular monoliths. This guarantees high speed of development and deployment simplicity while retaining strict boundary isolation.

       [ Request / Client ]
                │
                ▼
       [ Express Router Layer ]
                │
                ▼
      [ Controller (Zod Input) ]
                │
                ▼
      [ Service (Business Flow) ]
         │                    │
         ▼                    ▼
   [ Domain Policy ]    [ Domain Repo ]
   (Pure Validation)    (Prisma Engine)
                              │
                              ▼
                        [ PostgreSQL ]

1.1 Layer Strictness & Code Allocation

• Router Layer (Express): Exclusively maps endpoints. Contains zero business flow. Max length: 80 lines.
• Controller Layer: Decodes request payloads, triggers Zod validation, maps return states. The only layer authorized to import Request, Response, and NextFunction. Max length: 150 lines.
• Service Layer: Orchestrates database queries, evaluates policies, dispatches asynchronous jobs, and returns clean structures. Absolutely decoupled from Express. Max length: 200 lines.
• Policy Layer (Pure Functions): Contains core business validation logic (e.g. rate limits, permission checks). Must be 100% synchronous, completely isolated from databases or network I/O. Max length: 100 lines.
• Repository Layer: Encapsulates raw database queries. No business logic. Max length: 120 lines.