Understanding the Monorepo Structure

The entire architecture is built on a "Thin-Client, 4-Layer" model, which is explicitly designed to be robust, scalable, and easily managed by both humans and AI agents.

Here’s the breakdown of that structure and its purpose:

The 4 Layers:

1. Layer 4: Apps (The "Thin Clients")

   • Location: apps/ (e.g., web, api-v2, astro-app)
   • Purpose: These are the deployable units that users or other systems interact with. API apps (like api-v2) implement the oRPC contracts defined in Layer 1.
   • The "Why": The core principle is that these apps are "thin". They are deliberately kept simple, containing only logic related to routing and presentation (UI). They are not supposed to contain any business logic. This makes them easy to change, update, or even replace without affecting the core functionality of the system.

2. Layer 3: Orchestration (The "Services")

   • Location: packages/services/
   • Purpose: This layer acts as the bridge between the "thin" apps and the "core" logic. It contains the application services that execute specific use cases (e.g., createUser, processPayment).
   • The "Why": It separates the how a business process is executed from the what (the core rules). This layer is responsible for orchestrating operations, calling domain logic, and interacting with the database via repositories.

3. Layer 2: Data Access (The "Repositories")

   • Location: packages/db/
   • Purpose: This layer handles all database interactions. It uses Drizzle ORM for type-safe queries, using the schemas defined in Layer 1.
   • The "Why": Crucially, this package is isolated and has no dependencies on other workspace packages. This decouples the database from the rest of the system, making it possible to change the database or ORM with minimal impact on the business logic.

4. Layer 1: Core (The "Pure Business Logic & Schemas")

   • Location: packages/core/
   • Purpose: This is the heart of the monorepo and the single source of truth. It defines the data structures (schemas using Zod), the database schemas (using Drizzle), the API contracts (using oRPC), and the pure, universal business rules (domain).
   • The "Why": Like the db package, this is also isolated with zero workspace dependencies. This ensures the foundational rules of the application are stable and independent of any specific implementation. This "schema-first" approach is what enables end-to-end type safety.

Why This Structure is Effective:

• Separation of Concerns: Each layer has a clear and distinct responsibility, which makes the codebase easier to understand, navigate, and maintain.
• Automated Governance: The structure is not just a guideline; it's enforced by 7 automated validation checks (e.g., check:isolation, check:circular). This is the key to making the architecture "AI-Optimized," as it provides immediate and clear feedback, preventing architectural drift.
• Code Reusability: Common functionality like UI components (packages/ui), configuration (packages/eslint-config), and business logic (packages/services) are defined once in packages/ and shared across multiple applications in apps/.
• Scalability & Flexibility: New applications can be easily added to the apps/ directory, and they can immediately leverage the existing shared packages. The polyglot nature of MoonRepo means you could add a Python or Go service that still consumes the same core logic.

In essence, the structure is a deliberate and well-documented choice to build a maintainable, scalable, and highly-governed system where the flow of dependencies is strictly controlled from the outside in (Apps -> Services -> Core/DB).