## ADDED Requirements

### Requirement: Codebase structure document
The system SHALL include a document (`docs/engineering/04-codebase-structure.md`) that provides an annotated map of every top-level directory and key file in the repository, explaining what lives where and why.

#### Scenario: Full directory tree annotated
- **WHEN** a new engineer reads 04-codebase-structure.md
- **THEN** they SHALL find an annotated directory tree covering: `src/`, `tests/`, `docs/`, `sdk/`, `sdk-python/`, `sdk-go/`, `sdk-java/`, `terraform/`, `dashboard/`, `migrations/`, `openspec/`, `scripts/`

#### Scenario: src/ subdirectory roles explained
- **WHEN** a new engineer reads 04-codebase-structure.md
- **THEN** they SHALL understand the role of each `src/` subdirectory: `controllers/` (HTTP layer), `services/` (business logic), `repositories/` (data access), `middleware/` (cross-cutting concerns), `utils/` (shared utilities), `types/` (TypeScript interfaces), `routes/` (Express router definitions)

#### Scenario: Where to add new code explained
- **WHEN** a new engineer needs to add a new feature
- **THEN** the document SHALL tell them exactly where each type of code belongs: new endpoint → controller + route; new business logic → service; new DB query → repository; new shared utility → utils/

#### Scenario: Key files identified and explained
- **WHEN** a new engineer reads 04-codebase-structure.md
- **THEN** they SHALL find explanations of: `src/app.ts` (Express app setup), `src/server.ts` (entry point), `src/types/index.ts` (canonical type definitions), `src/utils/errors.ts` (error hierarchy), `docker-compose.yml` (local dev stack), `tsconfig.json` (TypeScript config)

#### Scenario: DRY principle mapped to structure
- **WHEN** a new engineer reads 04-codebase-structure.md
- **THEN** they SHALL understand how the directory structure enforces DRY: one location for types, one for crypto utilities, one for JWT utilities, one for validators — and why duplication across these is a blocking PR issue