feat(ADM-018): completed feature

legacy/specs-old/F-001-scaffold/DESIGN.md

@@ -0,0 +1,78 @@
+# DESIGN — F-001 Scaffold modular monolith skeleton
+
+## Affected modules
+- New: `project/` application skeleton (no business modules yet, only exemplar `health` module).
+
+## Modules touched
+- `src/modules/health` (exemplar module proving the layout and boundary rule)
+- `src/shared` (error envelope helper)
+- `src/infrastructure/http` (Fastify server bootstrap)
+- `src/app` (composition root)
+
+## Modules NOT touched
+- Everything else. No business modules exist yet. No harness files outside `work/artifacts/` and `specs/`.
+
+## New interfaces
+- `health` module public API: `registerHealthRoutes(app: FastifyInstance): Promise<void>` exported only from `src/modules/health/index.ts`.
+- Boundary checker script: `node scripts/check-module-boundaries.mjs src` → exit 0 ok / exit 1 violation.
+
+## API changes
+- Adds `GET /health` → `200 {"status":"ok"}`.
+
+## Database changes
+- None.
+
+## Events
+- None.
+
+## External integrations
+- None.
+
+## Cache changes
+- None.
+
+## Security considerations
+- Fastify default JSON error handler replaced with an envelope that never leaks stack traces.
+- No dependencies beyond Fastify + toolchain.
+
+## Layout
+
+```text
+project/
+├── package.json
+├── tsconfig.json
+├── eslint.config.mjs
+├── vitest.config.ts
+├── .gitignore
+├── scripts/
+│   └── check-module-boundaries.mjs
+└── src/
+    ├── app/
+    │   └── build-app.ts            # composition root: wires modules
+    ├── infrastructure/
+    │   └── http/
+    │       └── server.ts           # listen entrypoint
+    ├── modules/
+    │   └── health/
+    │       ├── index.ts            # public API
+    │       ├── api/
+    │       │   └── health.routes.ts
+    │       └── tests/
+    │           └── health.test.ts
+    └── shared/
+        └── errors.ts
+```
+
+## Boundary rules enforced by the checker
+1. Files inside `src/modules/<mod>/` may only import: own subtree (relative), `src/shared/...` (relative or alias-free path), Node builtins, and npm packages.
+2. Any relative import escaping `src/modules/<mod>/` toward another module or toward `src/app`/`src/infrastructure` is a violation.
+3. Files outside modules (`src/app`, `src/infrastructure`) may import a module only via its `index.ts` (direct deep import = violation).
+
+## Toolchain
+- TypeScript strict, Fastify 5, Vitest, ESLint (flat config) + Prettier, tsc build to `dist/`.
+
+## Migration strategy
+- None (greenfield).
+
+## Rollback strategy
+- Delete `project/` content added by this ticket; no other system depends on it yet.