feat(ADM-018): completed feature

work/artifacts/F-018/implementer.md

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+# Implementer — F-018 Cart module
+
+## Summary
+Implemented authenticated cart persistence that stores only product id, variant id and quantity, and recalculates totals/availability through injected `PricingService` and `InventoryService` on every read.
+
+## Files changed
+- `project/migrations/013_cart.js`
+- `project/src/app/build-app.ts`
+- `project/src/app/tests/cart.itest.ts`
+- `project/src/modules/cart/**`
+- `project/src/modules/inventory/index.ts`
+- `project/src/modules/pricing/index.ts`
+
+## Acceptance evidence
+- AC1 price changed after add: `cart.itest.ts` adds item at one price, changes server price, then `GET /cart` returns recalculated totals.
+- AC2 out of stock: `cart.itest.ts` sets stock to zero and verifies cart item is flagged unavailable.
+- AC3 client price ignored: `cart.itest.ts` sends bogus price fields; response uses server-side pricing and `cart_items` has no price/tax/stock columns.
+- `verify.sh`: passed.
+
+## Commands run
+- `cd project && npm run lint` — passed
+- `cd project && npm run typecheck` — passed
+- `cd project && npm run build` — passed
+- `cd project && npm test` — passed; DB tests skipped without `TEST_DATABASE_URL`
+- `cd project && TEST_DATABASE_URL='postgres://mdv:mdv_dev_only@localhost:5432/mdv_test' npm run test:integration -- cart.itest migrations.itest` — passed; 10 files, 42 tests
+- `./scripts/verify.sh` — passed
+
+## Notes
+- Cart routes require authentication; no guest cart persistence in this slice.
+- Cart imports only public pricing/inventory interfaces, not internals.
+- Added public service factories in inventory/pricing module indexes for composition-root injection.