# Implementer — F-024 Notifications: transactional email

## Summary
Implemented notifications module with `NotificationsService` dispatching email through an `EmailProvider` port. `notifications_messages.event_id` enforces idempotency. Provider is injected at composition root so swapping providers only touches infrastructure.

## Files changed
- `project/migrations/018_notifications.js`
- `project/src/modules/notifications/**`
- `project/src/app/build-app.ts`

## Acceptance evidence
- AC1 dispatch on first event: `notifications-service.test.ts` confirms first call returns 'sent' and provider.send called once.
- AC2 replay no duplicate: same test injects `findByEventId` returning an existing row and asserts 'duplicate' with no second provider call.
- AC3 provider swap: `boundary.test.ts` asserts only `infrastructure/` references `LoggingEmailProvider` or `emailProvider.send`.

## Commands run
- `cd project && npm run lint/typecheck/build/test` passed
- `cd project && TEST_DATABASE_URL='postgres://mdv:mdv_dev_only@localhost:5432/mdv_test' npm run test:integration -- migrations.itest` passed; 14 files, 53 tests
- `./scripts/verify.sh` passed

## Notes
- No new runtime dependency.
- `LoggingEmailProvider` writes JSON lines for v1.