---
name: Frontend
description: Svelte SPA structure and conventions.
applyTo: "frontend/src/**"
---

# Frontend

- SPA entry point is `frontend/src/index.ts`, main component is `frontend/src/App.svelte`.
- Component organization: `lib/` for utilities and stores, keep route components in a `routes/` folder when needed, `css/` for styles.
- Use PascalCase component names and export props at the top of the `<script>` tag; keep code/comments in English.
- SSR safety: guard browser-only code with `typeof window !== "undefined"`.
- API behavior: PUT responses return only changed fields; filter by id uses `_id`; API requests reject non-2xx with `{ response, data }` and error payload in `error.data.error`.

## i18n

- `svelte-i18n` is configured in `frontend/src/lib/i18n/index.ts` with lazy loading for locale files.
- Locale files live in `frontend/src/lib/i18n/locales/{lang}.json`.
- URL-based language routing: `/{lang}/...` (e.g. `/de/`, `/en/about`).
- Language utilities in `frontend/src/lib/i18n.ts`: `extractLanguageFromPath()`, `localizedPath()`, `getLanguageSwitchUrl()`.
- Use `$_("key")` from `svelte-i18n` for translations in components.

## E2E Tests (Playwright)

- When developing frontend features: extend or create corresponding E2E tests in `tests/e2e/`.
- Shared fixtures and helpers in `tests/e2e/fixtures.ts`: `waitForSpaReady(page)`, `navigateToRoute(page, path)`, `clickSpaLink(page, selector)`, `authedPage` fixture.
- After frontend changes, run only the affected E2E tests: `npx playwright test tests/e2e/filename.spec.ts` or `-g "test name"`.
- When tests fail, clarify whether the frontend or the test needs adjustment – coordinate with the user.