# ISSUE-226 — Shared key-map + locale-kontrakt (backend/frontend)

## Source of truth
- Single shared artifact: `shared/i18n/lobby.json`
- Ownership is documented under `contract.ownership` in the same artifact.

## Locale contract
Defined under `contract.locale`:
- default locale: `en`
- supported locales: `en`, `da`
- fallback rule: use default locale when requested locale is unsupported or a key translation is missing.

## Shared backend→frontend key-map
Defined under `contract.backend_to_frontend_error_keys`.

Examples:
- `session_not_found -> session_not_found`
- `session_not_joinable -> join_failed`
- `round_start_invalid_phase -> start_round_failed`

This allows backend error codes to remain stable while frontend copy keys stay UX-oriented.

## da/en example values
From `shared/i18n/lobby.json`:
- `frontend.errors.session_code_required.en = "Session code is required."`
- `frontend.errors.session_code_required.da = "Sessionskoden er påkrævet."`

## Verification
- Backend: `python manage.py test lobby.tests.I18nResolverTests`
- Frontend: `npm test -- --run tests/lobby-i18n.contract.test.ts`