feat: add canonical reveal payload for issue 289

Auto-merge by integrator: required checks green + official approval.

TODO.md

@@ -107,6 +107,7 @@ Byg **Weirsøe Party Protocol**: en dansk party-webapp platform ala Jackbox, hvo
 - [x] (Need-to-have) Tilføj spiller-auth/session-token for submit_lie (pt. baseret på player_id i payload)
 - [ ] (Nice-to-have) Endpoint til status/progress i løgnfasen (antal indsendt ud af total)
 - [ ] (Need-to-have) [Fejltype: CI/lint F401] [Fil/område: core_admin/*, fupogfakta/tests.py+views.py, lobby/admin.py+models.py, realtime/*, voice/*] [Branch/PR: feature/f3-lobby-create-join, feature/fase0-mvp-fup-og-fakta, feature/lobby-mvp (ingen åbne PRs fundet)] Fjern ubrugte scaffold-imports (eller kør ruff check --fix) så quality gate kan blive grøn før merge.
+- [x] (Need-to-have) [Issue #251] Release-often lane: SPA MVP opdelt i 3 merge-klare micro-PR batches (plan + acceptance criteria dokumenteret i `docs/ISSUE-251-RELEASE-OFTEN-SPA-MVP-BATCH-PLAN.md`).
 - [ ] (Need-to-have) Rate limiting på join/submit endpoints
 - [ ] (Need-to-have) Session-kode brute-force beskyttelse
 - [ ] (Need-to-have) Audit-log for host-handlinger (start/stop/skip)

docs/I18N_ARCHITECTURE.md

@@ -9,7 +9,7 @@ Issue #175 requires one shared i18n contract for MVP host/player flows across fr
   - supported: `en`, `da`
   - default/fallback: `en`
 
-Both Angular (`frontend/angular/src/app/lobby-i18n.ts`) and Django (`lobby/i18n.py`) read from this catalog.
+Django (`lobby/i18n.py`) reads directly from the catalog. Frontend runtimes are Angular-first and use a shared loader (`frontend/shared/i18n/lobby-loader.ts`) so Angular shell and SPA fallback consume the same keyspace + locale normalization.
 
 ## Key naming convention
 - Domain-first namespaces:
@@ -46,3 +46,4 @@ Both Angular (`frontend/angular/src/app/lobby-i18n.ts`) and Django (`lobby/i18n.
   - `frontend/angular/src/app/i18n-mvp-flow-smoke.spec.ts`
   - `frontend/angular/src/app/features/host/host-shell.component.spec.ts`
   - `frontend/angular/src/app/features/player/player-shell.component.spec.ts`
+  - `frontend/tests/lobby-loader.parity.test.ts` (minimal da/en key parity guard for shared keyspace)

docs/ISSUE-223-PLAYER-AUDIO-GUARD-ARTIFACT.md

@@ -0,0 +1,20 @@
+# Issue #223 — Telefon-klient audio guard (artifact)
+
+## Scope leveret
+- Telefon-/player-klient installerer en eksplicit audio guard ved mount (`installSecondaryDeviceAudioGuard`).
+- Guard overskriver `HTMLMediaElement.prototype.play` til en no-op på secondary device (client policy: `client_has_no_audio_output=true`).
+- Guard fjernes igen ved unmount (`ngOnDestroy`) så øvrige flows/enheder ikke påvirkes.
+- Ingen audio-controls er eksponeret i player-shell UI.
+
+## Acceptance mapping
+1. **Telefon-klient trigger ikke audio playback i kerneflow**
+   - Verificeret af test: `player-shell.component.spec.ts` (`installs secondary-device audio guard while player shell is mounted`).
+2. **Primær enhed påvirkes ikke negativt**
+   - Guard er scoped til player-shell lifecycle og restore'r original `play` ved destroy.
+3. **Enkel test/verifikation dokumenteret**
+   - Dokumenteret her + testkørsel nedenfor.
+
+## Testkørsel
+- Kommando:
+  - `cd frontend/angular && npm test -- src/app/features/player/player-shell.component.spec.ts`
+- Resultat: bestået (inkl. audio-guard test).

docs/ISSUE-224-TRUNK-SEQUENCE-175.md

@@ -0,0 +1,55 @@
+# Issue #224 — Trunk-sekvens for #175 (A/B/C)
+
+Formål: gøre #175 scheduler-klar som tre små, uafhængige og mergeklare bidder.
+
+## Sekvens
+
+### A) Backend i18n baseline
+- Tracking issue: #225
+- Scope:
+  - Backend resolver til locale (da/en)
+  - Fallback til `en` ved unsupported locale
+  - Stabil fejlkontrakt i payload (`error_code`, `error`, `locale`)
+- Mergebarhed: Kan merges uden frontend-ændringer.
+- Acceptance:
+  - Backend tests dækker `da` + fallback `en`
+  - Kontraktfelter er stabile i response
+
+### B) Shared key-map + locale-kontrakt
+- Tracking issue: #226
+- Scope:
+  - Én shared key-map for lobby/kerneflow
+  - Locale-kontrakt (tilladte locales, default locale, fallback-regler)
+  - Dokumentation af naming + ownership
+- Mergebarhed: Kan merges uden host/player UI-migrering.
+- Acceptance:
+  - Shared kontrakt findes ét sted
+  - Begge sider kan importere den
+  - Docs opdateret med da/en eksempler
+
+### C) Angular host/player integration + hardcoded-text cleanup
+- Tracking issue: #227
+- Scope:
+  - Angular host/player kerneflow bruger shared keys
+  - Hardcoded tekster fjernes i aftalte kernekomponenter
+  - Sprogskift verificeres i kritiske states
+- Mergebarhed: Kan merges selvstændigt når frontend-tests er grønne.
+- Acceptance:
+  - Korrekt i18n-copy i da/en i kerneflow
+  - Ingen hardcoded kerneflow-tekster tilbage
+  - Frontend tests/smoke grønne
+
+## PR-grænser (per bid)
+- 1 PR pr. bid (A/B/C) mod `main`
+- Mål: ~200–300 net LOC per PR (ekskl. generated artefakter)
+- Undgå cross-layer scope creep
+- Review-tid <30 min
+
+## Overordnet acceptance for #224
+- A/B/C-sekvens er tydelig med links
+- Hver bid er mergebar isoleret
+- Scheduler kan assign’e direkte uden ekstra afklaring
+
+## Verification (docs-only)
+- Verificeret at dokumentet kun beskriver trunk-sekvensen for issue #224 og linker til #225/#226/#227.
+- Ingen runtime-kode ændret; der er derfor ikke kørt kode/tests i denne PR.

docs/ISSUE-225-BACKEND-I18N-BASELINE-ARTIFACT.md

@@ -0,0 +1,44 @@
+# ISSUE-225 Artifact — Backend i18n baseline (resolver + fallback)
+
+Issue: **#225** (`[MVP][READY] #175-A: Backend i18n baseline (resolver + fallback)`)
+
+## Scope verified
+
+- Backend locale resolver supports `da` + `en` and normalizes language tags.
+- Unsupported locale requests fall back to default locale (`en`).
+- Error payload contract is stable for API errors:
+  - `error_code`
+  - `error`
+  - `locale`
+
+## Implementation references
+
+- Locale resolution + fallback chain:
+  - `lobby/i18n.py`
+  - `resolve_locale()`
+  - `resolve_error_message()`
+  - `api_error()`
+- Shared locale contract source:
+  - `shared/i18n/lobby.json` (`locales.default=en`, supported includes `en`, `da`)
+
+## Acceptance checks run
+
+Command:
+
+```bash
+.venv/bin/python manage.py test \
+  lobby.tests.I18nResolverTests \
+  lobby.tests.LobbyFlowTests \
+  lobby.tests.StartRoundTests
+```
+
+Result (2026-03-02):
+
+- `Ran 28 tests in 24.781s — OK`
+- `System check identified no issues (0 silenced).`
+- Confirms resolver behavior for locale normalization + fallback and stable error payload fields across flow endpoints.
+
+## Notes
+
+- Existing merged follow-ups in `main` include Accept-Language parsing fixes for q-values and locale tag normalization.
+- This artifact documents the final baseline state and verification evidence for #225.

docs/ISSUE-226-SHARED-KEYMAP-LOCALE-CONTRACT.md

@@ -0,0 +1,30 @@
+# 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`

docs/ISSUE-250-PRIMARY-DEVICE-AUDIO-POLICY-ARTIFACT.md

@@ -0,0 +1,16 @@
+# Issue #250 Artifact — MVP guardrail (telefon-klient uden lydafspilning)
+
+## Scope
+Implementeret guardrail for `primary-device only` audio policy i SPA player-flow.
+
+## Acceptance mapping
+1. **Telefon-klient flow indeholder ingen audio-play init-path**
+   - Test: `player-shell.component.spec.ts` → `does not trigger original media play during player-shell init path`.
+2. **Primær enhed policy er dokumenteret og testbar**
+   - Policy i contract: `shared/i18n/lobby.json` → `frontend.capabilities.client_has_no_audio_output=true`.
+   - Testbar via eksisterende guard-tests + init-path test i player-shell specs.
+3. **Krav er refereret i SPA-plan/cutover-noter**
+   - Dokumenteret i `docs/spa-cutover-flag.md` under *MVP audio policy guardrail (telefon-klient)*.
+
+## UX/i18n note
+- Player shell viser advarselstekst via i18n key: `frontend.ui.player.audio_policy_notice`.

docs/ISSUE-251-RELEASE-OFTEN-SPA-MVP-BATCH-PLAN.md

@@ -0,0 +1,124 @@
+# Issue #251 — Release-often lane for SPA MVP (3 micro-PR batches)
+
+## Formål
+Bryde SPA MVP-arbejdet op i **3 merge-klare micro-PRs** med tydelige acceptance criteria,
+så vi kan levere værdi oftere, reducere review-risiko og holde `main` grøn.
+
+## Scope (issue-bound)
+Denne plan dækker kun planlægning/acceptance for den kommende SPA MVP-lane.
+Implementering af de konkrete features sker i efterfølgende PRs.
+
+## Hard acceptance criteria for issue #251
+- [x] Der findes en dokumenteret plan med præcis **3 batches**.
+- [x] Hver batch har:
+  - [x] mål og afgrænsning
+  - [x] konkrete leverancer (kodeområder)
+  - [x] test/checks før merge
+  - [x] rollback-note
+  - [x] "ikke med i denne batch" for at undgå scope creep
+- [x] Batch-rækkefølgen er dependencies-sikker (batch B bygger på batch A, batch C på batch B).
+- [x] Hver batch kan merges/releaseres uafhængigt uden at blokere drift på `main`.
+- [x] Planen linker til konkrete dev-opgaver for lane-kørsel.
+
+## Batch-plan (merge-klare micro-PRs)
+
+### Batch A — SPA shell + routing baseline
+**Mål:** Et stabilt SPA-skelet med route-struktur og guard-basics.
+
+**Leverancer (kodeområder)**
+- `frontend/angular/src/app/app.routes.ts` (host/player entry routes + fallback)
+- `frontend/angular/src/app/session-route-context.ts` (baseline route guards)
+- `frontend/angular/src/app/app.component.*` (shell-nav + route outlet wiring)
+- `lobby/templates/lobby/spa_shell.html` (kompatibel shell-entry ved SPA cutover)
+
+**Done-kriterier**
+- Host- og player-entry routes kan åbnes uden runtime-fejl i samme SPA-shell.
+- Route guards afviser ugyldige parametre deterministisk (ingen hard crash).
+- `USE_SPA_UI=false` fortsætter med legacy-flow uden regression.
+
+**Checks før merge**
+- `cd frontend/angular && npm test -- --run src/app/app.routes.spec.ts src/app/session-route-context.spec.ts`
+- `cd frontend/angular && npm run build`
+- Manual smoke: `/lobby/ui/host` + `/lobby/ui/player` (både `USE_SPA_UI=false` og `true`).
+
+**Rollback-note**
+- Sæt `USE_SPA_UI=false` og redeploy; verificér legacy routes svarer 200.
+
+**Ikke med i batch A**
+- Fuld gameplay-state synkronisering.
+- Audio/polish og i18n finpudsning ud over baseline wiring.
+
+---
+
+### Batch B — Session-state + host/player sync MVP
+**Mål:** Korrekt synkronisering af session-state mellem host og spillerklient.
+
+**Leverancer (kodeområder)**
+- `frontend/angular/src/app/features/host/host-shell.component.ts`
+- `frontend/angular/src/app/features/player/player-shell.component.ts`
+- `frontend/src/api/angular-client.ts` (MVP-kald for status/phase-overgange)
+
+**Done-kriterier**
+- Host handlinger (`start`, `show`, `mix`, `score`, `next`, `finish`) afspejles hos player uden side-reload.
+- Session-phase transitions er deterministiske i happy-path (`lobby -> question -> score -> next/finish`).
+- Guardrails reducerer race-condition regressions ved hurtige phase-skift.
+
+**Checks før merge**
+- `cd frontend/angular && npm test -- --run src/app/features/host/host-shell.component.spec.ts src/app/features/player/player-shell.component.spec.ts`
+- `cd frontend && npm test -- --run tests/angular-api-client.test.ts`
+- Manual smoke: host action -> player phase sync indenfor forventet latenstid.
+
+**Rollback-note**
+- Slå `USE_SPA_UI=false`, redeploy, og kør hurtig gameplay-smoke i legacy flow.
+
+**Ikke med i batch B**
+- Avanceret UX-polish/animation.
+- Udvidet observability udenfor MVP-kritiske logs.
+
+---
+
+### Batch C — Lobby/join/start minimal flow + release readiness
+**Mål:** Gøre SPA MVP release-klar med fokus på stabilitet og driftssikkerhed omkring det minimale flow.
+
+**Leverancer (kodeområder)**
+- `frontend/angular/src/app/i18n-mvp-flow-smoke.spec.ts` + relevante shell-tests
+- `docs/UI_SMOKE.md` + `docs/STAGING_GAMEPLAY_SMOKE_ARTIFACT.md`
+- `CHANGELOG.md` release-input for SPA MVP lane
+
+**Done-kriterier**
+- End-to-end minimal flow (`lobby -> join -> start`) er dokumenteret PASS i SPA.
+- Fejl-/empty-/loading states for flowets kritiske skærme er verificeret.
+- Driftsteam kan udføre cutover + rollback uden tvetydighed.
+
+**Checks før merge**
+- `cd frontend/angular && npm test -- --run src/app/i18n-mvp-flow-smoke.spec.ts`
+- `python manage.py test lobby.tests.LobbyFlowTests`
+- Opdateret staging-smoke artifact med UTC tidsstempler og gate-resultat.
+
+**Rollback-note**
+- Brug eksisterende playbook i `docs/spa-cutover-flag.md` (`USE_SPA_UI=false` + asset-version rollback).
+
+**Ikke med i batch C**
+- Post-MVP featureudvidelser.
+- Større refactors uden direkte release-værdi.
+
+## Rækkefølge og parallel-kørsel
+- **Dependency-rækkefølge:** A -> B -> C.
+- **Kan køres parallelt uden konflikt:**
+  - Test-/doc-forberedelse til C kan startes parallelt med B (ingen blokering af runtime-kode), men merges først efter B.
+  - Drift-smoke templates kan opdateres tidligt, så længe de ikke ændrer runtime-adfærd.
+- **Må ikke køre parallelt:**
+  - Runtime routing/guard ændringer i A og session-sync logik i B på samme filer uden feature-flag koordinering.
+
+## Konkret lane-opgavebinding (dev-opgaver)
+- Batch A PR: `feat/issue-251-batch-1-spa-shell-routing`
+- Batch B PR: `feat/issue-251-batch-2-session-sync`
+- Batch C PR: `feat/issue-251-batch-3-lobby-join-start-release-readiness`
+
+Hver PR skal linke tilbage til issue #251 og inkludere test-evidence + rollback-check.
+
+## Merge-gate for alle 3 batches
+- Små PRs (mål: reviewbar størrelse, helst < ~300 netto-linjer når muligt).
+- Grøn CI/checks før review-request.
+- Tydelig PR-beskrivelse med: scope, test evidence, out-of-scope.
+- Ingen skjulte sideeffekter på tværs af apps/domæner.

docs/ISSUE-257-SHARED-I18N-KEYSPACE-FRONTEND-LOADER-ARTIFACT.md

@@ -0,0 +1,32 @@
+# ISSUE-257 Artifact — Shared i18n keyspace + frontend loader (da/en, Angular-first)
+
+Issue: **#257** (`[MVP][READY] #175-B: Shared i18n keyspace + frontend loader`)
+
+## Acceptance checklist
+
+- [x] **Delt key-strategi dokumenteret (frontend/backend)**
+  - Arkitektur/deling beskrevet i `docs/I18N_ARCHITECTURE.md`.
+  - Shared contract + keyspace source of truth: `shared/i18n/lobby.json`.
+
+- [x] **Frontend loader kan indlæse da+en med samme keyspace**
+  - Shared loader: `frontend/shared/i18n/lobby-loader.ts`.
+  - Angular-first integration via `frontend/angular/src/app/lobby-i18n.ts` (samme loader/samme keyspace).
+  - Locale-normalisering inkluderer underscore/hyphen variants (`da_DK` → `da`).
+
+- [x] **Minimal check for key-paritet da/en**
+  - `collectLocaleParityIssues(...)` i shared loader.
+  - Testet i `frontend/tests/lobby-loader.parity.test.ts`.
+
+- [x] **Ingen API-kontraktbrud**
+  - Contract-test: `frontend/tests/lobby-i18n.contract.test.ts`.
+  - Drift-check mellem manifest og katalog: `scripts/check_i18n_drift.py`.
+
+## Kørte checks
+
+```bash
+python3 scripts/check_i18n_drift.py
+cd frontend && npm test -- --run tests/lobby-loader.parity.test.ts tests/lobby-i18n.contract.test.ts
+cd frontend/angular && npm test -- --run src/app/lobby-i18n.spec.ts src/app/i18n-mvp-flow-smoke.spec.ts
+```
+
+Resultat: alle checks grønne.

docs/ISSUE-257-SHARED-I18N-LOADER-ARTIFACT.md

@@ -0,0 +1,37 @@
+# ISSUE-257 Artifact — shared i18n keyspace + frontend loader (Angular-first)
+
+Issue: **#257** (`[MVP][READY] #175-B: Shared i18n keyspace + frontend loader (da/en, Angular-first)`)
+
+## Acceptance mapping
+
+### 1) Delt key-strategi dokumenteret (frontend/backend)
+- Shared contract source: `shared/i18n/lobby.json`
+- Architecture doc: `docs/I18N_ARCHITECTURE.md`
+- Key-map/contract doc: `docs/ISSUE-226-SHARED-KEYMAP-LOCALE-CONTRACT.md`
+
+### 2) Frontend loader kan indlæse da+en med samme keyspace
+- Shared loader: `frontend/shared/i18n/lobby-loader.ts`
+- Angular-first consumer path:
+  - `frontend/src/spa/lobby-i18n.ts`
+  - Angular shell/tests continue to consume same shared catalog through shared loader contract.
+
+### 3) Minimal check for key-paritet da/en
+- Guard test: `frontend/tests/lobby-loader.parity.test.ts`
+- Contract test: `frontend/tests/lobby-i18n.contract.test.ts`
+
+### 4) Ingen API-kontraktbrud
+- Frontend API contract smoke:
+  - `frontend/angular/src/app/api-contract-smoke.spec.ts`
+  - `frontend/tests/angular-api-client.test.ts`
+
+## Verification run (this lane)
+
+```bash
+cd frontend
+npm test -- --run tests/lobby-loader.parity.test.ts tests/lobby-i18n.contract.test.ts tests/angular-api-client.test.ts
+
+cd ../frontend/angular
+npm test -- --run src/app/api-contract-smoke.spec.ts
+```
+
+Result: PASS (all selected suites green).

docs/ISSUE-260-PHONE-CLIENT-NO-AUDIO-GUARD-ARTIFACT.md

@@ -0,0 +1,18 @@
+# Issue #260 Artifact — Phone/client no-audio guard (primary-device only playback)
+
+## Scope
+Added regression coverage for MVP audio policy to ensure phone/client flows never claim playback ownership, while primary-device playback stays unaffected.
+
+## Acceptance mapping
+1. **client/phone triggers no playback**
+   - Existing test coverage retained in `player-shell.component.spec.ts`:
+     - `does not trigger original media play during player-shell init path`
+     - `installs secondary-device audio guard while player shell is mounted`
+2. **primary device playback unaffected**
+   - New negative test in `player-shell.component.spec.ts`:
+     - `keeps primary-device playback untouched when no-audio capability is disabled`
+3. **one negative test for phone audio**
+   - Existing negative path preserved:
+     - `does not trigger original media play during player-shell init path`
+4. **no backend contract changes**
+   - Frontend test/docs-only scope; no backend contract files changed.

docs/ISSUE-277-SHARED-I18N-PARITY-ARTIFACT.md

@@ -0,0 +1,80 @@
+# ISSUE-277 Artifact — shared i18n registry parity report (Django ↔ Angular MVP)
+
+Issue: **#277** (`[READY][#175][P3] Shared i18n registry artifact: backend/frontend keyspace parity report`)
+
+## Artifact metadata
+
+- `artifact_id`: `issue-277-shared-i18n-parity-report`
+- `artifact_version`: `1.0`
+- `catalog_source`: `shared/i18n/lobby.json`
+- `generator`: `scripts/report_i18n_parity.py`
+
+## Naming/version rules (email-manager-inspired strategy)
+
+- **Single canonical artifact per issue**: issue-bundne rapporter navngives `docs/ISSUE-<nr>-<slug>-ARTIFACT.md`.
+- **Stable artifact identity**: `artifact_id` ændres ikke ved tekstlige opdateringer i samme rapporttype; det er den faste reference i review/ops.
+- **Explicit artifact versioning**: `artifact_version` bumpes, når rapportlogik eller scope ændres, så drift/review kan se forskel på format- vs. dataændringer.
+- **Shared namespace first**: keys refereres med fulde navnerum (`frontend.ui.*`, `frontend.errors.*`, `backend.error_codes.*`, `backend.errors.*`) i stedet for lokale aliases i artefakter.
+- **Source-of-truth before consumers**: rapporten afledes fra `shared/i18n/lobby.json`; Django/Angular beskrives som consumers af samme registry og ikke som parallelle kontrakter.
+
+## MVP-critical parity summary
+
+- Frontend UI gameplay keys checked: **16** → `OK`
+- Frontend error keys checked: **7** → `OK`
+- Backend gameplay/error codes checked: **9** → `OK`
+- Distinct frontend error keys reached from backend MVP flow: **6** (`join_failed, nickname_invalid, nickname_taken, session_code_required, session_not_found, start_round_failed`)
+
+Status: **Shared locale matrix is aligned (`en`, `da`) and backend→frontend error handling is contract-complete for MVP-critical flow.**
+
+## Django ↔ Angular parity matrix (MVP-critical error contract)
+
+| Backend code (`backend.error_codes.*`) | Django message key (`backend.errors.*`) | Angular key (`frontend.errors.*`) | Locales `en/da` | Parity note |
+|---|---|---|---|---|
+| `session_code_required` | `session_code_required` | `session_code_required` | `OK` | 1:1 |
+| `nickname_invalid` | `nickname_invalid` | `nickname_invalid` | `OK` | 1:1 |
+| `session_not_found` | `session_not_found` | `session_not_found` | `OK` | 1:1 |
+| `session_not_joinable` | `session_not_joinable` | `join_failed` | `OK` | mapped alias |
+| `nickname_taken` | `nickname_taken` | `nickname_taken` | `OK` | 1:1 |
+| `category_slug_required` | `category_slug_required` | `start_round_failed` | `OK` | many:1 collapse |
+| `category_not_found` | `category_not_found` | `start_round_failed` | `OK` | many:1 collapse |
+| `round_start_invalid_phase` | `round_start_invalid_phase` | `start_round_failed` | `OK` | many:1 collapse |
+| `round_already_configured` | `round_already_configured` | `start_round_failed` | `OK` | many:1 collapse |
+
+## Scope notes
+
+- **Django** consumes backend codes/messages directly from `shared/i18n/lobby.json` via `lobby/i18n.py`.
+- **Angular** consumes the same registry via `frontend/shared/i18n/lobby-loader.ts` and runtime helpers in `frontend/angular/src/app/lobby-i18n.ts`.
+- **Parity in MVP** is therefore strongest on the shared error contract and locale matrix; gameplay UI labels are frontend-owned but still live in the same registry.
+
+## Verified MVP gameplay UI keyspace present in the shared registry
+
+- `frontend.ui.host.title`
+- `frontend.ui.player.title`
+- `frontend.ui.common.session_code`
+- `frontend.ui.player.nickname`
+- `frontend.ui.player.join`
+- `frontend.ui.host.start_round`
+- `frontend.ui.host.show_question`
+- `frontend.ui.player.lie_label`
+- `frontend.ui.player.submit_lie`
+- `frontend.ui.player.submit_guess`
+- `frontend.ui.host.mix_answers`
+- `frontend.ui.host.calculate_scores`
+- `frontend.ui.host.load_scoreboard`
+- `frontend.ui.host.final_leaderboard`
+- `frontend.ui.player.final_leaderboard`
+- `frontend.ui.common.points_short`
+
+## Concrete deviations / follow-up items
+
+1. **Error granularity collapse remains intentional**: backend codes `category_slug_required, category_not_found, round_start_invalid_phase, round_already_configured` all map to `frontend.errors.start_round_failed`. Follow-up only if product wants case-specific Angular copy instead of one shared host failure message.
+2. **Frontend-only fallback copy is not mirrored in Django**: `frontend.errors.unknown` and `frontend.errors.session_fetch_failed` are Angular-side resilience keys, not backend contract keys. Follow-up if API responses should expose stable backend equivalents for these states.
+3. **Gameplay UI labels are registry-shared but not backend-rendered**: `frontend.ui.host.*`, `frontend.ui.player.*`, and `frontend.ui.common.*` are available in the shared artifact, but Django currently consumes only the backend error slice. Follow-up only if server-rendered views must guarantee the same UI label surface as Angular.
+
+## Re-run
+
+```bash
+python3 scripts/check_i18n_drift.py
+python3 scripts/report_i18n_parity.py
+python3 scripts/check_i18n_parity_artifact.py
+```

docs/i18n-drift-check.md

@@ -0,0 +1,34 @@
+# i18n key manifest + drift check
+
+Issue: #240
+
+This repo keeps shared lobby keyspaces in two files:
+
+- Contract source: `shared/i18n/lobby.json`
+- Key manifest: `shared/i18n/key-manifest.json`
+
+The manifest is intentionally small and explicit. It lists:
+
+- Supported locales (`locales`)
+- Frontend error key set (`frontend_error_keys`)
+- Backend error code set (`backend_error_codes`)
+- Backend translation key set (`backend_error_keys`)
+- Optional contract-only aliases (`allowed_contract_only_backend_codes`)
+
+## Local check
+
+Run the read-only drift checker from repo root:
+
+```bash
+python3 scripts/check_i18n_drift.py
+```
+
+The script returns non-zero when it detects drift, including:
+
+- key set mismatch between manifest and shared catalog
+- missing backend→frontend mapping coverage
+- mapping to unknown frontend keys
+- mappings for unknown backend codes
+- missing/empty locale translations (`en`/`da`)
+
+No CI gating changes are included in this task; this is a local guardrail.

docs/i18n-keymap.md

@@ -0,0 +1,69 @@
+# i18n key-map bootstrap (Angular host/player MVP)
+
+Issue: #220  
+Scope: Lobby → Join → Start round → Round → Reveal → Scoreboard  
+Locales: `en`, `da`
+
+This document is the gameplay key-namespace map for Angular host/player MVP.
+It maps existing text keys only (no feature expansion) and stays aligned with `shared/i18n/lobby.json`.
+
+## Key families
+
+- `host` — `frontend.ui.host.*` host-facing gameplay actions and status text.
+- `player` — `frontend.ui.player.*` player-facing gameplay actions and status text.
+- `system` — shared UI labels used across host/player views (implemented under `frontend.ui.common.*` in `shared/i18n/lobby.json`).
+- `errors` — user-facing error keys shown by frontend (`frontend.errors.*`) plus backend code → frontend key bridge via `backend.error_codes.*` / `contract.backend_to_frontend_error_keys.*`.
+
+## Gameplay flow key map
+
+| Flow step | Family | Key | en | da |
+|---|---|---|---|---|
+| Lobby | `host` | `host.title` | Host gameplay flow | Vært gameplay-flow |
+| Lobby | `player` | `player.title` | Player gameplay flow | Spiller gameplay-flow |
+| Lobby | `system` (`frontend.ui.common`) | `common.session_code` | Session code | Sessionskode |
+| Lobby | `player` | `player.nickname` | Nickname | Kaldenavn |
+| Join | `player` | `player.join` | Join | Join |
+| Start round | `host` | `host.start_round` | Start round | Start runde |
+| Round | `host` | `host.show_question` | Show question | Vis spørgsmål |
+| Round | `player` | `player.lie_label` | Lie | Løgn |
+| Round | `player` | `player.submit_lie` | Submit lie | Send løgn |
+| Round | `player` | `player.submit_guess` | Submit guess | Send gæt |
+| Reveal | `host` | `host.mix_answers` | Mix answers → guess | Bland svar → gæt |
+| Reveal | `host` | `host.calculate_scores` | Calculate scores → reveal | Udregn score → afslør |
+| Scoreboard | `host` | `host.load_scoreboard` | Load scoreboard | Hent scoreboard |
+| Scoreboard | `host` | `host.final_leaderboard` | Final leaderboard | Finale leaderboard |
+| Scoreboard | `player` | `player.final_leaderboard` | Final leaderboard | Finale leaderboard |
+| Scoreboard | `system` (`frontend.ui.common`) | `common.points_short` | pts | point |
+
+## Frontend error keys used in flow scope
+
+| Error family | Key | en | da |
+|---|---|---|---|
+| Join | `frontend.errors.session_code_required` | Session code is required. | Sessionskoden er påkrævet. |
+| Join | `frontend.errors.session_not_found` | Session code is invalid or the session no longer exists. | Sessionskoden er ugyldig, eller sessionen findes ikke længere. |
+| Join | `frontend.errors.nickname_invalid` | Nickname must be between 2 and 40 characters. | Kaldenavn skal være mellem 2 og 40 tegn. |
+| Join | `frontend.errors.nickname_taken` | Nickname is already taken. | Kaldenavnet er allerede taget. |
+| Join | `frontend.errors.join_failed` | Join failed. Check code or nickname and try again. | Kunne ikke joine. Tjek kode eller kaldenavn og prøv igen. |
+| Start round | `frontend.errors.start_round_failed` | Could not start round. Refresh the lobby and try again. | Kunne ikke starte runden. Opdater lobbyen og prøv igen. |
+| Any | `frontend.errors.unknown` | Action failed. Refresh status and try again. | Handlingen fejlede. Opdater status og prøv igen. |
+
+## Backend→frontend mapping for gameplay errors
+
+Mapped in `contract.backend_to_frontend_error_keys` (source: `shared/i18n/lobby.json`):
+
+> Note: `host_only_action` is **not** part of the current shared contract mapping and is intentionally not listed here.
+
+- `session_code_required` → `session_code_required`
+- `nickname_invalid` → `nickname_invalid`
+- `session_not_found` → `session_not_found`
+- `session_not_joinable` → `join_failed`
+- `nickname_taken` → `nickname_taken`
+- `category_slug_required` → `start_round_failed`
+- `category_not_found` → `start_round_failed`
+- `round_start_invalid_phase` → `start_round_failed`
+- `round_already_configured` → `start_round_failed`
+
+## Notes
+
+- This is a bootstrap key-map doc for MVP mergeability.
+- The key/value source of truth remains `shared/i18n/lobby.json`.

docs/spa-cutover-flag.md

@@ -65,3 +65,10 @@ Target: rollback + sanity-verifikation inden for 10 minutter.
 - Flag ON (host deep-link): `UiScreenTests.test_host_screen_deeplink_preserves_spa_path_when_feature_flag_enabled`
 - Flag ON (player): `UiScreenTests.test_player_screen_can_render_angular_shell_when_feature_flag_enabled`
 - Smoke-checkliste for cutover paths: `docs/STAGING_GAMEPLAY_SMOKE_ARTIFACT.md` + `docs/UI_SMOKE.md`
+
+
+## MVP audio policy guardrail (telefon-klient)
+- Telefon-/player-klienten må ikke starte lydafspilning lokalt i MVP (`primary-device only`).
+- Policy er bundet til capability-flaget `frontend.capabilities.client_has_no_audio_output=true` i `shared/i18n/lobby.json`.
+- Brugeradvarsel i player UI leveres via i18n key: `frontend.ui.player.audio_policy_notice`.
+- Acceptance-spec er dækket i Angular tests (`player-shell.component.spec.ts`), inkl. at init-path ikke kalder original media `play`.

frontend/angular/src/app/app.config.ts

@@ -1,7 +1,15 @@
 import { ApplicationConfig } from '@angular/core';
 import { provideRouter, withHashLocation } from '@angular/router';
+
 import { routes } from './app.routes';
+import { createWppApiClient, WPP_API_CLIENT } from './wpp-api-client';
 
 export const appConfig: ApplicationConfig = {
-  providers: [provideRouter(routes, withHashLocation())],
+  providers: [
+    provideRouter(routes, withHashLocation()),
+    {
+      provide: WPP_API_CLIENT,
+      useFactory: () => createWppApiClient(),
+    },
+  ],
 };

frontend/angular/src/app/features/host/host-shell.component.ts

@@ -55,7 +55,7 @@ type LeaderboardResponse = FinishGameResponse;
       <pre *ngIf="scoreboardPayload">{{ scoreboardPayload }}</pre>
       <div *ngIf="finalLeaderboard.length">
         <h3>{{ copy('host.final_leaderboard') }}</h3>
-        <p *ngIf="finalWinner"><strong>{{ copy('host.winner') }}:</strong> {{ finalWinner.nickname }} ({{ finalWinner.score }} pts)</p>
+        <p *ngIf="finalWinner"><strong>{{ copy('host.winner') }}:</strong> {{ finalWinner.nickname }} ({{ finalWinner.score }} {{ copy('common.points_short') }})</p>
         <ol>
           <li *ngFor="let entry of finalLeaderboard">{{ entry.nickname }}: {{ entry.score }}</li>
         </ol>
@@ -156,7 +156,7 @@ export class HostShellComponent implements OnInit, OnDestroy {
     try {
       const state = await this.controller.hydrateLobby(this.sessionCode);
       if (!state.session || state.errorMessage) {
-        throw new Error(state.errorMessage ?? 'Unknown error');
+        throw new Error(state.errorMessage ?? this.copy('common.unknown_error'));
       }
       this.session = state.session as SessionDetail;
       this.sessionCode = this.session.session.code;
@@ -177,7 +177,7 @@ export class HostShellComponent implements OnInit, OnDestroy {
     await this.runAction(async () => {
       const state = await this.controller.startRound(this.sessionCode, this.categorySlug.trim());
       if (!state.session || state.errorMessage) {
-        throw new Error(state.errorMessage ?? 'Unknown error');
+        throw new Error(state.errorMessage ?? this.copy('common.unknown_error'));
       }
       this.session = state.session as SessionDetail;
       this.sessionCode = this.session.session.code;

frontend/angular/src/app/features/player/player-shell.component.spec.ts

@@ -1,5 +1,6 @@
 import { afterEach, describe, expect, it, vi } from 'vitest';
 
+import lobbyCatalog from '../../../../../../shared/i18n/lobby.json';
 import { PlayerShellComponent } from './player-shell.component';
 
 type FetchMock = ReturnType<typeof vi.fn>;
@@ -350,4 +351,171 @@ describe('PlayerShellComponent gameplay wiring', () => {
 
     component.ngOnDestroy();
   });
+
+  it('silences active media elements when secondary-device audio guard is installed', () => {
+    const pauseAudio = vi.fn();
+    const pauseVideo = vi.fn();
+    const audioElement = { muted: false, pause: pauseAudio };
+    const videoElement = { muted: false, pause: pauseVideo };
+    const querySelectorAll = vi.fn().mockReturnValue([audioElement, videoElement]);
+
+    vi.stubGlobal('document', { querySelectorAll });
+    vi.stubGlobal('window', {
+      location: { hash: '', search: '' },
+      history: { state: null, replaceState: vi.fn() },
+      localStorage: { getItem: vi.fn().mockReturnValue('en'), setItem: vi.fn(), removeItem: vi.fn() },
+      sessionStorage: { getItem: vi.fn().mockReturnValue(null), setItem: vi.fn(), removeItem: vi.fn() },
+      HTMLMediaElement: { prototype: { play: vi.fn().mockResolvedValue(undefined) } },
+      addEventListener: vi.fn(),
+      removeEventListener: vi.fn(),
+    });
+    vi.stubGlobal('navigator', { language: 'en-US', onLine: true });
+
+    const component = new PlayerShellComponent();
+    component.ngOnInit();
+
+    expect(querySelectorAll).toHaveBeenCalledWith('audio,video');
+    expect(audioElement.muted).toBe(true);
+    expect(videoElement.muted).toBe(true);
+    expect(pauseAudio).toHaveBeenCalledTimes(1);
+    expect(pauseVideo).toHaveBeenCalledTimes(1);
+
+    component.ngOnDestroy();
+  });
+
+  it('installs secondary-device audio guard while player shell is mounted', async () => {
+    const originalPlay = vi.fn().mockRejectedValue(new Error('original play'));
+    const mediaPrototype = { play: originalPlay };
+
+    vi.stubGlobal('window', {
+      location: { hash: '', search: '' },
+      history: { state: null, replaceState: vi.fn() },
+      localStorage: { getItem: vi.fn().mockReturnValue('en'), setItem: vi.fn(), removeItem: vi.fn() },
+      sessionStorage: { getItem: vi.fn().mockReturnValue(null), setItem: vi.fn(), removeItem: vi.fn() },
+      HTMLMediaElement: { prototype: mediaPrototype },
+      addEventListener: vi.fn(),
+      removeEventListener: vi.fn(),
+    });
+    vi.stubGlobal('navigator', { language: 'en-US', onLine: true });
+
+    const component = new PlayerShellComponent();
+    component.ngOnInit();
+
+    const pause = vi.fn();
+    const audioElement = { muted: false, defaultMuted: false, volume: 1, pause };
+
+    await expect(mediaPrototype.play.call(audioElement)).resolves.toBeUndefined();
+    expect(audioElement.muted).toBe(true);
+    expect(audioElement.defaultMuted).toBe(true);
+    expect(audioElement.volume).toBe(0);
+    expect(pause).toHaveBeenCalledTimes(1);
+
+    component.ngOnDestroy();
+
+    await expect(mediaPrototype.play()).rejects.toThrow('original play');
+  });
+
+  it('keeps audio guard active until the last mounted player shell is destroyed', async () => {
+    const originalPlay = vi.fn().mockRejectedValue(new Error('original play'));
+    const mediaPrototype = { play: originalPlay };
+
+    vi.stubGlobal('window', {
+      location: { hash: '', search: '' },
+      history: { state: null, replaceState: vi.fn() },
+      localStorage: { getItem: vi.fn().mockReturnValue('en'), setItem: vi.fn(), removeItem: vi.fn() },
+      sessionStorage: { getItem: vi.fn().mockReturnValue(null), setItem: vi.fn(), removeItem: vi.fn() },
+      HTMLMediaElement: { prototype: mediaPrototype },
+      addEventListener: vi.fn(),
+      removeEventListener: vi.fn(),
+    });
+    vi.stubGlobal('navigator', { language: 'en-US', onLine: true });
+
+    const firstComponent = new PlayerShellComponent();
+    const secondComponent = new PlayerShellComponent();
+
+    firstComponent.ngOnInit();
+    secondComponent.ngOnInit();
+
+    await expect(mediaPrototype.play()).resolves.toBeUndefined();
+
+    firstComponent.ngOnDestroy();
+    await expect(mediaPrototype.play()).resolves.toBeUndefined();
+
+    secondComponent.ngOnDestroy();
+    await expect(mediaPrototype.play()).rejects.toThrow('original play');
+  });
+
+  it('does not trigger original media play during player-shell init path', () => {
+    const originalPlay = vi.fn().mockResolvedValue(undefined);
+    const mediaPrototype = { play: originalPlay };
+
+    vi.stubGlobal('window', {
+      location: { hash: '', search: '' },
+      history: { state: null, replaceState: vi.fn() },
+      localStorage: { getItem: vi.fn().mockReturnValue('en'), setItem: vi.fn(), removeItem: vi.fn() },
+      sessionStorage: { getItem: vi.fn().mockReturnValue(null), setItem: vi.fn(), removeItem: vi.fn() },
+      HTMLMediaElement: { prototype: mediaPrototype },
+      addEventListener: vi.fn(),
+      removeEventListener: vi.fn(),
+    });
+    vi.stubGlobal('navigator', { language: 'en-US', onLine: true });
+
+    const component = new PlayerShellComponent();
+    component.ngOnInit();
+
+    expect(originalPlay).not.toHaveBeenCalled();
+
+    component.ngOnDestroy();
+  });
+
+  it('keeps primary-device playback untouched when no-audio capability is disabled', async () => {
+    const originalPlay = vi.fn().mockResolvedValue(undefined);
+    const mediaPrototype = { play: originalPlay };
+
+    vi.stubGlobal('window', {
+      location: { hash: '', search: '' },
+      history: { state: null, replaceState: vi.fn() },
+      localStorage: { getItem: vi.fn().mockReturnValue('en'), setItem: vi.fn(), removeItem: vi.fn() },
+      sessionStorage: { getItem: vi.fn().mockReturnValue(null), setItem: vi.fn(), removeItem: vi.fn() },
+      HTMLMediaElement: { prototype: mediaPrototype },
+      addEventListener: vi.fn(),
+      removeEventListener: vi.fn(),
+    });
+    vi.stubGlobal('navigator', { language: 'en-US', onLine: true });
+
+    const component = new PlayerShellComponent();
+    (component as any).clientHasNoAudioOutput = false;
+
+    component.ngOnInit();
+
+    await expect(mediaPrototype.play()).resolves.toBeUndefined();
+    expect(mediaPrototype.play).toBe(originalPlay);
+    expect((mediaPrototype as any).__wppSecondaryDeviceAudioGuard__).toBeUndefined();
+
+    component.ngOnDestroy();
+  });
+
+  it('resolves i18n warning copy from shared catalog without key fallback', () => {
+    const component = new PlayerShellComponent();
+
+    const notice = component.copy('player.audio_policy_notice');
+    const expected = lobbyCatalog.frontend.ui.player.audio_policy_notice[component.locale];
+
+    expect(notice).toBe(expected);
+    expect(notice).not.toBe('player.audio_policy_notice');
+  });
+
+  it('gates template warning notice on the no-audio-output capability flag', () => {
+    const templateSource = String((PlayerShellComponent as any).ɵcmp?.template);
+
+    expect(templateSource).toContain('clientHasNoAudioOutput');
+
+    const component = new PlayerShellComponent();
+    expect(component.copy('player.audio_policy_notice')).not.toBe('player.audio_policy_notice');
+    expect(component.clientHasNoAudioOutput).toBe(true);
+
+    (component as any).clientHasNoAudioOutput = false;
+    expect(component.clientHasNoAudioOutput).toBe(false);
+  });
+
 });

frontend/angular/src/app/features/player/player-shell.component.ts

@@ -16,6 +16,22 @@ interface SessionDetail {
 type ConnectionState = 'online' | 'reconnecting' | 'offline';
 type LoadingTransition = 'refresh' | 'join' | 'submit-lie' | 'submit-guess' | null;
 
+type GuardableMediaElement = {
+  muted?: boolean;
+  defaultMuted?: boolean;
+  volume?: number;
+  pause?: () => void;
+};
+
+type MediaPrototypeWithGuardState = {
+  play?: (this: GuardableMediaElement) => Promise<void>;
+  __wppSecondaryDeviceAudioGuard__?: {
+    originalPlay: (this: GuardableMediaElement) => Promise<void>;
+    installs: number;
+  };
+};
+
+
 function resolveLocalStorage(): Storage | undefined {
   if (typeof window === 'undefined') {
     return undefined;
@@ -29,6 +45,7 @@ function resolveLocalStorage(): Storage | undefined {
   imports: [CommonModule, FormsModule],
   template: `
     <h2>{{ copy('player.title') }}</h2>
+    <p *ngIf="clientHasNoAudioOutput" class="hint">{{ copy('player.audio_policy_notice') }}</p>
 
     <div class="panel" [attr.data-client-has-no-audio-output]="clientHasNoAudioOutput">
       <label>{{ copy('common.session_code') }} <input [(ngModel)]="sessionCode" /></label>
@@ -113,6 +130,7 @@ export class PlayerShellComponent implements OnInit, OnDestroy {
   private reconnectTimer: ReturnType<typeof setTimeout> | null = null;
   private stateSyncTimer: ReturnType<typeof setTimeout> | null = null;
   private unsubscribeLocale: (() => void) | null = null;
+  private restoreAudioGuard: (() => void) | null = null;
 
   constructor() {
     if (typeof navigator !== 'undefined' && !navigator.onLine) {
@@ -129,6 +147,7 @@ export class PlayerShellComponent implements OnInit, OnDestroy {
     this.unsubscribeLocale = subscribeToLocaleChanges((locale) => {
       this.locale = locale;
     });
+    this.installSecondaryDeviceAudioGuard();
 
     const hashRoute = window.location.hash.replace(/^#\/?/, '');
     const match = hashRoute.match(/^player(?:\/[^/]+)?(?:\/([^/?#]+))?/i);
@@ -158,6 +177,8 @@ export class PlayerShellComponent implements OnInit, OnDestroy {
     this.clearStateSyncTimer();
     this.unsubscribeLocale?.();
     this.unsubscribeLocale = null;
+    this.restoreAudioGuard?.();
+    this.restoreAudioGuard = null;
   }
 
   private readonly handleOnline = (): void => {
@@ -185,6 +206,79 @@ export class PlayerShellComponent implements OnInit, OnDestroy {
     }
   }
 
+  private installSecondaryDeviceAudioGuard(): void {
+    if (!this.clientHasNoAudioOutput || typeof window === 'undefined') {
+      return;
+    }
+
+    this.silenceExistingMediaElements();
+
+    const mediaPrototype = (window as Window & { HTMLMediaElement?: { prototype?: MediaPrototypeWithGuardState } }).HTMLMediaElement
+      ?.prototype;
+
+    if (!mediaPrototype || typeof mediaPrototype.play !== 'function') {
+      return;
+    }
+
+    const guardState = mediaPrototype.__wppSecondaryDeviceAudioGuard__;
+    if (guardState) {
+      guardState.installs += 1;
+    } else {
+      const originalPlay = mediaPrototype.play;
+      mediaPrototype.play = function mediaGuardedPlay(this: GuardableMediaElement): Promise<void> {
+        this.muted = true;
+        this.defaultMuted = true;
+        if (typeof this.volume === 'number') {
+          this.volume = 0;
+        }
+        this.pause?.();
+        return Promise.resolve();
+      };
+      mediaPrototype.__wppSecondaryDeviceAudioGuard__ = {
+        originalPlay,
+        installs: 1,
+      };
+    }
+
+    this.restoreAudioGuard = () => {
+      const currentState = mediaPrototype.__wppSecondaryDeviceAudioGuard__;
+      if (!currentState) {
+        return;
+      }
+
+      currentState.installs -= 1;
+      if (currentState.installs <= 0) {
+        mediaPrototype.play = currentState.originalPlay;
+        delete mediaPrototype.__wppSecondaryDeviceAudioGuard__;
+      }
+    };
+  }
+
+
+  private silenceExistingMediaElements(): void {
+    if (typeof document === 'undefined' || typeof document.querySelectorAll !== 'function') {
+      return;
+    }
+
+    const activeElements = document.querySelectorAll('audio,video') as
+      | NodeListOf<GuardableMediaElement>
+      | GuardableMediaElement[]
+      | undefined;
+
+    if (!activeElements || typeof (activeElements as { forEach?: unknown }).forEach !== 'function') {
+      return;
+    }
+
+    activeElements.forEach((element) => {
+      element.muted = true;
+      element.defaultMuted = true;
+      if (typeof element.volume === 'number') {
+        element.volume = 0;
+      }
+      element.pause?.();
+    });
+  }
+
   private scheduleStateSync(): void {
     this.clearStateSyncTimer();
 
@@ -232,7 +326,7 @@ export class PlayerShellComponent implements OnInit, OnDestroy {
     if (error instanceof Error && error.message) {
       return error.message;
     }
-    return 'Unknown error';
+    return this.copy('common.unknown_error');
   }
 
   private markOnline(): void {
@@ -356,7 +450,7 @@ export class PlayerShellComponent implements OnInit, OnDestroy {
     try {
       const state = await this.controller.hydrateLobby(this.sessionCode);
       if (!state.session || state.errorMessage) {
-        throw new Error(state.errorMessage ?? 'Unknown error');
+        throw new Error(state.errorMessage ?? this.copy('common.unknown_error'));
       }
       this.session = state.session as SessionDetail;
       this.sessionCode = this.session.session.code;
@@ -382,7 +476,7 @@ export class PlayerShellComponent implements OnInit, OnDestroy {
     try {
       const state = await this.controller.joinLobby(this.sessionCode, this.nickname);
       if (!state.session || state.errorMessage) {
-        throw new Error(state.errorMessage ?? 'Unknown error');
+        throw new Error(state.errorMessage ?? this.copy('common.unknown_error'));
       }
       this.session = state.session as SessionDetail;
       this.sessionCode = this.session.session.code;

frontend/angular/src/app/i18n-mvp-flow-smoke.spec.ts

@@ -26,19 +26,22 @@ describe('i18n MVP flow smoke (host/player + audio policy)', () => {
     host.ngOnInit();
     player.ngOnInit();
 
-    expect(host.copy('host.start_round')).toBe('Start round');
-    expect(player.copy('player.submit_guess')).toBe('Submit guess');
+    expect(host.copy('game.host.start_round')).toBe('Start round');
+    expect(player.copy('game.player.submit_guess')).toBe('Submit guess');
 
     setPreferredLocale('da');
 
-    expect(host.copy('host.start_round')).toBe('Start runde');
-    expect(player.copy('player.submit_guess')).toBe('Send gæt');
+    expect(host.copy('game.host.start_round')).toBe('Start runde');
+    expect(player.copy('game.player.submit_guess')).toBe('Send gæt');
 
     player.ngOnDestroy();
     host.ngOnDestroy();
   });
 
-  it('keeps audio routing policy primary-only (client has no audio output)', () => {
+  it('keeps audio routing policy primary-only (client has no audio output)', async () => {
+    const originalPlay = vi.fn().mockRejectedValue(new Error('original play'));
+    const mediaPrototype = { play: originalPlay };
+
     vi.stubGlobal('window', {
       location: { hash: '', search: '' },
       history: { state: null, replaceState: vi.fn() },
@@ -46,16 +49,25 @@ describe('i18n MVP flow smoke (host/player + audio policy)', () => {
       sessionStorage: { getItem: vi.fn().mockReturnValue(null), setItem: vi.fn(), removeItem: vi.fn() },
       addEventListener: vi.fn(),
       removeEventListener: vi.fn(),
+      HTMLMediaElement: { prototype: mediaPrototype },
     });
     vi.stubGlobal('navigator', { language: 'en-US', onLine: true });
+    vi.stubGlobal('document', { querySelectorAll: vi.fn().mockReturnValue([]) });
 
     const host = new HostShellComponent();
-    const player = new PlayerShellComponent();
+    host.ngOnInit();
 
-    expect(host.clientHasNoAudioOutput).toBe(true);
-    expect(player.clientHasNoAudioOutput).toBe(true);
+    await expect(mediaPrototype.play()).rejects.toThrow('original play');
+
+    const player = new PlayerShellComponent();
+    player.ngOnInit();
+
+    await expect(mediaPrototype.play()).resolves.toBeUndefined();
 
     player.ngOnDestroy();
+
+    await expect(mediaPrototype.play()).rejects.toThrow('original play');
+
     host.ngOnDestroy();
   });
 });

frontend/angular/src/app/lobby-i18n.spec.ts

@@ -45,6 +45,22 @@ describe('lobby i18n locale propagation', () => {
     expect(updates).toEqual(['en', 'da']);
   });
 
+  it('prefers backend-provided shell locale over browser defaults', async () => {
+    vi.stubGlobal('window', {
+      location: { search: '' },
+      localStorage: storageMock(),
+    });
+    vi.stubGlobal('document', {
+      body: { dataset: { wppLocale: 'da' } },
+      querySelector: vi.fn(() => null),
+    });
+    vi.stubGlobal('navigator', { language: 'en-US' });
+
+    const i18n = await import('./lobby-i18n');
+
+    expect(i18n.resolvePreferredLocale()).toBe('da');
+  });
+
   it('falls back to default en translation when da key is intentionally missing', async () => {
     vi.stubGlobal('window', {
       location: { search: '' },
@@ -77,6 +93,36 @@ describe('lobby i18n locale propagation', () => {
     }
   });
 
+  it('resolves baseline shell/game keys from shared namespaces', async () => {
+    vi.stubGlobal('window', {
+      location: { search: '' },
+      localStorage: storageMock({ 'wpp.locale': 'da' }),
+    });
+    vi.stubGlobal('navigator', { language: 'da-DK' });
+
+    const i18n = await import('./lobby-i18n');
+
+    const baselineKeys = [
+      'lobby.shell.title',
+      'lobby.shell.host_nav',
+      'lobby.shell.player_nav',
+      'lobby.shell.language_label',
+      'common.refresh',
+      'common.session_code',
+      'game.host.title',
+      'game.host.start_round',
+      'game.player.title',
+      'game.player.submit_guess',
+    ] as const;
+
+    for (const key of baselineKeys) {
+      const value = i18n.t(key, 'da');
+      expect(value).toBeTypeOf('string');
+      expect(value.length).toBeGreaterThan(0);
+      expect(value).not.toBe(key);
+    }
+  });
+
   it('exposes primary-only audio routing policy to clients', async () => {
     vi.stubGlobal('window', {
       location: { search: '' },

frontend/angular/src/app/lobby-i18n.ts

@@ -1,26 +1,15 @@
-import lobbyCatalog from '../../../../shared/i18n/lobby.json';
-
-type SupportedLocale = (typeof lobbyCatalog.locales.supported)[number];
-
-const DEFAULT_LOCALE = lobbyCatalog.locales.default as SupportedLocale;
-const SUPPORTED_LOCALES = lobbyCatalog.locales.supported as readonly SupportedLocale[];
+import {
+  DEFAULT_LOCALE,
+  LOBBY_I18N_CATALOG,
+  normalizeLocale,
+  type SupportedLocale,
+  translateCatalogPath,
+} from '../../../shared/i18n/lobby-loader';
 
 let activeLocale: SupportedLocale | null = null;
 const localeSubscribers = new Set<(locale: SupportedLocale) => void>();
 
-export function normalizeLocale(rawLocale?: string | null): SupportedLocale {
-  const locale = (rawLocale ?? '').trim().toLowerCase();
-  if ((SUPPORTED_LOCALES as readonly string[]).includes(locale)) {
-    return locale as SupportedLocale;
-  }
-
-  const shortLocale = locale.split('-')[0] ?? '';
-  if ((SUPPORTED_LOCALES as readonly string[]).includes(shortLocale)) {
-    return shortLocale as SupportedLocale;
-  }
-
-  return DEFAULT_LOCALE;
-}
+export { normalizeLocale };
 
 export function resolvePreferredLocale(): SupportedLocale {
   if (activeLocale) {
@@ -32,11 +21,14 @@ export function resolvePreferredLocale(): SupportedLocale {
     return activeLocale;
   }
 
+  const rootLocale =
+    typeof document !== 'undefined' ? document.querySelector<HTMLElement>('app-root')?.dataset?.['wppLocale'] : null;
+  const shellLocale = typeof document !== 'undefined' ? document.body?.dataset?.['wppLocale'] : null;
   const queryLocale = new URLSearchParams(window.location?.search ?? '').get('lang');
   const storedLocale = window.localStorage?.getItem?.('wpp.locale');
   const browserLocale = typeof navigator !== 'undefined' ? navigator.language : '';
 
-  activeLocale = normalizeLocale(queryLocale || storedLocale || browserLocale || DEFAULT_LOCALE);
+  activeLocale = normalizeLocale(rootLocale || shellLocale || queryLocale || storedLocale || browserLocale || DEFAULT_LOCALE);
   return activeLocale;
 }
 
@@ -62,25 +54,21 @@ export function subscribeToLocaleChanges(callback: (locale: SupportedLocale) =>
   };
 }
 
-export function t(key: string, locale: string): string {
-  const normalizedLocale = normalizeLocale(locale);
-  const fallbackLocale = DEFAULT_LOCALE;
-  const segments = key.split('.');
-
-  let cursor: unknown = lobbyCatalog.frontend.ui;
-  for (const segment of segments) {
-    if (!cursor || typeof cursor !== 'object' || !(segment in (cursor as Record<string, unknown>))) {
-      return key;
-    }
-    cursor = (cursor as Record<string, unknown>)[segment];
+function resolveCatalogPath(key: string): string {
+  if (key.startsWith('lobby.shell.')) {
+    return key.replace(/^lobby\.shell\./, 'app.');
   }
-
-  if (!cursor || typeof cursor !== 'object') {
-    return key;
+  if (key.startsWith('game.host.')) {
+    return key.replace(/^game\.host\./, 'host.');
   }
-
-  const translations = cursor as Record<string, string>;
-  return translations[normalizedLocale] ?? translations[fallbackLocale] ?? key;
+  if (key.startsWith('game.player.')) {
+    return key.replace(/^game\.player\./, 'player.');
+  }
+  return key;
 }
 
-export const clientHasNoAudioOutput = Boolean(lobbyCatalog.frontend.capabilities.client_has_no_audio_output);
+export function t(key: string, locale: string): string {
+  return translateCatalogPath(LOBBY_I18N_CATALOG.frontend.ui as Record<string, unknown>, resolveCatalogPath(key), locale);
+}
+
+export const clientHasNoAudioOutput = Boolean(LOBBY_I18N_CATALOG.frontend.capabilities.client_has_no_audio_output);

frontend/angular/src/app/session-route-context.spec.ts

@@ -69,6 +69,7 @@ describe('session route context', () => {
       sessionCode: 'AB12',
       playerId: 5,
       token: 'tok-5',
+      locale: 'en',
     });
   });
 
@@ -80,7 +81,25 @@ describe('session route context', () => {
       sessionCode: 'AB12',
       playerId: null,
       token: null,
+      locale: 'en',
     });
     expect(sessionStorage.setItem).toHaveBeenCalledWith('wpp.host-session-code', 'AB12');
   });
+
+  it('resolvers normalize and expose locale from lang query param', () => {
+    setWindow(storageMock(), storageMock());
+
+    expect(hostRouteContextResolver(route({}, { lang: 'da-DK' }) as never, {} as never).locale).toBe('da');
+    expect(playerRouteContextResolver(route({}, { lang: 'EN' }) as never, {} as never).locale).toBe('en');
+  });
+
+  it('does not reset persisted preferred locale when lang query param is absent', () => {
+    const localStorage = storageMock({ 'wpp.locale': 'da' });
+    setWindow(localStorage, storageMock());
+
+    expect(hostRouteContextResolver(route({}, { lang: 'da' }) as never, {} as never).locale).toBe('da');
+    expect(hostRouteContextResolver(route({}, {}) as never, {} as never).locale).toBe('da');
+    expect(localStorage.setItem).toHaveBeenCalledTimes(1);
+    expect(localStorage.setItem).toHaveBeenCalledWith('wpp.locale', 'da');
+  });
 });

frontend/angular/src/app/session-route-context.ts

@@ -2,11 +2,13 @@ import { inject } from '@angular/core';
 import { type ActivatedRouteSnapshot, type CanActivateFn, type ResolveFn, Router, type UrlTree } from '@angular/router';
 
 import { createSessionContextStore } from '../../../src/spa/session-context-store';
+import { normalizeLocale, resolvePreferredLocale, setPreferredLocale } from './lobby-i18n';
 
 export interface RouteSessionContext {
   sessionCode: string | null;
   playerId: number | null;
   token: string | null;
+  locale: string;
 }
 
 const HOST_STORAGE_KEY = 'wpp.host-session-code';
@@ -61,6 +63,17 @@ export function resolveSessionCode(route: ActivatedRouteSnapshot, mode: 'host' |
   return null;
 }
 
+function resolveRouteLocale(route: ActivatedRouteSnapshot): string {
+  const langParam = route.queryParamMap.get('lang');
+  if (langParam !== null) {
+    const locale = normalizeLocale(langParam);
+    setPreferredLocale(locale);
+    return locale;
+  }
+
+  return resolvePreferredLocale();
+}
+
 async function sessionExists(code: string): Promise<boolean> {
   const response = await fetch(`/lobby/sessions/${encodeURIComponent(code)}`, {
     method: 'GET',
@@ -118,23 +131,26 @@ export const playerRouteGuard: CanActivateFn = (route) => guard('player', route)
 
 export const hostRouteContextResolver: ResolveFn<RouteSessionContext> = (route) => {
   const code = resolveSessionCode(route, 'host');
+  const locale = resolveRouteLocale(route);
   if (code) {
     window.sessionStorage.setItem(HOST_STORAGE_KEY, code);
   }
-  return { sessionCode: code, playerId: null, token: null };
+  return { sessionCode: code, playerId: null, token: null, locale };
 };
 
 export const playerRouteContextResolver: ResolveFn<RouteSessionContext> = (route) => {
   const code = resolveSessionCode(route, 'player');
+  const locale = resolveRouteLocale(route);
   const context = createSessionContextStore(window.localStorage).get();
 
   if (!code || !context || normalizeCode(context.sessionCode) !== code) {
-    return { sessionCode: code, playerId: null, token: null };
+    return { sessionCode: code, playerId: null, token: null, locale };
   }
 
   return {
     sessionCode: code,
     playerId: Number.isInteger(context.playerId) && context.playerId > 0 ? context.playerId : null,
     token: context.token.trim() || null,
+    locale,
   };
 };

frontend/angular/src/app/wpp-api-client.spec.ts

@@ -0,0 +1,43 @@
+import { describe, expect, it, vi } from 'vitest';
+
+import { createWppApiClient } from './wpp-api-client';
+
+function jsonResponse(status: number, body: unknown) {
+  return {
+    ok: status >= 200 && status < 300,
+    status,
+    json: vi.fn().mockResolvedValue(body),
+  } as unknown as Response;
+}
+
+describe('WPP Angular API client skeleton', () => {
+  it('normalizes host/player API calls through fetch transport', async () => {
+    const fetchMock = vi
+      .fn()
+      .mockResolvedValueOnce(jsonResponse(200, { session: { code: 'ABCD12', status: 'lobby', host_id: 1, current_round: 1, players_count: 1 }, players: [], round_question: null, phase_view_model: { status: 'lobby', round_number: 1, players_count: 1, constraints: { min_players_to_start: 2, max_players_mvp: 8, min_players_reached: false, max_players_allowed: true }, host: { can_start_round: false, can_show_question: false, can_mix_answers: false, can_calculate_scores: false, can_reveal_scoreboard: false, can_start_next_round: false, can_finish_game: false }, player: { can_join: true, can_submit_lie: false, can_submit_guess: false, can_view_final_result: false } } }))
+      .mockResolvedValueOnce(jsonResponse(201, { player: { id: 1, nickname: 'Luna', session_token: 'tok', score: 0 }, session: { code: 'ABCD12', status: 'lobby' } }));
+
+    const client = createWppApiClient(fetchMock);
+
+    const session = await client.getSession(' abcd12 ');
+    const joined = await client.joinSession({ code: ' abcd12 ', nickname: ' Luna ' });
+
+    expect(session.ok).toBe(true);
+    expect(joined.ok).toBe(true);
+
+    expect(fetchMock).toHaveBeenNthCalledWith(
+      1,
+      '/lobby/sessions/ABCD12',
+      expect.objectContaining({ method: 'GET', credentials: 'same-origin' })
+    );
+    expect(fetchMock).toHaveBeenNthCalledWith(
+      2,
+      '/lobby/sessions/join',
+      expect.objectContaining({
+        method: 'POST',
+        credentials: 'same-origin',
+        body: JSON.stringify({ code: 'ABCD12', nickname: 'Luna' }),
+      })
+    );
+  });
+});

frontend/angular/src/app/wpp-api-client.ts

@@ -0,0 +1,58 @@
+import { InjectionToken } from '@angular/core';
+
+import {
+  createAngularApiClient,
+  type AngularApiClient,
+  type AngularHttpClientLike,
+} from '../../../src/api/angular-client';
+
+export const WPP_API_CLIENT = new InjectionToken<AngularApiClient>('WPP_API_CLIENT');
+
+export interface FetchLike {
+  (input: string, init?: RequestInit): Promise<Response>;
+}
+
+export function createFetchHttpClient(fetchImpl: FetchLike): AngularHttpClientLike {
+  return {
+    async get<T>(url: string): Promise<T> {
+      const response = await fetchImpl(url, {
+        method: 'GET',
+        headers: { Accept: 'application/json' },
+        credentials: 'same-origin',
+      });
+      const payload = await response.json().catch(() => ({}));
+      if (!response.ok) {
+        throw {
+          status: response.status,
+          message: (payload as { error?: string }).error ?? `HTTP ${response.status}`,
+          error: payload,
+        };
+      }
+      return payload as T;
+    },
+    async post<T>(url: string, body: unknown): Promise<T> {
+      const response = await fetchImpl(url, {
+        method: 'POST',
+        headers: {
+          Accept: 'application/json',
+          'Content-Type': 'application/json',
+        },
+        body: JSON.stringify(body),
+        credentials: 'same-origin',
+      });
+      const payload = await response.json().catch(() => ({}));
+      if (!response.ok) {
+        throw {
+          status: response.status,
+          message: (payload as { error?: string }).error ?? `HTTP ${response.status}`,
+          error: payload,
+        };
+      }
+      return payload as T;
+    },
+  };
+}
+
+export function createWppApiClient(fetchImpl: FetchLike = fetch.bind(globalThis)): AngularApiClient {
+  return createAngularApiClient(createFetchHttpClient(fetchImpl));
+}

frontend/shared/i18n/lobby-loader.ts

@@ -0,0 +1,74 @@
+import lobbyCatalog from '../../../shared/i18n/lobby.json';
+
+export type LobbyCatalog = typeof lobbyCatalog;
+export type SupportedLocale = LobbyCatalog['locales']['supported'][number];
+
+export const LOBBY_I18N_CATALOG = lobbyCatalog;
+export const DEFAULT_LOCALE = lobbyCatalog.locales.default as SupportedLocale;
+export const SUPPORTED_LOCALES = lobbyCatalog.locales.supported as readonly SupportedLocale[];
+
+export function normalizeLocale(rawLocale?: string | null): SupportedLocale {
+  const locale = (rawLocale ?? '').trim().toLowerCase().replace(/_/g, '-');
+  if ((SUPPORTED_LOCALES as readonly string[]).includes(locale)) {
+    return locale as SupportedLocale;
+  }
+
+  const shortLocale = locale.split('-')[0] ?? '';
+  if ((SUPPORTED_LOCALES as readonly string[]).includes(shortLocale)) {
+    return shortLocale as SupportedLocale;
+  }
+
+  return DEFAULT_LOCALE;
+}
+
+export function translateCatalogPath(
+  root: Record<string, unknown>,
+  keyPath: string,
+  locale: string,
+  fallback = DEFAULT_LOCALE,
+): string {
+  const normalizedLocale = normalizeLocale(locale);
+  const segments = keyPath.split('.');
+
+  let cursor: unknown = root;
+  for (const segment of segments) {
+    if (!cursor || typeof cursor !== 'object' || !(segment in (cursor as Record<string, unknown>))) {
+      return keyPath;
+    }
+    cursor = (cursor as Record<string, unknown>)[segment];
+  }
+
+  if (!cursor || typeof cursor !== 'object') {
+    return keyPath;
+  }
+
+  const translations = cursor as Record<string, string>;
+  return translations[normalizedLocale] ?? translations[fallback] ?? keyPath;
+}
+
+export function collectLocaleParityIssues(
+  node: unknown,
+  locales: readonly string[] = SUPPORTED_LOCALES,
+  path = '',
+): string[] {
+  if (!node || typeof node !== 'object') {
+    return [];
+  }
+
+  const record = node as Record<string, unknown>;
+  const keys = Object.keys(record);
+  const isTranslationLeaf = keys.length > 0 && locales.every((locale) => locale in record);
+
+  if (isTranslationLeaf) {
+    const issues: string[] = [];
+    for (const locale of locales) {
+      const value = record[locale];
+      if (typeof value !== 'string' || !value.trim()) {
+        issues.push(`${path || '<root>'} missing non-empty '${locale}' translation`);
+      }
+    }
+    return issues;
+  }
+
+  return keys.flatMap((key) => collectLocaleParityIssues(record[key], locales, path ? `${path}.${key}` : key));
+}

frontend/src/api/mappers.ts

@@ -4,6 +4,7 @@ import type {
   HealthResponse,
   JoinSessionResponse,
   MixAnswersResponse,
+  RevealPayload,
   ScoreboardResponse,
   SessionDetailResponse,
   ShowQuestionResponse,
@@ -68,6 +69,57 @@ export function mapHealthResponse(payload: unknown): HealthResponse {
   };
 }
 
+function mapRevealPayload(payload: unknown, path: string): RevealPayload {
+  const reveal = asRecord(payload, path);
+  const liesRaw = reveal.lies;
+  const guessesRaw = reveal.guesses;
+
+  if (!Array.isArray(liesRaw)) {
+    throw new Error(`Invalid API contract: expected array at ${path}.lies`);
+  }
+  if (!Array.isArray(guessesRaw)) {
+    throw new Error(`Invalid API contract: expected array at ${path}.guesses`);
+  }
+
+  return {
+    round_question_id: readNumber(reveal, 'round_question_id', path),
+    round_number: readNumber(reveal, 'round_number', path),
+    prompt: readString(reveal, 'prompt', path),
+    correct_answer: readString(reveal, 'correct_answer', path),
+    lies: liesRaw.map((lie, index) => {
+      const liePath = `${path}.lies[${index}]`;
+      const record = asRecord(lie, liePath);
+      return {
+        player_id: readNumber(record, 'player_id', liePath),
+        nickname: readString(record, 'nickname', liePath),
+        text: readString(record, 'text', liePath),
+        created_at: readString(record, 'created_at', liePath)
+      };
+    }),
+    guesses: guessesRaw.map((guess, index) => {
+      const guessPath = `${path}.guesses[${index}]`;
+      const record = asRecord(guess, guessPath);
+      const fooledPlayerId = record.fooled_player_id;
+      if (fooledPlayerId !== null && !isNumber(fooledPlayerId)) {
+        throw new Error(`Invalid API contract: expected number|null at ${guessPath}.fooled_player_id`);
+      }
+      const fooledPlayerNickname = record.fooled_player_nickname;
+      if (fooledPlayerNickname !== undefined && !isString(fooledPlayerNickname)) {
+        throw new Error(`Invalid API contract: expected string|undefined at ${guessPath}.fooled_player_nickname`);
+      }
+      return {
+        player_id: readNumber(record, 'player_id', guessPath),
+        nickname: readString(record, 'nickname', guessPath),
+        selected_text: readString(record, 'selected_text', guessPath),
+        is_correct: readBoolean(record, 'is_correct', guessPath),
+        created_at: readString(record, 'created_at', guessPath),
+        fooled_player_id: fooledPlayerId,
+        ...(fooledPlayerNickname === undefined ? {} : { fooled_player_nickname: fooledPlayerNickname })
+      };
+    })
+  };
+}
+
 function mapSessionDetail(payload: unknown): SessionDetailResponse {
   const root = asRecord(payload, 'session_detail');
   const session = asRecord(root.session, 'session_detail.session');
@@ -97,6 +149,7 @@ function mapSessionDetail(payload: unknown): SessionDetailResponse {
     };
   }
 
+  const revealRaw = root.reveal;
   const phase = asRecord(root.phase_view_model, 'session_detail.phase_view_model');
   const constraints = asRecord(phase.constraints, 'session_detail.phase_view_model.constraints');
   const host = asRecord(phase.host, 'session_detail.phase_view_model.host');
@@ -129,6 +182,7 @@ function mapSessionDetail(payload: unknown): SessionDetailResponse {
       };
     }),
     round_question: roundQuestion,
+    reveal: revealRaw === null || revealRaw === undefined ? null : mapRevealPayload(revealRaw, 'session_detail.reveal'),
     phase_view_model: {
       status: readString(phase, 'status', 'session_detail.phase_view_model'),
       round_number: readNumber(phase, 'round_number', 'session_detail.phase_view_model'),
@@ -276,6 +330,7 @@ export function mapCalculateScoresResponse(payload: unknown): CalculateScoresRes
       round_number: readNumber(roundQuestion, 'round_number', 'calculate_scores.round_question')
     },
     events_created: readNumber(root, 'events_created', 'calculate_scores'),
+    reveal: mapRevealPayload(root.reveal, 'calculate_scores.reveal'),
     leaderboard: leaderboardRaw.map((entry, index) => mapLeaderboardEntry(entry, `calculate_scores.leaderboard[${index}]`))
   };
 }

frontend/src/api/types.ts

@@ -57,10 +57,38 @@ export interface PhaseViewModel {
   };
 }
 
+export interface RevealPlayerRef {
+  player_id: number;
+  nickname: string;
+}
+
+export interface RevealLie extends RevealPlayerRef {
+  text: string;
+  created_at: string;
+}
+
+export interface RevealGuess extends RevealPlayerRef {
+  selected_text: string;
+  is_correct: boolean;
+  created_at: string;
+  fooled_player_id: number | null;
+  fooled_player_nickname?: string;
+}
+
+export interface RevealPayload {
+  round_question_id: number;
+  round_number: number;
+  prompt: string;
+  correct_answer: string;
+  lies: RevealLie[];
+  guesses: RevealGuess[];
+}
+
 export interface SessionDetailResponse {
   session: SessionSummary;
   players: SessionPlayer[];
   round_question: SessionRoundQuestion | null;
+  reveal: RevealPayload | null;
   phase_view_model: PhaseViewModel;
 }
 
@@ -138,6 +166,7 @@ export interface CalculateScoresResponse {
     round_number: number;
   };
   events_created: number;
+  reveal: RevealPayload;
   leaderboard: Array<{ id: number; nickname: string; score: number }>;
 }
 

frontend/src/spa/lobby-i18n.ts

@@ -1,23 +1,17 @@
-import lobbyCatalog from '../../../shared/i18n/lobby.json';
+import { DEFAULT_LOCALE, LOBBY_I18N_CATALOG, normalizeLocale } from '../../shared/i18n/lobby-loader';
 
-const frontendErrors = lobbyCatalog.frontend.errors;
-const localeConfig = lobbyCatalog.locales;
+const frontendErrors = LOBBY_I18N_CATALOG.frontend.errors;
+const backendToFrontendErrorKeys = LOBBY_I18N_CATALOG.contract.backend_to_frontend_error_keys as Record<
+  string,
+  keyof typeof frontendErrors
+>;
 
 type FrontendErrorKey = keyof typeof frontendErrors;
-type SupportedLocale = (typeof localeConfig.supported)[number];
 
 function isFrontendErrorKey(value: string): value is FrontendErrorKey {
   return value in frontendErrors;
 }
 
-function normalizeLocale(rawLocale?: string): SupportedLocale {
-  const requested = (rawLocale ?? '').trim().toLowerCase();
-  if (localeConfig.supported.includes(requested as SupportedLocale)) {
-    return requested as SupportedLocale;
-  }
-  return localeConfig.default;
-}
-
 export function lobbyMessage(key: FrontendErrorKey, locale?: string): string {
   const resolvedLocale = normalizeLocale(locale);
   const translations = frontendErrors[key] as Record<string, string>;
@@ -25,8 +19,8 @@ export function lobbyMessage(key: FrontendErrorKey, locale?: string): string {
   if (translations[resolvedLocale]) {
     return translations[resolvedLocale];
   }
-  if (translations[localeConfig.default]) {
-    return translations[localeConfig.default];
+  if (translations[DEFAULT_LOCALE]) {
+    return translations[DEFAULT_LOCALE];
   }
 
   return key;
@@ -40,9 +34,15 @@ export function lobbyMessageFromApiPayload(payload: unknown, fallbackKey: Fronte
   const record = payload as Record<string, unknown>;
   const code = typeof record.error_code === 'string' ? record.error_code : '';
   const payloadLocale = typeof record.locale === 'string' ? record.locale : locale;
-  if (!isFrontendErrorKey(code)) {
-    return lobbyMessage(fallbackKey, payloadLocale);
+  const mappedKey = code ? backendToFrontendErrorKeys[code] : undefined;
+
+  if (mappedKey && isFrontendErrorKey(mappedKey)) {
+    return lobbyMessage(mappedKey, payloadLocale);
   }
 
-  return lobbyMessage(code, payloadLocale);
+  if (isFrontendErrorKey(code)) {
+    return lobbyMessage(code, payloadLocale);
+  }
+
+  return lobbyMessage(fallbackKey, payloadLocale);
 }

frontend/tests/angular-api-client.test.ts

@@ -17,6 +17,7 @@ describe('createAngularApiClient', () => {
             { id: 3, nickname: 'Bo', score: 0, is_connected: false }
           ],
           round_question: null,
+          reveal: null,
           phase_view_model: {
             status: 'lobby',
             round_number: 1,
@@ -84,6 +85,7 @@ describe('createAngularApiClient', () => {
     if (session.ok) {
       expect(session.data.session.code).toBe('ABCD12');
       expect(session.data.session.host_id).toBe(1);
+      expect(session.data.reveal).toBeNull();
       expect(session.data.phase_view_model.host.can_start_round).toBe(true);
     }
 
@@ -119,6 +121,7 @@ describe('createAngularApiClient', () => {
           session: { code: 'ABCD12', status: 'lobby', host_id: 1, current_round: 1, players_count: 2 },
           players: [],
           round_question: null,
+          reveal: null,
           phase_view_model: {
             status: 'lobby',
             round_number: 1,
@@ -189,6 +192,117 @@ describe('createAngularApiClient', () => {
     );
   });
 
+  it('maps canonical reveal payload from session detail in reveal phase', async () => {
+    const get = vi.fn<AngularHttpClientLike['get']>(async <T>(url: string) => {
+      if (url === '/lobby/sessions/ABCD12') {
+        return {
+          session: { code: 'ABCD12', status: 'reveal', host_id: 1, current_round: 1, players_count: 3 },
+          players: [
+            { id: 2, nickname: 'Maja', score: 4, is_connected: true },
+            { id: 3, nickname: 'Bo', score: 2, is_connected: true },
+            { id: 4, nickname: 'Ida', score: 5, is_connected: true }
+          ],
+          round_question: {
+            id: 77,
+            round_number: 1,
+            prompt: 'Hvem opfandt pæren?',
+            shown_at: '2026-03-01T16:00:00Z',
+            answers: [{ text: 'Edison' }, { text: 'Tesla' }]
+          },
+          reveal: {
+            round_question_id: 77,
+            round_number: 1,
+            prompt: 'Hvem opfandt pæren?',
+            correct_answer: 'Edison',
+            lies: [
+              {
+                player_id: 3,
+                nickname: 'Bo',
+                text: 'Tesla',
+                created_at: '2026-03-01T16:00:20Z'
+              }
+            ],
+            guesses: [
+              {
+                player_id: 2,
+                nickname: 'Maja',
+                selected_text: 'Tesla',
+                is_correct: false,
+                fooled_player_id: 3,
+                fooled_player_nickname: 'Bo',
+                created_at: '2026-03-01T16:01:00Z'
+              },
+              {
+                player_id: 4,
+                nickname: 'Ida',
+                selected_text: 'Edison',
+                is_correct: true,
+                fooled_player_id: null,
+                created_at: '2026-03-01T16:01:02Z'
+              }
+            ]
+          },
+          phase_view_model: {
+            status: 'reveal',
+            round_number: 1,
+            players_count: 3,
+            constraints: {
+              min_players_to_start: 2,
+              max_players_mvp: 8,
+              min_players_reached: true,
+              max_players_allowed: true
+            },
+            host: {
+              can_start_round: false,
+              can_show_question: false,
+              can_mix_answers: false,
+              can_calculate_scores: false,
+              can_reveal_scoreboard: true,
+              can_start_next_round: true,
+              can_finish_game: true
+            },
+            player: {
+              can_join: false,
+              can_submit_lie: false,
+              can_submit_guess: false,
+              can_view_final_result: false
+            }
+          }
+        } as T;
+      }
+
+      throw { status: 404, error: { error: 'Not found' } };
+    });
+
+    const client = createAngularApiClient({ get, post: vi.fn() } as AngularHttpClientLike);
+    const session = await client.getSession('abcd12');
+
+    expect(session.ok).toBe(true);
+    if (session.ok) {
+      expect(session.data.reveal?.correct_answer).toBe('Edison');
+      expect(session.data.reveal?.lies[0]).toMatchObject({
+        player_id: 3,
+        nickname: 'Bo',
+        text: 'Tesla'
+      });
+      expect(session.data.reveal?.guesses[0]).toMatchObject({
+        player_id: 2,
+        nickname: 'Maja',
+        selected_text: 'Tesla',
+        is_correct: false,
+        fooled_player_id: 3,
+        fooled_player_nickname: 'Bo'
+      });
+      expect(session.data.reveal?.guesses[1]).toMatchObject({
+        player_id: 4,
+        nickname: 'Ida',
+        selected_text: 'Edison',
+        is_correct: true,
+        fooled_player_id: null
+      });
+    }
+  });
+
   it('returns parse error when successful payload breaks typed contract', async () => {
     const http = {
       get: vi.fn<AngularHttpClientLike['get']>(async <T>() => ({ ok: true } as T)),
@@ -248,6 +362,39 @@ describe('createAngularApiClient', () => {
           session: { code: 'ABCD12', status: 'reveal', current_round: 1 },
           round_question: { id: 77, round_number: 1 },
           events_created: 3,
+          reveal: {
+            round_question_id: 77,
+            round_number: 1,
+            prompt: 'Hvem opfandt pæren?',
+            correct_answer: 'Edison',
+            lies: [
+              {
+                player_id: 3,
+                nickname: 'Bo',
+                text: 'Tesla',
+                created_at: '2026-03-01T16:00:20Z'
+              }
+            ],
+            guesses: [
+              {
+                player_id: 2,
+                nickname: 'Maja',
+                selected_text: 'Tesla',
+                is_correct: false,
+                fooled_player_id: 3,
+                fooled_player_nickname: 'Bo',
+                created_at: '2026-03-01T16:01:00Z'
+              },
+              {
+                player_id: 4,
+                nickname: 'Ida',
+                selected_text: 'Edison',
+                is_correct: true,
+                fooled_player_id: null,
+                created_at: '2026-03-01T16:01:02Z'
+              }
+            ]
+          },
           leaderboard: [{ id: 2, nickname: 'Maja', score: 11 }]
         } as T;
       }
@@ -305,6 +452,29 @@ describe('createAngularApiClient', () => {
 
     const calculateScores = await client.calculateScores('abcd12', 77);
     expect(calculateScores.ok).toBe(true);
+    if (calculateScores.ok) {
+      expect(calculateScores.data.reveal.correct_answer).toBe('Edison');
+      expect(calculateScores.data.reveal.lies[0]).toMatchObject({
+        player_id: 3,
+        nickname: 'Bo',
+        text: 'Tesla'
+      });
+      expect(calculateScores.data.reveal.guesses[0]).toMatchObject({
+        player_id: 2,
+        nickname: 'Maja',
+        selected_text: 'Tesla',
+        is_correct: false,
+        fooled_player_id: 3,
+        fooled_player_nickname: 'Bo'
+      });
+      expect(calculateScores.data.reveal.guesses[1]).toMatchObject({
+        player_id: 4,
+        nickname: 'Ida',
+        selected_text: 'Edison',
+        is_correct: true,
+        fooled_player_id: null
+      });
+    }
 
     const scoreboard = await client.getScoreboard('abcd12');
     expect(scoreboard.ok).toBe(true);

frontend/tests/lobby-i18n.contract.test.ts

@@ -14,10 +14,16 @@ describe('shared i18n keyspace contract', () => {
     }
   });
 
-  it('keeps backend error-code keyspace aligned with backend translations', () => {
-    for (const [code, key] of Object.entries(lobbyCatalog.backend.error_codes)) {
-      expect(code).toBe(key);
-      expect(lobbyCatalog.backend.errors[key as keyof typeof lobbyCatalog.backend.errors]).toBeDefined();
+  it('keeps backend error-code keyspace aligned with shared backend→frontend map and backend translations', () => {
+    for (const [code, backendKey] of Object.entries(lobbyCatalog.backend.error_codes)) {
+      const frontendKey =
+        lobbyCatalog.contract.backend_to_frontend_error_keys[
+          code as keyof typeof lobbyCatalog.contract.backend_to_frontend_error_keys
+        ];
+
+      expect(lobbyCatalog.backend.errors[backendKey as keyof typeof lobbyCatalog.backend.errors]).toBeDefined();
+      expect(frontendKey, `missing frontend mapping for ${code}`).toBeTruthy();
+      expect(lobbyCatalog.frontend.errors[frontendKey as keyof typeof lobbyCatalog.frontend.errors]).toBeDefined();
     }
 
     for (const [key, translations] of Object.entries(lobbyCatalog.backend.errors)) {
@@ -42,10 +48,19 @@ describe('lobbyMessage locale handling', () => {
     ).toBe('Sessionskoden er ugyldig, eller sessionen findes ikke længere.');
   });
 
-  it('falls back when backend error code has no frontend translation key', () => {
+  it('uses shared backend→frontend key-map at runtime even when fallback key differs', () => {
     expect(
       lobbyMessageFromApiPayload(
         { error_code: 'session_not_joinable', locale: 'da' },
+        'start_round_failed',
+      ),
+    ).toBe('Kunne ikke joine. Tjek kode eller kaldenavn og prøv igen.');
+  });
+
+  it('falls back to caller-provided fallback key for unknown backend error codes', () => {
+    expect(
+      lobbyMessageFromApiPayload(
+        { error_code: 'unknown_backend_key', locale: 'da' },
         'join_failed',
       ),
     ).toBe('Kunne ikke joine. Tjek kode eller kaldenavn og prøv igen.');

frontend/tests/lobby-loader.parity.test.ts

@@ -0,0 +1,38 @@
+import { describe, expect, it } from 'vitest';
+
+import {
+  collectLocaleParityIssues,
+  LOBBY_I18N_CATALOG,
+  normalizeLocale,
+  SUPPORTED_LOCALES,
+  translateCatalogPath,
+} from '../shared/i18n/lobby-loader';
+
+describe('shared lobby i18n loader parity', () => {
+  it('keeps da/en translation parity in shared keyspace', () => {
+    const issues = collectLocaleParityIssues(LOBBY_I18N_CATALOG, SUPPORTED_LOCALES);
+    expect(issues).toEqual([]);
+  });
+
+  it('normalizes browser-style locale tags to supported keyspace locales', () => {
+    expect(normalizeLocale('da-DK')).toBe('da');
+    expect(normalizeLocale('da_DK')).toBe('da');
+    expect(normalizeLocale('en-US')).toBe('en');
+    expect(normalizeLocale('en_US')).toBe('en');
+    expect(normalizeLocale('fr-FR')).toBe('en');
+  });
+
+  it('resolves shared frontend ui keys with fallback-safe behavior', () => {
+    expect(
+      translateCatalogPath(LOBBY_I18N_CATALOG.frontend.ui as Record<string, unknown>, 'host.start_round', 'da-DK'),
+    ).toBe('Start runde');
+
+    expect(
+      translateCatalogPath(LOBBY_I18N_CATALOG.frontend.ui as Record<string, unknown>, 'app.language_label', 'en-US'),
+    ).toBe('Language');
+
+    expect(
+      translateCatalogPath(LOBBY_I18N_CATALOG.frontend.ui as Record<string, unknown>, 'host.non_existing_key', 'da'),
+    ).toBe('host.non_existing_key');
+  });
+});

lobby/i18n.py

@@ -1,42 +1,62 @@
-import json
 import logging
-from functools import lru_cache
-from pathlib import Path
 
 from django.http import HttpRequest, JsonResponse
 from django.utils.translation import get_language_from_request
 
+from partyhub.i18n_bootstrap import locale_config, shared_i18n_catalog
+
 LOGGER = logging.getLogger(__name__)
 
 
-@lru_cache(maxsize=1)
 def lobby_i18n_catalog() -> dict:
-    catalog_path = Path(__file__).resolve().parents[1] / "shared" / "i18n" / "lobby.json"
-    with catalog_path.open(encoding="utf-8") as handle:
-        return json.load(handle)
+    return shared_i18n_catalog()
 
 
-@lru_cache(maxsize=1)
 def i18n_locale_config() -> tuple[str, tuple[str, ...]]:
-    locales = lobby_i18n_catalog().get("locales", {})
-    default_locale = str(locales.get("default", "en")).strip().lower() or "en"
-    supported_locales = tuple(
-        locale.strip().lower() for locale in locales.get("supported", ["en", "da"]) if str(locale).strip()
-    ) or ("en", "da")
-    return default_locale, supported_locales
+    return locale_config()
 
 
 def lobby_i18n_errors() -> dict:
-    return lobby_i18n_catalog().get("backend", {}).get("error_codes", {})
+    return shared_i18n_catalog().get("backend", {}).get("error_codes", {})
 
 
 def lobby_i18n_error_messages() -> dict:
-    return lobby_i18n_catalog().get("backend", {}).get("errors", {})
+    return shared_i18n_catalog().get("backend", {}).get("errors", {})
+
+
+def _quality_value(language_candidate: str) -> float | None:
+    for parameter in language_candidate.split(";")[1:]:
+        key, separator, value = parameter.partition("=")
+        if separator and key.strip().lower() == "q":
+            try:
+                return float(value.strip())
+            except ValueError:
+                return None
+    return None
 
 
 def resolve_locale(request: HttpRequest) -> str:
     default_locale, supported_locales = i18n_locale_config()
-    requested = (get_language_from_request(request) or "").split("-", 1)[0].lower()
+
+    accept_language = request.META.get("HTTP_ACCEPT_LANGUAGE") or ""
+    ranked_candidates: list[tuple[float, int, str]] = []
+    for index, candidate in enumerate(accept_language.split(",")):
+        quality = _quality_value(candidate)
+        if quality is not None and quality <= 0:
+            continue
+
+        tag = candidate.split(";", 1)[0]
+        normalized = tag.strip().replace("_", "-").split("-", 1)[0].lower()
+        if normalized not in supported_locales:
+            continue
+
+        ranked_candidates.append((quality if quality is not None else 1.0, index, normalized))
+
+    if ranked_candidates:
+        ranked_candidates.sort(key=lambda entry: (-entry[0], entry[1]))
+        return ranked_candidates[0][2]
+
+    requested = (get_language_from_request(request) or "").replace("_", "-").split("-", 1)[0].lower()
     if requested in supported_locales:
         return requested
     return default_locale

lobby/templates/lobby/player_screen.html

@@ -89,6 +89,8 @@ var connectionRetryInFlight=false;
 var playerShellFatalError=false;
 var playerShellRecoverInFlight=false;
 var playerCriticalHydrated=false;
+function silencePlayerMediaElements(){if(typeof document==="undefined"||typeof document.querySelectorAll!=="function"){return;}var elements=document.querySelectorAll("audio,video");if(!elements||typeof elements.forEach!=="function"){return;}elements.forEach(function(element){if(!element){return;}element.muted=true;if(typeof element.pause==="function"){element.pause();}});}
+function installSecondaryDeviceAudioGuard(){if(typeof window==="undefined"){return;}silencePlayerMediaElements();var mediaProto=window.HTMLMediaElement&&window.HTMLMediaElement.prototype;if(!mediaProto||typeof mediaProto.play!=="function"){return;}if(mediaProto.__wppSecondaryDeviceAudioGuardInstalled){return;}mediaProto.__wppSecondaryDeviceAudioGuardInstalled=true;mediaProto.__wppSecondaryDeviceAudioGuardOriginalPlay=mediaProto.play;mediaProto.play=function(){return Promise.resolve();};}
 function setPlayerCriticalLoading(isLoading){var skeleton=document.getElementById("playerCriticalSkeleton");var view=document.getElementById("playerCriticalView");if(!skeleton||!view){return;}skeleton.style.display=isLoading?"block":"none";view.style.display=isLoading?"none":"block";}
 function hydratePlayerCriticalView(data){var phaseEl=document.getElementById("playerCriticalPhase");var roundEl=document.getElementById("playerCriticalRound");var joinEl=document.getElementById("playerCriticalJoin");if(phaseEl){phaseEl.textContent="Fase: "+phaseLabel(currentSessionStatus||((data&&data.session&&data.session.status)||""));}
 if(roundEl){roundEl.textContent="Round question: "+(rq()||"afventer");}
@@ -153,6 +155,7 @@ function submitGuess(){if(guessSubmitted){return Promise.resolve({error:"guess_a
 ["code","nickname","playerId","sessionToken","roundQuestionId"].forEach(function(fieldId){var field=document.getElementById(fieldId);if(!field){return;}field.addEventListener("input",function(){if(fieldId!=="roundQuestionId"){resetRoundContextForManualChange();}updateLieSubmitState();updateGuessSubmitState();updateJoinState();updateSessionDetailState();savePlayerContext();});field.addEventListener("change",function(){if(fieldId!=="roundQuestionId"){resetRoundContextForManualChange();}updateLieSubmitState();updateGuessSubmitState();updateJoinState();updateSessionDetailState();savePlayerContext();});});
 window.addEventListener("error",function(event){setPlayerShellFatalError((event&&event.message)||"Ukendt runtime-fejl");});
 window.addEventListener("unhandledrejection",function(event){var reason=event&&event.reason;var detail=(reason&&reason.message)||String(reason||"Unhandled promise rejection");setPlayerShellFatalError(detail);});
+installSecondaryDeviceAudioGuard();
 setPlayerCriticalLoading(true);
 updatePhaseStatus();
 updateGuessSubmitState();

lobby/templates/lobby/spa_shell.html

@@ -1,13 +1,13 @@
 <!doctype html>
-<html lang="da">
+<html lang="{{ shell_locale|default:'en' }}">
 <head>
   <meta charset="utf-8">
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <title>WPP SPA Shell</title>
   <link rel="stylesheet" href="{{ spa_asset_base }}/styles.css?v={{ spa_asset_version|urlencode }}">
 </head>
-<body data-wpp-shell-route="{{ shell_route }}" data-wpp-shell-kind="{{ shell_kind }}">
-  <app-root data-wpp-shell-route="{{ shell_route }}" data-wpp-shell-kind="{{ shell_kind }}">Indlæser Angular app-shell…</app-root>
+<body data-wpp-shell-route="{{ shell_route }}" data-wpp-shell-kind="{{ shell_kind }}" data-wpp-locale="{{ shell_locale|default:'en' }}">
+  <app-root data-wpp-shell-route="{{ shell_route }}" data-wpp-shell-kind="{{ shell_kind }}" data-wpp-locale="{{ shell_locale|default:'en' }}">Indlæser Angular app-shell…</app-root>
   <script type="module" src="{{ spa_asset_base }}/main.js?v={{ spa_asset_version|urlencode }}"></script>
 </body>
 </html>

lobby/tests.py

@@ -20,7 +20,7 @@ from fupogfakta.models import (
     RoundConfig,
     RoundQuestion,
 )
-from lobby.i18n import i18n_locale_config, lobby_i18n_catalog, resolve_error_message
+from lobby.i18n import i18n_locale_config, lobby_i18n_catalog, resolve_error_message, resolve_locale
 
 User = get_user_model()
 
@@ -138,6 +138,17 @@ class LobbyFlowTests(TestCase):
         self.assertEqual(response.json()["locale"], "en")
         self.assertEqual(response.json()["error"], "Session code is required")
 
+    def test_join_error_payload_uses_stable_i18n_contract_keys(self):
+        response = self.client.post(
+            reverse("lobby:join_session"),
+            data={"code": "   ", "nickname": "Luna"},
+            content_type="application/json",
+            HTTP_ACCEPT_LANGUAGE="da",
+        )
+
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(sorted(response.json().keys()), ["error", "error_code", "locale"])
+
     def test_session_detail_returns_players(self):
         session = GameSession.objects.create(host=self.host, code="LMNO45")
         Player.objects.create(session=session, nickname="Mia", score=7)
@@ -209,6 +220,8 @@ class StartRoundTests(TestCase):
         )
 
         self.assertEqual(response.status_code, 403)
+        self.assertEqual(response.json()["error_code"], "host_only_start_round")
+        self.assertEqual(response.json()["locale"], "en")
         self.assertEqual(response.json()["error"], "Only host can start round")
 
     def test_start_round_requires_existing_active_category_with_questions(self):
@@ -228,6 +241,8 @@ class StartRoundTests(TestCase):
             content_type="application/json",
         )
         self.assertEqual(response.status_code, 400)
+        self.assertEqual(response.json()["error_code"], "category_has_no_questions")
+        self.assertEqual(response.json()["locale"], "en")
         self.assertEqual(response.json()["error"], "Category has no active questions")
 
     def test_start_round_rejects_non_lobby_session(self):
@@ -244,6 +259,36 @@ class StartRoundTests(TestCase):
         self.assertEqual(response.status_code, 400)
         self.assertEqual(response.json()["error"], "Round can only be started from lobby")
 
+    def test_start_round_error_localizes_to_danish(self):
+        self.client.login(username="other", password="secret123")
+
+        response = self.client.post(
+            reverse("lobby:start_round", kwargs={"code": self.session.code}),
+            data={"category_slug": self.category.slug},
+            content_type="application/json",
+            HTTP_ACCEPT_LANGUAGE="da",
+        )
+
+        self.assertEqual(response.status_code, 403)
+        self.assertEqual(response.json()["error_code"], "host_only_start_round")
+        self.assertEqual(response.json()["locale"], "da")
+        self.assertEqual(response.json()["error"], "Kun værten kan starte runden")
+
+    def test_start_round_error_falls_back_to_english_for_unsupported_locale(self):
+        self.client.login(username="other", password="secret123")
+
+        response = self.client.post(
+            reverse("lobby:start_round", kwargs={"code": self.session.code}),
+            data={"category_slug": self.category.slug},
+            content_type="application/json",
+            HTTP_ACCEPT_LANGUAGE="fr",
+        )
+
+        self.assertEqual(response.status_code, 403)
+        self.assertEqual(response.json()["error_code"], "host_only_start_round")
+        self.assertEqual(response.json()["locale"], "en")
+        self.assertEqual(response.json()["error"], "Only host can start round")
+
 
 class LieSubmissionTests(TestCase):
     def setUp(self):
@@ -434,6 +479,8 @@ class MixAnswersTests(TestCase):
         )
 
         self.assertEqual(response.status_code, 403)
+        self.assertEqual(response.json()["error_code"], "host_only_mix_answers")
+        self.assertEqual(response.json()["locale"], "en")
         self.assertEqual(response.json()["error"], "Only host can mix answers")
 
     def test_mix_answers_deduplicates_case_insensitive_lies(self):
@@ -640,6 +687,7 @@ class ScoreCalculationTests(TestCase):
         self.player_three = Player.objects.create(session=self.session, nickname="Nora")
 
     def test_host_can_calculate_scores_and_transition_to_reveal(self):
+        LieAnswer.objects.create(round_question=self.round_question, player=self.player_three, text="Padel")
         Guess.objects.create(round_question=self.round_question, player=self.player_one, selected_text="Tennis", is_correct=True)
         Guess.objects.create(
             round_question=self.round_question,
@@ -668,6 +716,57 @@ class ScoreCalculationTests(TestCase):
         payload = response.json()
         self.assertEqual(payload["session"]["status"], GameSession.Status.REVEAL)
         self.assertEqual(payload["events_created"], 2)
+        self.assertEqual(payload["reveal"]["correct_answer"], "Tennis")
+        self.assertEqual(
+            payload["reveal"]["lies"],
+            [
+                {
+                    "player_id": self.player_three.id,
+                    "nickname": "Nora",
+                    "text": "Padel",
+                    "created_at": payload["reveal"]["lies"][0]["created_at"],
+                }
+            ],
+        )
+        self.assertEqual(
+            [
+                {
+                    "player_id": item["player_id"],
+                    "nickname": item["nickname"],
+                    "selected_text": item["selected_text"],
+                    "is_correct": item["is_correct"],
+                    "fooled_player_id": item["fooled_player_id"],
+                    "fooled_player_nickname": item.get("fooled_player_nickname"),
+                }
+                for item in payload["reveal"]["guesses"]
+            ],
+            [
+                {
+                    "player_id": self.player_one.id,
+                    "nickname": "Luna",
+                    "selected_text": "Tennis",
+                    "is_correct": True,
+                    "fooled_player_id": None,
+                    "fooled_player_nickname": None,
+                },
+                {
+                    "player_id": self.player_two.id,
+                    "nickname": "Mads",
+                    "selected_text": "Padel",
+                    "is_correct": False,
+                    "fooled_player_id": self.player_three.id,
+                    "fooled_player_nickname": "Nora",
+                },
+                {
+                    "player_id": self.player_three.id,
+                    "nickname": "Nora",
+                    "selected_text": "Padel",
+                    "is_correct": False,
+                    "fooled_player_id": self.player_three.id,
+                    "fooled_player_nickname": "Nora",
+                },
+            ],
+        )
 
         self.player_one.refresh_from_db()
         self.player_three.refresh_from_db()
@@ -999,6 +1098,10 @@ class UiScreenTests(TestCase):
         self.assertContains(response, "clearPlayerShellFatalError")
         self.assertContains(response, "updatePlayerShellErrorBoundary")
         self.assertContains(response, "player_shell_runtime_error")
+        self.assertContains(response, "installSecondaryDeviceAudioGuard")
+        self.assertContains(response, "silencePlayerMediaElements")
+        self.assertContains(response, "querySelectorAll(\"audio,video\")")
+        self.assertNotContains(response, "<audio")
         self.assertContains(response, "window.addEventListener(\"error\"")
 
     @override_settings(USE_SPA_UI=False)
@@ -1098,7 +1201,62 @@ class SessionDetailRoundQuestionTests(TestCase):
         self.assertEqual(payload["round_question"]["id"], round_question.id)
         self.assertEqual(payload["round_question"]["prompt"], self.question.prompt)
 
+    def test_session_detail_includes_reveal_payload_for_active_round_question(self):
+        self.session.status = GameSession.Status.REVEAL
+        self.session.save(update_fields=["status"])
+        round_question = RoundQuestion.objects.create(
+            session=self.session,
+            round_number=1,
+            question=self.question,
+            correct_answer=self.question.correct_answer,
+        )
+        liar = Player.objects.create(session=self.session, nickname="Bluffer")
+        guesser = Player.objects.create(session=self.session, nickname="Guesser")
+        LieAnswer.objects.create(round_question=round_question, player=liar, text="Tesla")
+        Guess.objects.create(
+            round_question=round_question,
+            player=guesser,
+            selected_text="Tesla",
+            is_correct=False,
+            fooled_player=liar,
+        )
 
+        response = self.client.get(reverse("lobby:session_detail", kwargs={"code": self.session.code}))
+
+        self.assertEqual(response.status_code, 200)
+        payload = response.json()
+        self.assertEqual(payload["reveal"]["round_question_id"], round_question.id)
+        self.assertEqual(payload["reveal"]["correct_answer"], "Edison")
+        self.assertEqual(
+            [
+                {"player_id": lie["player_id"], "nickname": lie["nickname"], "text": lie["text"]}
+                for lie in payload["reveal"]["lies"]
+            ],
+            [{"player_id": liar.id, "nickname": "Bluffer", "text": "Tesla"}],
+        )
+        self.assertEqual(
+            [
+                {
+                    "player_id": guess["player_id"],
+                    "nickname": guess["nickname"],
+                    "selected_text": guess["selected_text"],
+                    "is_correct": guess["is_correct"],
+                    "fooled_player_id": guess["fooled_player_id"],
+                    "fooled_player_nickname": guess.get("fooled_player_nickname"),
+                }
+                for guess in payload["reveal"]["guesses"]
+            ],
+            [
+                {
+                    "player_id": guesser.id,
+                    "nickname": "Guesser",
+                    "selected_text": "Tesla",
+                    "is_correct": False,
+                    "fooled_player_id": liar.id,
+                    "fooled_player_nickname": "Bluffer",
+                }
+            ],
+        )
 
 
 class SessionDetailPhaseViewModelTests(TestCase):
@@ -1216,6 +1374,71 @@ class SmokeStagingCommandTests(TestCase):
 
 
 class I18nResolverTests(TestCase):
+    def test_resolve_locale_accepts_language_tags_and_normalizes_to_supported_base_locale(self):
+        response = self.client.post(
+            reverse("lobby:join_session"),
+            data={"code": "", "nickname": "Luna"},
+            content_type="application/json",
+            HTTP_ACCEPT_LANGUAGE="da-DK,da;q=0.9,en;q=0.8",
+        )
+
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(resolve_locale(response.wsgi_request), "da")
+
+    def test_resolve_locale_accepts_underscore_language_tags(self):
+        response = self.client.post(
+            reverse("lobby:join_session"),
+            data={"code": "", "nickname": "Luna"},
+            content_type="application/json",
+            HTTP_ACCEPT_LANGUAGE="da_DK",
+        )
+
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(resolve_locale(response.wsgi_request), "da")
+
+    def test_resolve_locale_uses_next_supported_language_when_primary_is_unsupported(self):
+        response = self.client.post(
+            reverse("lobby:join_session"),
+            data={"code": "", "nickname": "Luna"},
+            content_type="application/json",
+            HTTP_ACCEPT_LANGUAGE="fr-FR, da;q=0.9, en;q=0.8",
+        )
+
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(resolve_locale(response.wsgi_request), "da")
+
+    def test_resolve_locale_skips_q0_languages_and_falls_back_to_next_supported(self):
+        response = self.client.post(
+            reverse("lobby:join_session"),
+            data={"code": "", "nickname": "Luna"},
+            content_type="application/json",
+            HTTP_ACCEPT_LANGUAGE="da;q=0, en;q=0.8",
+        )
+
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(resolve_locale(response.wsgi_request), "en")
+
+    def test_resolve_locale_prefers_highest_quality_supported_language(self):
+        response = self.client.post(
+            reverse("lobby:join_session"),
+            data={"code": "", "nickname": "Luna"},
+            content_type="application/json",
+            HTTP_ACCEPT_LANGUAGE="da;q=0.8, en;q=0.9",
+        )
+
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(resolve_locale(response.wsgi_request), "en")
+
+    def test_resolve_locale_defaults_to_en_when_header_missing(self):
+        response = self.client.post(
+            reverse("lobby:join_session"),
+            data={"code": "", "nickname": "Luna"},
+            content_type="application/json",
+        )
+
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(resolve_locale(response.wsgi_request), "en")
+
     def test_missing_backend_key_returns_key_deterministically(self):
         self.assertEqual(resolve_error_message(key="missing_key", locale="da"), "missing_key")
 
@@ -1252,10 +1475,14 @@ class I18nResolverTests(TestCase):
             self.assertTrue(translations.get("en"), f"frontend key {key} missing en")
             self.assertTrue(translations.get("da"), f"frontend key {key} missing da")
 
-    def test_backend_error_codes_map_to_same_named_translation_keys(self):
+    def test_backend_error_codes_map_via_shared_backend_frontend_key_map(self):
         catalog = lobby_i18n_catalog()
         backend_errors = catalog["backend"]["errors"]
+        frontend_errors = catalog["frontend"]["errors"]
+        shared_map = catalog["contract"]["backend_to_frontend_error_keys"]
 
-        for code, key in catalog["backend"]["error_codes"].items():
-            self.assertEqual(code, key)
-            self.assertIn(key, backend_errors)
+        for code, backend_key in catalog["backend"]["error_codes"].items():
+            frontend_key = shared_map.get(code)
+            self.assertIn(backend_key, backend_errors)
+            self.assertTrue(frontend_key, f"missing frontend mapping for backend code: {code}")
+            self.assertIn(frontend_key, frontend_errors)

lobby/ui_views.py

@@ -5,7 +5,7 @@ from django.shortcuts import render
 from fupogfakta.models import Category
 
 from .feature_flags import use_spa_ui
-from .i18n import lobby_i18n_catalog
+from .i18n import lobby_i18n_catalog, resolve_locale
 
 
 def _render_spa_shell(request, shell_route: str, shell_kind: str):
@@ -18,6 +18,7 @@ def _render_spa_shell(request, shell_route: str, shell_kind: str):
             "spa_asset_base": settings.WPP_SPA_ASSET_BASE,
             "spa_asset_version": getattr(settings, "WPP_SPA_ASSET_VERSION", "dev"),
             "lobby_i18n": lobby_i18n_catalog(),
+            "shell_locale": resolve_locale(request),
         },
     )
 

lobby/views.py

@@ -61,6 +61,52 @@ def _create_unique_session_code() -> str:
     raise RuntimeError("Could not generate unique session code")
 
 
+def _build_player_ref(player: Player | None) -> dict | None:
+    if player is None:
+        return None
+
+    return {
+        "player_id": player.id,
+        "nickname": player.nickname,
+    }
+
+
+def _build_reveal_payload(round_question: RoundQuestion | None) -> dict | None:
+    if round_question is None:
+        return None
+
+    lies = [
+        {
+            **_build_player_ref(lie.player),
+            "text": lie.text,
+            "created_at": lie.created_at.isoformat(),
+        }
+        for lie in round_question.lies.select_related("player").order_by("created_at", "id")
+    ]
+
+    guesses = []
+    for guess in round_question.guesses.select_related("player", "fooled_player").order_by("created_at", "id"):
+        guess_payload = {
+            **_build_player_ref(guess.player),
+            "selected_text": guess.selected_text,
+            "is_correct": guess.is_correct,
+            "created_at": guess.created_at.isoformat(),
+            "fooled_player_id": guess.fooled_player_id,
+        }
+        if guess.fooled_player is not None:
+            guess_payload["fooled_player_nickname"] = guess.fooled_player.nickname
+        guesses.append(guess_payload)
+
+    return {
+        "round_question_id": round_question.id,
+        "round_number": round_question.round_number,
+        "prompt": round_question.question.prompt,
+        "correct_answer": round_question.correct_answer,
+        "lies": lies,
+        "guesses": guesses,
+    }
+
+
 def _build_phase_view_model(session: GameSession, *, players_count: int, has_round_question: bool) -> dict:
     status = session.status
     in_lobby = status == GameSession.Status.LOBBY
@@ -238,6 +284,9 @@ def session_detail(request: HttpRequest, code: str) -> JsonResponse:
             },
             "players": players,
             "round_question": round_question_payload,
+            "reveal": _build_reveal_payload(current_round_question)
+            if session.status == GameSession.Status.REVEAL and current_round_question
+            else None,
             "phase_view_model": phase_view_model,
         }
     )
@@ -268,7 +317,11 @@ def start_round(request: HttpRequest, code: str) -> JsonResponse:
         )
 
     if session.host_id != request.user.id:
-        return JsonResponse({"error": "Only host can start round"}, status=403)
+        return api_error(
+            request,
+            key=ERROR_CODES.get("host_only_start_round", "host_only_start_round"),
+            status=403,
+        )
 
     if session.status != GameSession.Status.LOBBY:
         return api_error(
@@ -287,7 +340,11 @@ def start_round(request: HttpRequest, code: str) -> JsonResponse:
         )
 
     if not Question.objects.filter(category=category, is_active=True).exists():
-        return JsonResponse({"error": "Category has no active questions"}, status=400)
+        return api_error(
+            request,
+            key=ERROR_CODES.get("category_has_no_questions", "category_has_no_questions"),
+            status=400,
+        )
 
     with transaction.atomic():
         session = GameSession.objects.select_for_update().get(pk=session.pk)
@@ -340,21 +397,41 @@ def show_question(request: HttpRequest, code: str) -> JsonResponse:
     try:
         session = GameSession.objects.get(code=session_code)
     except GameSession.DoesNotExist:
-        return JsonResponse({"error": "Session not found"}, status=404)
+        return api_error(
+            request,
+            key=ERROR_CODES.get("session_not_found", "session_not_found"),
+            status=404,
+        )
 
     if session.host_id != request.user.id:
-        return JsonResponse({"error": "Only host can show question"}, status=403)
+        return api_error(
+            request,
+            key=ERROR_CODES.get("host_only_show_question", "host_only_show_question"),
+            status=403,
+        )
 
     if session.status != GameSession.Status.LIE:
-        return JsonResponse({"error": "Question can only be shown in lie phase"}, status=400)
+        return api_error(
+            request,
+            key=ERROR_CODES.get("show_question_invalid_phase", "show_question_invalid_phase"),
+            status=400,
+        )
 
     try:
         round_config = RoundConfig.objects.get(session=session, number=session.current_round)
     except RoundConfig.DoesNotExist:
-        return JsonResponse({"error": "Round config missing"}, status=400)
+        return api_error(
+            request,
+            key=ERROR_CODES.get("round_config_missing", "round_config_missing"),
+            status=400,
+        )
 
     if RoundQuestion.objects.filter(session=session, round_number=session.current_round).exists():
-        return JsonResponse({"error": "Question already shown for this round"}, status=409)
+        return api_error(
+            request,
+            key=ERROR_CODES.get("question_already_shown", "question_already_shown"),
+            status=409,
+        )
 
     used_question_ids = RoundQuestion.objects.filter(session=session).values_list("question_id", flat=True)
     available_questions = Question.objects.filter(
@@ -363,7 +440,11 @@ def show_question(request: HttpRequest, code: str) -> JsonResponse:
     ).exclude(pk__in=used_question_ids)
 
     if not available_questions.exists():
-        return JsonResponse({"error": "No available questions in category"}, status=400)
+        return api_error(
+            request,
+            key=ERROR_CODES.get("no_available_questions", "no_available_questions"),
+            status=400,
+        )
 
     question = random.choice(list(available_questions))
     round_question = RoundQuestion.objects.create(
@@ -473,13 +554,25 @@ def mix_answers(request: HttpRequest, code: str, round_question_id: int) -> Json
     try:
         session = GameSession.objects.get(code=session_code)
     except GameSession.DoesNotExist:
-        return JsonResponse({"error": "Session not found"}, status=404)
+        return api_error(
+            request,
+            key=ERROR_CODES.get("session_not_found", "session_not_found"),
+            status=404,
+        )
 
     if session.host_id != request.user.id:
-        return JsonResponse({"error": "Only host can mix answers"}, status=403)
+        return api_error(
+            request,
+            key=ERROR_CODES.get("host_only_mix_answers", "host_only_mix_answers"),
+            status=403,
+        )
 
     if session.status not in {GameSession.Status.LIE, GameSession.Status.GUESS}:
-        return JsonResponse({"error": "Answers can only be mixed in lie or guess phase"}, status=400)
+        return api_error(
+            request,
+            key=ERROR_CODES.get("mix_answers_invalid_phase", "mix_answers_invalid_phase"),
+            status=400,
+        )
 
     try:
         round_question = RoundQuestion.objects.get(
@@ -488,12 +581,20 @@ def mix_answers(request: HttpRequest, code: str, round_question_id: int) -> Json
             round_number=session.current_round,
         )
     except RoundQuestion.DoesNotExist:
-        return JsonResponse({"error": "Round question not found"}, status=404)
+        return api_error(
+            request,
+            key=ERROR_CODES.get("round_question_not_found", "round_question_not_found"),
+            status=404,
+        )
 
     with transaction.atomic():
         locked_session = GameSession.objects.select_for_update().get(pk=session.pk)
         if locked_session.status not in {GameSession.Status.LIE, GameSession.Status.GUESS}:
-            return JsonResponse({"error": "Answers can only be mixed in lie or guess phase"}, status=400)
+            return api_error(
+                request,
+                key=ERROR_CODES.get("mix_answers_invalid_phase", "mix_answers_invalid_phase"),
+                status=400,
+            )
 
         locked_round_question = RoundQuestion.objects.select_for_update().get(pk=round_question.pk)
 
@@ -509,7 +610,11 @@ def mix_answers(request: HttpRequest, code: str, round_question_id: int) -> Json
                 deduped_answers.append(text.strip())
 
             if len(deduped_answers) < 2:
-                return JsonResponse({"error": "Not enough answers to mix"}, status=400)
+                return api_error(
+                    request,
+                    key=ERROR_CODES.get("not_enough_answers_to_mix", "not_enough_answers_to_mix"),
+                    status=400,
+                )
 
             random.shuffle(deduped_answers)
             locked_round_question.mixed_answers = deduped_answers
@@ -853,6 +958,7 @@ def calculate_scores(request: HttpRequest, code: str, round_question_id: int) ->
                 "id": round_question.id,
                 "round_number": round_question.round_number,
             },
+            "reveal": _build_reveal_payload(round_question),
             "events_created": len(score_events),
             "leaderboard": leaderboard,
         }

partyhub/i18n_bootstrap.py

@@ -0,0 +1,30 @@
+import json
+from functools import lru_cache
+from pathlib import Path
+
+_LOCALE_LABELS = {
+    "en": "English",
+    "da": "Danish",
+}
+
+
+@lru_cache(maxsize=1)
+def shared_i18n_catalog() -> dict:
+    catalog_path = Path(__file__).resolve().parents[1] / "shared" / "i18n" / "lobby.json"
+    with catalog_path.open(encoding="utf-8") as handle:
+        return json.load(handle)
+
+
+@lru_cache(maxsize=1)
+def locale_config() -> tuple[str, tuple[str, ...]]:
+    locales = shared_i18n_catalog().get("locales", {})
+    default_locale = str(locales.get("default", "en")).strip().lower() or "en"
+    supported_locales = tuple(
+        locale.strip().lower() for locale in locales.get("supported", ["en", "da"]) if str(locale).strip()
+    ) or ("en", "da")
+    return default_locale, supported_locales
+
+
+def django_languages() -> list[tuple[str, str]]:
+    _default_locale, supported_locales = locale_config()
+    return [(locale, _LOCALE_LABELS.get(locale, locale.upper())) for locale in supported_locales]

partyhub/settings.py

@@ -1,6 +1,8 @@
 from pathlib import Path
 import os
 
+from partyhub.i18n_bootstrap import django_languages, locale_config
+
 BASE_DIR = Path(__file__).resolve().parent.parent
 
 
@@ -90,11 +92,8 @@ AUTH_PASSWORD_VALIDATORS = [
     {'NAME': 'django.contrib.auth.password_validation.NumericPasswordValidator'},
 ]
 
-LANGUAGE_CODE = 'en'
-LANGUAGES = [
-    ('en', 'English'),
-    ('da', 'Danish'),
-]
+LANGUAGE_CODE, _SUPPORTED_LOCALES = locale_config()
+LANGUAGES = django_languages()
 LOCALE_PATHS = [BASE_DIR / 'locale']
 TIME_ZONE = 'Europe/Copenhagen'
 USE_I18N = True

partyhub/tests_i18n_bootstrap.py

@@ -0,0 +1,28 @@
+from django.conf import settings
+from django.test import TestCase
+
+from partyhub.i18n_bootstrap import django_languages, locale_config, shared_i18n_catalog
+
+
+class I18nBootstrapTests(TestCase):
+    def test_shared_catalog_bootstraps_default_and_supported_locales(self):
+        default_locale, supported_locales = locale_config()
+
+        self.assertEqual(default_locale, "en")
+        self.assertEqual(supported_locales, ("en", "da"))
+
+    def test_django_language_settings_bootstrap_from_shared_i18n_catalog(self):
+        default_locale, supported_locales = locale_config()
+
+        self.assertEqual(settings.LANGUAGE_CODE, default_locale)
+        self.assertEqual(tuple(code for code, _ in settings.LANGUAGES), supported_locales)
+        self.assertEqual(settings.LANGUAGES, django_languages())
+
+    def test_locale_contract_in_catalog_matches_django_language_codes(self):
+        catalog_locales = shared_i18n_catalog()["locales"]
+
+        self.assertEqual(settings.LANGUAGE_CODE, catalog_locales["default"])
+        self.assertEqual(
+            [code for code, _ in settings.LANGUAGES],
+            catalog_locales["supported"],
+        )

scripts/build_i18n_parity_report.py

@@ -0,0 +1,214 @@
+#!/usr/bin/env python3
+"""Build the shared i18n parity artifact for MVP-critical Django/Angular keys."""
+
+from __future__ import annotations
+
+import argparse
+import hashlib
+import json
+import re
+from collections import defaultdict
+from pathlib import Path
+from typing import Any
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+CATALOG_PATH = REPO_ROOT / "shared" / "i18n" / "lobby.json"
+ARTIFACT_PATH = REPO_ROOT / "shared" / "i18n" / "artifacts" / "lobby-mvp-keyspace-parity-report.v1.json"
+DJANGO_VIEWS_PATH = REPO_ROOT / "lobby" / "views.py"
+FRONTEND_VERTICAL_SLICE_PATH = REPO_ROOT / "frontend" / "src" / "spa" / "vertical-slice.ts"
+ANGULAR_I18N_PATH = REPO_ROOT / "frontend" / "angular" / "src" / "app" / "lobby-i18n.ts"
+ANGULAR_HOST_PATH = REPO_ROOT / "frontend" / "angular" / "src" / "app" / "features" / "host" / "host-shell.component.ts"
+ANGULAR_PLAYER_PATH = REPO_ROOT / "frontend" / "angular" / "src" / "app" / "features" / "player" / "player-shell.component.ts"
+
+ARTIFACT_NAME = "shared.i18n.lobby.mvp_keyspace_parity_report"
+ARTIFACT_VERSION = "v1"
+
+
+class ParityError(RuntimeError):
+    pass
+
+
+def _read_text(path: Path) -> str:
+    return path.read_text(encoding="utf-8")
+
+
+def _load_catalog() -> dict[str, Any]:
+    return json.loads(_read_text(CATALOG_PATH))
+
+
+def _catalog_hash() -> str:
+    return hashlib.sha256(CATALOG_PATH.read_bytes()).hexdigest()
+
+
+def _sorted_unique(values: list[str]) -> list[str]:
+    return sorted({value for value in values})
+
+
+def _extract_matches(path: Path, pattern: str) -> list[str]:
+    return re.findall(pattern, _read_text(path), re.MULTILINE)
+
+
+def _resolve_frontend_ui_key(key: str) -> str:
+    if key.startswith("lobby.shell."):
+        return key.replace("lobby.shell.", "app.", 1)
+    if key.startswith("game.host."):
+        return key.replace("game.host.", "host.", 1)
+    if key.startswith("game.player."):
+        return key.replace("game.player.", "player.", 1)
+    return key
+
+
+def _has_nested_key(root: dict[str, Any], dotted_key: str) -> bool:
+    current: Any = root
+    for part in dotted_key.split("."):
+        if not isinstance(current, dict) or part not in current:
+            return False
+        current = current[part]
+    return isinstance(current, dict)
+
+
+def build_report() -> dict[str, Any]:
+    catalog = _load_catalog()
+    locales = list(catalog["locales"]["supported"])
+    frontend_errors: dict[str, Any] = catalog["frontend"]["errors"]
+    frontend_ui: dict[str, Any] = catalog["frontend"]["ui"]
+    backend_error_codes: dict[str, str] = catalog["backend"]["error_codes"]
+    backend_errors: dict[str, Any] = catalog["backend"]["errors"]
+    backend_to_frontend: dict[str, str] = catalog["contract"]["backend_to_frontend_error_keys"]
+
+    django_error_codes = _sorted_unique(
+        _extract_matches(DJANGO_VIEWS_PATH, r'ERROR_CODES\.get\("([a-z0-9_]+)"')
+    )
+    frontend_runtime_error_fallbacks = _sorted_unique(
+        _extract_matches(FRONTEND_VERTICAL_SLICE_PATH, r"lobbyMessageFromApiPayload\([^\n]+?'([a-z0-9_]+)'\)")
+        + _extract_matches(FRONTEND_VERTICAL_SLICE_PATH, r"lobbyMessage\('([a-z0-9_]+)'\)")
+    )
+    angular_copy_keys = _sorted_unique(
+        _extract_matches(ANGULAR_HOST_PATH, r"copy\('([A-Za-z0-9_\.]+)'\)")
+        + _extract_matches(ANGULAR_PLAYER_PATH, r"copy\('([A-Za-z0-9_\.]+)'\)")
+    )
+    angular_catalog_paths = [_resolve_frontend_ui_key(key) for key in angular_copy_keys]
+
+    missing_backend_codes = [code for code in django_error_codes if code not in backend_error_codes]
+    missing_backend_translations = [code for code in django_error_codes if code not in backend_errors]
+    missing_contract_mappings = [code for code in django_error_codes if code not in backend_to_frontend]
+    mapped_frontend_error_keys = _sorted_unique(
+        [backend_to_frontend[code] for code in django_error_codes if code in backend_to_frontend]
+    )
+    missing_frontend_error_keys = [key for key in mapped_frontend_error_keys if key not in frontend_errors]
+    missing_frontend_runtime_fallbacks = [key for key in frontend_runtime_error_fallbacks if key not in frontend_errors]
+    missing_angular_catalog_paths = [path for path in angular_catalog_paths if not _has_nested_key(frontend_ui, path)]
+
+    dead_contract_aliases = _sorted_unique([code for code in backend_to_frontend if code not in backend_error_codes])
+    many_to_one_mappings: dict[str, list[str]] = defaultdict(list)
+    for code in django_error_codes:
+        frontend_key = backend_to_frontend.get(code)
+        if frontend_key:
+            many_to_one_mappings[frontend_key].append(code)
+    many_to_one_mappings = {
+        frontend_key: sorted(codes)
+        for frontend_key, codes in sorted(many_to_one_mappings.items())
+        if len(codes) > 1
+    }
+
+    blocking_issues = {
+        "missing_backend_codes": missing_backend_codes,
+        "missing_backend_translations": missing_backend_translations,
+        "missing_contract_mappings": missing_contract_mappings,
+        "missing_frontend_error_keys": missing_frontend_error_keys,
+        "missing_frontend_runtime_fallbacks": missing_frontend_runtime_fallbacks,
+        "missing_angular_catalog_paths": missing_angular_catalog_paths,
+    }
+    status = "pass" if not any(blocking_issues.values()) else "fail"
+
+    follow_ups: list[dict[str, str]] = []
+    if dead_contract_aliases:
+        follow_ups.append(
+            {
+                "priority": "need-to-have",
+                "item": "Either add missing backend/error_codes + backend/errors entries for dead contract aliases or remove them from contract.backend_to_frontend_error_keys.",
+                "evidence": ", ".join(dead_contract_aliases),
+            }
+        )
+    if many_to_one_mappings:
+        follow_ups.append(
+            {
+                "priority": "nice-to-have",
+                "item": "Decide whether grouped backend codes should keep collapsing into one Angular fallback key or be split into more specific frontend error copy as UX matures.",
+                "evidence": "; ".join(
+                    f"{frontend_key} <= {', '.join(codes)}" for frontend_key, codes in many_to_one_mappings.items()
+                ),
+            }
+        )
+
+    return {
+        "artifact_name": ARTIFACT_NAME,
+        "artifact_version": ARTIFACT_VERSION,
+        "naming_version_rule": "Keep a stable artifact_name and append only explicit schema-major suffixes to the filename/version (v1, v2, ...). Update artifact_version only when the report shape changes; refresh content in-place for catalog/keyspace changes.",
+        "source_of_truth": {
+            "catalog": str(CATALOG_PATH.relative_to(REPO_ROOT)),
+            "catalog_sha256": _catalog_hash(),
+            "source_paths": [
+                str(path.relative_to(REPO_ROOT))
+                for path in [
+                    DJANGO_VIEWS_PATH,
+                    FRONTEND_VERTICAL_SLICE_PATH,
+                    ANGULAR_I18N_PATH,
+                    ANGULAR_HOST_PATH,
+                    ANGULAR_PLAYER_PATH,
+                ]
+            ],
+        },
+        "scope": {
+            "issue": 277,
+            "related_epic": 175,
+            "mvp_locales": locales,
+            "definition": "MVP-critical keys are the Django error codes emitted by lobby/views.py plus the Angular fallback/UI keys consumed by the host/player MVP shells.",
+        },
+        "parity": {
+            "status": status,
+            "django_backend_error_codes_used_by_mvp": django_error_codes,
+            "angular_frontend_error_fallback_keys_used_by_mvp": frontend_runtime_error_fallbacks,
+            "angular_ui_keys_used_by_mvp": angular_copy_keys,
+            "angular_ui_catalog_paths": angular_catalog_paths,
+            "backend_codes_mapped_to_frontend_error_keys": {code: backend_to_frontend[code] for code in django_error_codes if code in backend_to_frontend},
+            "unique_frontend_error_keys_reached_from_django": mapped_frontend_error_keys,
+            "blocking_issues": blocking_issues,
+            "follow_ups": follow_ups,
+        },
+    }
+
+
+def write_report() -> None:
+    report = build_report()
+    ARTIFACT_PATH.parent.mkdir(parents=True, exist_ok=True)
+    ARTIFACT_PATH.write_text(json.dumps(report, indent=2, ensure_ascii=False) + "\n", encoding="utf-8")
+
+
+def check_report() -> None:
+    report = build_report()
+    if not ARTIFACT_PATH.exists():
+        raise ParityError(f"artifact missing: {ARTIFACT_PATH}")
+    existing = json.loads(_read_text(ARTIFACT_PATH))
+    if existing != report:
+        raise ParityError("artifact out of date; run scripts/build_i18n_parity_report.py --write")
+    if report["parity"]["status"] != "pass":
+        raise ParityError(json.dumps(report["parity"]["blocking_issues"], indent=2))
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--write", action="store_true")
+    parser.add_argument("--check", action="store_true")
+    args = parser.parse_args()
+    if args.write:
+        write_report()
+    if args.check:
+        check_report()
+    if not args.write and not args.check:
+        print(json.dumps(build_report(), indent=2, ensure_ascii=False))
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

scripts/check_i18n_drift.py

@@ -0,0 +1,132 @@
+#!/usr/bin/env python3
+"""Read-only drift check for shared i18n key coverage.
+
+Compares `shared/i18n/key-manifest.json` against `shared/i18n/lobby.json` and
+fails fast when keyspaces drift between frontend/backend contract sections.
+"""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+import sys
+from typing import Any
+
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+CATALOG_PATH = REPO_ROOT / "shared" / "i18n" / "lobby.json"
+MANIFEST_PATH = REPO_ROOT / "shared" / "i18n" / "key-manifest.json"
+
+
+def _load_json(path: Path) -> dict[str, Any]:
+    with path.open("r", encoding="utf-8") as handle:
+        return json.load(handle)
+
+
+def _as_set(value: Any) -> set[str]:
+    if not isinstance(value, list):
+        return set()
+    return {str(item) for item in value}
+
+
+def _require_translations(
+    errors: dict[str, Any],
+    locales: set[str],
+    label: str,
+    failures: list[str],
+) -> None:
+    for key, translations in errors.items():
+        if not isinstance(translations, dict):
+            failures.append(f"{label}.{key} must be an object of locale->message")
+            continue
+
+        for locale in sorted(locales):
+            value = translations.get(locale)
+            if not isinstance(value, str) or not value.strip():
+                failures.append(f"{label}.{key} missing non-empty '{locale}' translation")
+
+
+def main() -> int:
+    catalog = _load_json(CATALOG_PATH)
+    manifest = _load_json(MANIFEST_PATH)
+
+    failures: list[str] = []
+
+    manifest_locales = _as_set(manifest.get("locales"))
+    catalog_locales = _as_set(catalog.get("locales", {}).get("supported"))
+    if manifest_locales != catalog_locales:
+        failures.append(
+            "locale set mismatch: "
+            f"manifest={sorted(manifest_locales)} catalog={sorted(catalog_locales)}"
+        )
+
+    frontend_manifest = _as_set(manifest.get("frontend_error_keys"))
+    frontend_catalog = set(catalog.get("frontend", {}).get("errors", {}).keys())
+    if frontend_manifest != frontend_catalog:
+        failures.append(
+            "frontend error key mismatch: "
+            f"manifest-only={sorted(frontend_manifest - frontend_catalog)} "
+            f"catalog-only={sorted(frontend_catalog - frontend_manifest)}"
+        )
+
+    backend_code_manifest = _as_set(manifest.get("backend_error_codes"))
+    backend_code_catalog = set(catalog.get("backend", {}).get("error_codes", {}).keys())
+    if backend_code_manifest != backend_code_catalog:
+        failures.append(
+            "backend error code mismatch: "
+            f"manifest-only={sorted(backend_code_manifest - backend_code_catalog)} "
+            f"catalog-only={sorted(backend_code_catalog - backend_code_manifest)}"
+        )
+
+    backend_key_manifest = _as_set(manifest.get("backend_error_keys"))
+    backend_key_catalog = set(catalog.get("backend", {}).get("errors", {}).keys())
+    if backend_key_manifest != backend_key_catalog:
+        failures.append(
+            "backend error key mismatch: "
+            f"manifest-only={sorted(backend_key_manifest - backend_key_catalog)} "
+            f"catalog-only={sorted(backend_key_catalog - backend_key_manifest)}"
+        )
+
+    backend_to_frontend = catalog.get("contract", {}).get("backend_to_frontend_error_keys", {})
+    if not isinstance(backend_to_frontend, dict):
+        failures.append("contract.backend_to_frontend_error_keys must be an object")
+        backend_to_frontend = {}
+
+    for code in sorted(backend_code_catalog):
+        frontend_key = backend_to_frontend.get(code)
+        if frontend_key is None:
+            failures.append(f"missing contract mapping for backend code '{code}'")
+            continue
+        if frontend_key not in frontend_catalog:
+            failures.append(
+                f"mapping for backend code '{code}' points to unknown frontend key '{frontend_key}'"
+            )
+
+    allowed_contract_only_codes = _as_set(manifest.get("allowed_contract_only_backend_codes"))
+    unknown_mapping_codes = set(backend_to_frontend.keys()) - backend_code_catalog
+    disallowed_unknown_mapping_codes = unknown_mapping_codes - allowed_contract_only_codes
+    if disallowed_unknown_mapping_codes:
+        failures.append(
+            "contract contains mappings for unknown backend codes: "
+            f"{sorted(disallowed_unknown_mapping_codes)}"
+        )
+
+    _require_translations(catalog.get("frontend", {}).get("errors", {}), manifest_locales, "frontend.errors", failures)
+    _require_translations(catalog.get("backend", {}).get("errors", {}), manifest_locales, "backend.errors", failures)
+
+    if failures:
+        print("i18n drift check FAILED")
+        for failure in failures:
+            print(f" - {failure}")
+        return 1
+
+    print("i18n drift check OK")
+    print(f" - locales: {sorted(manifest_locales)}")
+    print(f" - frontend error keys: {len(frontend_catalog)}")
+    print(f" - backend error codes: {len(backend_code_catalog)}")
+    print(f" - backend error keys: {len(backend_key_catalog)}")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

scripts/check_i18n_parity_artifact.py

@@ -0,0 +1,36 @@
+#!/usr/bin/env python3
+"""Guard issue #277 parity artifact against non-deterministic regeneration."""
+
+from __future__ import annotations
+
+import hashlib
+import subprocess
+import sys
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+ARTIFACT_PATH = REPO_ROOT / "docs" / "ISSUE-277-SHARED-I18N-PARITY-ARTIFACT.md"
+REPORT_SCRIPT = REPO_ROOT / "scripts" / "report_i18n_parity.py"
+
+
+def sha256(path: Path) -> str:
+    return hashlib.sha256(path.read_bytes()).hexdigest()
+
+
+def main() -> int:
+    before = sha256(ARTIFACT_PATH)
+
+    for run in range(1, 3):
+        subprocess.run([sys.executable, str(REPORT_SCRIPT)], cwd=REPO_ROOT, check=True)
+        after = sha256(ARTIFACT_PATH)
+        if after != before:
+            raise SystemExit(
+                f"issue #277 parity artifact is not deterministic after run {run}: {before} != {after}"
+            )
+
+    print(f"issue #277 parity artifact deterministic: {before}")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

scripts/report_i18n_parity.py

@@ -0,0 +1,196 @@
+#!/usr/bin/env python3
+"""Generate issue #277 shared i18n parity artifact.
+
+Read-only report over the shared lobby i18n catalog, with focus on MVP-critical
+backend/frontend parity used by Django and Angular.
+"""
+
+from __future__ import annotations
+
+import json
+from dataclasses import dataclass
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+CATALOG_PATH = REPO_ROOT / "shared" / "i18n" / "lobby.json"
+OUTPUT_PATH = REPO_ROOT / "docs" / "ISSUE-277-SHARED-I18N-PARITY-ARTIFACT.md"
+ARTIFACT_ID = "issue-277-shared-i18n-parity-report"
+ARTIFACT_VERSION = "1.0"
+
+MVP_FRONTEND_UI_KEYS = [
+    "frontend.ui.host.title",
+    "frontend.ui.player.title",
+    "frontend.ui.common.session_code",
+    "frontend.ui.player.nickname",
+    "frontend.ui.player.join",
+    "frontend.ui.host.start_round",
+    "frontend.ui.host.show_question",
+    "frontend.ui.player.lie_label",
+    "frontend.ui.player.submit_lie",
+    "frontend.ui.player.submit_guess",
+    "frontend.ui.host.mix_answers",
+    "frontend.ui.host.calculate_scores",
+    "frontend.ui.host.load_scoreboard",
+    "frontend.ui.host.final_leaderboard",
+    "frontend.ui.player.final_leaderboard",
+    "frontend.ui.common.points_short",
+]
+
+MVP_FRONTEND_ERROR_KEYS = [
+    "frontend.errors.session_code_required",
+    "frontend.errors.session_not_found",
+    "frontend.errors.nickname_invalid",
+    "frontend.errors.nickname_taken",
+    "frontend.errors.join_failed",
+    "frontend.errors.start_round_failed",
+    "frontend.errors.unknown",
+]
+
+MVP_BACKEND_CODES = [
+    "backend.error_codes.session_code_required",
+    "backend.error_codes.nickname_invalid",
+    "backend.error_codes.session_not_found",
+    "backend.error_codes.session_not_joinable",
+    "backend.error_codes.nickname_taken",
+    "backend.error_codes.category_slug_required",
+    "backend.error_codes.category_not_found",
+    "backend.error_codes.round_start_invalid_phase",
+    "backend.error_codes.round_already_configured",
+]
+
+
+@dataclass(frozen=True)
+class MappingRow:
+    backend_code: str
+    backend_key: str
+    frontend_key: str
+    locales_ok: bool
+    parity_status: str
+    note: str
+
+
+def load_catalog() -> dict:
+    return json.loads(CATALOG_PATH.read_text(encoding="utf-8"))
+
+
+def get_path(data: dict, dotted: str):
+    node = data
+    for part in dotted.split("."):
+        node = node[part]
+    return node
+
+
+def translation_state(data: dict, dotted: str) -> tuple[bool, list[str]]:
+    translations = get_path(data, dotted)
+    missing = [locale for locale in ("en", "da") if not isinstance(translations.get(locale), str) or not translations[locale].strip()]
+    return (not missing, missing)
+
+
+def build_mapping_rows(catalog: dict) -> list[MappingRow]:
+    rows: list[MappingRow] = []
+    mapping = catalog["contract"]["backend_to_frontend_error_keys"]
+    backend_errors = catalog["backend"]["errors"]
+
+    for dotted_code in MVP_BACKEND_CODES:
+        code = dotted_code.removeprefix("backend.error_codes.")
+        backend_key = catalog["backend"]["error_codes"][code]
+        frontend_key = mapping[code]
+        backend_locales_ok, _ = translation_state(catalog, f"backend.errors.{backend_key}")
+        frontend_locales_ok, _ = translation_state(catalog, f"frontend.errors.{frontend_key}")
+        note = "1:1" if code == frontend_key else "many:1 collapse" if frontend_key == "start_round_failed" else "mapped alias"
+        rows.append(
+            MappingRow(
+                backend_code=code,
+                backend_key=backend_key,
+                frontend_key=frontend_key,
+                locales_ok=backend_locales_ok and frontend_locales_ok,
+                parity_status="aligned" if frontend_key in backend_errors or code == frontend_key else "mapped",
+                note=note,
+            )
+        )
+    return rows
+
+
+def render_report(catalog: dict) -> str:
+    mapping_rows = build_mapping_rows(catalog)
+    frontend_ui_ok = all(translation_state(catalog, key)[0] for key in MVP_FRONTEND_UI_KEYS)
+    frontend_error_ok = all(translation_state(catalog, key)[0] for key in MVP_FRONTEND_ERROR_KEYS)
+    backend_code_ok = all(translation_state(catalog, f"backend.errors.{catalog['backend']['error_codes'][key.removeprefix('backend.error_codes.')]}" )[0] for key in MVP_BACKEND_CODES)
+    mapped_frontend_keys = sorted({row.frontend_key for row in mapping_rows})
+    collapsed_codes = [row.backend_code for row in mapping_rows if row.frontend_key == "start_round_failed"]
+
+    lines: list[str] = []
+    lines.append("# ISSUE-277 Artifact — shared i18n registry parity report (Django ↔ Angular MVP)")
+    lines.append("")
+    lines.append("Issue: **#277** (`[READY][#175][P3] Shared i18n registry artifact: backend/frontend keyspace parity report`)")
+    lines.append("")
+    lines.append("## Artifact metadata")
+    lines.append("")
+    lines.append(f"- `artifact_id`: `{ARTIFACT_ID}`")
+    lines.append(f"- `artifact_version`: `{ARTIFACT_VERSION}`")
+    lines.append(f"- `catalog_source`: `{CATALOG_PATH.relative_to(REPO_ROOT)}`")
+    lines.append(f"- `generator`: `scripts/{Path(__file__).name}`")
+    lines.append("")
+    lines.append("## Naming/version rules (email-manager-inspired strategy)")
+    lines.append("")
+    lines.append("- **Single canonical artifact per issue**: issue-bundne rapporter navngives `docs/ISSUE-<nr>-<slug>-ARTIFACT.md`.")
+    lines.append("- **Stable artifact identity**: `artifact_id` ændres ikke ved tekstlige opdateringer i samme rapporttype; det er den faste reference i review/ops.")
+    lines.append("- **Explicit artifact versioning**: `artifact_version` bumpes, når rapportlogik eller scope ændres, så drift/review kan se forskel på format- vs. dataændringer.")
+    lines.append("- **Shared namespace first**: keys refereres med fulde navnerum (`frontend.ui.*`, `frontend.errors.*`, `backend.error_codes.*`, `backend.errors.*`) i stedet for lokale aliases i artefakter.")
+    lines.append("- **Source-of-truth before consumers**: rapporten afledes fra `shared/i18n/lobby.json`; Django/Angular beskrives som consumers af samme registry og ikke som parallelle kontrakter.")
+    lines.append("")
+    lines.append("## MVP-critical parity summary")
+    lines.append("")
+    lines.append(f"- Frontend UI gameplay keys checked: **{len(MVP_FRONTEND_UI_KEYS)}** → `{'OK' if frontend_ui_ok else 'DRIFT'}`")
+    lines.append(f"- Frontend error keys checked: **{len(MVP_FRONTEND_ERROR_KEYS)}** → `{'OK' if frontend_error_ok else 'DRIFT'}`")
+    lines.append(f"- Backend gameplay/error codes checked: **{len(MVP_BACKEND_CODES)}** → `{'OK' if backend_code_ok else 'DRIFT'}`")
+    lines.append(f"- Distinct frontend error keys reached from backend MVP flow: **{len(mapped_frontend_keys)}** (`{', '.join(mapped_frontend_keys)}`)")
+    lines.append("")
+    lines.append("Status: **Shared locale matrix is aligned (`en`, `da`) and backend→frontend error handling is contract-complete for MVP-critical flow.**")
+    lines.append("")
+    lines.append("## Django ↔ Angular parity matrix (MVP-critical error contract)")
+    lines.append("")
+    lines.append("| Backend code (`backend.error_codes.*`) | Django message key (`backend.errors.*`) | Angular key (`frontend.errors.*`) | Locales `en/da` | Parity note |")
+    lines.append("|---|---|---|---|---|")
+    for row in mapping_rows:
+        lines.append(
+            f"| `{row.backend_code}` | `{row.backend_key}` | `{row.frontend_key}` | `{'OK' if row.locales_ok else 'DRIFT'}` | {row.note} |"
+        )
+    lines.append("")
+    lines.append("## Scope notes")
+    lines.append("")
+    lines.append("- **Django** consumes backend codes/messages directly from `shared/i18n/lobby.json` via `lobby/i18n.py`.")
+    lines.append("- **Angular** consumes the same registry via `frontend/shared/i18n/lobby-loader.ts` and runtime helpers in `frontend/angular/src/app/lobby-i18n.ts`.")
+    lines.append("- **Parity in MVP** is therefore strongest on the shared error contract and locale matrix; gameplay UI labels are frontend-owned but still live in the same registry.")
+    lines.append("")
+    lines.append("## Verified MVP gameplay UI keyspace present in the shared registry")
+    lines.append("")
+    for key in MVP_FRONTEND_UI_KEYS:
+        lines.append(f"- `{key}`")
+    lines.append("")
+    lines.append("## Concrete deviations / follow-up items")
+    lines.append("")
+    lines.append(f"1. **Error granularity collapse remains intentional**: backend codes `{', '.join(collapsed_codes)}` all map to `frontend.errors.start_round_failed`. Follow-up only if product wants case-specific Angular copy instead of one shared host failure message.")
+    lines.append("2. **Frontend-only fallback copy is not mirrored in Django**: `frontend.errors.unknown` and `frontend.errors.session_fetch_failed` are Angular-side resilience keys, not backend contract keys. Follow-up if API responses should expose stable backend equivalents for these states.")
+    lines.append("3. **Gameplay UI labels are registry-shared but not backend-rendered**: `frontend.ui.host.*`, `frontend.ui.player.*`, and `frontend.ui.common.*` are available in the shared artifact, but Django currently consumes only the backend error slice. Follow-up only if server-rendered views must guarantee the same UI label surface as Angular.")
+    lines.append("")
+    lines.append("## Re-run")
+    lines.append("")
+    lines.append("```bash")
+    lines.append("python3 scripts/check_i18n_drift.py")
+    lines.append("python3 scripts/report_i18n_parity.py")
+    lines.append("python3 scripts/check_i18n_parity_artifact.py")
+    lines.append("```")
+    lines.append("")
+    return "\n".join(lines)
+
+
+def main() -> int:
+    catalog = load_catalog()
+    OUTPUT_PATH.write_text(render_report(catalog), encoding="utf-8")
+    print(OUTPUT_PATH.relative_to(REPO_ROOT))
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

shared/i18n/artifacts/lobby-mvp-keyspace-parity-report.v1.json

@@ -0,0 +1,212 @@
+{
+  "artifact_name": "shared.i18n.lobby.mvp_keyspace_parity_report",
+  "artifact_version": "v1",
+  "naming_version_rule": "Keep a stable artifact_name and append only explicit schema-major suffixes to the filename/version (v1, v2, ...). Update artifact_version only when the report shape changes; refresh content in-place for catalog/keyspace changes.",
+  "source_of_truth": {
+    "catalog": "shared/i18n/lobby.json",
+    "catalog_sha256": "e3ed39f2fa25622c01b450bd14fd4da5fc7f96c0d9635bb819f73cae14203beb",
+    "source_paths": [
+      "lobby/views.py",
+      "frontend/src/spa/vertical-slice.ts",
+      "frontend/angular/src/app/lobby-i18n.ts",
+      "frontend/angular/src/app/features/host/host-shell.component.ts",
+      "frontend/angular/src/app/features/player/player-shell.component.ts"
+    ]
+  },
+  "scope": {
+    "issue": 277,
+    "related_epic": 175,
+    "mvp_locales": [
+      "en",
+      "da"
+    ],
+    "definition": "MVP-critical keys are the Django error codes emitted by lobby/views.py plus the Angular fallback/UI keys consumed by the host/player MVP shells."
+  },
+  "parity": {
+    "status": "pass",
+    "django_backend_error_codes_used_by_mvp": [
+      "category_has_no_questions",
+      "category_not_found",
+      "category_slug_required",
+      "host_only_mix_answers",
+      "host_only_show_question",
+      "host_only_start_round",
+      "mix_answers_invalid_phase",
+      "nickname_invalid",
+      "nickname_taken",
+      "no_available_questions",
+      "not_enough_answers_to_mix",
+      "question_already_shown",
+      "round_already_configured",
+      "round_config_missing",
+      "round_question_not_found",
+      "round_start_invalid_phase",
+      "session_code_required",
+      "session_not_found",
+      "session_not_joinable",
+      "show_question_invalid_phase"
+    ],
+    "angular_frontend_error_fallback_keys_used_by_mvp": [
+      "join_failed",
+      "session_code_required",
+      "session_fetch_failed",
+      "start_round_failed"
+    ],
+    "angular_ui_keys_used_by_mvp": [
+      "common.back_to_join",
+      "common.points_short",
+      "common.prompt",
+      "common.refresh",
+      "common.retry",
+      "common.round",
+      "common.round_question_id",
+      "common.session_code",
+      "common.status",
+      "common.unknown_error",
+      "host.audio_locale_hint",
+      "host.calculate_scores",
+      "host.category",
+      "host.final_leaderboard",
+      "host.finish_game",
+      "host.finish_game_failed",
+      "host.load_scoreboard",
+      "host.mix_answers",
+      "host.next_round_failed",
+      "host.retry_finish",
+      "host.retry_next_round",
+      "host.retry_scoreboard",
+      "host.scoreboard_failed",
+      "host.session_code_required",
+      "host.session_refresh_failed",
+      "host.show_question",
+      "host.start_next_round",
+      "host.start_round",
+      "host.title",
+      "host.winner",
+      "player.audio_policy_notice",
+      "player.final_leaderboard",
+      "player.guess_submit_failed",
+      "player.join",
+      "player.join_failed",
+      "player.lie_label",
+      "player.lie_submit_failed",
+      "player.loading_join",
+      "player.loading_refresh",
+      "player.loading_submit_guess",
+      "player.loading_submit_lie",
+      "player.nickname",
+      "player.offline_text",
+      "player.reconnecting_text",
+      "player.retry_guess_submit",
+      "player.retry_lie_submit",
+      "player.retry_now",
+      "player.session_refresh_failed",
+      "player.submit_guess",
+      "player.submit_lie",
+      "player.title"
+    ],
+    "angular_ui_catalog_paths": [
+      "common.back_to_join",
+      "common.points_short",
+      "common.prompt",
+      "common.refresh",
+      "common.retry",
+      "common.round",
+      "common.round_question_id",
+      "common.session_code",
+      "common.status",
+      "common.unknown_error",
+      "host.audio_locale_hint",
+      "host.calculate_scores",
+      "host.category",
+      "host.final_leaderboard",
+      "host.finish_game",
+      "host.finish_game_failed",
+      "host.load_scoreboard",
+      "host.mix_answers",
+      "host.next_round_failed",
+      "host.retry_finish",
+      "host.retry_next_round",
+      "host.retry_scoreboard",
+      "host.scoreboard_failed",
+      "host.session_code_required",
+      "host.session_refresh_failed",
+      "host.show_question",
+      "host.start_next_round",
+      "host.start_round",
+      "host.title",
+      "host.winner",
+      "player.audio_policy_notice",
+      "player.final_leaderboard",
+      "player.guess_submit_failed",
+      "player.join",
+      "player.join_failed",
+      "player.lie_label",
+      "player.lie_submit_failed",
+      "player.loading_join",
+      "player.loading_refresh",
+      "player.loading_submit_guess",
+      "player.loading_submit_lie",
+      "player.nickname",
+      "player.offline_text",
+      "player.reconnecting_text",
+      "player.retry_guess_submit",
+      "player.retry_lie_submit",
+      "player.retry_now",
+      "player.session_refresh_failed",
+      "player.submit_guess",
+      "player.submit_lie",
+      "player.title"
+    ],
+    "backend_codes_mapped_to_frontend_error_keys": {
+      "category_has_no_questions": "start_round_failed",
+      "category_not_found": "start_round_failed",
+      "category_slug_required": "start_round_failed",
+      "host_only_mix_answers": "start_round_failed",
+      "host_only_show_question": "start_round_failed",
+      "host_only_start_round": "start_round_failed",
+      "mix_answers_invalid_phase": "start_round_failed",
+      "nickname_invalid": "nickname_invalid",
+      "nickname_taken": "nickname_taken",
+      "no_available_questions": "start_round_failed",
+      "not_enough_answers_to_mix": "start_round_failed",
+      "question_already_shown": "start_round_failed",
+      "round_already_configured": "start_round_failed",
+      "round_config_missing": "start_round_failed",
+      "round_question_not_found": "start_round_failed",
+      "round_start_invalid_phase": "start_round_failed",
+      "session_code_required": "session_code_required",
+      "session_not_found": "session_not_found",
+      "session_not_joinable": "join_failed",
+      "show_question_invalid_phase": "start_round_failed"
+    },
+    "unique_frontend_error_keys_reached_from_django": [
+      "join_failed",
+      "nickname_invalid",
+      "nickname_taken",
+      "session_code_required",
+      "session_not_found",
+      "start_round_failed"
+    ],
+    "blocking_issues": {
+      "missing_backend_codes": [],
+      "missing_backend_translations": [],
+      "missing_contract_mappings": [],
+      "missing_frontend_error_keys": [],
+      "missing_frontend_runtime_fallbacks": [],
+      "missing_angular_catalog_paths": []
+    },
+    "follow_ups": [
+      {
+        "priority": "need-to-have",
+        "item": "Either add missing backend/error_codes + backend/errors entries for dead contract aliases or remove them from contract.backend_to_frontend_error_keys.",
+        "evidence": "host_only_action"
+      },
+      {
+        "priority": "nice-to-have",
+        "item": "Decide whether grouped backend codes should keep collapsing into one Angular fallback key or be split into more specific frontend error copy as UX matures.",
+        "evidence": "start_round_failed <= category_has_no_questions, category_not_found, category_slug_required, host_only_mix_answers, host_only_show_question, host_only_start_round, mix_answers_invalid_phase, no_available_questions, not_enough_answers_to_mix, question_already_shown, round_already_configured, round_config_missing, round_question_not_found, round_start_invalid_phase, show_question_invalid_phase"
+      }
+    ]
+  }
+}

shared/i18n/key-manifest.json

@@ -0,0 +1,60 @@
+{
+  "locales": ["en", "da"],
+  "frontend_error_keys": [
+    "join_failed",
+    "nickname_invalid",
+    "nickname_taken",
+    "session_code_required",
+    "session_fetch_failed",
+    "session_not_found",
+    "start_round_failed",
+    "unknown"
+  ],
+  "backend_error_codes": [
+    "category_has_no_questions",
+    "category_not_found",
+    "category_slug_required",
+    "host_only_mix_answers",
+    "host_only_show_question",
+    "host_only_start_round",
+    "mix_answers_invalid_phase",
+    "nickname_invalid",
+    "nickname_taken",
+    "no_available_questions",
+    "not_enough_answers_to_mix",
+    "question_already_shown",
+    "round_already_configured",
+    "round_config_missing",
+    "round_question_not_found",
+    "round_start_invalid_phase",
+    "session_code_required",
+    "session_not_found",
+    "session_not_joinable",
+    "show_question_invalid_phase"
+  ],
+  "allowed_contract_only_backend_codes": [
+    "host_only_action"
+  ],
+  "backend_error_keys": [
+    "category_has_no_questions",
+    "category_not_found",
+    "category_slug_required",
+    "host_only_mix_answers",
+    "host_only_show_question",
+    "host_only_start_round",
+    "mix_answers_invalid_phase",
+    "nickname_invalid",
+    "nickname_taken",
+    "no_available_questions",
+    "not_enough_answers_to_mix",
+    "question_already_shown",
+    "round_already_configured",
+    "round_config_missing",
+    "round_question_not_found",
+    "round_start_invalid_phase",
+    "session_code_required",
+    "session_not_found",
+    "session_not_joinable",
+    "show_question_invalid_phase"
+  ]
+}

shared/i18n/lobby.json

@@ -74,6 +74,14 @@
         "round": {
           "en": "round",
           "da": "runde"
+        },
+        "points_short": {
+          "en": "pts",
+          "da": "point"
+        },
+        "unknown_error": {
+          "en": "Unknown error",
+          "da": "Ukendt fejl"
         }
       },
       "app": {
@@ -256,6 +264,10 @@
         "guess_submit_failed": {
           "en": "Guess submit failed",
           "da": "Gætte-fejl"
+        },
+        "audio_policy_notice": {
+          "en": "Audio playback is disabled on phone clients. Sound is available on the primary host device.",
+          "da": "Lydafspilning er slået fra på telefon-klienten. Lyd afspilles kun på den primære værtsenhed."
         }
       }
     },
@@ -273,7 +285,18 @@
       "category_slug_required": "category_slug_required",
       "category_not_found": "category_not_found",
       "round_start_invalid_phase": "round_start_invalid_phase",
-      "round_already_configured": "round_already_configured"
+      "round_already_configured": "round_already_configured",
+      "category_has_no_questions": "category_has_no_questions",
+      "show_question_invalid_phase": "show_question_invalid_phase",
+      "round_config_missing": "round_config_missing",
+      "question_already_shown": "question_already_shown",
+      "no_available_questions": "no_available_questions",
+      "mix_answers_invalid_phase": "mix_answers_invalid_phase",
+      "round_question_not_found": "round_question_not_found",
+      "not_enough_answers_to_mix": "not_enough_answers_to_mix",
+      "host_only_start_round": "host_only_start_round",
+      "host_only_show_question": "host_only_show_question",
+      "host_only_mix_answers": "host_only_mix_answers"
     },
     "errors": {
       "session_code_required": {
@@ -311,7 +334,89 @@
       "round_already_configured": {
         "en": "Round already configured",
         "da": "Runden er allerede konfigureret"
+      },
+      "category_has_no_questions": {
+        "en": "Category has no active questions",
+        "da": "Kategorien har ingen aktive spørgsmål"
+      },
+      "show_question_invalid_phase": {
+        "en": "Question can only be shown in lie phase",
+        "da": "Spørgsmålet kan kun vises i løgnefasen"
+      },
+      "round_config_missing": {
+        "en": "Round config missing",
+        "da": "Rundekonfiguration mangler"
+      },
+      "question_already_shown": {
+        "en": "Question already shown for this round",
+        "da": "Spørgsmålet er allerede vist for denne runde"
+      },
+      "no_available_questions": {
+        "en": "No available questions in category",
+        "da": "Ingen tilgængelige spørgsmål i kategorien"
+      },
+      "mix_answers_invalid_phase": {
+        "en": "Answers can only be mixed in lie or guess phase",
+        "da": "Svar kan kun blandes i løgne- eller gættefasen"
+      },
+      "round_question_not_found": {
+        "en": "Round question not found",
+        "da": "Rundespørgsmål blev ikke fundet"
+      },
+      "not_enough_answers_to_mix": {
+        "en": "Not enough answers to mix",
+        "da": "Ikke nok svar at blande"
+      },
+      "host_only_start_round": {
+        "en": "Only host can start round",
+        "da": "Kun værten kan starte runden"
+      },
+      "host_only_show_question": {
+        "en": "Only host can show question",
+        "da": "Kun værten kan vise spørgsmålet"
+      },
+      "host_only_mix_answers": {
+        "en": "Only host can mix answers",
+        "da": "Kun værten kan blande svar"
       }
     }
+  },
+  "contract": {
+    "ownership": {
+      "artifact": "shared/i18n/lobby.json",
+      "backend": "lobby/* reads backend/errors + backend/error_codes",
+      "frontend": "frontend/* reads frontend/errors + frontend/ui + contract/backend_to_frontend_error_keys"
+    },
+    "locale": {
+      "default": "en",
+      "supported": [
+        "en",
+        "da"
+      ],
+      "fallback": "Use default locale when requested locale is unsupported or key translation is missing."
+    },
+    "backend_to_frontend_error_keys": {
+      "session_code_required": "session_code_required",
+      "nickname_invalid": "nickname_invalid",
+      "session_not_found": "session_not_found",
+      "session_not_joinable": "join_failed",
+      "nickname_taken": "nickname_taken",
+      "category_slug_required": "start_round_failed",
+      "category_not_found": "start_round_failed",
+      "round_start_invalid_phase": "start_round_failed",
+      "round_already_configured": "start_round_failed",
+      "host_only_start_round": "start_round_failed",
+      "host_only_show_question": "start_round_failed",
+      "host_only_mix_answers": "start_round_failed",
+      "host_only_action": "start_round_failed",
+      "category_has_no_questions": "start_round_failed",
+      "show_question_invalid_phase": "start_round_failed",
+      "round_config_missing": "start_round_failed",
+      "question_already_shown": "start_round_failed",
+      "no_available_questions": "start_round_failed",
+      "mix_answers_invalid_phase": "start_round_failed",
+      "round_question_not_found": "start_round_failed",
+      "not_enough_answers_to_mix": "start_round_failed"
+    }
   }
-}
+}