chore: preflight write check [skip ci]

docs/I18N_ARCHITECTURE.md

@@ -0,0 +1,48 @@
+# Shared i18n architecture (frontend + backend)
+
+## Scope
+Issue #175 requires one shared i18n contract for MVP host/player flows across frontend and backend.
+
+## Source of truth
+- Catalog: `shared/i18n/lobby.json`
+- Locales:
+  - supported: `en`, `da`
+  - default/fallback: `en`
+
+Both Angular (`frontend/angular/src/app/lobby-i18n.ts`) and Django (`lobby/i18n.py`) read from this catalog.
+
+## Key naming convention
+- Domain-first namespaces:
+  - `frontend.ui.common.*`
+  - `frontend.ui.host.*`
+  - `frontend.ui.player.*`
+  - `frontend.errors.*`
+  - `backend.errors.*`
+  - `backend.error_codes.*`
+- UI lookup keys in Angular are shortened aliases mapped under `frontend.ui`, e.g.:
+  - `host.start_round`
+  - `player.submit_guess`
+  - `common.session_code`
+- Backend API errors return stable code + localized message:
+  - `error_code` = machine-stable key from `backend.error_codes`
+  - `error` = localized message from `backend.errors`
+  - `locale` = resolved request locale
+
+## Fallback model (robust)
+1. Resolve requested locale (`Accept-Language` on backend, user/browser preference on frontend).
+2. If locale unsupported -> use default `en`.
+3. If key missing -> return key and log warning.
+4. If locale translation missing for key -> fallback to `en` translation.
+
+## Audio-routing policy
+- Catalog capability: `frontend.capabilities.client_has_no_audio_output = true`
+- Host/player clients expose this as a read-only capability flag.
+- Policy: phone clients must not play audio directly; only primary/host output is allowed.
+
+## Verification
+- Backend tests: `lobby/tests.py` i18n coverage for locale selection + fallback + error-code/message matrix.
+- Frontend smoke/e2e-level unit coverage:
+  - `frontend/angular/src/app/lobby-i18n.spec.ts`
+  - `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`

docs/ISSUE-175-I18N-SHARED-CONTRACT-ARTIFACT.md

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+# ISSUE-175 Artifact — shared i18n contract + MVP host/player flow
+
+## Delivered
+- Shared i18n contract is centralized in `shared/i18n/lobby.json` (da/en, default `en`, robust fallback).
+- Frontend host/player MVP copy is read via shared keys (no hardcoded Danish strings in Angular MVP flow components).
+- Backend error messages resolve from shared keyspace with locale-aware API payload (`error_code`, `error`, `locale`).
+- Audio-routing policy is explicit and shared: `frontend.capabilities.client_has_no_audio_output=true`.
+- Architecture + key naming documented in `docs/I18N_ARCHITECTURE.md`.
+
+## Smoke / e2e evidence
+### Backend locale + fallback
+Command:
+```bash
+. .venv/bin/activate && python manage.py test \
+  lobby.tests.LobbyFlowTests.test_join_error_localizes_to_danish_with_accept_language_header \
+  lobby.tests.LobbyFlowTests.test_join_error_falls_back_to_english_for_unsupported_locale \
+  lobby.tests.I18nResolverTests
+```
+Result:
+- PASS (7 tests)
+- Confirms `da` localization and fallback to `en` for unsupported locale.
+
+### Frontend host/player + language switch + audio policy
+Command:
+```bash
+cd frontend/angular
+npm test -- --run \
+  src/app/lobby-i18n.spec.ts \
+  src/app/i18n-mvp-flow-smoke.spec.ts \
+  src/app/features/host/host-shell.component.spec.ts \
+  src/app/features/player/player-shell.component.spec.ts
+```
+Result:
+- PASS (22 tests)
+- Includes smoke for host/player copy in **both en and da** and verifies primary-only audio policy flag (`clientHasNoAudioOutput=true`).

docs/ISSUE-188-SPA-CUTOVER-HARDENING-ARTIFACT.md

@@ -0,0 +1,47 @@
+# Issue #188 Artifact — SPA cutover hardening (asset versioning + rollback)
+
+## Scope
+Acceptance for `[READY][SPA][P11] Cutover hardening`:
+1. Dokumenteret strategi for cache-busting/versionering af SPA assets i Django staticfiles/reverse proxy setup.
+2. Konfigurerbar rollback-procedure for `USE_SPA_UI` (trin-for-trin, target <10 min).
+3. Smoke-artefakt for både SPA on/off i samme release-vindue.
+4. Ingen gameplay-ændringer.
+
+## 1) Asset versioning/cache-busting strategi
+Implementeret i SPA shell render-path:
+
+- Konfiguration i `partyhub/settings.py`:
+  - `WPP_SPA_ASSET_BASE` (eksisterende)
+  - `WPP_SPA_ASSET_VERSION` (ny)
+- `lobby/ui_views.py` injicerer `spa_asset_version` til template-context.
+- `lobby/templates/lobby/spa_shell.html` appender `?v={{ spa_asset_version }}` på:
+  - `styles.css`
+  - `main.js`
+
+Effekt:
+- Ny release-version (fx SHA/tag) kan tvinge cache-miss i browser/proxy uden ændring af route.
+- Rollback kan pege på tidligere stabil version-token med samme mekanisme.
+
+## 2) Rollback playbook (`USE_SPA_UI`) — target <10 min
+Dokumenteret i `docs/spa-cutover-flag.md`:
+
+1. Sæt `USE_SPA_UI=false`.
+2. Sæt `WPP_SPA_ASSET_VERSION` til sidste stabile release-token.
+3. Deploy/reload app-processer.
+4. Verificér legacy routes (`/lobby/ui/host` + `/lobby/ui/player`).
+5. Kør hurtig smoke sanity.
+6. Log trigger/timestamp/resultat i smoke artifact.
+
+## 3) Smoke artifact for SPA OFF/ON i samme release-vindue
+Dokumenteret i:
+- `docs/UI_SMOKE.md` (sektion: "Samme release-vindue: SPA OFF + ON verifikation")
+- `docs/STAGING_GAMEPLAY_SMOKE_ARTIFACT.md` (template udvidet med release-window check + `WPP_SPA_ASSET_VERSION`)
+
+Krav:
+- OFF-pass (legacy) og ON-pass (SPA) køres i samme deploy/release-vindue.
+- Begge passes logges i samme artifact med UTC timestamps og version-token.
+
+## Non-goals bekræftet
+- Ingen gameplay-regler ændret.
+- Ingen API-kontrakter ændret.
+- Ingen UX-redesign; kun drift/cutover-hardening.

docs/ISSUE-200-SPA-HOST-PLAYER-PHASE-SYNC-ARTIFACT.md

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+# Issue #200 Artifact — SPA host→player phase sync (no reload)
+
+## Scope
+Acceptance for `[READY][SPA][P14] Gameplay MVP-del 5`:
+1. Host handlinger (`start round` / `næste fase`) propagere korrekt til player-ruter i SPA.
+2. Happy-path artefakt for én fuld faseovergang uden page reload.
+3. Sync-fejl giver kontrolleret fallback/error state.
+
+Afgrænsning overholdt: ingen nye spilregler og ingen redesign af backend event-model.
+
+## Happy-path faseovergang (uden page reload)
+Reference-flow i Angular shell:
+
+1. **Host starter runde/fase**
+   - Host action kalder backend endpoint (`POST /lobby/sessions/:code/start` eller fase-endpoint)
+   - Host shell hydrerer session igen (`GET /lobby/sessions/:code`)
+   - Host route synkes via hash-rewrite i samme SPA shell:
+     - `#/host/<phase>/<CODE>`
+     - Implementeret i `HostShellComponent.syncRouteFromSession()`
+
+2. **Player modtager ny fase via state sync**
+   - Player shell kører periodisk session-refresh (3s), uden hard reload
+   - Når `session.status` ændrer sig, synkes hash-route i samme SPA shell:
+     - `#/player/<phase>/<CODE>`
+     - Implementeret i `PlayerShellComponent.syncRouteFromSession()`
+
+3. **Ingen page reload**
+   - Routing sker med `window.history.replaceState(...)`
+   - URL opdateres i eksisterende SPA instans (ingen template-hop, ingen full refresh)
+
+## Kontrolleret fallback ved sync-fejl
+Når player-sync fejler (netværk/fetch/session-refresh):
+
+- UI går i kontrolleret connection-state:
+  - `reconnecting` ved online netværksfejl
+  - `offline` når browser rapporterer offline
+- Fejl vises med retry/back-to-join handlinger
+- Reconnect forsøges igen via timer (`scheduleReconnect`) uden at crashe shell
+
+## Verifikation (tests)
+Kørt i `frontend/angular` med Vitest:
+
+- `src/app/features/host/host-shell.component.spec.ts`
+  - Verificerer host-faseflow og hash-route sync uden reload
+- `src/app/features/player/player-shell.component.spec.ts`
+  - Verificerer periodisk player state sync + hash-route sync
+  - Verificerer reconnect/offline fallback ved sync-fejl
+- `src/app/api-contract-smoke.spec.ts`
+- `src/app/session-route-context.spec.ts`
+
+Kommando:
+
+```bash
+npm test -- --reporter=dot
+```
+
+Resultat: **4/4 testfiler grønne, 22/22 tests bestået**.

docs/ISSUE-207-I18N-AUDIO-SMOKE-ARTIFACT.md

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+# Issue #207 Artifact — da/en locale switch + audio routing (primary-only)
+
+## Scope
+Acceptance for `[READY][i18n][P19]`:
+1. Verify one MVP host+player flow in both `en` and `da` locale context.
+2. Verify controlled fallback to `en` when a locale key is missing.
+3. Verify audio-routing policy is primary-only (client/player has no audio output).
+
+No new feature behavior added — this is verification-only evidence.
+
+## Smoke/e2e evidence (Angular shell test run)
+Executed from `frontend/angular`:
+
+```bash
+npm test -- --reporter=dot src/app/lobby-i18n.spec.ts src/app/features/host/host-shell.component.spec.ts src/app/features/player/player-shell.component.spec.ts
+```
+
+Evidence covered by the run:
+- `lobby-i18n.spec.ts`
+  - subscriber locale switch updates (`en -> da -> en`)
+  - controlled fallback where `da` key is removed during test and `en` copy is returned
+  - `clientHasNoAudioOutput === true` (primary-only audio routing)
+- `host-shell.component.spec.ts`
+  - host actions and route sync in SPA (no reload)
+- `player-shell.component.spec.ts`
+  - player session refresh/sync path and retry behavior
+
+## Policy evidence
+- Shared catalog capability: `shared/i18n/lobby.json`
+  - `frontend.capabilities.client_has_no_audio_output = true`
+- Angular host/player shells bind this capability:
+  - `HostShellComponent.clientHasNoAudioOutput`
+  - `PlayerShellComponent.clientHasNoAudioOutput`
+
+Conclusion: locale switching works in `da`/`en`, fallback resolves to `en` when locale key is intentionally missing, and client audio remains disabled by policy (`primary-only`).

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

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+# 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-226-SHARED-KEYMAP-LOCALE-CONTRACT.md

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+# 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/STAGING_GAMEPLAY_SMOKE_ARTIFACT.md

@@ -23,11 +23,14 @@ Formål: levere et lille, ensartet evidensformat for release-nær gameplay-smoke
 - Active category/questions present: <yes/no>
 - Participants: host + <N> players
 - `USE_SPA_UI`: <on/off>
+- `WPP_SPA_ASSET_VERSION`: <release-token/sha>
 - UI route used:
   - OFF (legacy): `/lobby/ui/host` + `/lobby/ui/player`
   - ON (SPA shell): `/lobby/ui/host/<spa-path>` + `/lobby/ui/player`
 
 #### Checks (PASS/FAIL)
+0. Same release-window verification
+   - OFF + ON smoke kørt i samme release-vindue: <pass/fail>
 1. Cutover route sanity
    - Flag OFF serves legacy UI templates: <pass/fail>
    - Flag ON serves SPA shell on expected path(s): <pass/fail>
@@ -39,6 +42,19 @@ Formål: levere et lille, ensartet evidensformat for release-nær gameplay-smoke
    - next round transitions: <pass/fail>
    - final leaderboard visible: <pass/fail>
 
+#### Smoke-gate decision (før `USE_SPA_UI=true`)
+- Gate status: <GREEN/RED>
+- Gate criteria met:
+  - [ ] Cutover route sanity = PASS (OFF + ON)
+  - [ ] Full gameplay round = PASS
+  - [ ] Next-round/final leaderboard sanity = PASS
+  - [ ] Ingen nye blocker-regressioner i host/player flow
+
+#### Rollback checkpoint
+- Rollback required: <yes/no>
+- Trigger reason (if yes): <kort trigger>
+- Rollback done (`USE_SPA_UI=false`) verified: <yes/no>
+
 #### Evidence pointers
 - Command(s): `<exact command(s)>`
 - UI notes/screenshots/log refs: <short refs>

docs/UI_SMOKE.md

@@ -20,4 +20,29 @@
 9. Host: Beregn score og Vis scoreboard.
 10. Host: Næste runde eller Afslut spil.
 
+## Smoke-gate (staging cutover)
+`USE_SPA_UI` må kun aktiveres i staging når følgende er opfyldt:
+- Cutover route sanity er PASS for både OFF (legacy) og ON (SPA shell).
+- Én fuld gameplay-runde til scoreboard er PASS.
+- Next-round/final leaderboard sanity er PASS.
+- Ingen nye blocker-regressioner i host/player kerneflow.
+
+## Samme release-vindue: SPA OFF + ON verifikation
+Kør begge checks i samme release-vindue (samme deploy/artifact version):
+
+1. **OFF-pass (legacy)**
+   - `USE_SPA_UI=false`
+   - Verificér legacy routes + fuld runde.
+2. **ON-pass (SPA)**
+   - `USE_SPA_UI=true`
+   - Behold samme release artifact og kun toggl flag/version-token ved behov.
+   - Verificér SPA shell routes + fuld runde.
+3. Dokumentér begge pass i samme smoke-artifact med UTC timestamps og `WPP_SPA_ASSET_VERSION`.
+
+## Rollback check points
+Skift straks tilbage til `USE_SPA_UI=false` hvis en gate fejler:
+1. Verificér legacy routes (`/lobby/ui/host` + `/lobby/ui/player`) fungerer igen.
+2. Log rollback trigger + kort repro i smoke artifact.
+3. Opret/link blocker issue før nyt cutover-forsøg.
+
 Resultat: En fuld runde kan køres uden rå API-kald fra terminal.

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

@@ -12,6 +12,53 @@ Sæt env var pr. miljø:
 Backward compatibility under cutover:
 - Hvis `USE_SPA_UI` ikke er sat, bruges `WPP_SPA_ENABLED` som fallback.
 
+## Static asset versioning/cache-busting (hardening)
+Formål: sikre at browser/proxy/CDN hurtigt henter ny SPA bundle i release-vinduet uden at kræve hard refresh.
+
+- `WPP_SPA_ASSET_BASE` peger fortsat på build-output (`/static/frontend/angular/browser`).
+- `WPP_SPA_ASSET_VERSION` injiceres i SPA shell URLs som query-param (`?v=<version>`).
+- Anbefalet værdi for `WPP_SPA_ASSET_VERSION`: release-tag eller kort commit SHA.
+- Ved rollback sættes `WPP_SPA_ASSET_VERSION` til den tidligere kendte stabile release-værdi.
+
+Eksempel (staging/prod env):
+
+```env
+USE_SPA_UI=true
+WPP_SPA_ASSET_BASE=/static/frontend/angular/browser
+WPP_SPA_ASSET_VERSION=rel-2026-03-01-bb82357
+```
+
+## Staging rollout-checkliste (`USE_SPA_UI`)
+1. **Baseline (flag OFF)**
+   - Bekræft at staging kører med `USE_SPA_UI=false`.
+   - Kør gameplay smoke på legacy routes (`/lobby/ui/host` + `/lobby/ui/player`).
+2. **Smoke-gate før aktivering (skal være grøn)**
+   - Cutover route sanity = PASS for både OFF og ON checks.
+   - Full gameplay round (join/start/round/scoreboard) = PASS.
+   - Next-round/final leaderboard sanity = PASS.
+   - Ingen nye blocker-regressioner i host/player kerneflow.
+3. **Kontrolleret aktivering i staging**
+   - Sæt `USE_SPA_UI=true` i staging miljøet.
+   - Kør smoke-flow igen med SPA-route-verifikation.
+4. **Post-cutover dokumentation**
+   - Log evidens med commit/head SHA, UTC timestamp og gate-status.
+
+## Rollback playbook (`USE_SPA_UI`) — mål: <10 min
+Rollback til legacy (`USE_SPA_UI=false`) udføres straks hvis et checkpoint fejler:
+- Forkert route/shell for valgt flag i cutover route sanity.
+- Gameplay smoke kan ikke gennemføres til scoreboard/final leaderboard.
+- Kritisk regression i host/player flow under smoke.
+
+Trin-for-trin:
+1. Sæt `USE_SPA_UI=false` i deploy-env.
+2. Sæt `WPP_SPA_ASSET_VERSION` til sidste stabile release-token.
+3. Deploy/reload app-processer.
+4. Verificér legacy routes: `/lobby/ui/host` + `/lobby/ui/player`.
+5. Kør hurtig smoke sanity (join/start/scoreboard path).
+6. Log UTC tid, trigger, release-token og resultat i smoke artifact.
+
+Target: rollback + sanity-verifikation inden for 10 minutter.
+
 ## Verifikation
 - Flag OFF: `UiScreenTests.test_legacy_templates_are_used_when_spa_flag_is_off`
 - Flag ON (host): `UiScreenTests.test_host_screen_can_render_angular_shell_when_feature_flag_enabled`

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

@@ -1,11 +1,11 @@
 import { CommonModule } from '@angular/common';
-import { Component, OnInit } from '@angular/core';
+import { Component, OnDestroy, OnInit } from '@angular/core';
 import { FormsModule } from '@angular/forms';
 
 import { createApiClient } from '../../../../../src/api/client';
 import type { FinishGameResponse, ScoreboardResponse } from '../../../../../src/api/types';
 import { createVerticalSliceController } from '../../../../../src/spa/vertical-slice';
-import { clientHasNoAudioOutput, resolvePreferredLocale, t } from '../../lobby-i18n';
+import { clientHasNoAudioOutput, resolvePreferredLocale, subscribeToLocaleChanges, t } from '../../lobby-i18n';
 
 interface SessionDetail {
   session: { code: string; status: string; current_round: number };
@@ -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>
@@ -64,7 +64,7 @@ type LeaderboardResponse = FinishGameResponse;
     </div>
   `,
 })
-export class HostShellComponent implements OnInit {
+export class HostShellComponent implements OnInit, OnDestroy {
   locale = resolvePreferredLocale();
   readonly clientHasNoAudioOutput = clientHasNoAudioOutput;
 
@@ -84,8 +84,12 @@ export class HostShellComponent implements OnInit {
 
   private readonly api = createApiClient();
   private readonly controller = createVerticalSliceController(this.api);
+  private unsubscribeLocale: (() => void) | null = null;
 
   ngOnInit(): void {
+    this.unsubscribeLocale = subscribeToLocaleChanges((locale) => {
+      this.locale = locale;
+    });
     if (typeof window === 'undefined') {
       return;
     }
@@ -105,6 +109,11 @@ export class HostShellComponent implements OnInit {
     void this.refreshSession();
   }
 
+  ngOnDestroy(): void {
+    this.unsubscribeLocale?.();
+    this.unsubscribeLocale = null;
+  }
+
   copy(key: string): string {
     return t(key, this.locale);
   }
@@ -147,7 +156,7 @@ export class HostShellComponent implements OnInit {
     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;
@@ -168,7 +177,7 @@ export class HostShellComponent implements OnInit {
     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

@@ -350,4 +350,90 @@ 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();
+
+    await expect(mediaPrototype.play()).resolves.toBeUndefined();
+
+    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');
+  });
 });

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

@@ -5,7 +5,7 @@ import { FormsModule } from '@angular/forms';
 import { createApiClient } from '../../../../../src/api/client';
 import { createSessionContextStore } from '../../../../../src/spa/session-context-store';
 import { createVerticalSliceController } from '../../../../../src/spa/vertical-slice';
-import { clientHasNoAudioOutput, resolvePreferredLocale, t } from '../../lobby-i18n';
+import { clientHasNoAudioOutput, resolvePreferredLocale, subscribeToLocaleChanges, t } from '../../lobby-i18n';
 
 interface SessionDetail {
   session: { code: string; status: string; current_round: number };
@@ -16,6 +16,19 @@ interface SessionDetail {
 type ConnectionState = 'online' | 'reconnecting' | 'offline';
 type LoadingTransition = 'refresh' | 'join' | 'submit-lie' | 'submit-guess' | null;
 
+type MediaPrototypeWithGuardState = {
+  play?: () => Promise<void>;
+  __wppSecondaryDeviceAudioGuard__?: {
+    originalPlay: () => Promise<void>;
+    installs: number;
+  };
+};
+
+type GuardableMediaElement = {
+  muted?: boolean;
+  pause?: () => void;
+};
+
 function resolveLocalStorage(): Storage | undefined {
   if (typeof window === 'undefined') {
     return undefined;
@@ -112,6 +125,8 @@ export class PlayerShellComponent implements OnInit, OnDestroy {
   private readonly controller = createVerticalSliceController(createApiClient(), this.sessionContextStore);
   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) {
@@ -125,6 +140,11 @@ export class PlayerShellComponent implements OnInit, OnDestroy {
   }
 
   ngOnInit(): void {
+    this.unsubscribeLocale = subscribeToLocaleChanges((locale) => {
+      this.locale = locale;
+    });
+    this.installSecondaryDeviceAudioGuard();
+
     const hashRoute = window.location.hash.replace(/^#\/?/, '');
     const match = hashRoute.match(/^player(?:\/[^/]+)?(?:\/([^/?#]+))?/i);
     const codeFromRoute = match?.[1] ?? '';
@@ -151,6 +171,10 @@ export class PlayerShellComponent implements OnInit, OnDestroy {
     }
     this.clearReconnectTimer();
     this.clearStateSyncTimer();
+    this.unsubscribeLocale?.();
+    this.unsubscribeLocale = null;
+    this.restoreAudioGuard?.();
+    this.restoreAudioGuard = null;
   }
 
   private readonly handleOnline = (): void => {
@@ -178,6 +202,66 @@ 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 = () => 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.pause?.();
+    });
+  }
+
   private scheduleStateSync(): void {
     this.clearStateSyncTimer();
 
@@ -225,7 +309,7 @@ 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 {
@@ -349,7 +433,7 @@ 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;
@@ -375,7 +459,7 @@ 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/gameplay-phase-machine.spec.ts

@@ -0,0 +1,96 @@
+import { describe, expect, it } from 'vitest';
+
+import { deriveGameplayPhase, transitionGameplayPhase } from '../../../src/spa/gameplay-phase-machine';
+
+describe('gameplay phase machine sync guards', () => {
+  it('keeps explicit scoreboard status as scoreboard phase', () => {
+    const phase = deriveGameplayPhase({
+      session: {
+        code: 'ABCD12',
+        status: 'scoreboard',
+        host_id: 1,
+        current_round: 1,
+        players_count: 2,
+      },
+      round_question: null,
+      players: [],
+      phase_view_model: {
+        status: 'scoreboard',
+        round_number: 1,
+        players_count: 2,
+        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: false,
+          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,
+        },
+      },
+    });
+
+    expect(phase).toBe('scoreboard');
+  });
+
+  it('maps finished status to scoreboard phase fallback', () => {
+    const phase = deriveGameplayPhase({
+      session: {
+        code: 'ABCD12',
+        status: 'finished',
+        host_id: 1,
+        current_round: 1,
+        players_count: 2,
+      },
+      round_question: null,
+      players: [],
+      phase_view_model: {
+        status: 'finished',
+        round_number: 1,
+        players_count: 2,
+        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: false,
+          can_start_next_round: false,
+          can_finish_game: false,
+        },
+        player: {
+          can_join: false,
+          can_submit_lie: false,
+          can_submit_guess: false,
+          can_view_final_result: true,
+        },
+      },
+    });
+
+    expect(phase).toBe('scoreboard');
+  });
+
+  it('transitions reveal -> scoreboard on SCOREBOARD_READY', () => {
+    expect(transitionGameplayPhase('reveal', 'SCOREBOARD_READY')).toEqual({
+      phase: 'scoreboard',
+      changed: true,
+    });
+  });
+});

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

@@ -0,0 +1,61 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+
+import { HostShellComponent } from './features/host/host-shell.component';
+import { PlayerShellComponent } from './features/player/player-shell.component';
+import { setPreferredLocale } from './lobby-i18n';
+
+describe('i18n MVP flow smoke (host/player + audio policy)', () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+    vi.unstubAllGlobals();
+  });
+
+  it('resolves host/player copy in en and da from shared catalog', () => {
+    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() },
+      addEventListener: vi.fn(),
+      removeEventListener: vi.fn(),
+    });
+    vi.stubGlobal('navigator', { language: 'en-US', onLine: true });
+
+    const host = new HostShellComponent();
+    const player = new PlayerShellComponent();
+    host.ngOnInit();
+    player.ngOnInit();
+
+    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('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)', () => {
+    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() },
+      addEventListener: vi.fn(),
+      removeEventListener: vi.fn(),
+    });
+    vi.stubGlobal('navigator', { language: 'en-US', onLine: true });
+
+    const host = new HostShellComponent();
+    const player = new PlayerShellComponent();
+
+    expect(host.clientHasNoAudioOutput).toBe(true);
+    expect(player.clientHasNoAudioOutput).toBe(true);
+
+    player.ngOnDestroy();
+    host.ngOnDestroy();
+  });
+});

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

@@ -0,0 +1,137 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+
+type StorageLike = {
+  getItem: (key: string) => string | null;
+  setItem: (key: string, value: string) => void;
+};
+
+function storageMock(initial: Record<string, string> = {}): StorageLike {
+  const data = new Map<string, string>(Object.entries(initial));
+  return {
+    getItem: vi.fn((key: string) => data.get(key) ?? null),
+    setItem: vi.fn((key: string, value: string) => {
+      data.set(key, value);
+    }),
+  };
+}
+
+describe('lobby i18n locale propagation', () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+    vi.unstubAllGlobals();
+    vi.resetModules();
+  });
+
+  it('notifies subscribers immediately and on locale changes', async () => {
+    const localStorage = storageMock({ 'wpp.locale': 'en' });
+    vi.stubGlobal('window', {
+      location: { search: '' },
+      localStorage,
+    });
+    vi.stubGlobal('navigator', { language: 'en-US' });
+
+    const i18n = await import('./lobby-i18n');
+
+    const updates: string[] = [];
+    const unsubscribe = i18n.subscribeToLocaleChanges((locale) => updates.push(locale));
+
+    expect(updates).toEqual(['en']);
+
+    i18n.setPreferredLocale('da');
+    expect(updates).toEqual(['en', 'da']);
+
+    unsubscribe();
+    i18n.setPreferredLocale('en');
+    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: '' },
+      localStorage: storageMock({ 'wpp.locale': 'da' }),
+    });
+    vi.stubGlobal('navigator', { language: 'da-DK' });
+
+    const i18n = await import('./lobby-i18n');
+    const catalogModule = await import('../../../../shared/i18n/lobby.json');
+    const catalog = catalogModule.default as {
+      frontend: {
+        ui: {
+          common: {
+            refresh: {
+              en?: string;
+              da?: string;
+            };
+          };
+        };
+      };
+    };
+
+    const originalDa = catalog.frontend.ui.common.refresh.da;
+    catalog.frontend.ui.common.refresh.da = undefined;
+
+    try {
+      expect(i18n.t('common.refresh', 'da')).toBe(catalog.frontend.ui.common.refresh.en);
+    } finally {
+      catalog.frontend.ui.common.refresh.da = originalDa;
+    }
+  });
+
+  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: '' },
+      localStorage: storageMock({ 'wpp.locale': 'en' }),
+    });
+    vi.stubGlobal('navigator', { language: 'en-US' });
+
+    const i18n = await import('./lobby-i18n');
+
+    expect(i18n.clientHasNoAudioOutput).toBe(true);
+  });
+});

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

@@ -5,6 +5,9 @@ type SupportedLocale = (typeof lobbyCatalog.locales.supported)[number];
 const DEFAULT_LOCALE = lobbyCatalog.locales.default as SupportedLocale;
 const SUPPORTED_LOCALES = lobbyCatalog.locales.supported as readonly SupportedLocale[];
 
+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)) {
@@ -20,29 +23,65 @@ export function normalizeLocale(rawLocale?: string | null): SupportedLocale {
 }
 
 export function resolvePreferredLocale(): SupportedLocale {
-  if (typeof window === 'undefined') {
-    return DEFAULT_LOCALE;
+  if (activeLocale) {
+    return activeLocale;
   }
 
+  if (typeof window === 'undefined') {
+    activeLocale = DEFAULT_LOCALE;
+    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 : '';
 
-  return normalizeLocale(queryLocale || storedLocale || browserLocale || DEFAULT_LOCALE);
+  activeLocale = normalizeLocale(rootLocale || shellLocale || queryLocale || storedLocale || browserLocale || DEFAULT_LOCALE);
+  return activeLocale;
 }
 
 export function setPreferredLocale(locale: string): SupportedLocale {
   const normalized = normalizeLocale(locale);
+  activeLocale = normalized;
   if (typeof window !== 'undefined') {
     window.localStorage?.setItem?.('wpp.locale', normalized);
   }
+
+  for (const subscriber of localeSubscribers) {
+    subscriber(normalized);
+  }
+
   return normalized;
 }
 
+export function subscribeToLocaleChanges(callback: (locale: SupportedLocale) => void): () => void {
+  localeSubscribers.add(callback);
+  callback(resolvePreferredLocale());
+  return () => {
+    localeSubscribers.delete(callback);
+  };
+}
+
+function resolveCatalogPath(key: string): string {
+  if (key.startsWith('lobby.shell.')) {
+    return key.replace(/^lobby\.shell\./, 'app.');
+  }
+  if (key.startsWith('game.host.')) {
+    return key.replace(/^game\.host\./, 'host.');
+  }
+  if (key.startsWith('game.player.')) {
+    return key.replace(/^game\.player\./, 'player.');
+  }
+  return key;
+}
+
 export function t(key: string, locale: string): string {
   const normalizedLocale = normalizeLocale(locale);
   const fallbackLocale = DEFAULT_LOCALE;
-  const segments = key.split('.');
+  const segments = resolveCatalogPath(key).split('.');
 
   let cursor: unknown = lobbyCatalog.frontend.ui;
   for (const segment of segments) {

frontend/src/spa/gameplay-phase-machine.ts

@@ -46,7 +46,7 @@ export function deriveGameplayPhase(session: SessionDetailResponse | null): Game
     return null;
   }
 
-  if (status === 'lie' || status === 'guess' || status === 'reveal') {
+  if (status === 'lie' || status === 'guess' || status === 'reveal' || status === 'scoreboard') {
     return status;
   }
 

frontend/src/spa/lobby-i18n.ts

@@ -1,31 +1,55 @@
 import lobbyCatalog from '../../../shared/i18n/lobby.json';
 
-type FrontendErrorKey = keyof typeof lobbyCatalog.frontend.errors;
-
 const frontendErrors = lobbyCatalog.frontend.errors;
+const localeConfig = lobbyCatalog.locales;
+const backendToFrontendErrorKeys = lobbyCatalog.contract.backend_to_frontend_error_keys as Record<string, keyof typeof frontendErrors>;
 
-const apiErrorMap: Record<string, FrontendErrorKey> = {
-  session_code_required: 'session_code_required',
-  session_not_found: 'session_not_found',
-  nickname_invalid: 'nickname_invalid',
-  nickname_taken: 'nickname_taken'
-};
+type FrontendErrorKey = keyof typeof frontendErrors;
+type SupportedLocale = (typeof localeConfig.supported)[number];
 
-export function lobbyMessage(key: FrontendErrorKey): string {
-  return frontendErrors[key] ?? frontendErrors.unknown;
+function isFrontendErrorKey(value: string): value is FrontendErrorKey {
+  return value in frontendErrors;
 }
 
-export function lobbyMessageFromApiPayload(payload: unknown, fallbackKey: FrontendErrorKey): string {
+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>;
+
+  if (translations[resolvedLocale]) {
+    return translations[resolvedLocale];
+  }
+  if (translations[localeConfig.default]) {
+    return translations[localeConfig.default];
+  }
+
+  return key;
+}
+
+export function lobbyMessageFromApiPayload(payload: unknown, fallbackKey: FrontendErrorKey, locale?: string): string {
   if (!payload || typeof payload !== 'object') {
-    return lobbyMessage(fallbackKey);
+    return lobbyMessage(fallbackKey, locale);
   }
 
   const record = payload as Record<string, unknown>;
   const code = typeof record.error_code === 'string' ? record.error_code : '';
-  const mappedKey = apiErrorMap[code];
-  if (!mappedKey) {
-    return lobbyMessage(fallbackKey);
+  const payloadLocale = typeof record.locale === 'string' ? record.locale : locale;
+  const mappedKey = code ? backendToFrontendErrorKeys[code] : undefined;
+
+  if (mappedKey && isFrontendErrorKey(mappedKey)) {
+    return lobbyMessage(mappedKey, payloadLocale);
   }
 
-  return lobbyMessage(mappedKey);
+  if (isFrontendErrorKey(code)) {
+    return lobbyMessage(code, payloadLocale);
+  }
+
+  return lobbyMessage(fallbackKey, payloadLocale);
 }

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

@@ -0,0 +1,68 @@
+import { describe, expect, it } from 'vitest';
+
+import lobbyCatalog from '../../shared/i18n/lobby.json';
+import { lobbyMessage, lobbyMessageFromApiPayload } from '../src/spa/lobby-i18n';
+
+describe('shared i18n keyspace contract', () => {
+  it('keeps en as default and da/en matrix for frontend error keys', () => {
+    expect(lobbyCatalog.locales.default).toBe('en');
+    expect(lobbyCatalog.locales.supported).toEqual(expect.arrayContaining(['en', 'da']));
+
+    for (const [key, translations] of Object.entries(lobbyCatalog.frontend.errors)) {
+      expect(translations.en, `${key} missing en`).toBeTruthy();
+      expect(translations.da, `${key} missing da`).toBeTruthy();
+    }
+  });
+
+  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 ${code}`).toBeTruthy();
+      expect(lobbyCatalog.frontend.errors[frontendKey as keyof typeof lobbyCatalog.frontend.errors]).toBeDefined();
+    }
+
+    for (const [key, translations] of Object.entries(lobbyCatalog.backend.errors)) {
+      expect(translations.en, `${key} missing en`).toBeTruthy();
+      expect(translations.da, `${key} missing da`).toBeTruthy();
+    }
+  });
+});
+
+describe('lobbyMessage locale handling', () => {
+  it('uses english by default and falls back to default for unsupported locale', () => {
+    expect(lobbyMessage('session_code_required')).toBe('Session code is required.');
+    expect(lobbyMessage('session_code_required', 'fr')).toBe('Session code is required.');
+  });
+
+  it('resolves locale from api payload and maps known backend error codes directly', () => {
+    expect(
+      lobbyMessageFromApiPayload(
+        { error_code: 'session_not_found', locale: 'da' },
+        'join_failed',
+      ),
+    ).toBe('Sessionskoden er ugyldig, eller sessionen findes ikke længere.');
+  });
+
+  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.');
+  });
+});

lobby/i18n.py

@@ -36,7 +36,13 @@ def lobby_i18n_error_messages() -> dict:
 
 def resolve_locale(request: HttpRequest) -> str:
     default_locale, supported_locales = i18n_locale_config()
-    requested = (get_language_from_request(request) or "").split("-", 1)[0].lower()
+
+    raw_accept_language = (request.META.get("HTTP_ACCEPT_LANGUAGE") or "").split(",", 1)[0]
+    raw_requested = raw_accept_language.split(";", 1)[0].strip().replace("_", "-").split("-", 1)[0].lower()
+    if raw_requested in supported_locales:
+        return raw_requested
+
+    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">
+  <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>
-  <script type="module" src="{{ spa_asset_base }}/main.js"></script>
+<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

@@ -2,6 +2,7 @@ import json
 import tempfile
 from datetime import timedelta
 from pathlib import Path
+from unittest.mock import patch
 
 from django.contrib.auth import get_user_model
 from django.core.management import call_command
@@ -19,7 +20,7 @@ from fupogfakta.models import (
     RoundConfig,
     RoundQuestion,
 )
-from lobby.i18n import resolve_error_message
+from lobby.i18n import i18n_locale_config, lobby_i18n_catalog, resolve_error_message, resolve_locale
 
 User = get_user_model()
 
@@ -208,6 +209,8 @@ 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):
@@ -227,6 +230,8 @@ 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):
@@ -243,6 +248,36 @@ 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):
@@ -433,6 +468,8 @@ 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):
@@ -998,6 +1035,10 @@ 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)
@@ -1022,7 +1063,8 @@ class UiScreenTests(TestCase):
         self.assertContains(response, "<app-root")
         self.assertContains(response, "data-wpp-shell-route=\"/host\"")
         self.assertContains(response, "data-wpp-shell-kind=\"host\"")
-        self.assertContains(response, "/static/frontend/angular/browser/main.js")
+        self.assertContains(response, "/static/frontend/angular/browser/main.js?v=dev")
+        self.assertContains(response, "/static/frontend/angular/browser/styles.css?v=dev")
 
     @override_settings(USE_SPA_UI=True)
     def test_host_screen_deeplink_preserves_spa_path_when_feature_flag_enabled(self):
@@ -1056,7 +1098,17 @@ class UiScreenTests(TestCase):
         self.assertContains(response, "<app-root")
         self.assertContains(response, "data-wpp-shell-route=\"/player\"")
         self.assertContains(response, "data-wpp-shell-kind=\"player\"")
-        self.assertContains(response, "/static/frontend/angular/browser/main.js")
+        self.assertContains(response, "/static/frontend/angular/browser/main.js?v=dev")
+
+    @override_settings(USE_SPA_UI=True, WPP_SPA_ASSET_VERSION="release-2026-03-01")
+    def test_spa_shell_uses_configured_asset_version_for_cache_busting(self):
+        self.client.login(username="host_ui", password="secret123")
+
+        response = self.client.get(reverse("lobby:host_screen"))
+
+        self.assertEqual(response.status_code, 200)
+        self.assertContains(response, "/static/frontend/angular/browser/styles.css?v=release-2026-03-01")
+        self.assertContains(response, "/static/frontend/angular/browser/main.js?v=release-2026-03-01")
 
 
 class SessionDetailRoundQuestionTests(TestCase):
@@ -1204,5 +1256,82 @@ 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_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")
+
+    def test_missing_backend_key_is_logged_with_context(self):
+        with self.assertLogs("lobby.i18n", level="WARNING") as logs:
+            result = resolve_error_message(key="missing_key", locale="da")
+
+        self.assertEqual(result, "missing_key")
+        self.assertTrue(any("i18n key missing in shared catalog" in entry for entry in logs.output))
+
+    def test_missing_locale_translation_falls_back_to_default_locale(self):
+        with patch(
+            "lobby.i18n.lobby_i18n_error_messages",
+            return_value={"session_code_required": {"en": "Session code is required"}},
+        ):
+            self.assertEqual(
+                resolve_error_message(key="session_code_required", locale="da"),
+                "Session code is required",
+            )
+
+    def test_shared_catalog_uses_en_default_and_da_en_matrix(self):
+        default_locale, supported_locales = i18n_locale_config()
+        catalog = lobby_i18n_catalog()
+
+        self.assertEqual(default_locale, "en")
+        self.assertIn("en", supported_locales)
+        self.assertIn("da", supported_locales)
+
+        for key, translations in catalog["backend"]["errors"].items():
+            self.assertTrue(translations.get("en"), f"backend key {key} missing en")
+            self.assertTrue(translations.get("da"), f"backend key {key} missing da")
+
+        for key, translations in catalog["frontend"]["errors"].items():
+            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_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, 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):
@@ -16,7 +16,9 @@ def _render_spa_shell(request, shell_route: str, shell_kind: str):
             "shell_route": shell_route,
             "shell_kind": shell_kind,
             "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

@@ -268,7 +268,11 @@ 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 +291,11 @@ 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 +348,41 @@ 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 +391,11 @@ 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 +505,25 @@ 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 +532,20 @@ 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 +561,11 @@ 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

partyhub/settings.py

@@ -111,6 +111,9 @@ if USE_SPA_UI_RAW is None:
     USE_SPA_UI_RAW = env('WPP_SPA_ENABLED', 'false')
 USE_SPA_UI = USE_SPA_UI_RAW.lower() == 'true'
 WPP_SPA_ASSET_BASE = env('WPP_SPA_ASSET_BASE', '/static/frontend/angular/browser').rstrip('/')
+# Cache-busting token for SPA shell static asset URLs (querystring versioning).
+# Set to release id / commit SHA in deploy env for deterministic invalidation.
+WPP_SPA_ASSET_VERSION = env('WPP_SPA_ASSET_VERSION', 'dev')
 
 CHANNEL_REDIS_HOST = env('CHANNEL_REDIS_HOST', '127.0.0.1')
 CHANNEL_REDIS_PORT = int(env('CHANNEL_REDIS_PORT', '6379'))

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())

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": {
@@ -273,7 +281,18 @@
       "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 +330,89 @@
       "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"
+    }
   }
-}
+}