Merge pull request 'diplomail (Stage A→D): backend in-game diplomatic mail' (#10) from feature/diplomail-backend into development

Closes the documentation gaps from the freshly-audited diplomail
implementation. FUNCTIONAL.md gains a §11 "Diplomatic mail" with
the full user-facing story across all five stages, mirrored into
FUNCTIONAL_ru.md as the project conventions require. A new
backend/docs/diplomail-translator-setup.md captures the
LibreTranslate operational recipe (Docker image, env wiring,
manual smoke test, troubleshooting). The package README gains a
"Multi-instance posture" note documenting the deliberate absence
of FOR UPDATE in the worker pickup query — single-instance is
safe today; multi-instance scaling will revisit the claim
mechanism.

Two small edge-case tests round things out: malformed
LibreTranslate response bodies (single string, short array,
empty array, missing field) must surface as errors so the worker
falls back instead of crashing; and an empty translation queue
must produce zero events on three consecutive Worker.Tick calls.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/ui-test.yaml

@@ -16,6 +16,18 @@ on:
       - '.gitea/workflows/ui-test.yaml'
       - '!**/*.md'
 
+# Playwright launches its own `pnpm dev` on :5173, and in host-mode
+# the runner shares the host's port namespace with every other job,
+# so two parallel ui-test runs collide on EADDRINUSE. Serialise via a
+# singleton concurrency group with queueing — new runs wait their
+# turn instead of cancelling the in-progress one. cancel-in-progress
+# is explicitly false because Gitea has shown spurious self-cancel
+# behaviour under cancel-in-progress: true even when no other run
+# shares the group.
+concurrency:
+  group: ui-test-singleton
+  cancel-in-progress: false
+
 jobs:
   test:
     runs-on: ubuntu-latest
@@ -59,6 +71,15 @@ jobs:
         working-directory: ui/frontend
         run: pnpm test
 
+      - name: Clear stale Vite from :5173
+        # Defence in depth in case a previous job's webServer survived
+        # the concurrency-cancel — `pkill` does not fail when there is
+        # nothing to kill, and `fuser -k` cleans up anything else
+        # holding the port.
+        run: |
+          pkill -f 'vite dev' || true
+          fuser -k 5173/tcp 2>/dev/null || true
+
       - name: Run Playwright
         working-directory: ui/frontend
         run: pnpm exec playwright test

backend/README.md

@@ -45,6 +45,7 @@ backend/
 │   ├── admin/           # admin_accounts, Basic Auth verifier, admin operations
 │   ├── auth/            # email-code challenges, device sessions, Ed25519 keys
 │   ├── config/          # env-var loader, Validate
+│   ├── diplomail/       # diplomatic-mail messages, recipients, translations
 │   ├── dockerclient/    # docker/docker wrapper for container ops
 │   ├── engineclient/    # net/http client to galaxy-game containers
 │   ├── geo/             # geoip lookup, declared_country, per-user counters
@@ -131,6 +132,12 @@ fast.
 | `BACKEND_NOTIFICATION_ADMIN_EMAIL`      | no       | —                             | Recipient address for admin-channel notifications (`runtime.*` kinds). When empty, admin-channel routes are recorded as `skipped` and the catalog is partially silenced. |
 | `BACKEND_NOTIFICATION_WORKER_INTERVAL`  | no       | `5s`                          | Notification route worker scan interval. |
 | `BACKEND_NOTIFICATION_MAX_ATTEMPTS`     | no       | `8`                           | Notification route delivery attempts before dead-lettering. |
+| `BACKEND_DIPLOMAIL_MAX_BODY_BYTES`      | no       | `4096`                        | Maximum size of `diplomail_messages.body` enforced at send time. Tune at runtime without a migration. |
+| `BACKEND_DIPLOMAIL_MAX_SUBJECT_BYTES`   | no       | `256`                         | Maximum size of `diplomail_messages.subject`. Subject is optional; empty is always accepted. |
+| `BACKEND_DIPLOMAIL_TRANSLATOR_URL`      | no       | —                             | Base URL of a LibreTranslate-compatible instance (`http://libretranslate:5000`). Empty → translator falls through to no-op (recipients are delivered with the original body). |
+| `BACKEND_DIPLOMAIL_TRANSLATOR_TIMEOUT`  | no       | `10s`                         | Per-request HTTP timeout for the translation worker. |
+| `BACKEND_DIPLOMAIL_TRANSLATOR_MAX_ATTEMPTS` | no   | `5`                           | Number of failed HTTP attempts before the worker delivers the message with the original body (fallback). |
+| `BACKEND_DIPLOMAIL_WORKER_INTERVAL`     | no       | `2s`                          | How often the async translation worker scans for pending pairs. The worker processes one pair per tick. |
 
 If `BACKEND_ADMIN_BOOTSTRAP_USER` is set without
 `BACKEND_ADMIN_BOOTSTRAP_PASSWORD`, `Validate()` fails. If neither is

backend/cmd/backend/main.go

@@ -12,6 +12,7 @@ import (
 	"os"
 	"os/signal"
 	"syscall"
+	"time"
 
 	// time/tzdata embeds the IANA timezone database so time.LoadLocation
 	// works in container images without /usr/share/zoneinfo (distroless
@@ -25,6 +26,9 @@ import (
 	"galaxy/backend/internal/auth"
 	"galaxy/backend/internal/config"
 	"galaxy/backend/internal/devsandbox"
+	"galaxy/backend/internal/diplomail"
+	"galaxy/backend/internal/diplomail/detector"
+	"galaxy/backend/internal/diplomail/translator"
 	"galaxy/backend/internal/dockerclient"
 	"galaxy/backend/internal/engineclient"
 	"galaxy/backend/internal/geo"
@@ -131,6 +135,7 @@ func run(ctx context.Context) (err error) {
 	lobbyCascade := &lobbyCascadeAdapter{}
 	userNotifyCascade := &userNotificationCascadeAdapter{}
 	lobbyNotifyPublisher := &lobbyNotificationPublisherAdapter{}
+	lobbyDiplomailPublisher := &lobbyDiplomailPublisherAdapter{}
 	runtimeNotifyPublisher := &runtimeNotificationPublisherAdapter{}
 
 	userSvc := user.NewService(user.Deps{
@@ -197,6 +202,7 @@ func run(ctx context.Context) (err error) {
 		Cache:        lobbyCache,
 		Runtime:      runtimeGateway,
 		Notification: lobbyNotifyPublisher,
+		Diplomail:    lobbyDiplomailPublisher,
 		Entitlement:  &userEntitlementAdapter{svc: userSvc},
 		Config:       cfg.Lobby,
 		Logger:       logger,
@@ -301,6 +307,25 @@ func run(ctx context.Context) (err error) {
 	userNotifyCascade.svc = notifSvc
 	lobbyNotifyPublisher.svc = notifSvc
 	runtimeNotifyPublisher.svc = notifSvc
+
+	diplomailStore := diplomail.NewStore(db)
+	diplomailTranslator, err := buildDiplomailTranslator(cfg.Diplomail, logger)
+	if err != nil {
+		return fmt.Errorf("build diplomail translator: %w", err)
+	}
+	diplomailSvc := diplomail.NewService(diplomail.Deps{
+		Store:        diplomailStore,
+		Memberships:  &diplomailMembershipAdapter{lobby: lobbySvc, users: userSvc},
+		Notification: &diplomailNotificationPublisherAdapter{svc: notifSvc},
+		Entitlements: &diplomailEntitlementAdapter{users: userSvc},
+		Games:        &diplomailGameAdapter{lobby: lobbySvc},
+		Detector:     detector.New(),
+		Translator:   diplomailTranslator,
+		Config:       cfg.Diplomail,
+		Logger:       logger,
+	})
+	lobbyDiplomailPublisher.svc = diplomailSvc
+	diplomailWorker := diplomail.NewWorker(diplomailSvc)
 	if email := cfg.Notification.AdminEmail; email == "" {
 		logger.Info("notification admin email not configured (BACKEND_NOTIFICATION_ADMIN_EMAIL); admin-channel routes will be skipped")
 	} else {
@@ -325,9 +350,11 @@ func run(ctx context.Context) (err error) {
 	adminEngineVersionsHandlers := backendserver.NewAdminEngineVersionsHandlers(engineVersionSvc, logger)
 	adminRuntimesHandlers := backendserver.NewAdminRuntimesHandlers(runtimeSvc, logger)
 	adminMailHandlers := backendserver.NewAdminMailHandlers(mailSvc, logger)
+	adminDiplomailHandlers := backendserver.NewAdminDiplomailHandlers(diplomailSvc, logger)
 	adminNotificationsHandlers := backendserver.NewAdminNotificationsHandlers(notifSvc, logger)
 	adminGeoHandlers := backendserver.NewAdminGeoHandlers(geoSvc, logger)
 	userGamesHandlers := backendserver.NewUserGamesHandlers(runtimeSvc, engineCli, logger)
+	userMailHandlers := backendserver.NewUserMailHandlers(diplomailSvc, lobbySvc, userSvc, logger)
 
 	ready := func() bool {
 		return authCache.Ready() && userCache.Ready() && adminCache.Ready() && lobbyCache.Ready() && runtimeCache.Ready()
@@ -356,9 +383,11 @@ func run(ctx context.Context) (err error) {
 		AdminRuntimes:         adminRuntimesHandlers,
 		AdminEngineVersions:   adminEngineVersionsHandlers,
 		AdminMail:             adminMailHandlers,
+		AdminDiplomail:        adminDiplomailHandlers,
 		AdminNotifications:    adminNotificationsHandlers,
 		AdminGeo:              adminGeoHandlers,
 		UserGames:             userGamesHandlers,
+		UserMail:              userMailHandlers,
 	})
 	if err != nil {
 		return fmt.Errorf("build backend router: %w", err)
@@ -374,7 +403,7 @@ func run(ctx context.Context) (err error) {
 	runtimeScheduler := runtimeSvc.SchedulerComponent()
 	runtimeReconciler := runtimeSvc.Reconciler()
 
-	components := []app.Component{httpServer, pushServer, mailWorker, notifWorker, lobbySweeper, runtimeWorkers, runtimeScheduler, runtimeReconciler}
+	components := []app.Component{httpServer, pushServer, mailWorker, notifWorker, diplomailWorker, lobbySweeper, runtimeWorkers, runtimeScheduler, runtimeReconciler}
 	if metricsServer.Enabled() {
 		components = append(components, metricsServer)
 	}
@@ -579,3 +608,288 @@ func (a *runtimeNotificationPublisherAdapter) PublishRuntimeEvent(ctx context.Co
 	}
 	return a.svc.RuntimeAdapter().PublishRuntimeEvent(ctx, kind, idempotencyKey, payload)
 }
+
+// diplomailMembershipAdapter implements `diplomail.MembershipLookup`
+// by walking the lobby cache (for active rows) and the lobby service
+// (for any-status rows) and stitching each membership row to the
+// immutable `accounts.user_name` resolved through `*user.Service`.
+type diplomailMembershipAdapter struct {
+	lobby *lobby.Service
+	users *user.Service
+}
+
+func (a *diplomailMembershipAdapter) GetActiveMembership(ctx context.Context, gameID, userID uuid.UUID) (diplomail.ActiveMembership, error) {
+	if a == nil || a.lobby == nil || a.users == nil {
+		return diplomail.ActiveMembership{}, diplomail.ErrNotFound
+	}
+	cache := a.lobby.Cache()
+	if cache == nil {
+		return diplomail.ActiveMembership{}, diplomail.ErrNotFound
+	}
+	game, ok := cache.GetGame(gameID)
+	if !ok {
+		return diplomail.ActiveMembership{}, diplomail.ErrNotFound
+	}
+	var found *lobby.Membership
+	for _, m := range cache.MembershipsForGame(gameID) {
+		if m.UserID == userID {
+			mm := m
+			found = &mm
+			break
+		}
+	}
+	if found == nil {
+		return diplomail.ActiveMembership{}, diplomail.ErrNotFound
+	}
+	account, err := a.users.GetAccount(ctx, userID)
+	if err != nil {
+		return diplomail.ActiveMembership{}, err
+	}
+	return diplomail.ActiveMembership{
+		UserID:            userID,
+		GameID:            gameID,
+		GameName:          game.GameName,
+		UserName:          account.UserName,
+		RaceName:          found.RaceName,
+		PreferredLanguage: account.PreferredLanguage,
+	}, nil
+}
+
+func (a *diplomailMembershipAdapter) GetMembershipAnyStatus(ctx context.Context, gameID, userID uuid.UUID) (diplomail.MemberSnapshot, error) {
+	if a == nil || a.lobby == nil || a.users == nil {
+		return diplomail.MemberSnapshot{}, diplomail.ErrNotFound
+	}
+	game, ok := a.lobby.Cache().GetGame(gameID)
+	if !ok {
+		return diplomail.MemberSnapshot{}, diplomail.ErrNotFound
+	}
+	members, err := a.lobby.ListMembershipsForGame(ctx, gameID)
+	if err != nil {
+		return diplomail.MemberSnapshot{}, err
+	}
+	var found *lobby.Membership
+	for _, m := range members {
+		if m.UserID == userID {
+			mm := m
+			found = &mm
+			break
+		}
+	}
+	if found == nil {
+		return diplomail.MemberSnapshot{}, diplomail.ErrNotFound
+	}
+	account, err := a.users.GetAccount(ctx, userID)
+	if err != nil {
+		return diplomail.MemberSnapshot{}, err
+	}
+	return diplomail.MemberSnapshot{
+		UserID:            userID,
+		GameID:            gameID,
+		GameName:          game.GameName,
+		UserName:          account.UserName,
+		RaceName:          found.RaceName,
+		Status:            found.Status,
+		PreferredLanguage: account.PreferredLanguage,
+	}, nil
+}
+
+func (a *diplomailMembershipAdapter) ListMembers(ctx context.Context, gameID uuid.UUID, scope string) ([]diplomail.MemberSnapshot, error) {
+	if a == nil || a.lobby == nil || a.users == nil {
+		return nil, diplomail.ErrNotFound
+	}
+	game, ok := a.lobby.Cache().GetGame(gameID)
+	if !ok {
+		return nil, diplomail.ErrNotFound
+	}
+	members, err := a.lobby.ListMembershipsForGame(ctx, gameID)
+	if err != nil {
+		return nil, err
+	}
+	matches := func(status string) bool {
+		switch scope {
+		case diplomail.RecipientScopeActive:
+			return status == lobby.MembershipStatusActive
+		case diplomail.RecipientScopeActiveAndRemoved:
+			return status == lobby.MembershipStatusActive || status == lobby.MembershipStatusRemoved
+		case diplomail.RecipientScopeAllMembers:
+			return true
+		default:
+			return status == lobby.MembershipStatusActive
+		}
+	}
+	out := make([]diplomail.MemberSnapshot, 0, len(members))
+	for _, m := range members {
+		if !matches(m.Status) {
+			continue
+		}
+		account, err := a.users.GetAccount(ctx, m.UserID)
+		if err != nil {
+			return nil, fmt.Errorf("resolve user_name for %s: %w", m.UserID, err)
+		}
+		out = append(out, diplomail.MemberSnapshot{
+			UserID:            m.UserID,
+			GameID:            gameID,
+			GameName:          game.GameName,
+			UserName:          account.UserName,
+			RaceName:          m.RaceName,
+			Status:            m.Status,
+			PreferredLanguage: account.PreferredLanguage,
+		})
+	}
+	return out, nil
+}
+
+// lobbyDiplomailPublisherAdapter implements `lobby.DiplomailPublisher`
+// by translating each lobby.LifecycleEvent into the diplomail
+// vocabulary and delegating to `*diplomail.Service.PublishLifecycle`.
+// The svc pointer is patched once diplomailSvc exists — diplomail
+// depends on lobby through MembershipLookup, so the lobby service
+// is constructed first and patched up.
+type lobbyDiplomailPublisherAdapter struct {
+	svc *diplomail.Service
+}
+
+func (a *lobbyDiplomailPublisherAdapter) PublishLifecycle(ctx context.Context, ev lobby.LifecycleEvent) error {
+	if a == nil || a.svc == nil {
+		return nil
+	}
+	return a.svc.PublishLifecycle(ctx, diplomail.LifecycleEvent{
+		GameID:     ev.GameID,
+		Kind:       ev.Kind,
+		Actor:      ev.Actor,
+		Reason:     ev.Reason,
+		TargetUser: ev.TargetUser,
+	})
+}
+
+// buildDiplomailTranslator selects the diplomail translator backend
+// from configuration: a non-empty `TranslatorURL` constructs the
+// LibreTranslate HTTP client; an empty URL falls through to the
+// noop translator so deployments without a translation service still
+// boot and deliver mail with the fallback path.
+func buildDiplomailTranslator(cfg config.DiplomailConfig, logger *zap.Logger) (translator.Translator, error) {
+	if cfg.TranslatorURL == "" {
+		logger.Info("diplomail translator URL not configured, using noop translator")
+		return translator.NewNoop(), nil
+	}
+	return translator.NewLibreTranslate(translator.LibreTranslateConfig{
+		URL:     cfg.TranslatorURL,
+		Timeout: cfg.TranslatorTimeout,
+	})
+}
+
+// diplomailEntitlementAdapter implements
+// `diplomail.EntitlementReader` by reading the user-service
+// entitlement snapshot. The IsPaid flag mirrors the per-tier policy
+// defined in `internal/user`, so updates to the tier set (monthly,
+// yearly, permanent, …) flow through without changes here.
+type diplomailEntitlementAdapter struct {
+	users *user.Service
+}
+
+func (a *diplomailEntitlementAdapter) IsPaidTier(ctx context.Context, userID uuid.UUID) (bool, error) {
+	if a == nil || a.users == nil {
+		return false, nil
+	}
+	snap, err := a.users.GetEntitlementSnapshot(ctx, userID)
+	if err != nil {
+		return false, err
+	}
+	return snap.IsPaid, nil
+}
+
+// diplomailGameAdapter implements `diplomail.GameLookup`. The
+// running-games and finished-games queries walk the lobby cache so
+// the admin multi-game broadcast and bulk-purge endpoints do not
+// fan out a per-game DB query each time. GetGame falls back to the
+// cache; an unknown id is surfaced as ErrNotFound (the diplomail
+// sentinel).
+type diplomailGameAdapter struct {
+	lobby *lobby.Service
+}
+
+func (a *diplomailGameAdapter) ListRunningGames(_ context.Context) ([]diplomail.GameSnapshot, error) {
+	if a == nil || a.lobby == nil || a.lobby.Cache() == nil {
+		return nil, nil
+	}
+	var out []diplomail.GameSnapshot
+	for _, game := range a.lobby.Cache().ListGames() {
+		if !isRunningStatus(game.Status) {
+			continue
+		}
+		out = append(out, gameSnapshot(game))
+	}
+	return out, nil
+}
+
+func (a *diplomailGameAdapter) ListFinishedGamesBefore(ctx context.Context, cutoff time.Time) ([]diplomail.GameSnapshot, error) {
+	if a == nil || a.lobby == nil {
+		return nil, nil
+	}
+	games, err := a.lobby.ListFinishedGamesBefore(ctx, cutoff)
+	if err != nil {
+		return nil, err
+	}
+	out := make([]diplomail.GameSnapshot, 0, len(games))
+	for _, g := range games {
+		out = append(out, gameSnapshot(g))
+	}
+	return out, nil
+}
+
+func (a *diplomailGameAdapter) GetGame(_ context.Context, gameID uuid.UUID) (diplomail.GameSnapshot, error) {
+	if a == nil || a.lobby == nil || a.lobby.Cache() == nil {
+		return diplomail.GameSnapshot{}, diplomail.ErrNotFound
+	}
+	game, ok := a.lobby.Cache().GetGame(gameID)
+	if !ok {
+		return diplomail.GameSnapshot{}, diplomail.ErrNotFound
+	}
+	return gameSnapshot(game), nil
+}
+
+func gameSnapshot(g lobby.GameRecord) diplomail.GameSnapshot {
+	out := diplomail.GameSnapshot{
+		GameID:   g.GameID,
+		GameName: g.GameName,
+		Status:   g.Status,
+	}
+	if g.FinishedAt != nil {
+		f := *g.FinishedAt
+		out.FinishedAt = &f
+	}
+	return out
+}
+
+func isRunningStatus(status string) bool {
+	switch status {
+	case lobby.GameStatusReadyToStart, lobby.GameStatusStarting, lobby.GameStatusRunning, lobby.GameStatusPaused:
+		return true
+	default:
+		return false
+	}
+}
+
+// diplomailNotificationPublisherAdapter implements
+// `diplomail.NotificationPublisher` by translating each
+// DiplomailNotification into a notification.Intent and routing it
+// through `*notification.Service.Submit`. The publisher leaves the
+// `diplomail.message.received` catalog entry to handle channel
+// fan-out (push only in Stage A).
+type diplomailNotificationPublisherAdapter struct {
+	svc *notification.Service
+}
+
+func (a *diplomailNotificationPublisherAdapter) PublishDiplomailEvent(ctx context.Context, ev diplomail.DiplomailNotification) error {
+	if a == nil || a.svc == nil {
+		return nil
+	}
+	intent := notification.Intent{
+		Kind:           ev.Kind,
+		IdempotencyKey: ev.IdempotencyKey,
+		Recipients:     []uuid.UUID{ev.Recipient},
+		Payload:        ev.Payload,
+	}
+	_, err := a.svc.Submit(ctx, intent)
+	return err
+}

backend/docs/diplomail-translator-setup.md

@@ -0,0 +1,164 @@
+# LibreTranslate setup for diplomatic mail
+
+This document describes how to run the LibreTranslate backend that the
+diplomatic-mail subsystem uses for body translation. The instructions
+target three audiences: developers spinning up LibreTranslate
+alongside `tools/local-dev`, operators preparing a real deployment,
+and reviewers verifying the end-to-end translation flow by hand.
+
+## When you need LibreTranslate
+
+The diplomatic-mail worker runs unconditionally — `make up` and `make
+test` both work without any translator. With
+`BACKEND_DIPLOMAIL_TRANSLATOR_URL` unset, the noop translator
+short-circuits the pipeline: messages are delivered in the original
+language, and the inbox handler returns the original body to every
+reader.
+
+You only need LibreTranslate when you want to exercise the cross-
+language path: sender writes in language X, recipient's
+`accounts.preferred_language` is Y, the worker is expected to fetch
+a Y rendering. The pipeline is otherwise identical and unaware of
+which engine is producing translations.
+
+## Running a local instance
+
+LibreTranslate ships a public Docker image at
+`libretranslate/libretranslate`. The image is ~3 GB on first pull
+because it bundles every supported language model; subsequent runs
+reuse the layer cache.
+
+The simplest setup is a one-shot container:
+
+```bash
+docker run --rm -d --name libretranslate \
+  -p 5000:5000 \
+  -e LT_LOAD_ONLY=en,ru \
+  libretranslate/libretranslate:latest
+```
+
+The `LT_LOAD_ONLY` whitelist trims the loaded model set so the
+container fits in ~600 MB of RAM. Drop the variable to load every
+language pair LibreTranslate ships.
+
+LibreTranslate boots in ~30 seconds (cold) or ~5 seconds (warm
+model cache). Wait until `curl -s http://localhost:5000/languages`
+returns a JSON array before pointing backend at it.
+
+## Wiring backend at it
+
+Add three env vars to the backend process:
+
+```
+BACKEND_DIPLOMAIL_TRANSLATOR_URL=http://localhost:5000
+BACKEND_DIPLOMAIL_TRANSLATOR_TIMEOUT=10s
+BACKEND_DIPLOMAIL_TRANSLATOR_MAX_ATTEMPTS=5
+```
+
+When backend lives inside the `tools/local-dev` Docker network and
+LibreTranslate runs on the host, replace `localhost` with the host's
+docker-bridge address (`http://host.docker.internal:5000` on
+Docker Desktop; `http://172.17.0.1:5000` on a Linux bridge by
+default).
+
+For a stack-internal deployment, drop LibreTranslate into the same
+Docker compose file alongside backend and reach it by its service
+name:
+
+```yaml
+services:
+  libretranslate:
+    image: libretranslate/libretranslate:latest
+    environment:
+      LT_LOAD_ONLY: "en,ru"
+    healthcheck:
+      test: ["CMD", "wget", "-qO-", "http://localhost:5000/languages"]
+      interval: 5s
+      timeout: 2s
+      retries: 12
+
+  backend:
+    environment:
+      BACKEND_DIPLOMAIL_TRANSLATOR_URL: "http://libretranslate:5000"
+    depends_on:
+      libretranslate:
+        condition: service_healthy
+```
+
+## Manual smoke test
+
+Once both services are up:
+
+1. Register two accounts via the public auth flow. Set the second
+   account's `preferred_language` to a value that differs from the
+   sender's writing language (e.g. sender writes in English, second
+   account is `ru`).
+2. Create a private game with the first account, invite the second,
+   land both as active members.
+3. Send a personal message: `POST /api/v1/user/games/{id}/mail/messages`
+   with the body in English.
+4. Watch backend logs for the diplomail worker. After ~2 seconds you
+   should see `translator attempt succeeded` (or equivalent INFO
+   line) and the recipient flipped to `available_at`.
+5. As the second account, fetch
+   `GET /api/v1/user/games/{id}/mail/messages/{message_id}`. The
+   response should carry both `body` (English original) and
+   `translated_body` (Russian) along with the `translation_lang`
+   and `translator` fields.
+
+## Operational notes
+
+- **Resource budget.** With `LT_LOAD_ONLY=en,ru` the container peaks
+  around 800 MB resident; with all languages, ~3 GB. Plan accordingly.
+- **CPU.** LibreTranslate is CPU-bound. One translation of a 200-
+  word body takes ~200 ms on a modern x86 core; the diplomail worker
+  is single-threaded by design, so steady-state throughput is
+  `1 / avg_latency` per backend instance.
+- **Outage behaviour.** A LibreTranslate outage stalls delivery of
+  pending pairs by at most ~31 seconds per pair (the worker's
+  exponential backoff schedule), then falls back to the original
+  body. Inbox listings never depend on the translator's
+  availability.
+- **API key.** Backend does not send an API key. Self-hosted
+  deployments without `LT_API_KEYS` configured accept anonymous
+  POSTs by default, which matches our deployment posture
+  (LibreTranslate sits on the internal docker network, not
+  reachable from outside).
+- **Models.** Adding a new target language is an operator-side
+  task: install the corresponding Argos model into the
+  LibreTranslate container (`argospm install …`) and either restart
+  the container or send a SIGHUP. The diplomail pipeline notices
+  the new language pair automatically — there is no allow-list
+  inside backend.
+
+## Troubleshooting
+
+- **`translator: do request: dial tcp ...: connect: connection refused`.**
+  LibreTranslate is not listening on the configured address. Verify
+  with `curl http://${URL}/languages`. On Docker setups, double-
+  check the bridge address discussion above.
+- **`translator: libretranslate http 400`** in worker logs but the
+  language pair clearly exists.
+  Make sure the request used the two-letter codes (`en`, not
+  `en-US`). Backend normalises before sending; if you see a region
+  subtag in the log, file an issue against `internal/diplomail` —
+  the normalisation should be unconditional.
+- **`translator: libretranslate http 503`.**
+  Container is still loading models. Wait for `/languages` to
+  respond `200`. The worker retries with backoff, so steady-state
+  recovers automatically.
+- **Worker logs only "noop translator returned, delivering
+  fallback".**
+  `BACKEND_DIPLOMAIL_TRANSLATOR_URL` is empty in the backend
+  process. Confirm with `docker compose exec backend env | grep
+  DIPLOMAIL`.
+
+## Future work
+
+- Adding an OpenTelemetry counter and histogram for translator
+  outcomes is tracked in the diplomail package README; the metrics
+  will surface in Grafana once LibreTranslate is deployed.
+- Email-alerting on prolonged outage (e.g. ≥ N consecutive failures
+  in M minutes) is planned through a new
+  `diplomail.translator.unhealthy` notification kind. Not wired
+  yet — current monitoring lives in zap logs.

backend/go.mod

@@ -36,6 +36,7 @@ require (
 )
 
 require (
+	github.com/abadojack/whatlanggo v1.0.1 // indirect
 	github.com/oschwald/geoip2-golang/v2 v2.1.0 // indirect
 	github.com/oschwald/maxminddb-golang/v2 v2.1.1 // indirect
 	github.com/robfig/cron/v3 v3.0.1 // indirect

backend/go.sum

@@ -10,6 +10,8 @@ github.com/Microsoft/go-winio v0.6.2 h1:F2VQgta7ecxGYO8k3ZZz3RS8fVIXVxONVUPlNERo
 github.com/Microsoft/go-winio v0.6.2/go.mod h1:yd8OoFMLzJbo9gZq8j5qaps8bJ9aShtEA8Ipt1oGCvU=
 github.com/XSAM/otelsql v0.42.0 h1:Li0xF4eJUxG2e0x3D4rvRlys1f27yJKvjTh7ljkUP5o=
 github.com/XSAM/otelsql v0.42.0/go.mod h1:4mOrEv+cS1KmKzrvTktvJnstr5GtKSAK+QHvFR9OcpI=
+github.com/abadojack/whatlanggo v1.0.1 h1:19N6YogDnf71CTHm3Mp2qhYfkRdyvbgwWdd2EPxJRG4=
+github.com/abadojack/whatlanggo v1.0.1/go.mod h1:66WiQbSbJBIlOZMsvbKe5m6pzQovxCH9B/K8tQB2uoc=
 github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
 github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
 github.com/bytedance/gopkg v0.1.4 h1:oZnQwnX82KAIWb7033bEwtxvTqXcYMxDBaQxo5JJHWM=

backend/internal/config/config.go

@@ -96,6 +96,13 @@ const (
 	envNotificationWorkerInterval = "BACKEND_NOTIFICATION_WORKER_INTERVAL"
 	envNotificationMaxAttempts = "BACKEND_NOTIFICATION_MAX_ATTEMPTS"
 
+	envDiplomailMaxBodyBytes = "BACKEND_DIPLOMAIL_MAX_BODY_BYTES"
+	envDiplomailMaxSubjectBytes = "BACKEND_DIPLOMAIL_MAX_SUBJECT_BYTES"
+	envDiplomailTranslatorURL = "BACKEND_DIPLOMAIL_TRANSLATOR_URL"
+	envDiplomailTranslatorTimeout = "BACKEND_DIPLOMAIL_TRANSLATOR_TIMEOUT"
+	envDiplomailTranslatorMaxAttempts = "BACKEND_DIPLOMAIL_TRANSLATOR_MAX_ATTEMPTS"
+	envDiplomailWorkerInterval = "BACKEND_DIPLOMAIL_WORKER_INTERVAL"
+
 	envDevSandboxEmail = "BACKEND_DEV_SANDBOX_EMAIL"
 	envDevSandboxEngineImage = "BACKEND_DEV_SANDBOX_ENGINE_IMAGE"
 	envDevSandboxEngineVersion = "BACKEND_DEV_SANDBOX_ENGINE_VERSION"
@@ -163,6 +170,12 @@ const (
 	defaultNotificationWorkerInterval = 5 * time.Second
 	defaultNotificationMaxAttempts = 8
 
+	defaultDiplomailMaxBodyBytes = 4096
+	defaultDiplomailMaxSubjectBytes = 256
+	defaultDiplomailTranslatorTimeout = 10 * time.Second
+	defaultDiplomailTranslatorMaxAttempts = 5
+	defaultDiplomailWorkerInterval = 2 * time.Second
+
 	defaultDevSandboxEngineVersion = "0.1.0"
 	defaultDevSandboxPlayerCount = 20
 )
@@ -201,6 +214,7 @@ type Config struct {
 	Engine EngineConfig
 	Runtime RuntimeConfig
 	Notification NotificationConfig
+	Diplomail DiplomailConfig
 	DevSandbox DevSandboxConfig
 
 	// FreshnessWindow mirrors the gateway freshness window and is used by the
@@ -397,6 +411,42 @@ type RuntimeConfig struct {
 	StopGracePeriod time.Duration
 }
 
+// DiplomailConfig bounds the diplomatic-mail subsystem. Both limits
+// are enforced in the service layer, so they can be tuned at runtime
+// without a schema migration. Body and subject are stored as plain
+// UTF-8 text; HTML is neither parsed nor sanitised on the server.
+type DiplomailConfig struct {
+	// MaxBodyBytes caps the length of `diplomail_messages.body` in
+	// bytes (not runes). A send whose body exceeds the limit is
+	// rejected with ErrInvalidInput.
+	MaxBodyBytes int
+
+	// MaxSubjectBytes caps the length of `diplomail_messages.subject`
+	// in bytes. Subjects are optional; the empty-string default
+	// passes the limit trivially.
+	MaxSubjectBytes int
+
+	// TranslatorURL is the base URL of the LibreTranslate-compatible
+	// instance the async translation worker calls. When empty, the
+	// worker still runs but falls through to "deliver original"
+	// (the noop translator returns engine=noop).
+	TranslatorURL string
+
+	// TranslatorTimeout bounds a single HTTP request to the
+	// translator. Worker retries (exponential backoff up to
+	// TranslatorMaxAttempts) layer on top.
+	TranslatorTimeout time.Duration
+
+	// TranslatorMaxAttempts is the number of times the worker tries
+	// to translate one (message, target_lang) pair before falling
+	// back to delivering the original body.
+	TranslatorMaxAttempts int
+
+	// WorkerInterval bounds how often the async translation worker
+	// scans for pending pairs. The worker handles one pair per tick.
+	WorkerInterval time.Duration
+}
+
 // NotificationConfig configures the notification fan-out module
 // implemented in `backend/internal/notification`. AdminEmail receives
 // admin-channel kinds (the `runtime.*` set in `backend/README.md` §10);
@@ -494,6 +544,13 @@ func DefaultConfig() Config {
 			WorkerInterval: defaultNotificationWorkerInterval,
 			MaxAttempts: defaultNotificationMaxAttempts,
 		},
+		Diplomail: DiplomailConfig{
+			MaxBodyBytes: defaultDiplomailMaxBodyBytes,
+			MaxSubjectBytes: defaultDiplomailMaxSubjectBytes,
+			TranslatorTimeout: defaultDiplomailTranslatorTimeout,
+			TranslatorMaxAttempts: defaultDiplomailTranslatorMaxAttempts,
+			WorkerInterval: defaultDiplomailWorkerInterval,
+		},
 		DevSandbox: DevSandboxConfig{
 			EngineVersion: defaultDevSandboxEngineVersion,
 			PlayerCount: defaultDevSandboxPlayerCount,
@@ -657,6 +714,23 @@ func LoadFromEnv() (Config, error) {
 		return Config{}, err
 	}
 
+	if cfg.Diplomail.MaxBodyBytes, err = loadInt(envDiplomailMaxBodyBytes, cfg.Diplomail.MaxBodyBytes); err != nil {
+		return Config{}, err
+	}
+	if cfg.Diplomail.MaxSubjectBytes, err = loadInt(envDiplomailMaxSubjectBytes, cfg.Diplomail.MaxSubjectBytes); err != nil {
+		return Config{}, err
+	}
+	cfg.Diplomail.TranslatorURL = loadString(envDiplomailTranslatorURL, cfg.Diplomail.TranslatorURL)
+	if cfg.Diplomail.TranslatorTimeout, err = loadDuration(envDiplomailTranslatorTimeout, cfg.Diplomail.TranslatorTimeout); err != nil {
+		return Config{}, err
+	}
+	if cfg.Diplomail.TranslatorMaxAttempts, err = loadInt(envDiplomailTranslatorMaxAttempts, cfg.Diplomail.TranslatorMaxAttempts); err != nil {
+		return Config{}, err
+	}
+	if cfg.Diplomail.WorkerInterval, err = loadDuration(envDiplomailWorkerInterval, cfg.Diplomail.WorkerInterval); err != nil {
+		return Config{}, err
+	}
+
 	cfg.DevSandbox.Email = strings.TrimSpace(loadString(envDevSandboxEmail, cfg.DevSandbox.Email))
 	cfg.DevSandbox.EngineImage = strings.TrimSpace(loadString(envDevSandboxEngineImage, cfg.DevSandbox.EngineImage))
 	cfg.DevSandbox.EngineVersion = strings.TrimSpace(loadString(envDevSandboxEngineVersion, cfg.DevSandbox.EngineVersion))
@@ -853,6 +927,22 @@ func (c Config) Validate() error {
 	if c.Notification.MaxAttempts <= 0 {
 		return fmt.Errorf("%s must be positive", envNotificationMaxAttempts)
 	}
+
+	if c.Diplomail.MaxBodyBytes <= 0 {
+		return fmt.Errorf("%s must be positive", envDiplomailMaxBodyBytes)
+	}
+	if c.Diplomail.MaxSubjectBytes < 0 {
+		return fmt.Errorf("%s must not be negative", envDiplomailMaxSubjectBytes)
+	}
+	if c.Diplomail.TranslatorTimeout <= 0 {
+		return fmt.Errorf("%s must be positive", envDiplomailTranslatorTimeout)
+	}
+	if c.Diplomail.TranslatorMaxAttempts <= 0 {
+		return fmt.Errorf("%s must be positive", envDiplomailTranslatorMaxAttempts)
+	}
+	if c.Diplomail.WorkerInterval <= 0 {
+		return fmt.Errorf("%s must be positive", envDiplomailWorkerInterval)
+	}
 	if email := strings.TrimSpace(c.Notification.AdminEmail); email != "" {
 		if _, err := netmail.ParseAddress(email); err != nil {
 			return fmt.Errorf("%s must be a valid RFC 5322 address: %w", envNotificationAdminEmail, err)

backend/internal/diplomail/README.md

@@ -0,0 +1,196 @@
+# diplomail
+
+`diplomail` owns the diplomatic-mail subsystem of the Galaxy backend
+service. Messages live in the lobby-side domain (their storage and
+lifecycle are tied to a game), but they are surfaced inside the game UI
+— the lobby exposes only an unread-count badge per game.
+
+## Stages
+
+The package ships in four staged increments. Stage A is the surface
+described below; the remaining stages add admin / system mail,
+lifecycle hooks, paid-tier broadcast, multi-game broadcast, bulk
+purge, and the language-detection / translation cache.
+
+| Stage | Scope | Status |
+|-------|-------|--------|
+| A | Schema, personal single-recipient send / read / delete, unread badge, push event with body-language `und` | shipped |
+| B | Owner / admin sends + lifecycle hooks (paused, cancelled, kick); strict soft-access for kicked players | shipped |
+| C | Paid-tier personal broadcast + admin multi-game broadcast + bulk purge + admin observability | shipped |
+| D | Body-language detection (whatlanggo) + translation cache + lazy per-read translator dispatch | shipped |
+| E | LibreTranslate HTTP client + async translation worker with exponential backoff + delivery gating on translation completion | shipped |
+
+## Tables
+
+Three Postgres tables in the `backend` schema:
+
+- `diplomail_messages` — one row per send (personal, admin, or
+  system). Captures `game_name` and IP at insert time so audit
+  rendering survives renames and purges.
+- `diplomail_recipients` — one row per (message, recipient). Holds
+  per-user `read_at`, `deleted_at`, `delivered_at`, `notified_at`
+  state. Snapshot fields (`recipient_user_name`,
+  `recipient_race_name`) are captured at insert time and survive
+  membership revocation.
+- `diplomail_translations` — cached per (message, target_lang)
+  rendering. One translation is reused across every recipient that
+  asks for that language.
+
+## Permissions
+
+| Action | Caller | Pre-conditions |
+|--------|--------|----------------|
+| Send personal | user | active membership in game; recipient is active member |
+| Paid-tier broadcast | paid-tier user | active membership; recipients = every other active member |
+| Send admin (single user) | game owner OR site admin | recipient is any-status member of the game |
+| Send admin (broadcast) | game owner OR site admin | recipient scope ∈ `active` / `active_and_removed` / `all_members`; sender excluded |
+| Multi-game admin broadcast | site admin | scope `selected` (with `game_ids`) or `all_running` |
+| Bulk purge | site admin | `older_than_years >= 1`; targets games with terminal status finished more than N years ago |
+| Read message | the recipient | row exists in `diplomail_recipients(message_id, user_id)`; non-active members see admin-kind only |
+| Mark read | the recipient | row exists; idempotent if already marked |
+| Soft delete | the recipient | `read_at IS NOT NULL` (open-then-delete, item 10) |
+
+Stage D will add body-language detection (whatlanggo) and the
+translation cache + async worker.
+
+System mail is produced internally by lobby lifecycle hooks:
+`Service.transition()` emits `game.paused` / `game.cancelled` system
+mail to every active member; `Service.changeMembershipStatus` /
+`Service.AdminBanMember` emit `membership.removed` /
+`membership.blocked` system mail addressed to the affected user.
+
+## Content rules
+
+- Body is plain UTF-8 text. The server does **not** parse, sanitise,
+  or escape HTML — the UI renders messages via `textContent`.
+- Body length is capped by `BACKEND_DIPLOMAIL_MAX_BODY_BYTES` (default
+  4096). Subject length is capped by
+  `BACKEND_DIPLOMAIL_MAX_SUBJECT_BYTES` (default 256). Both limits
+  live in the service layer so they can be tuned without a schema
+  migration.
+- `body_lang` is filled at send time by the configured
+  `detector.LanguageDetector` (default: `whatlanggo`, body-only,
+  ≥ 25 runes; shorter bodies stay `und`).
+
+## Translation
+
+Stage D adds a lazy translation cache. When a recipient reads a
+message through `GET /api/v1/user/games/{game_id}/mail/messages/{id}`,
+the handler resolves the caller's `accounts.preferred_language` and
+asks `Service.GetMessage(…, targetLang)` to attach a translation:
+
+- on cache hit (row in `diplomail_translations`), the rendering is
+  returned directly under `translated_subject` / `translated_body`;
+- on cache miss, the configured `translator.Translator` is invoked.
+  A non-noop result is persisted and returned to the caller; the
+  noop translator that ships with Stage D returns `engine == "noop"`,
+  which is treated as "translation unavailable" and the caller falls
+  back to the original body.
+
+The inbox listing (`/inbox`) reuses cached translations but never
+calls the translator on miss — bulk listings stay fast even when a
+real translator (LibreTranslate, SaaS engine) introduces I/O cost.
+
+Future work plugs a real `translator.Translator` (LibreTranslate
+HTTP client is the documented next step) without touching the rest
+of the system.
+
+## Async translation (Stage E)
+
+Stage E switches the translation pipeline from "lazy at read" to
+"async at send". The send path stays synchronous from the
+caller's perspective: the message and recipient rows are inserted
+in one transaction. What changes is delivery semantics:
+
+- Recipients whose `preferred_language` matches the detected
+  `body_lang` (or whose body language is `und`) get
+  `available_at = now()` straight away and the push event fires
+  during the request.
+- Recipients whose `preferred_language` differs are inserted with
+  `available_at IS NULL`. They are **not** visible in inbox, unread
+  count, or push events until the worker translates the message.
+
+The worker (`internal/diplomail.Worker`, started as an
+`app.Component` in `cmd/backend/main`) ticks once every
+`BACKEND_DIPLOMAIL_WORKER_INTERVAL` (default `2s`). Each tick:
+
+1. Picks one distinct `(message_id, recipient_preferred_language)`
+   pair from `diplomail_recipients` where `available_at IS NULL`
+   and `next_translation_attempt_at` is unset or due.
+2. Loads the source message, checks the translation cache.
+3. On cache hit → marks every pending recipient of the pair
+   delivered and emits push.
+4. On cache miss → asks the configured `Translator`:
+   - success → caches the translation, marks delivered, push;
+   - HTTP 400 (unsupported pair) → marks delivered without a
+     translation (fallback to original);
+   - other failure → bumps `translation_attempts`, schedules the
+     retry via `next_translation_attempt_at`, leaves pending.
+5. After `BACKEND_DIPLOMAIL_TRANSLATOR_MAX_ATTEMPTS` (default `5`)
+   the worker falls back to delivering the original body so a
+   prolonged LibreTranslate outage does not strand messages.
+
+Retry backoff is exponential `1s → 2s → 4s → 8s → 16s` (capped at
+60s) per pair. Operators monitor the LibreTranslate dependency
+through standard OpenTelemetry export — translation outcomes
+surface in `diplomail.worker` logs at Info / Warn levels;
+Grafana / Prometheus dashboards live outside this package.
+
+### Multi-instance posture (known limitation)
+
+`PickPendingTranslationPair` intentionally drops `FOR UPDATE`: the
+worker is single-threaded per process, and we did not want a slow
+LibreTranslate HTTP call to keep a row-lock open. The cost is a
+small window where two backend instances pulling at the same
+moment can both claim the same pair: the cache-write side stays
+clean (`INSERT … ON CONFLICT DO NOTHING`), but each instance will
+publish its own push event to every recipient of the pair, so the
+duplicate push is the visible failure mode.
+
+The current deployment runs a single backend instance and the
+window does not exist. When the platform scales to multiple
+instances, we will revisit the pickup query — either by holding
+the lock through the HTTP call (with a short timeout to bound the
+worst case) or by introducing a `claimed_at` column and a
+short-lived advisory lease. The change is local to this package
+and does not affect callers.
+
+For the LibreTranslate operational recipe — installing, wiring,
+manual smoke test — see
+[`backend/docs/diplomail-translator-setup.md`](../../docs/diplomail-translator-setup.md).
+
+## Push integration
+
+Every successful send emits a `diplomail.message.received` push
+intent through the existing notification pipeline. The catalog entry
+limits delivery to the push channel — email is intentionally absent;
+the inbox endpoint is the durable fallback for offline users. The
+payload includes the recipient's freshly recomputed unread count for
+the lobby badge and for the in-game header.
+
+## Lifecycle hooks (Stage B)
+
+The lobby module is the producer of system mail. Stage B will add a
+`DiplomailPublisher` collaborator on `lobby.Service` and call it on
+`paused` / `cancelled` transitions and on `BlockMembership` /
+`AdminBanMember`. The publisher constructs a
+`kind='admin', sender_kind='system'` message with a templated body;
+the recipient receives the durable copy in their inbox even after the
+membership is revoked.
+
+If a future stage adds inactivity-based player removal at the lobby
+sweeper, that path **must** call the same publisher so the kicked
+player has the explanation in their inbox.
+
+## Wiring
+
+`cmd/backend/main.go` constructs `*diplomail.Service` with three
+collaborators:
+
+- `*Store` over the shared Postgres pool;
+- `MembershipLookup` adapter that walks the lobby cache for the
+  active `(game_id, user_id)` row and stitches in the immutable
+  `accounts.user_name`;
+- `NotificationPublisher` adapter that translates each
+  `DiplomailNotification` into a `notification.Intent` and routes it
+  through `*notification.Service.Submit`.

backend/internal/diplomail/admin_send.go

@@ -0,0 +1,615 @@
+package diplomail
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/google/uuid"
+	"go.uber.org/zap"
+)
+
+// SendAdminPersonal persists an admin-kind message addressed to a
+// single recipient and fan-outs the push event. The HTTP layer is
+// responsible for the owner-vs-admin authorisation decision; this
+// function trusts the caller designation it receives.
+//
+// The recipient may be in any membership status, so the lookup goes
+// through MembershipLookup.GetMembershipAnyStatus. This lets the
+// owner / admin reach a kicked player to explain the kick or follow
+// up after a removal.
+func (s *Service) SendAdminPersonal(ctx context.Context, in SendAdminPersonalInput) (Message, Recipient, error) {
+	subject, body, err := s.prepareContent(in.Subject, in.Body)
+	if err != nil {
+		return Message{}, Recipient{}, err
+	}
+	if err := validateCaller(in.CallerKind, in.CallerUserID, in.CallerUsername); err != nil {
+		return Message{}, Recipient{}, err
+	}
+
+	recipient, err := s.deps.Memberships.GetMembershipAnyStatus(ctx, in.GameID, in.RecipientUserID)
+	if err != nil {
+		if errors.Is(err, ErrNotFound) {
+			return Message{}, Recipient{}, fmt.Errorf("%w: recipient is not a member of the game", ErrForbidden)
+		}
+		return Message{}, Recipient{}, fmt.Errorf("diplomail: load admin recipient: %w", err)
+	}
+
+	msgInsert, err := s.buildAdminMessageInsert(in.CallerKind, in.CallerUserID, in.CallerUsername,
+		recipient.GameID, recipient.GameName, subject, body, in.SenderIP, BroadcastScopeSingle)
+	if err != nil {
+		return Message{}, Recipient{}, err
+	}
+	rcptInsert := buildRecipientInsert(msgInsert.MessageID, recipient, msgInsert.BodyLang, s.nowUTC())
+
+	msg, recipients, err := s.deps.Store.InsertMessageWithRecipients(ctx, msgInsert, []RecipientInsert{rcptInsert})
+	if err != nil {
+		return Message{}, Recipient{}, fmt.Errorf("diplomail: send admin personal: %w", err)
+	}
+	if len(recipients) != 1 {
+		return Message{}, Recipient{}, fmt.Errorf("diplomail: send admin personal: unexpected recipient count %d", len(recipients))
+	}
+
+	if recipients[0].AvailableAt != nil { s.publishMessageReceived(ctx, msg, recipients[0]) }
+	return msg, recipients[0], nil
+}
+
+// SendAdminBroadcast persists an admin-kind broadcast addressed to
+// every member matching `RecipientScope`, then emits one push event
+// per recipient. The caller's own membership row, when present, is
+// excluded from the recipient list — broadcasters do not get a copy
+// of their own message.
+func (s *Service) SendAdminBroadcast(ctx context.Context, in SendAdminBroadcastInput) (Message, []Recipient, error) {
+	subject, body, err := s.prepareContent(in.Subject, in.Body)
+	if err != nil {
+		return Message{}, nil, err
+	}
+	if err := validateCaller(in.CallerKind, in.CallerUserID, in.CallerUsername); err != nil {
+		return Message{}, nil, err
+	}
+	scope, err := normaliseScope(in.RecipientScope)
+	if err != nil {
+		return Message{}, nil, err
+	}
+
+	members, err := s.deps.Memberships.ListMembers(ctx, in.GameID, scope)
+	if err != nil {
+		return Message{}, nil, fmt.Errorf("diplomail: list members for broadcast: %w", err)
+	}
+	members = filterOutCaller(members, in.CallerUserID)
+	if len(members) == 0 {
+		return Message{}, nil, fmt.Errorf("%w: no recipients for broadcast", ErrInvalidInput)
+	}
+
+	gameName := members[0].GameName
+	msgInsert, err := s.buildAdminMessageInsert(in.CallerKind, in.CallerUserID, in.CallerUsername,
+		in.GameID, gameName, subject, body, in.SenderIP, BroadcastScopeGameBroadcast)
+	if err != nil {
+		return Message{}, nil, err
+	}
+	rcptInserts := make([]RecipientInsert, 0, len(members))
+	for _, m := range members {
+		rcptInserts = append(rcptInserts, buildRecipientInsert(msgInsert.MessageID, m, msgInsert.BodyLang, s.nowUTC()))
+	}
+
+	msg, recipients, err := s.deps.Store.InsertMessageWithRecipients(ctx, msgInsert, rcptInserts)
+	if err != nil {
+		return Message{}, nil, fmt.Errorf("diplomail: send admin broadcast: %w", err)
+	}
+	for _, r := range recipients {
+		if r.AvailableAt != nil { s.publishMessageReceived(ctx, msg, r) }
+	}
+	return msg, recipients, nil
+}
+
+// SendPlayerBroadcast persists a paid-tier player broadcast and
+// fans out the push event to every other active member of the game.
+// The send is `kind="personal"`, `sender_kind="player"`,
+// `broadcast_scope="game_broadcast"` — recipients reply to it as if
+// it were a single-recipient personal send, and the reply targets
+// only the broadcaster. The caller's entitlement tier is checked
+// against `EntitlementReader`; free-tier callers are rejected with
+// ErrForbidden.
+func (s *Service) SendPlayerBroadcast(ctx context.Context, in SendPlayerBroadcastInput) (Message, []Recipient, error) {
+	subject, body, err := s.prepareContent(in.Subject, in.Body)
+	if err != nil {
+		return Message{}, nil, err
+	}
+	if s.deps.Entitlements == nil {
+		return Message{}, nil, fmt.Errorf("%w: entitlement reader is not wired", ErrForbidden)
+	}
+	paid, err := s.deps.Entitlements.IsPaidTier(ctx, in.SenderUserID)
+	if err != nil {
+		return Message{}, nil, fmt.Errorf("diplomail: entitlement lookup: %w", err)
+	}
+	if !paid {
+		return Message{}, nil, fmt.Errorf("%w: in-game broadcast requires a paid tier", ErrForbidden)
+	}
+
+	sender, err := s.deps.Memberships.GetActiveMembership(ctx, in.GameID, in.SenderUserID)
+	if err != nil {
+		if errors.Is(err, ErrNotFound) {
+			return Message{}, nil, fmt.Errorf("%w: sender is not an active member of the game", ErrForbidden)
+		}
+		return Message{}, nil, fmt.Errorf("diplomail: load sender membership: %w", err)
+	}
+
+	members, err := s.deps.Memberships.ListMembers(ctx, in.GameID, RecipientScopeActive)
+	if err != nil {
+		return Message{}, nil, fmt.Errorf("diplomail: list active members: %w", err)
+	}
+	callerID := in.SenderUserID
+	members = filterOutCaller(members, &callerID)
+	if len(members) == 0 {
+		return Message{}, nil, fmt.Errorf("%w: no other active members in this game", ErrInvalidInput)
+	}
+
+	username := sender.UserName
+	msgInsert := MessageInsert{
+		MessageID:      uuid.New(),
+		GameID:         in.GameID,
+		GameName:       sender.GameName,
+		Kind:           KindPersonal,
+		SenderKind:     SenderKindPlayer,
+		SenderUserID:   &callerID,
+		SenderUsername: &username,
+		SenderIP:       in.SenderIP,
+		Subject:        subject,
+		Body:           body,
+		BodyLang:       s.deps.Detector.Detect(body),
+		BroadcastScope: BroadcastScopeGameBroadcast,
+	}
+	rcptInserts := make([]RecipientInsert, 0, len(members))
+	for _, m := range members {
+		rcptInserts = append(rcptInserts, buildRecipientInsert(msgInsert.MessageID, m, msgInsert.BodyLang, s.nowUTC()))
+	}
+	msg, recipients, err := s.deps.Store.InsertMessageWithRecipients(ctx, msgInsert, rcptInserts)
+	if err != nil {
+		return Message{}, nil, fmt.Errorf("diplomail: send player broadcast: %w", err)
+	}
+	for _, r := range recipients {
+		if r.AvailableAt != nil { s.publishMessageReceived(ctx, msg, r) }
+	}
+	return msg, recipients, nil
+}
+
+// SendAdminMultiGameBroadcast emits one admin-kind message per game
+// resolved from the input scope and fans out the push events. A
+// recipient who plays in multiple addressed games receives one
+// independently-deletable inbox entry per game; this avoids cross-
+// game leakage of admin context and keeps the per-game unread badge
+// honest.
+func (s *Service) SendAdminMultiGameBroadcast(ctx context.Context, in SendMultiGameBroadcastInput) ([]Message, int, error) {
+	subject, body, err := s.prepareContent(in.Subject, in.Body)
+	if err != nil {
+		return nil, 0, err
+	}
+	if err := validateCaller(CallerKindAdmin, nil, in.CallerUsername); err != nil {
+		return nil, 0, err
+	}
+	scope, err := normaliseScope(in.RecipientScope)
+	if err != nil {
+		return nil, 0, err
+	}
+	if s.deps.Games == nil {
+		return nil, 0, fmt.Errorf("%w: game lookup is not wired", ErrInvalidInput)
+	}
+	games, err := s.resolveMultiGameTargets(ctx, in)
+	if err != nil {
+		return nil, 0, err
+	}
+	if len(games) == 0 {
+		return nil, 0, fmt.Errorf("%w: no games match the broadcast scope", ErrInvalidInput)
+	}
+
+	totalRecipients := 0
+	out := make([]Message, 0, len(games))
+	for _, game := range games {
+		members, err := s.deps.Memberships.ListMembers(ctx, game.GameID, scope)
+		if err != nil {
+			return nil, 0, fmt.Errorf("diplomail: list members for %s: %w", game.GameID, err)
+		}
+		if len(members) == 0 {
+			s.deps.Logger.Debug("multi-game broadcast skips empty game",
+				zap.String("game_id", game.GameID.String()),
+				zap.String("scope", scope))
+			continue
+		}
+		msgInsert, err := s.buildAdminMessageInsert(CallerKindAdmin, nil, in.CallerUsername,
+			game.GameID, game.GameName, subject, body, in.SenderIP, BroadcastScopeMultiGameBroadcast)
+		if err != nil {
+			return nil, 0, err
+		}
+		rcptInserts := make([]RecipientInsert, 0, len(members))
+		for _, m := range members {
+			rcptInserts = append(rcptInserts, buildRecipientInsert(msgInsert.MessageID, m, msgInsert.BodyLang, s.nowUTC()))
+		}
+		msg, recipients, err := s.deps.Store.InsertMessageWithRecipients(ctx, msgInsert, rcptInserts)
+		if err != nil {
+			return nil, 0, fmt.Errorf("diplomail: insert multi-game broadcast for %s: %w", game.GameID, err)
+		}
+		for _, r := range recipients {
+			if r.AvailableAt != nil { s.publishMessageReceived(ctx, msg, r) }
+		}
+		out = append(out, msg)
+		totalRecipients += len(recipients)
+	}
+	return out, totalRecipients, nil
+}
+
+func (s *Service) resolveMultiGameTargets(ctx context.Context, in SendMultiGameBroadcastInput) ([]GameSnapshot, error) {
+	switch in.Scope {
+	case MultiGameScopeAllRunning:
+		games, err := s.deps.Games.ListRunningGames(ctx)
+		if err != nil {
+			return nil, fmt.Errorf("diplomail: list running games: %w", err)
+		}
+		return games, nil
+	case MultiGameScopeSelected, "":
+		if len(in.GameIDs) == 0 {
+			return nil, fmt.Errorf("%w: selected scope requires game_ids", ErrInvalidInput)
+		}
+		out := make([]GameSnapshot, 0, len(in.GameIDs))
+		for _, id := range in.GameIDs {
+			game, err := s.deps.Games.GetGame(ctx, id)
+			if err != nil {
+				if errors.Is(err, ErrNotFound) {
+					return nil, fmt.Errorf("%w: game %s not found", ErrInvalidInput, id)
+				}
+				return nil, fmt.Errorf("diplomail: load game %s: %w", id, err)
+			}
+			out = append(out, game)
+		}
+		return out, nil
+	default:
+		return nil, fmt.Errorf("%w: unknown multi-game scope %q", ErrInvalidInput, in.Scope)
+	}
+}
+
+// BulkCleanup deletes every diplomail_messages row tied to games that
+// finished more than `OlderThanYears` years ago. Returns the affected
+// game ids and the count of removed messages. The minimum allowed
+// value is 1 year — finer-grained pruning would risk wiping live
+// arbitration evidence.
+func (s *Service) BulkCleanup(ctx context.Context, in BulkCleanupInput) (CleanupResult, error) {
+	if in.OlderThanYears < 1 {
+		return CleanupResult{}, fmt.Errorf("%w: older_than_years must be >= 1", ErrInvalidInput)
+	}
+	if s.deps.Games == nil {
+		return CleanupResult{}, fmt.Errorf("%w: game lookup is not wired", ErrInvalidInput)
+	}
+	cutoff := s.nowUTC().AddDate(-in.OlderThanYears, 0, 0)
+	games, err := s.deps.Games.ListFinishedGamesBefore(ctx, cutoff)
+	if err != nil {
+		return CleanupResult{}, fmt.Errorf("diplomail: list finished games: %w", err)
+	}
+	if len(games) == 0 {
+		return CleanupResult{}, nil
+	}
+	gameIDs := make([]uuid.UUID, 0, len(games))
+	for _, g := range games {
+		gameIDs = append(gameIDs, g.GameID)
+	}
+	deleted, err := s.deps.Store.DeleteMessagesForGames(ctx, gameIDs)
+	if err != nil {
+		return CleanupResult{}, fmt.Errorf("diplomail: bulk delete: %w", err)
+	}
+	return CleanupResult{GameIDs: gameIDs, MessagesDeleted: deleted}, nil
+}
+
+// ListMessagesForAdmin returns a paginated, optionally-filtered view
+// of every persisted message. Used by the admin observability
+// endpoint to inspect what has been sent and trace abuse reports.
+func (s *Service) ListMessagesForAdmin(ctx context.Context, filter AdminMessageListing) (AdminMessagePage, error) {
+	rows, total, err := s.deps.Store.ListMessagesForAdmin(ctx, filter)
+	if err != nil {
+		return AdminMessagePage{}, err
+	}
+	page := filter.Page
+	if page < 1 {
+		page = 1
+	}
+	pageSize := filter.PageSize
+	if pageSize < 1 {
+		pageSize = 50
+	}
+	return AdminMessagePage{
+		Items:    rows,
+		Total:    total,
+		Page:     page,
+		PageSize: pageSize,
+	}, nil
+}
+
+// PublishLifecycle persists a system-kind message in response to a
+// lobby lifecycle transition and fan-outs push events to the
+// affected recipients. Game-scoped transitions (`game.paused`,
+// `game.cancelled`) reach every active member; membership-scoped
+// transitions (`membership.removed`, `membership.blocked`) reach the
+// kicked player only. Failures inside the function are logged at
+// Warn level — lifecycle hooks must not block the lobby state
+// machine on a downstream mail failure.
+func (s *Service) PublishLifecycle(ctx context.Context, ev LifecycleEvent) error {
+	switch ev.Kind {
+	case LifecycleKindGamePaused, LifecycleKindGameCancelled:
+		return s.publishGameLifecycle(ctx, ev)
+	case LifecycleKindMembershipRemoved, LifecycleKindMembershipBlocked:
+		return s.publishMembershipLifecycle(ctx, ev)
+	default:
+		return fmt.Errorf("%w: unknown lifecycle kind %q", ErrInvalidInput, ev.Kind)
+	}
+}
+
+func (s *Service) publishGameLifecycle(ctx context.Context, ev LifecycleEvent) error {
+	members, err := s.deps.Memberships.ListMembers(ctx, ev.GameID, RecipientScopeActive)
+	if err != nil {
+		return fmt.Errorf("diplomail lifecycle: list members for %s: %w", ev.GameID, err)
+	}
+	if len(members) == 0 {
+		s.deps.Logger.Debug("lifecycle skip: no active members",
+			zap.String("game_id", ev.GameID.String()),
+			zap.String("kind", ev.Kind))
+		return nil
+	}
+	gameName := members[0].GameName
+	subject, body := renderGameLifecycle(ev.Kind, gameName, ev.Actor, ev.Reason)
+
+	msgInsert, err := s.buildAdminMessageInsert(CallerKindSystem, nil, "",
+		ev.GameID, gameName, subject, body, "", BroadcastScopeGameBroadcast)
+	if err != nil {
+		return err
+	}
+	rcptInserts := make([]RecipientInsert, 0, len(members))
+	for _, m := range members {
+		rcptInserts = append(rcptInserts, buildRecipientInsert(msgInsert.MessageID, m, msgInsert.BodyLang, s.nowUTC()))
+	}
+	msg, recipients, err := s.deps.Store.InsertMessageWithRecipients(ctx, msgInsert, rcptInserts)
+	if err != nil {
+		return fmt.Errorf("diplomail lifecycle: insert %s system mail: %w", ev.Kind, err)
+	}
+	for _, r := range recipients {
+		if r.AvailableAt != nil { s.publishMessageReceived(ctx, msg, r) }
+	}
+	return nil
+}
+
+func (s *Service) publishMembershipLifecycle(ctx context.Context, ev LifecycleEvent) error {
+	if ev.TargetUser == nil {
+		return fmt.Errorf("%w: membership lifecycle requires TargetUser", ErrInvalidInput)
+	}
+	target, err := s.deps.Memberships.GetMembershipAnyStatus(ctx, ev.GameID, *ev.TargetUser)
+	if err != nil {
+		return fmt.Errorf("diplomail lifecycle: load target membership: %w", err)
+	}
+	subject, body := renderMembershipLifecycle(ev.Kind, target.GameName, ev.Actor, ev.Reason)
+
+	msgInsert, err := s.buildAdminMessageInsert(CallerKindSystem, nil, "",
+		ev.GameID, target.GameName, subject, body, "", BroadcastScopeSingle)
+	if err != nil {
+		return err
+	}
+	rcptInsert := buildRecipientInsert(msgInsert.MessageID, target, msgInsert.BodyLang, s.nowUTC())
+	msg, recipients, err := s.deps.Store.InsertMessageWithRecipients(ctx, msgInsert, []RecipientInsert{rcptInsert})
+	if err != nil {
+		return fmt.Errorf("diplomail lifecycle: insert %s system mail: %w", ev.Kind, err)
+	}
+	if len(recipients) == 1 && recipients[0].AvailableAt != nil {
+		s.publishMessageReceived(ctx, msg, recipients[0])
+	}
+	return nil
+}
+
+// prepareContent normalises subject and body the same way SendPersonal
+// does. Factored out so admin and lifecycle paths share the
+// length-and-utf8 validation rules.
+func (s *Service) prepareContent(subject, body string) (string, string, error) {
+	subj := strings.TrimRight(subject, " \t")
+	bod := strings.TrimRight(body, " \t\n")
+	if err := s.validateContent(subj, bod); err != nil {
+		return "", "", err
+	}
+	return subj, bod, nil
+}
+
+// buildAdminMessageInsert encapsulates the message-row construction
+// for every admin-kind send. The CHECK constraint maps sender
+// shapes:
+//
+//	sender_kind='player'  → CallerKind owner; sender_user_id set
+//	sender_kind='admin'   → CallerKind admin; sender_user_id nil
+//	sender_kind='system'  → CallerKind system; sender_username nil
+func (s *Service) buildAdminMessageInsert(callerKind string, callerUserID *uuid.UUID, callerUsername string,
+	gameID uuid.UUID, gameName, subject, body, senderIP, scope string) (MessageInsert, error) {
+	out := MessageInsert{
+		MessageID:      uuid.New(),
+		GameID:         gameID,
+		GameName:       gameName,
+		Kind:           KindAdmin,
+		SenderIP:       senderIP,
+		Subject:        subject,
+		Body:           body,
+		BodyLang:       s.deps.Detector.Detect(body),
+		BroadcastScope: scope,
+	}
+	switch callerKind {
+	case CallerKindOwner:
+		if callerUserID == nil {
+			return MessageInsert{}, fmt.Errorf("%w: owner send requires caller user id", ErrInvalidInput)
+		}
+		uid := *callerUserID
+		uname := callerUsername
+		out.SenderKind = SenderKindPlayer
+		out.SenderUserID = &uid
+		out.SenderUsername = &uname
+	case CallerKindAdmin:
+		uname := callerUsername
+		out.SenderKind = SenderKindAdmin
+		out.SenderUsername = &uname
+	case CallerKindSystem:
+		out.SenderKind = SenderKindSystem
+	default:
+		return MessageInsert{}, fmt.Errorf("%w: unknown caller kind %q", ErrInvalidInput, callerKind)
+	}
+	return out, nil
+}
+
+// buildRecipientInsert turns a MemberSnapshot into a RecipientInsert.
+// The race-name snapshot is nullable so a kicked player with no race
+// name on file is still addressable.
+//
+// `bodyLang` is the detected language of the message body. When the
+// recipient's preferred_language matches body_lang (or body_lang is
+// undetermined), the function fills AvailableAt with `now` so the
+// recipient row is materialised already-delivered; otherwise
+// AvailableAt stays nil and the translation worker takes over.
+func buildRecipientInsert(messageID uuid.UUID, m MemberSnapshot, bodyLang string, now time.Time) RecipientInsert {
+	in := RecipientInsert{
+		RecipientID:                uuid.New(),
+		MessageID:                  messageID,
+		GameID:                     m.GameID,
+		UserID:                     m.UserID,
+		RecipientUserName:          m.UserName,
+		RecipientPreferredLanguage: normaliseLang(m.PreferredLanguage),
+	}
+	if m.RaceName != "" {
+		race := m.RaceName
+		in.RecipientRaceName = &race
+	}
+	if needsTranslation(bodyLang, in.RecipientPreferredLanguage) {
+		// AvailableAt left nil → worker will deliver after the
+		// translation cache is materialised (or after fallback).
+	} else {
+		t := now.UTC()
+		in.AvailableAt = &t
+	}
+	return in
+}
+
+// needsTranslation reports whether a recipient with preferredLang
+// needs to wait for a translated rendering before the message is
+// considered delivered. Undetermined body language and empty
+// recipient preferences are short-circuited to "no translation
+// needed" so we never block delivery on something the detector
+// could not label.
+func needsTranslation(bodyLang, preferredLang string) bool {
+	bodyLang = normaliseLang(bodyLang)
+	preferredLang = normaliseLang(preferredLang)
+	if bodyLang == "" || bodyLang == LangUndetermined {
+		return false
+	}
+	if preferredLang == "" || preferredLang == LangUndetermined {
+		return false
+	}
+	return bodyLang != preferredLang
+}
+
+// normaliseLang strips any region subtag and lowercases the result so
+// `en-US` and `EN` both collapse to `en`. The diplomail layer uses
+// ISO 639-1 codes; whatlanggo and LibreTranslate share that
+// vocabulary.
+func normaliseLang(tag string) string {
+	tag = strings.TrimSpace(tag)
+	if tag == "" {
+		return ""
+	}
+	if i := strings.IndexAny(tag, "-_"); i > 0 {
+		tag = tag[:i]
+	}
+	return strings.ToLower(tag)
+}
+
+func validateCaller(callerKind string, callerUserID *uuid.UUID, callerUsername string) error {
+	switch callerKind {
+	case CallerKindOwner:
+		if callerUserID == nil {
+			return fmt.Errorf("%w: owner send requires caller_user_id", ErrInvalidInput)
+		}
+		if callerUsername == "" {
+			return fmt.Errorf("%w: owner send requires caller_username", ErrInvalidInput)
+		}
+	case CallerKindAdmin:
+		if callerUsername == "" {
+			return fmt.Errorf("%w: admin send requires caller_username", ErrInvalidInput)
+		}
+	case CallerKindSystem:
+		// no extra checks
+	default:
+		return fmt.Errorf("%w: unknown caller_kind %q", ErrInvalidInput, callerKind)
+	}
+	return nil
+}
+
+func normaliseScope(scope string) (string, error) {
+	switch scope {
+	case "", RecipientScopeActive:
+		return RecipientScopeActive, nil
+	case RecipientScopeActiveAndRemoved, RecipientScopeAllMembers:
+		return scope, nil
+	default:
+		return "", fmt.Errorf("%w: unknown recipient scope %q", ErrInvalidInput, scope)
+	}
+}
+
+func filterOutCaller(members []MemberSnapshot, callerUserID *uuid.UUID) []MemberSnapshot {
+	if callerUserID == nil {
+		return members
+	}
+	out := make([]MemberSnapshot, 0, len(members))
+	for _, m := range members {
+		if m.UserID == *callerUserID {
+			continue
+		}
+		out = append(out, m)
+	}
+	return out
+}
+
+// renderGameLifecycle returns the (subject, body) pair persisted for
+// the `game.paused` / `game.cancelled` system message. Bodies are in
+// English; Stage D will translate them on demand into each
+// recipient's preferred_language and cache the result.
+func renderGameLifecycle(kind, gameName, actor, reason string) (string, string) {
+	actor = strings.TrimSpace(actor)
+	if actor == "" {
+		actor = "the system"
+	}
+	reasonTail := ""
+	if r := strings.TrimSpace(reason); r != "" {
+		reasonTail = " Reason: " + r + "."
+	}
+	switch kind {
+	case LifecycleKindGamePaused:
+		return "Game paused",
+			fmt.Sprintf("The game %q has been paused by %s.%s", gameName, actor, reasonTail)
+	case LifecycleKindGameCancelled:
+		return "Game cancelled",
+			fmt.Sprintf("The game %q has been cancelled by %s.%s", gameName, actor, reasonTail)
+	}
+	return "Game lifecycle update",
+		fmt.Sprintf("The game %q has changed state.%s", gameName, reasonTail)
+}
+
+// renderMembershipLifecycle returns the (subject, body) pair persisted
+// for the `membership.removed` / `membership.blocked` system message.
+func renderMembershipLifecycle(kind, gameName, actor, reason string) (string, string) {
+	actor = strings.TrimSpace(actor)
+	if actor == "" {
+		actor = "the system"
+	}
+	reasonTail := ""
+	if r := strings.TrimSpace(reason); r != "" {
+		reasonTail = " Reason: " + r + "."
+	}
+	switch kind {
+	case LifecycleKindMembershipRemoved:
+		return "Membership removed",
+			fmt.Sprintf("Your membership in %q has been removed by %s.%s", gameName, actor, reasonTail)
+	case LifecycleKindMembershipBlocked:
+		return "Membership blocked",
+			fmt.Sprintf("Your membership in %q has been blocked by %s.%s", gameName, actor, reasonTail)
+	}
+	return "Membership update",
+		fmt.Sprintf("Your membership in %q has changed.%s", gameName, reasonTail)
+}

backend/internal/diplomail/deps.go

@@ -0,0 +1,181 @@
+package diplomail
+
+import (
+	"context"
+	"time"
+
+	"galaxy/backend/internal/config"
+	"galaxy/backend/internal/diplomail/detector"
+	"galaxy/backend/internal/diplomail/translator"
+
+	"github.com/google/uuid"
+	"go.uber.org/zap"
+)
+
+// Deps aggregates every collaborator the diplomail Service depends on.
+//
+// Store and Memberships are required. Logger and Now default to
+// zap.NewNop / time.Now when nil. Notification falls back to a no-op
+// publisher so unit tests can construct a Service with only the
+// required collaborators populated. Entitlements and Games are
+// optional — they are used by Stage C surfaces (paid-tier player
+// broadcast, multi-game admin broadcast, bulk cleanup). Wiring may
+// pass nil for tests that do not exercise those paths.
+type Deps struct {
+	Store        *Store
+	Memberships  MembershipLookup
+	Notification NotificationPublisher
+	Entitlements EntitlementReader
+	Games        GameLookup
+	Detector     detector.LanguageDetector
+	Translator   translator.Translator
+	Config       config.DiplomailConfig
+	Logger       *zap.Logger
+	Now          func() time.Time
+}
+
+// EntitlementReader is the read-only surface diplomail uses to gate
+// the paid-tier player broadcast. The canonical implementation in
+// `cmd/backend/main` reads
+// `*user.Service.GetEntitlementSnapshot(userID).IsPaid`.
+type EntitlementReader interface {
+	IsPaidTier(ctx context.Context, userID uuid.UUID) (bool, error)
+}
+
+// GameLookup exposes the slim view of `games` the multi-game admin
+// broadcast and bulk-cleanup paths consume. The canonical
+// implementation walks the lobby cache plus an explicit store call
+// for finished-game pruning.
+type GameLookup interface {
+	// ListRunningGames returns every game whose `status` is one of
+	// the still-active values (running, paused, starting, …). The
+	// admin `all_running` broadcast scope iterates over the result.
+	ListRunningGames(ctx context.Context) ([]GameSnapshot, error)
+
+	// ListFinishedGamesBefore returns every game whose `finished_at`
+	// is older than `cutoff`. The bulk-purge admin endpoint reads
+	// this to compose the cascade-delete IN list.
+	ListFinishedGamesBefore(ctx context.Context, cutoff time.Time) ([]GameSnapshot, error)
+
+	// GetGame returns one game snapshot identified by id, or
+	// ErrNotFound. Used by the multi-game broadcast to verify the
+	// caller-supplied id list before enqueuing fan-out work.
+	GetGame(ctx context.Context, gameID uuid.UUID) (GameSnapshot, error)
+}
+
+// GameSnapshot is the trim view of `games` consumed by the multi-game
+// admin broadcast and the cleanup paths. The struct intentionally
+// avoids the full `lobby.GameRecord` so the diplomail package stays
+// decoupled from the lobby domain.
+type GameSnapshot struct {
+	GameID      uuid.UUID
+	GameName    string
+	Status      string
+	FinishedAt  *time.Time
+}
+
+// ActiveMembership is the slim view of a single (user, game) roster
+// row the diplomail package needs at send time: it confirms the
+// participant is active in the game and captures the snapshot fields
+// (`game_name`, `user_name`, `race_name`, `preferred_language`) that
+// we persist on each new message / recipient row.
+type ActiveMembership struct {
+	UserID            uuid.UUID
+	GameID            uuid.UUID
+	GameName          string
+	UserName          string
+	RaceName          string
+	PreferredLanguage string
+}
+
+// MembershipLookup is the read-only surface diplomail uses to verify
+// "is this user an active member of this game" and to snapshot the
+// roster metadata. The canonical implementation in `cmd/backend/main`
+// adapts the `*lobby.Service` membership cache to this interface.
+//
+// GetActiveMembership returns ErrNotFound (the diplomail sentinel)
+// when the user is not an active member of the game; the service
+// boundary maps that to 403 forbidden.
+//
+// GetMembershipAnyStatus returns the same shape regardless of
+// membership status (`active`, `removed`, `blocked`). Used by the
+// inbox read path to check whether a kicked recipient still belongs
+// to the game's roster; ErrNotFound is surfaced when the user has
+// never been a member.
+//
+// ListMembers returns every roster row matching scope, in stable
+// order. Scope values are `active`, `active_and_removed`, and
+// `all_members` (the spec calls these out by name). Used by the
+// broadcast composition step in admin / owner sends.
+type MembershipLookup interface {
+	GetActiveMembership(ctx context.Context, gameID, userID uuid.UUID) (ActiveMembership, error)
+	GetMembershipAnyStatus(ctx context.Context, gameID, userID uuid.UUID) (MemberSnapshot, error)
+	ListMembers(ctx context.Context, gameID uuid.UUID, scope string) ([]MemberSnapshot, error)
+}
+
+// Recipient scope values accepted by ListMembers and by the
+// `recipients` request field on admin / owner broadcasts.
+const (
+	RecipientScopeActive            = "active"
+	RecipientScopeActiveAndRemoved  = "active_and_removed"
+	RecipientScopeAllMembers        = "all_members"
+)
+
+// MemberSnapshot is the slim view of a membership row that survives
+// all three status values. RaceName is the immutable string captured
+// at registration time; an empty value is legal for rare cases where
+// the row was inserted without one. PreferredLanguage is included so
+// the broadcast and lifecycle paths can decide whether the recipient
+// needs to wait for a translation before delivery.
+type MemberSnapshot struct {
+	UserID            uuid.UUID
+	GameID            uuid.UUID
+	GameName          string
+	UserName          string
+	RaceName          string
+	PreferredLanguage string
+	Status            string
+}
+
+// NotificationPublisher is the outbound surface diplomail uses to
+// emit the `diplomail.message.received` push event. The canonical
+// implementation in `cmd/backend/main` adapts the notification.Service
+// the same way it adapts `lobby.NotificationPublisher`; tests pass
+// the no-op publisher below to avoid wiring the dispatcher.
+type NotificationPublisher interface {
+	PublishDiplomailEvent(ctx context.Context, ev DiplomailNotification) error
+}
+
+// DiplomailNotification is the open shape carried by a per-recipient
+// push intent. The struct lives in the diplomail package so the
+// producer vocabulary stays here; the publisher adapter translates it
+// into a `notification.Intent` at the wiring boundary.
+type DiplomailNotification struct {
+	Kind           string
+	IdempotencyKey string
+	Recipient      uuid.UUID
+	Payload        map[string]any
+}
+
+// NewNoopNotificationPublisher returns a publisher that logs every
+// call at debug level and returns nil. Used by unit tests and as the
+// fallback inside NewService when callers leave Deps.Notification nil.
+func NewNoopNotificationPublisher(logger *zap.Logger) NotificationPublisher {
+	if logger == nil {
+		logger = zap.NewNop()
+	}
+	return &noopNotificationPublisher{logger: logger.Named("diplomail.notify.noop")}
+}
+
+type noopNotificationPublisher struct {
+	logger *zap.Logger
+}
+
+func (p *noopNotificationPublisher) PublishDiplomailEvent(_ context.Context, ev DiplomailNotification) error {
+	p.logger.Debug("noop notification",
+		zap.String("kind", ev.Kind),
+		zap.String("idempotency_key", ev.IdempotencyKey),
+		zap.String("recipient", ev.Recipient.String()),
+	)
+	return nil
+}

backend/internal/diplomail/detector/detector.go

@@ -0,0 +1,79 @@
+// Package detector wraps the body-language detection used by the
+// diplomail subsystem. The package exposes a narrow `LanguageDetector`
+// interface so the implementation can be swapped without touching the
+// callers; the default backed-by-whatlanggo detector handles 84
+// natural languages and ships with the embedded statistical profiles.
+//
+// Detection happens only on the body. Subjects are short and
+// frequently template-like ("Re: ..."), so detecting on them adds
+// noise. The diplomail Service feeds the body, captures the BCP 47
+// tag returned here, and stores it in `diplomail_messages.body_lang`.
+package detector
+
+import (
+	"strings"
+	"unicode/utf8"
+
+	"github.com/abadojack/whatlanggo"
+)
+
+// Undetermined is the BCP 47 placeholder stored when detection cannot
+// confidently identify a language (empty body, too-short body, mixed
+// scripts the detector refuses to bet on).
+const Undetermined = "und"
+
+// LanguageDetector is the read-only surface diplomail consumes when
+// it needs to label a message body. Detect must never panic and
+// must never return an error: detection failure simply yields
+// `Undetermined`.
+type LanguageDetector interface {
+	Detect(body string) string
+}
+
+// New returns the package-default detector backed by `whatlanggo`.
+// The instance is safe for concurrent use; whatlanggo's `Detect`
+// reads the embedded profiles without state mutation. Callers that
+// want a fixed allow-list can build their own implementation around
+// the same interface.
+func New() LanguageDetector {
+	return &whatlangDetector{}
+}
+
+type whatlangDetector struct{}
+
+// minRunes is the lower bound on body length below which whatlanggo
+// can flip between near-synonyms; for shorter bodies we return
+// `Undetermined` and let the noop translator skip the slot. The
+// value matches whatlanggo's documented "stable above ~25 runes"
+// guidance.
+const minRunes = 25
+
+// Detect returns the BCP 47 tag for body, or `Undetermined` when the
+// body is empty / too short / whatlanggo refuses to label it. The
+// trim is applied so leading whitespace does not bias the script
+// detector toward Latin. We deliberately do not gate on
+// `info.IsReliable()` because the gate is too conservative for the
+// short sentences typical of in-game mail; a misclassification only
+// hurts the translation cache key, never correctness.
+func (d *whatlangDetector) Detect(body string) string {
+	body = strings.TrimSpace(body)
+	if body == "" {
+		return Undetermined
+	}
+	if utf8.RuneCountInString(body) < minRunes {
+		return Undetermined
+	}
+	info := whatlanggo.Detect(body)
+	tag := info.Lang.Iso6391()
+	if tag == "" {
+		return Undetermined
+	}
+	return tag
+}
+
+// NoopDetector returns the placeholder unconditionally. Used by
+// tests and by Stage A code paths that predate the real detector.
+type NoopDetector struct{}
+
+// Detect always returns `Undetermined` regardless of input.
+func (NoopDetector) Detect(string) string { return Undetermined }

backend/internal/diplomail/detector/detector_test.go

@@ -0,0 +1,49 @@
+package detector
+
+import "testing"
+
+func TestDetectKnownLanguages(t *testing.T) {
+	t.Parallel()
+	d := New()
+	cases := []struct {
+		name string
+		text string
+		want string
+	}{
+		{
+			name: "english paragraph",
+			text: "The trade agreement should be signed before the next turn. " +
+				"I expect a written response by the time the engine generates the next report.",
+			want: "en",
+		},
+		{
+			name: "russian paragraph",
+			text: "Привет! Я предлагаю заключить дипломатическое соглашение и провести " +
+				"совместную операцию по освоению гиперпространственных маршрутов. " +
+				"Жду твоего письменного ответа до конца следующего хода игры, " +
+				"чтобы мы успели согласовать детали и подписать договор вовремя.",
+			want: "ru",
+		},
+	}
+	for _, tc := range cases {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got := d.Detect(tc.text)
+			if got != tc.want {
+				t.Fatalf("Detect = %q, want %q", got, tc.want)
+			}
+		})
+	}
+}
+
+func TestDetectShortOrEmpty(t *testing.T) {
+	t.Parallel()
+	d := New()
+	short := []string{"", "hi", "    "}
+	for _, s := range short {
+		if got := d.Detect(s); got != Undetermined {
+			t.Errorf("Detect(%q) = %q, want %q", s, got, Undetermined)
+		}
+	}
+}

backend/internal/diplomail/diplomail.go

@@ -0,0 +1,135 @@
+// Package diplomail owns the diplomatic-mail subsystem of the Galaxy
+// backend service. Messages live in the lobby-side domain (their
+// storage and lifecycle are tied to a game), but they are surfaced
+// in-game: lobby exposes only an unread-count badge per game while the
+// in-game mail view reads and writes through this package.
+//
+// Stage A implements the personal single-recipient subset:
+//
+//   - send/read/mark-read/soft-delete handlers for a player addressing
+//     one other active member of the game;
+//   - a push event (`diplomail.message.received`) materialised through
+//     the existing notification pipeline so the recipient gets a live
+//     toast when online;
+//   - an unread-counts endpoint that drives the lobby badge.
+//
+// Later stages add admin/owner/system mail, lifecycle hooks, paid-tier
+// player broadcasts, multi-game broadcasts, bulk purge, and the
+// language-detection / translation cache.
+package diplomail
+
+import (
+	"time"
+
+	"galaxy/backend/internal/config"
+	"galaxy/backend/internal/diplomail/detector"
+	"galaxy/backend/internal/diplomail/translator"
+
+	"go.uber.org/zap"
+)
+
+// Kind values stored verbatim in `diplomail_messages.kind`. The schema
+// CHECK constraint pins this to the closed set declared below.
+const (
+	// KindPersonal is a replyable player-to-player message. The
+	// sender is always a `sender_kind='player'`.
+	KindPersonal = "personal"
+
+	// KindAdmin is a non-replyable administrative notification.
+	// The sender is either a human admin (`sender_kind='admin'`)
+	// or the system itself (`sender_kind='system'`).
+	KindAdmin = "admin"
+)
+
+// Sender kind values stored verbatim in `diplomail_messages.sender_kind`.
+const (
+	// SenderKindPlayer marks the sender as an end-user account.
+	// `sender_user_id` and `sender_username` carry the player's id
+	// and immutable `accounts.user_name`.
+	SenderKindPlayer = "player"
+
+	// SenderKindAdmin marks the sender as a site administrator.
+	// `sender_username` carries `admin_accounts.username`.
+	SenderKindAdmin = "admin"
+
+	// SenderKindSystem marks the sender as the service itself
+	// (lifecycle hooks). Both id and username are NULL.
+	SenderKindSystem = "system"
+)
+
+// Broadcast scope values stored verbatim in
+// `diplomail_messages.broadcast_scope`. Stage A only emits `single`;
+// Stage B / C add `game_broadcast` and `multi_game_broadcast`.
+const (
+	BroadcastScopeSingle             = "single"
+	BroadcastScopeGameBroadcast      = "game_broadcast"
+	BroadcastScopeMultiGameBroadcast = "multi_game_broadcast"
+)
+
+// LangUndetermined is the BCP 47 placeholder stored in
+// `diplomail_messages.body_lang` when language detection has not yet
+// been performed or could not produce a result. Stage A writes this
+// value unconditionally; Stage D replaces it with the detected tag.
+const LangUndetermined = "und"
+
+// Service is the diplomatic-mail entry point. Every public method is
+// goroutine-safe; concurrency safety is delegated to Postgres for
+// persisted state.
+type Service struct {
+	deps Deps
+}
+
+// NewService constructs a Service from deps. Logger and Now are
+// defaulted; Store must be non-nil and Memberships must be non-nil
+// because every send path queries the active membership roster.
+func NewService(deps Deps) *Service {
+	if deps.Logger == nil {
+		deps.Logger = zap.NewNop()
+	}
+	deps.Logger = deps.Logger.Named("diplomail")
+	if deps.Now == nil {
+		deps.Now = time.Now
+	}
+	if deps.Notification == nil {
+		deps.Notification = NewNoopNotificationPublisher(deps.Logger)
+	}
+	if deps.Detector == nil {
+		deps.Detector = detector.NoopDetector{}
+	}
+	if deps.Translator == nil {
+		deps.Translator = translator.NewNoop()
+	}
+	if deps.Config.MaxBodyBytes <= 0 {
+		deps.Config.MaxBodyBytes = 4096
+	}
+	if deps.Config.MaxSubjectBytes < 0 {
+		deps.Config.MaxSubjectBytes = 256
+	}
+	return &Service{deps: deps}
+}
+
+// Config returns the service's runtime configuration. Tests and the
+// HTTP layer occasionally surface the limits to clients (the OpenAPI
+// schema documents them too).
+func (s *Service) Config() config.DiplomailConfig {
+	if s == nil {
+		return config.DiplomailConfig{}
+	}
+	return s.deps.Config
+}
+
+// Logger returns the package-named logger. Used by the optional async
+// worker and by tests asserting on log output.
+func (s *Service) Logger() *zap.Logger {
+	if s == nil {
+		return zap.NewNop()
+	}
+	return s.deps.Logger
+}
+
+// nowUTC returns the configured clock normalised to UTC. Matches the
+// convention used everywhere else in `backend` so persisted
+// timestamps compare cleanly regardless of host timezone.
+func (s *Service) nowUTC() time.Time {
+	return s.deps.Now().UTC()
+}

backend/internal/diplomail/errors.go

@@ -0,0 +1,32 @@
+package diplomail
+
+import "errors"
+
+// Sentinel errors surface common rejection reasons across the
+// diplomail package. Handlers map them to HTTP envelopes through
+// `respondDiplomailError` in `internal/server/handlers_user_mail.go`.
+//
+// Adding a new sentinel here is a deliberate API change: it appears in
+// the handler error map and may surface as a new wire `code` value.
+// Reuse the existing set when the behaviour overlaps.
+var (
+	// ErrInvalidInput reports request-level validation failures
+	// (empty body, body or subject over the configured byte limit,
+	// invalid UUID, non-UTF-8 bytes). Maps to 400 invalid_request.
+	ErrInvalidInput = errors.New("diplomail: invalid input")
+
+	// ErrNotFound reports that the requested message does not exist
+	// or is not visible to the caller. Maps to 404 not_found.
+	ErrNotFound = errors.New("diplomail: not found")
+
+	// ErrForbidden reports that the caller is authenticated but not
+	// authorised for the requested action (not an active member of
+	// the game; not a recipient of the message). Maps to 403
+	// forbidden.
+	ErrForbidden = errors.New("diplomail: forbidden")
+
+	// ErrConflict reports that the requested action conflicts with
+	// the current persisted state (e.g. soft-deleting a message
+	// that has not been marked read yet). Maps to 409 conflict.
+	ErrConflict = errors.New("diplomail: conflict")
+)

backend/internal/diplomail/service.go

@@ -0,0 +1,389 @@
+package diplomail
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+	"unicode/utf8"
+
+	"github.com/google/uuid"
+	"go.uber.org/zap"
+)
+
+// previewMaxRunes bounds the body excerpt embedded in the push event
+// so the gRPC payload stays small. The value matches the UI's
+// "two lines" tease and is intentionally not configurable — clients
+// drive their own truncation off the canonical fetch.
+const previewMaxRunes = 120
+
+// SendPersonal persists a single-recipient personal message and
+// fan-outs a `diplomail.message.received` push event to the
+// recipient. Validation rules:
+//
+//   - both sender and recipient must be active members of GameID;
+//   - the recipient must differ from the sender;
+//   - the body must be non-empty, valid UTF-8, and within the
+//     configured byte limit;
+//   - the subject must be valid UTF-8 and within the configured
+//     byte limit (zero is allowed).
+//
+// On any rule violation the function returns ErrInvalidInput or
+// ErrForbidden; the inserted Message is never persisted in those
+// cases.
+func (s *Service) SendPersonal(ctx context.Context, in SendPersonalInput) (Message, Recipient, error) {
+	if in.SenderUserID == in.RecipientUserID {
+		return Message{}, Recipient{}, fmt.Errorf("%w: cannot send mail to yourself", ErrInvalidInput)
+	}
+	subject := strings.TrimRight(in.Subject, " \t")
+	body := strings.TrimRight(in.Body, " \t\n")
+	if err := s.validateContent(subject, body); err != nil {
+		return Message{}, Recipient{}, err
+	}
+
+	sender, err := s.deps.Memberships.GetActiveMembership(ctx, in.GameID, in.SenderUserID)
+	if err != nil {
+		if errors.Is(err, ErrNotFound) {
+			return Message{}, Recipient{}, fmt.Errorf("%w: sender is not an active member of the game", ErrForbidden)
+		}
+		return Message{}, Recipient{}, fmt.Errorf("diplomail: load sender membership: %w", err)
+	}
+	recipient, err := s.deps.Memberships.GetActiveMembership(ctx, in.GameID, in.RecipientUserID)
+	if err != nil {
+		if errors.Is(err, ErrNotFound) {
+			return Message{}, Recipient{}, fmt.Errorf("%w: recipient is not an active member of the game", ErrForbidden)
+		}
+		return Message{}, Recipient{}, fmt.Errorf("diplomail: load recipient membership: %w", err)
+	}
+
+	username := sender.UserName
+	msgInsert := MessageInsert{
+		MessageID:      uuid.New(),
+		GameID:         in.GameID,
+		GameName:       sender.GameName,
+		Kind:           KindPersonal,
+		SenderKind:     SenderKindPlayer,
+		SenderUserID:   &in.SenderUserID,
+		SenderUsername: &username,
+		SenderIP:       in.SenderIP,
+		Subject:        subject,
+		Body:           body,
+		BodyLang:       s.deps.Detector.Detect(body),
+		BroadcastScope: BroadcastScopeSingle,
+	}
+	raceName := recipient.RaceName
+	rcptInsert := buildRecipientInsert(
+		msgInsert.MessageID,
+		MemberSnapshot{
+			UserID:            in.RecipientUserID,
+			GameID:            in.GameID,
+			GameName:          recipient.GameName,
+			UserName:          recipient.UserName,
+			RaceName:          raceName,
+			PreferredLanguage: recipient.PreferredLanguage,
+			Status:            "active",
+		},
+		msgInsert.BodyLang,
+		s.nowUTC(),
+	)
+
+	msg, recipients, err := s.deps.Store.InsertMessageWithRecipients(ctx, msgInsert, []RecipientInsert{rcptInsert})
+	if err != nil {
+		return Message{}, Recipient{}, fmt.Errorf("diplomail: send personal: %w", err)
+	}
+	if len(recipients) != 1 {
+		return Message{}, Recipient{}, fmt.Errorf("diplomail: send personal: unexpected recipient count %d", len(recipients))
+	}
+
+	if recipients[0].AvailableAt != nil {
+		s.publishMessageReceived(ctx, msg, recipients[0])
+	}
+	return msg, recipients[0], nil
+}
+
+// GetMessage returns the InboxEntry for messageID addressed to
+// userID. ErrNotFound is returned when the caller is not a recipient
+// of the message — handlers translate that to 404 so the existence
+// of the message is not leaked. The same sentinel is returned when
+// the caller is no longer an active member of the game and the
+// message is personal-kind: post-kick visibility is restricted to
+// admin/system mail (item 8 of the spec).
+//
+// When `targetLang` is non-empty and differs from the message's
+// `body_lang`, the function consults the translation cache; on a
+// miss it asks the configured Translator to produce a rendering and
+// persists the result. The noop translator returns the input
+// unchanged with `engine == "noop"`, which is treated as
+// "translation unavailable" — the entry comes back with `Translation
+// == nil` and the caller renders the original body.
+func (s *Service) GetMessage(ctx context.Context, userID, messageID uuid.UUID, targetLang string) (InboxEntry, error) {
+	entry, err := s.deps.Store.LoadInboxEntry(ctx, messageID, userID)
+	if err != nil {
+		return InboxEntry{}, err
+	}
+	allowed, err := s.allowedKinds(ctx, entry.GameID, userID)
+	if err != nil {
+		return InboxEntry{}, err
+	}
+	if !allowed[entry.Kind] {
+		return InboxEntry{}, ErrNotFound
+	}
+	if tr := s.resolveTranslation(ctx, entry.Message, targetLang); tr != nil {
+		entry.Translation = tr
+	}
+	return entry, nil
+}
+
+// resolveTranslation returns the cached translation for
+// (message, targetLang), lazily computing and persisting one on
+// cache miss. Returns nil when no translation is needed (target is
+// empty, matches `body_lang`, or the message body is itself
+// undetermined) or when the configured translator declares the
+// rendering unavailable.
+func (s *Service) resolveTranslation(ctx context.Context, msg Message, targetLang string) *Translation {
+	if targetLang == "" || targetLang == msg.BodyLang || msg.BodyLang == LangUndetermined {
+		return nil
+	}
+	if existing, err := s.deps.Store.LoadTranslation(ctx, msg.MessageID, targetLang); err == nil {
+		t := existing
+		return &t
+	} else if !errors.Is(err, ErrNotFound) {
+		s.deps.Logger.Warn("load translation failed",
+			zap.String("message_id", msg.MessageID.String()),
+			zap.String("target_lang", targetLang),
+			zap.Error(err))
+		return nil
+	}
+	if s.deps.Translator == nil {
+		return nil
+	}
+	result, err := s.deps.Translator.Translate(ctx, msg.BodyLang, targetLang, msg.Subject, msg.Body)
+	if err != nil {
+		s.deps.Logger.Warn("translator call failed",
+			zap.String("message_id", msg.MessageID.String()),
+			zap.String("target_lang", targetLang),
+			zap.Error(err))
+		return nil
+	}
+	if result.Engine == "" || result.Engine == "noop" {
+		return nil
+	}
+	tr := Translation{
+		TranslationID:    uuid.New(),
+		MessageID:        msg.MessageID,
+		TargetLang:       targetLang,
+		TranslatedSubject: result.Subject,
+		TranslatedBody:   result.Body,
+		Translator:       result.Engine,
+	}
+	stored, err := s.deps.Store.InsertTranslation(ctx, tr)
+	if err != nil {
+		s.deps.Logger.Warn("insert translation failed",
+			zap.String("message_id", msg.MessageID.String()),
+			zap.String("target_lang", targetLang),
+			zap.Error(err))
+		return nil
+	}
+	return &stored
+}
+
+// ListInbox returns every non-deleted message addressed to userID in
+// gameID, newest first. Read state is preserved per entry; the HTTP
+// layer renders both the message and the recipient row. Personal
+// messages are filtered out when the caller is no longer an active
+// member of the game so a kicked player keeps read access to the
+// admin/system explanation of the kick but not to historical
+// player-to-player threads.
+//
+// When `targetLang` is non-empty and differs from a row's body
+// language, the function consults the translation cache (without
+// re-translating on miss; the per-message read endpoint owns that
+// path so the bulk listing never blocks on translator I/O).
+func (s *Service) ListInbox(ctx context.Context, gameID, userID uuid.UUID, targetLang string) ([]InboxEntry, error) {
+	entries, err := s.deps.Store.ListInbox(ctx, gameID, userID)
+	if err != nil {
+		return nil, err
+	}
+	allowed, err := s.allowedKinds(ctx, gameID, userID)
+	if err != nil {
+		return nil, err
+	}
+	out := entries
+	if !(allowed[KindPersonal] && allowed[KindAdmin]) {
+		out = make([]InboxEntry, 0, len(entries))
+		for _, e := range entries {
+			if allowed[e.Kind] {
+				out = append(out, e)
+			}
+		}
+	}
+	if targetLang == "" {
+		return out, nil
+	}
+	for i := range out {
+		out[i].Translation = s.lookupCachedTranslation(ctx, out[i].Message, targetLang)
+	}
+	return out, nil
+}
+
+// lookupCachedTranslation reads an existing translation row without
+// asking the Translator to compute one. The bulk inbox listing uses
+// this to avoid per-row translator I/O; GetMessage uses the full
+// `resolveTranslation` helper which falls through to the translator
+// on cache miss.
+func (s *Service) lookupCachedTranslation(ctx context.Context, msg Message, targetLang string) *Translation {
+	if targetLang == "" || targetLang == msg.BodyLang || msg.BodyLang == LangUndetermined {
+		return nil
+	}
+	existing, err := s.deps.Store.LoadTranslation(ctx, msg.MessageID, targetLang)
+	if err != nil {
+		if !errors.Is(err, ErrNotFound) {
+			s.deps.Logger.Debug("inbox translation lookup failed",
+				zap.String("message_id", msg.MessageID.String()),
+				zap.Error(err))
+		}
+		return nil
+	}
+	out := existing
+	return &out
+}
+
+// allowedKinds resolves the set of message kinds the caller may read
+// in gameID. An active member can read everything; a former member
+// (status removed or blocked) can read admin-kind only. A user who
+// has never been a member of the game but is still listed as a
+// recipient (legacy / system message) is granted the same admin-only
+// view. The function never returns an empty set: even non-members
+// keep their read access to admin mail.
+func (s *Service) allowedKinds(ctx context.Context, gameID, userID uuid.UUID) (map[string]bool, error) {
+	if s.deps.Memberships == nil {
+		return map[string]bool{KindPersonal: true, KindAdmin: true}, nil
+	}
+	if _, err := s.deps.Memberships.GetActiveMembership(ctx, gameID, userID); err == nil {
+		return map[string]bool{KindPersonal: true, KindAdmin: true}, nil
+	} else if !errors.Is(err, ErrNotFound) {
+		return nil, err
+	}
+	return map[string]bool{KindAdmin: true}, nil
+}
+
+// ListSent returns personal messages authored by senderUserID in
+// gameID, newest first. Admin/system rows have no `sender_user_id`
+// and are therefore excluded; the user surface does not need them.
+func (s *Service) ListSent(ctx context.Context, gameID, senderUserID uuid.UUID) ([]Message, error) {
+	return s.deps.Store.ListSent(ctx, gameID, senderUserID)
+}
+
+// MarkRead transitions a recipient row to `read`. Idempotent: a
+// second call on an already-read row is a no-op. Returns the
+// resulting Recipient. ErrNotFound is surfaced when the caller is
+// not a recipient of the message.
+func (s *Service) MarkRead(ctx context.Context, userID, messageID uuid.UUID) (Recipient, error) {
+	return s.deps.Store.MarkRead(ctx, messageID, userID, s.nowUTC())
+}
+
+// DeleteMessage soft-deletes the recipient row identified by
+// (messageID, userID). The row must already have `read_at` set, or
+// the call returns ErrConflict (item 10 of the spec: open-then-delete).
+// Returns ErrNotFound when the caller is not a recipient.
+func (s *Service) DeleteMessage(ctx context.Context, userID, messageID uuid.UUID) (Recipient, error) {
+	return s.deps.Store.SoftDelete(ctx, messageID, userID, s.nowUTC())
+}
+
+// UnreadCountsForUser returns the lobby badge breakdown.
+func (s *Service) UnreadCountsForUser(ctx context.Context, userID uuid.UUID) ([]UnreadCount, error) {
+	return s.deps.Store.UnreadCountsForUser(ctx, userID)
+}
+
+// validateContent enforces the body/subject byte limits and rejects
+// non-UTF-8 input. Stage A applies the rules to plain text only; HTML
+// is treated as plain text by the server (the UI renders via
+// textContent) and gets no special handling.
+func (s *Service) validateContent(subject, body string) error {
+	if body == "" {
+		return fmt.Errorf("%w: body must not be empty", ErrInvalidInput)
+	}
+	if !utf8.ValidString(body) {
+		return fmt.Errorf("%w: body must be valid UTF-8", ErrInvalidInput)
+	}
+	if len(body) > s.deps.Config.MaxBodyBytes {
+		return fmt.Errorf("%w: body exceeds %d bytes", ErrInvalidInput, s.deps.Config.MaxBodyBytes)
+	}
+	if subject != "" {
+		if !utf8.ValidString(subject) {
+			return fmt.Errorf("%w: subject must be valid UTF-8", ErrInvalidInput)
+		}
+		if len(subject) > s.deps.Config.MaxSubjectBytes {
+			return fmt.Errorf("%w: subject exceeds %d bytes", ErrInvalidInput, s.deps.Config.MaxSubjectBytes)
+		}
+	}
+	return nil
+}
+
+// publishMessageReceived emits the per-recipient push notification.
+// Failures are logged at debug level: notifications are best-effort
+// over the gRPC stream, and clients always have the unread-counts
+// endpoint as the durable fallback.
+func (s *Service) publishMessageReceived(ctx context.Context, msg Message, recipient Recipient) {
+	unreadGame, err := s.deps.Store.UnreadCountForUserGame(ctx, msg.GameID, recipient.UserID)
+	if err != nil {
+		s.deps.Logger.Warn("compute unread count for push payload failed",
+			zap.String("message_id", msg.MessageID.String()),
+			zap.String("recipient", recipient.UserID.String()),
+			zap.Error(err))
+		unreadGame = 0
+	}
+	unreadTotals, err := s.deps.Store.UnreadCountsForUser(ctx, recipient.UserID)
+	if err != nil {
+		s.deps.Logger.Warn("compute unread totals for push payload failed",
+			zap.String("recipient", recipient.UserID.String()),
+			zap.Error(err))
+		unreadTotals = nil
+	}
+	unreadTotal := 0
+	for _, u := range unreadTotals {
+		unreadTotal += u.Unread
+	}
+
+	payload := map[string]any{
+		"message_id":   msg.MessageID.String(),
+		"game_id":      msg.GameID.String(),
+		"kind":         msg.Kind,
+		"sender_kind":  msg.SenderKind,
+		"subject":      msg.Subject,
+		"preview":      preview(msg.Body, previewMaxRunes),
+		"preview_lang": msg.BodyLang,
+		"unread_total": unreadTotal,
+		"unread_game":  unreadGame,
+	}
+	ev := DiplomailNotification{
+		Kind:           "diplomail.message.received",
+		IdempotencyKey: "diplomail.message.received:" + msg.MessageID.String() + ":" + recipient.UserID.String(),
+		Recipient:      recipient.UserID,
+		Payload:        payload,
+	}
+	if err := s.deps.Notification.PublishDiplomailEvent(ctx, ev); err != nil {
+		s.deps.Logger.Warn("publish diplomail event failed",
+			zap.String("message_id", msg.MessageID.String()),
+			zap.String("recipient", recipient.UserID.String()),
+			zap.Error(err))
+	}
+}
+
+// preview truncates s to at most max runes and appends a horizontal
+// ellipsis when truncation actually happened. The function operates
+// on runes, not bytes, so multibyte UTF-8 sequences (Cyrillic,
+// emoji) survive without corruption.
+func preview(s string, max int) string {
+	if max <= 0 || utf8.RuneCountInString(s) <= max {
+		return s
+	}
+	count := 0
+	for i := range s {
+		if count == max {
+			return s[:i] + "…"
+		}
+		count++
+	}
+	return s
+}

backend/internal/diplomail/store.go

@@ -0,0 +1,803 @@
+package diplomail
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"time"
+
+	"galaxy/backend/internal/postgres/jet/backend/model"
+	"galaxy/backend/internal/postgres/jet/backend/table"
+
+	"github.com/go-jet/jet/v2/postgres"
+	"github.com/go-jet/jet/v2/qrm"
+	"github.com/google/uuid"
+)
+
+// Store is the Postgres-backed query surface for the diplomail
+// package. All queries are built through go-jet against the generated
+// table bindings under `backend/internal/postgres/jet/backend/table`.
+type Store struct {
+	db *sql.DB
+}
+
+// NewStore constructs a Store wrapping db.
+func NewStore(db *sql.DB) *Store { return &Store{db: db} }
+
+// messageColumns is the canonical projection for diplomail_messages
+// reads.
+func messageColumns() postgres.ColumnList {
+	m := table.DiplomailMessages
+	return postgres.ColumnList{
+		m.MessageID, m.GameID, m.GameName, m.Kind, m.SenderKind,
+		m.SenderUserID, m.SenderUsername, m.SenderIP,
+		m.Subject, m.Body, m.BodyLang, m.BroadcastScope, m.CreatedAt,
+	}
+}
+
+// recipientColumns is the canonical projection for
+// diplomail_recipients reads.
+func recipientColumns() postgres.ColumnList {
+	r := table.DiplomailRecipients
+	return postgres.ColumnList{
+		r.RecipientID, r.MessageID, r.GameID, r.UserID,
+		r.RecipientUserName, r.RecipientRaceName, r.RecipientPreferredLanguage,
+		r.AvailableAt, r.TranslationAttempts, r.NextTranslationAttemptAt,
+		r.DeliveredAt, r.ReadAt, r.DeletedAt, r.NotifiedAt,
+	}
+}
+
+// MessageInsert carries the immutable per-message fields. The store
+// fills MessageID, sets CreatedAt to `now()` via the column default,
+// and leaves recipient-side state to InsertRecipient.
+type MessageInsert struct {
+	MessageID      uuid.UUID
+	GameID         uuid.UUID
+	GameName       string
+	Kind           string
+	SenderKind     string
+	SenderUserID   *uuid.UUID
+	SenderUsername *string
+	SenderIP       string
+	Subject        string
+	Body           string
+	BodyLang       string
+	BroadcastScope string
+}
+
+// RecipientInsert carries the per-recipient snapshot. AvailableAt
+// captures the async-delivery contract: when non-nil, the recipient
+// row is materialised already-delivered (no translation needed or
+// the language matches); when nil, the recipient is queued for the
+// translation worker.
+type RecipientInsert struct {
+	RecipientID                uuid.UUID
+	MessageID                  uuid.UUID
+	GameID                     uuid.UUID
+	UserID                     uuid.UUID
+	RecipientUserName          string
+	RecipientRaceName          *string
+	RecipientPreferredLanguage string
+	AvailableAt                *time.Time
+}
+
+// InsertMessageWithRecipients persists a Message together with one or
+// more Recipient rows inside a single transaction. The function is
+// the canonical write path for every send variant: Stage A passes a
+// single-element slice; later stages reuse the same path for
+// broadcasts.
+func (s *Store) InsertMessageWithRecipients(ctx context.Context, msg MessageInsert, recipients []RecipientInsert) (Message, []Recipient, error) {
+	if len(recipients) == 0 {
+		return Message{}, nil, errors.New("diplomail store: at least one recipient required")
+	}
+
+	tx, err := s.db.BeginTx(ctx, nil)
+	if err != nil {
+		return Message{}, nil, fmt.Errorf("diplomail store: begin tx: %w", err)
+	}
+	defer func() { _ = tx.Rollback() }()
+
+	m := table.DiplomailMessages
+	msgStmt := m.INSERT(
+		m.MessageID, m.GameID, m.GameName, m.Kind, m.SenderKind,
+		m.SenderUserID, m.SenderUsername, m.SenderIP,
+		m.Subject, m.Body, m.BodyLang, m.BroadcastScope,
+	).VALUES(
+		msg.MessageID,
+		msg.GameID,
+		msg.GameName,
+		msg.Kind,
+		msg.SenderKind,
+		uuidPtrArg(msg.SenderUserID),
+		stringPtrArg(msg.SenderUsername),
+		msg.SenderIP,
+		msg.Subject,
+		msg.Body,
+		msg.BodyLang,
+		msg.BroadcastScope,
+	).RETURNING(messageColumns())
+
+	var msgRow model.DiplomailMessages
+	if err := msgStmt.QueryContext(ctx, tx, &msgRow); err != nil {
+		return Message{}, nil, fmt.Errorf("diplomail store: insert message: %w", err)
+	}
+
+	r := table.DiplomailRecipients
+	rcptStmt := r.INSERT(
+		r.RecipientID, r.MessageID, r.GameID, r.UserID,
+		r.RecipientUserName, r.RecipientRaceName,
+		r.RecipientPreferredLanguage, r.AvailableAt,
+	)
+	for _, in := range recipients {
+		rcptStmt = rcptStmt.VALUES(
+			in.RecipientID,
+			in.MessageID,
+			in.GameID,
+			in.UserID,
+			in.RecipientUserName,
+			stringPtrArg(in.RecipientRaceName),
+			in.RecipientPreferredLanguage,
+			timePtrArg(in.AvailableAt),
+		)
+	}
+	rcptStmt = rcptStmt.RETURNING(recipientColumns())
+
+	var rcptRows []model.DiplomailRecipients
+	if err := rcptStmt.QueryContext(ctx, tx, &rcptRows); err != nil {
+		return Message{}, nil, fmt.Errorf("diplomail store: insert recipients: %w", err)
+	}
+
+	if err := tx.Commit(); err != nil {
+		return Message{}, nil, fmt.Errorf("diplomail store: commit: %w", err)
+	}
+
+	return messageFromModel(msgRow), recipientsFromModel(rcptRows), nil
+}
+
+// LoadMessage returns the Message row identified by messageID. The
+// function is used by readers that already verified recipient
+// authorisation; callers that need both the message and the
+// recipient's per-user state should use LoadInboxEntry.
+func (s *Store) LoadMessage(ctx context.Context, messageID uuid.UUID) (Message, error) {
+	m := table.DiplomailMessages
+	stmt := postgres.SELECT(messageColumns()).
+		FROM(m).
+		WHERE(m.MessageID.EQ(postgres.UUID(messageID))).
+		LIMIT(1)
+	var row model.DiplomailMessages
+	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
+		if errors.Is(err, qrm.ErrNoRows) {
+			return Message{}, ErrNotFound
+		}
+		return Message{}, fmt.Errorf("diplomail store: load message %s: %w", messageID, err)
+	}
+	return messageFromModel(row), nil
+}
+
+// LoadInboxEntry returns a Message together with the caller's
+// Recipient row, both for messageID. Returns ErrNotFound when the
+// caller is not a recipient of the message — this is also how the
+// service layer enforces "only recipients may read".
+func (s *Store) LoadInboxEntry(ctx context.Context, messageID, userID uuid.UUID) (InboxEntry, error) {
+	m := table.DiplomailMessages
+	r := table.DiplomailRecipients
+	cols := append(messageColumns(), recipientColumns()...)
+	stmt := postgres.SELECT(cols).
+		FROM(r.INNER_JOIN(m, m.MessageID.EQ(r.MessageID))).
+		WHERE(
+			r.MessageID.EQ(postgres.UUID(messageID)).
+				AND(r.UserID.EQ(postgres.UUID(userID))),
+		).
+		LIMIT(1)
+	var dest struct {
+		model.DiplomailMessages
+		Recipient model.DiplomailRecipients `alias:"diplomail_recipients"`
+	}
+	if err := stmt.QueryContext(ctx, s.db, &dest); err != nil {
+		if errors.Is(err, qrm.ErrNoRows) {
+			return InboxEntry{}, ErrNotFound
+		}
+		return InboxEntry{}, fmt.Errorf("diplomail store: load inbox entry %s/%s: %w", messageID, userID, err)
+	}
+	return InboxEntry{
+		Message:   messageFromModel(dest.DiplomailMessages),
+		Recipient: recipientFromModel(dest.Recipient),
+	}, nil
+}
+
+// ListInbox returns the recipient view of messages addressed to
+// userID in gameID, newest first. Soft-deleted rows
+// (`deleted_at IS NOT NULL`) are excluded. Rows still waiting for
+// the async translation worker (`available_at IS NULL`) are also
+// excluded — they will appear once delivery is complete.
+func (s *Store) ListInbox(ctx context.Context, gameID, userID uuid.UUID) ([]InboxEntry, error) {
+	m := table.DiplomailMessages
+	r := table.DiplomailRecipients
+	cols := append(messageColumns(), recipientColumns()...)
+	stmt := postgres.SELECT(cols).
+		FROM(r.INNER_JOIN(m, m.MessageID.EQ(r.MessageID))).
+		WHERE(
+			r.UserID.EQ(postgres.UUID(userID)).
+				AND(r.GameID.EQ(postgres.UUID(gameID))).
+				AND(r.DeletedAt.IS_NULL()).
+				AND(r.AvailableAt.IS_NOT_NULL()),
+		).
+		ORDER_BY(m.CreatedAt.DESC(), m.MessageID.DESC())
+	var dest []struct {
+		model.DiplomailMessages
+		Recipient model.DiplomailRecipients `alias:"diplomail_recipients"`
+	}
+	if err := stmt.QueryContext(ctx, s.db, &dest); err != nil {
+		return nil, fmt.Errorf("diplomail store: list inbox %s/%s: %w", gameID, userID, err)
+	}
+	out := make([]InboxEntry, 0, len(dest))
+	for _, row := range dest {
+		out = append(out, InboxEntry{
+			Message:   messageFromModel(row.DiplomailMessages),
+			Recipient: recipientFromModel(row.Recipient),
+		})
+	}
+	return out, nil
+}
+
+// ListSent returns messages authored by senderUserID in gameID,
+// newest first. Personal messages only — admin/system rows have
+// `sender_user_id IS NULL` and are filtered out by the WHERE clause.
+func (s *Store) ListSent(ctx context.Context, gameID, senderUserID uuid.UUID) ([]Message, error) {
+	m := table.DiplomailMessages
+	stmt := postgres.SELECT(messageColumns()).
+		FROM(m).
+		WHERE(
+			m.GameID.EQ(postgres.UUID(gameID)).
+				AND(m.SenderUserID.EQ(postgres.UUID(senderUserID))),
+		).
+		ORDER_BY(m.CreatedAt.DESC(), m.MessageID.DESC())
+	var rows []model.DiplomailMessages
+	if err := stmt.QueryContext(ctx, s.db, &rows); err != nil {
+		return nil, fmt.Errorf("diplomail store: list sent %s/%s: %w", gameID, senderUserID, err)
+	}
+	out := make([]Message, 0, len(rows))
+	for _, row := range rows {
+		out = append(out, messageFromModel(row))
+	}
+	return out, nil
+}
+
+// MarkRead sets `read_at = at` on the recipient row identified by
+// (messageID, userID). Idempotent: a row that is already marked read
+// is left untouched but the existing Recipient is returned.
+// Returns ErrNotFound when the user is not a recipient of the message.
+func (s *Store) MarkRead(ctx context.Context, messageID, userID uuid.UUID, at time.Time) (Recipient, error) {
+	r := table.DiplomailRecipients
+	stmt := r.UPDATE(r.ReadAt).
+		SET(postgres.TimestampzT(at.UTC())).
+		WHERE(
+			r.MessageID.EQ(postgres.UUID(messageID)).
+				AND(r.UserID.EQ(postgres.UUID(userID))).
+				AND(r.ReadAt.IS_NULL()),
+		).
+		RETURNING(recipientColumns())
+	var row model.DiplomailRecipients
+	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
+		if !errors.Is(err, qrm.ErrNoRows) {
+			return Recipient{}, fmt.Errorf("diplomail store: mark read %s/%s: %w", messageID, userID, err)
+		}
+		// The row exists but read_at was already set, or the row
+		// does not exist at all. Fetch to disambiguate.
+		existing, loadErr := s.LoadRecipient(ctx, messageID, userID)
+		if loadErr != nil {
+			return Recipient{}, loadErr
+		}
+		return existing, nil
+	}
+	return recipientFromModel(row), nil
+}
+
+// SoftDelete sets `deleted_at = at` on the recipient row identified by
+// (messageID, userID). The row must already have `read_at` set;
+// otherwise the call returns ErrConflict so a hostile client cannot
+// erase a message before opening it (item 10 of the spec).
+// Returns ErrNotFound when the user is not a recipient.
+func (s *Store) SoftDelete(ctx context.Context, messageID, userID uuid.UUID, at time.Time) (Recipient, error) {
+	r := table.DiplomailRecipients
+	stmt := r.UPDATE(r.DeletedAt).
+		SET(postgres.TimestampzT(at.UTC())).
+		WHERE(
+			r.MessageID.EQ(postgres.UUID(messageID)).
+				AND(r.UserID.EQ(postgres.UUID(userID))).
+				AND(r.ReadAt.IS_NOT_NULL()).
+				AND(r.DeletedAt.IS_NULL()),
+		).
+		RETURNING(recipientColumns())
+	var row model.DiplomailRecipients
+	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
+		if !errors.Is(err, qrm.ErrNoRows) {
+			return Recipient{}, fmt.Errorf("diplomail store: soft delete %s/%s: %w", messageID, userID, err)
+		}
+		existing, loadErr := s.LoadRecipient(ctx, messageID, userID)
+		if loadErr != nil {
+			return Recipient{}, loadErr
+		}
+		if existing.ReadAt == nil {
+			return Recipient{}, fmt.Errorf("%w: message must be read before delete", ErrConflict)
+		}
+		// Already deleted: return the existing row idempotently.
+		return existing, nil
+	}
+	return recipientFromModel(row), nil
+}
+
+// LoadRecipient fetches the Recipient row keyed on (messageID, userID).
+// Returns ErrNotFound when no such recipient exists.
+func (s *Store) LoadRecipient(ctx context.Context, messageID, userID uuid.UUID) (Recipient, error) {
+	r := table.DiplomailRecipients
+	stmt := postgres.SELECT(recipientColumns()).
+		FROM(r).
+		WHERE(
+			r.MessageID.EQ(postgres.UUID(messageID)).
+				AND(r.UserID.EQ(postgres.UUID(userID))),
+		).
+		LIMIT(1)
+	var row model.DiplomailRecipients
+	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
+		if errors.Is(err, qrm.ErrNoRows) {
+			return Recipient{}, ErrNotFound
+		}
+		return Recipient{}, fmt.Errorf("diplomail store: load recipient %s/%s: %w", messageID, userID, err)
+	}
+	return recipientFromModel(row), nil
+}
+
+// UnreadCountForUserGame returns the count of unread, non-deleted,
+// delivered messages addressed to userID in gameID. Recipients
+// still waiting for translation (`available_at IS NULL`) are
+// excluded so the badge does not flicker.
+func (s *Store) UnreadCountForUserGame(ctx context.Context, gameID, userID uuid.UUID) (int, error) {
+	r := table.DiplomailRecipients
+	stmt := postgres.SELECT(postgres.COUNT(postgres.STAR).AS("count")).
+		FROM(r).
+		WHERE(
+			r.UserID.EQ(postgres.UUID(userID)).
+				AND(r.GameID.EQ(postgres.UUID(gameID))).
+				AND(r.ReadAt.IS_NULL()).
+				AND(r.DeletedAt.IS_NULL()).
+				AND(r.AvailableAt.IS_NOT_NULL()),
+		)
+	var dest struct {
+		Count int64 `alias:"count"`
+	}
+	if err := stmt.QueryContext(ctx, s.db, &dest); err != nil {
+		return 0, fmt.Errorf("diplomail store: unread count %s/%s: %w", gameID, userID, err)
+	}
+	return int(dest.Count), nil
+}
+
+// PendingTranslationPair carries one unit of work picked by the
+// translation worker. Multiple recipients of the same message that
+// share a preferred_language collapse into one pair, because the
+// translation is shared via the diplomail_translations cache.
+// CurrentAttempts is the highest `translation_attempts` value across
+// the matching recipient rows, so the worker can decide whether the
+// next attempt is the last one before falling back.
+type PendingTranslationPair struct {
+	MessageID       uuid.UUID
+	TargetLang      string
+	CurrentAttempts int32
+}
+
+// PickPendingTranslationPair returns one pair eligible for the
+// translation worker, or `ok == false` when the queue is empty. The
+// pair is the (message, target_lang) of any recipient where
+// `available_at IS NULL` and `next_translation_attempt_at` is either
+// unset or already due. The query intentionally drops the
+// `FOR UPDATE` clause — the worker is single-threaded per process,
+// and the optimistic UPDATE in `MarkPairDelivered` /
+// `MarkPairFallback` filters by `available_at IS NULL`, so a stale
+// pickup never delivers twice.
+func (s *Store) PickPendingTranslationPair(ctx context.Context, now time.Time) (PendingTranslationPair, bool, error) {
+	r := table.DiplomailRecipients
+	stmt := postgres.SELECT(
+		r.MessageID.AS("message_id"),
+		r.RecipientPreferredLanguage.AS("target_lang"),
+		postgres.MAX(r.TranslationAttempts).AS("attempts"),
+	).
+		FROM(r).
+		WHERE(
+			r.AvailableAt.IS_NULL().
+				AND(r.RecipientPreferredLanguage.NOT_EQ(postgres.String(""))).
+				AND(r.NextTranslationAttemptAt.IS_NULL().
+					OR(r.NextTranslationAttemptAt.LT_EQ(postgres.TimestampzT(now.UTC())))),
+		).
+		GROUP_BY(r.MessageID, r.RecipientPreferredLanguage).
+		ORDER_BY(r.MessageID.ASC(), r.RecipientPreferredLanguage.ASC()).
+		LIMIT(1)
+	var dest struct {
+		MessageID  uuid.UUID `alias:"message_id"`
+		TargetLang string    `alias:"target_lang"`
+		Attempts   int32     `alias:"attempts"`
+	}
+	if err := stmt.QueryContext(ctx, s.db, &dest); err != nil {
+		if errors.Is(err, qrm.ErrNoRows) {
+			return PendingTranslationPair{}, false, nil
+		}
+		return PendingTranslationPair{}, false, fmt.Errorf("diplomail store: pick pending pair: %w", err)
+	}
+	if dest.MessageID == (uuid.UUID{}) {
+		return PendingTranslationPair{}, false, nil
+	}
+	return PendingTranslationPair{
+		MessageID:       dest.MessageID,
+		TargetLang:      dest.TargetLang,
+		CurrentAttempts: dest.Attempts,
+	}, true, nil
+}
+
+// MarkPairDelivered flips every still-pending recipient of (messageID,
+// targetLang) to `available_at = at`, optionally persisting the
+// translation row alongside in the same transaction. Returns the
+// recipients that were just delivered (used by the worker to fan out
+// push events).
+func (s *Store) MarkPairDelivered(ctx context.Context, messageID uuid.UUID, targetLang string, translation *Translation, at time.Time) ([]Recipient, error) {
+	tx, err := s.db.BeginTx(ctx, nil)
+	if err != nil {
+		return nil, fmt.Errorf("diplomail store: begin deliver tx: %w", err)
+	}
+	defer func() { _ = tx.Rollback() }()
+
+	if translation != nil {
+		t := table.DiplomailTranslations
+		ins := t.INSERT(
+			t.TranslationID, t.MessageID, t.TargetLang,
+			t.TranslatedSubject, t.TranslatedBody, t.Translator,
+		).VALUES(
+			translation.TranslationID, translation.MessageID, translation.TargetLang,
+			translation.TranslatedSubject, translation.TranslatedBody, translation.Translator,
+		).ON_CONFLICT(t.MessageID, t.TargetLang).DO_NOTHING()
+		if _, err := ins.ExecContext(ctx, tx); err != nil {
+			return nil, fmt.Errorf("diplomail store: upsert translation: %w", err)
+		}
+	}
+
+	r := table.DiplomailRecipients
+	upd := r.UPDATE(r.AvailableAt, r.NextTranslationAttemptAt).
+		SET(postgres.TimestampzT(at.UTC()), postgres.NULL).
+		WHERE(
+			r.MessageID.EQ(postgres.UUID(messageID)).
+				AND(r.RecipientPreferredLanguage.EQ(postgres.String(targetLang))).
+				AND(r.AvailableAt.IS_NULL()),
+		).
+		RETURNING(recipientColumns())
+
+	var rows []model.DiplomailRecipients
+	if err := upd.QueryContext(ctx, tx, &rows); err != nil {
+		return nil, fmt.Errorf("diplomail store: mark pair delivered: %w", err)
+	}
+	if err := tx.Commit(); err != nil {
+		return nil, fmt.Errorf("diplomail store: commit deliver: %w", err)
+	}
+	out := make([]Recipient, 0, len(rows))
+	for _, row := range rows {
+		out = append(out, recipientFromModel(row))
+	}
+	return out, nil
+}
+
+// SchedulePairRetry bumps the attempt counter and schedules the next
+// translation attempt for `next`. The recipient rows stay in the
+// pending queue (`available_at IS NULL`). Returns the new attempt
+// counter so the worker can decide whether to fall back to the
+// original on the next pickup.
+func (s *Store) SchedulePairRetry(ctx context.Context, messageID uuid.UUID, targetLang string, next time.Time) (int32, error) {
+	r := table.DiplomailRecipients
+	upd := r.UPDATE(r.TranslationAttempts, r.NextTranslationAttemptAt).
+		SET(r.TranslationAttempts.ADD(postgres.Int(1)), postgres.TimestampzT(next.UTC())).
+		WHERE(
+			r.MessageID.EQ(postgres.UUID(messageID)).
+				AND(r.RecipientPreferredLanguage.EQ(postgres.String(targetLang))).
+				AND(r.AvailableAt.IS_NULL()),
+		).
+		RETURNING(r.TranslationAttempts)
+	var dest []struct {
+		TranslationAttempts int32 `alias:"diplomail_recipients.translation_attempts"`
+	}
+	if err := upd.QueryContext(ctx, s.db, &dest); err != nil {
+		return 0, fmt.Errorf("diplomail store: schedule pair retry: %w", err)
+	}
+	if len(dest) == 0 {
+		return 0, nil
+	}
+	max := dest[0].TranslationAttempts
+	for _, d := range dest[1:] {
+		if d.TranslationAttempts > max {
+			max = d.TranslationAttempts
+		}
+	}
+	return max, nil
+}
+
+// translationColumns is the canonical projection for
+// diplomail_translations reads.
+func translationColumns() postgres.ColumnList {
+	t := table.DiplomailTranslations
+	return postgres.ColumnList{
+		t.TranslationID, t.MessageID, t.TargetLang,
+		t.TranslatedSubject, t.TranslatedBody, t.Translator, t.TranslatedAt,
+	}
+}
+
+// LoadTranslation returns the cached translation row for
+// (messageID, targetLang). Returns ErrNotFound when no cache row
+// exists yet — the caller decides whether to compute and persist
+// one.
+func (s *Store) LoadTranslation(ctx context.Context, messageID uuid.UUID, targetLang string) (Translation, error) {
+	t := table.DiplomailTranslations
+	stmt := postgres.SELECT(translationColumns()).
+		FROM(t).
+		WHERE(t.MessageID.EQ(postgres.UUID(messageID)).
+			AND(t.TargetLang.EQ(postgres.String(targetLang)))).
+		LIMIT(1)
+	var row model.DiplomailTranslations
+	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
+		if errors.Is(err, qrm.ErrNoRows) {
+			return Translation{}, ErrNotFound
+		}
+		return Translation{}, fmt.Errorf("diplomail store: load translation %s/%s: %w", messageID, targetLang, err)
+	}
+	return translationFromModel(row), nil
+}
+
+// InsertTranslation persists a new translation cache row. The unique
+// constraint on (message_id, target_lang) prevents duplicate
+// renderings. Callers that race on the same (message, lang) pair
+// should be prepared for a UNIQUE violation; the second writer can
+// fall back to LoadTranslation.
+func (s *Store) InsertTranslation(ctx context.Context, in Translation) (Translation, error) {
+	t := table.DiplomailTranslations
+	stmt := t.INSERT(
+		t.TranslationID, t.MessageID, t.TargetLang,
+		t.TranslatedSubject, t.TranslatedBody, t.Translator,
+	).VALUES(
+		in.TranslationID, in.MessageID, in.TargetLang,
+		in.TranslatedSubject, in.TranslatedBody, in.Translator,
+	).RETURNING(translationColumns())
+
+	var row model.DiplomailTranslations
+	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
+		return Translation{}, fmt.Errorf("diplomail store: insert translation %s/%s: %w", in.MessageID, in.TargetLang, err)
+	}
+	return translationFromModel(row), nil
+}
+
+func translationFromModel(row model.DiplomailTranslations) Translation {
+	return Translation{
+		TranslationID:    row.TranslationID,
+		MessageID:        row.MessageID,
+		TargetLang:       row.TargetLang,
+		TranslatedSubject: row.TranslatedSubject,
+		TranslatedBody:   row.TranslatedBody,
+		Translator:       row.Translator,
+		TranslatedAt:     row.TranslatedAt,
+	}
+}
+
+// DeleteMessagesForGames removes every diplomail_messages row whose
+// game_id falls in the supplied set. The cascade defined on the
+// `diplomail_recipients` and `diplomail_translations` foreign keys
+// removes the per-recipient state and the cached translations in
+// the same transaction. Returns the count of messages removed.
+//
+// Used by the admin bulk-purge endpoint; callers are expected to
+// have already filtered the input set to terminal-state games.
+func (s *Store) DeleteMessagesForGames(ctx context.Context, gameIDs []uuid.UUID) (int, error) {
+	if len(gameIDs) == 0 {
+		return 0, nil
+	}
+	args := make([]postgres.Expression, 0, len(gameIDs))
+	for _, id := range gameIDs {
+		args = append(args, postgres.UUID(id))
+	}
+	m := table.DiplomailMessages
+	stmt := m.DELETE().WHERE(m.GameID.IN(args...))
+	res, err := stmt.ExecContext(ctx, s.db)
+	if err != nil {
+		return 0, fmt.Errorf("diplomail store: bulk delete messages: %w", err)
+	}
+	affected, err := res.RowsAffected()
+	if err != nil {
+		return 0, fmt.Errorf("diplomail store: rows affected: %w", err)
+	}
+	return int(affected), nil
+}
+
+// ListMessagesForAdmin returns a paginated slice of messages
+// matching filter. The result is ordered by created_at DESC,
+// message_id DESC. Total is the count without pagination so the
+// caller can render a "page X of N" envelope.
+func (s *Store) ListMessagesForAdmin(ctx context.Context, filter AdminMessageListing) ([]Message, int, error) {
+	m := table.DiplomailMessages
+	page := filter.Page
+	if page < 1 {
+		page = 1
+	}
+	pageSize := filter.PageSize
+	if pageSize < 1 {
+		pageSize = 50
+	}
+
+	conditions := postgres.BoolExpression(nil)
+	addCondition := func(cond postgres.BoolExpression) {
+		if conditions == nil {
+			conditions = cond
+			return
+		}
+		conditions = conditions.AND(cond)
+	}
+	if filter.GameID != nil {
+		addCondition(m.GameID.EQ(postgres.UUID(*filter.GameID)))
+	}
+	if filter.Kind != "" {
+		addCondition(m.Kind.EQ(postgres.String(filter.Kind)))
+	}
+	if filter.SenderKind != "" {
+		addCondition(m.SenderKind.EQ(postgres.String(filter.SenderKind)))
+	}
+
+	countStmt := postgres.SELECT(postgres.COUNT(postgres.STAR).AS("count")).FROM(m)
+	if conditions != nil {
+		countStmt = countStmt.WHERE(conditions)
+	}
+	var countDest struct {
+		Count int64 `alias:"count"`
+	}
+	if err := countStmt.QueryContext(ctx, s.db, &countDest); err != nil {
+		return nil, 0, fmt.Errorf("diplomail store: count admin messages: %w", err)
+	}
+
+	listStmt := postgres.SELECT(messageColumns()).FROM(m)
+	if conditions != nil {
+		listStmt = listStmt.WHERE(conditions)
+	}
+	listStmt = listStmt.
+		ORDER_BY(m.CreatedAt.DESC(), m.MessageID.DESC()).
+		LIMIT(int64(pageSize)).
+		OFFSET(int64((page - 1) * pageSize))
+
+	var rows []model.DiplomailMessages
+	if err := listStmt.QueryContext(ctx, s.db, &rows); err != nil {
+		return nil, 0, fmt.Errorf("diplomail store: list admin messages: %w", err)
+	}
+	out := make([]Message, 0, len(rows))
+	for _, row := range rows {
+		out = append(out, messageFromModel(row))
+	}
+	return out, int(countDest.Count), nil
+}
+
+// UnreadCountsForUser returns a per-game breakdown of unread messages
+// addressed to userID, plus the matching game names so the lobby
+// badge UI can render entries even after the recipient's membership
+// has been revoked. The slice is ordered by game name.
+func (s *Store) UnreadCountsForUser(ctx context.Context, userID uuid.UUID) ([]UnreadCount, error) {
+	r := table.DiplomailRecipients
+	m := table.DiplomailMessages
+	stmt := postgres.SELECT(
+		r.GameID.AS("game_id"),
+		postgres.MAX(m.GameName).AS("game_name"),
+		postgres.COUNT(postgres.STAR).AS("count"),
+	).
+		FROM(r.INNER_JOIN(m, m.MessageID.EQ(r.MessageID))).
+		WHERE(
+			r.UserID.EQ(postgres.UUID(userID)).
+				AND(r.ReadAt.IS_NULL()).
+				AND(r.DeletedAt.IS_NULL()).
+				AND(r.AvailableAt.IS_NOT_NULL()),
+		).
+		GROUP_BY(r.GameID).
+		ORDER_BY(postgres.MAX(m.GameName).ASC())
+	var dest []struct {
+		GameID   uuid.UUID `alias:"game_id"`
+		GameName string    `alias:"game_name"`
+		Count    int64     `alias:"count"`
+	}
+	if err := stmt.QueryContext(ctx, s.db, &dest); err != nil {
+		return nil, fmt.Errorf("diplomail store: unread counts %s: %w", userID, err)
+	}
+	out := make([]UnreadCount, 0, len(dest))
+	for _, row := range dest {
+		out = append(out, UnreadCount{
+			GameID:   row.GameID,
+			GameName: row.GameName,
+			Unread:   int(row.Count),
+		})
+	}
+	return out, nil
+}
+
+// messageFromModel converts a jet-generated row to the domain type.
+func messageFromModel(row model.DiplomailMessages) Message {
+	out := Message{
+		MessageID:      row.MessageID,
+		GameID:         row.GameID,
+		GameName:       row.GameName,
+		Kind:           row.Kind,
+		SenderKind:     row.SenderKind,
+		SenderIP:       row.SenderIP,
+		Subject:        row.Subject,
+		Body:           row.Body,
+		BodyLang:       row.BodyLang,
+		BroadcastScope: row.BroadcastScope,
+		CreatedAt:      row.CreatedAt,
+	}
+	if row.SenderUserID != nil {
+		id := *row.SenderUserID
+		out.SenderUserID = &id
+	}
+	if row.SenderUsername != nil {
+		name := *row.SenderUsername
+		out.SenderUsername = &name
+	}
+	return out
+}
+
+// recipientFromModel converts a jet-generated row to the domain type.
+func recipientFromModel(row model.DiplomailRecipients) Recipient {
+	out := Recipient{
+		RecipientID:                row.RecipientID,
+		MessageID:                  row.MessageID,
+		GameID:                     row.GameID,
+		UserID:                     row.UserID,
+		RecipientUserName:          row.RecipientUserName,
+		RecipientPreferredLanguage: row.RecipientPreferredLanguage,
+		AvailableAt:                row.AvailableAt,
+		TranslationAttempts:        row.TranslationAttempts,
+		NextTranslationAttemptAt:   row.NextTranslationAttemptAt,
+		DeliveredAt:                row.DeliveredAt,
+		ReadAt:                     row.ReadAt,
+		DeletedAt:                  row.DeletedAt,
+		NotifiedAt:                 row.NotifiedAt,
+	}
+	if row.RecipientRaceName != nil {
+		name := *row.RecipientRaceName
+		out.RecipientRaceName = &name
+	}
+	return out
+}
+
+// recipientsFromModel converts a slice in place. Used by
+// InsertMessageWithRecipients.
+func recipientsFromModel(rows []model.DiplomailRecipients) []Recipient {
+	out := make([]Recipient, 0, len(rows))
+	for _, row := range rows {
+		out = append(out, recipientFromModel(row))
+	}
+	return out
+}
+
+// uuidPtrArg returns the jet argument expression for a nullable UUID.
+// Pre-NULL handling here avoids a custom NULL literal at every call
+// site.
+func uuidPtrArg(v *uuid.UUID) postgres.Expression {
+	if v == nil {
+		return postgres.NULL
+	}
+	return postgres.UUID(*v)
+}
+
+// stringPtrArg returns the jet argument expression for a nullable
+// text column.
+func stringPtrArg(v *string) postgres.Expression {
+	if v == nil {
+		return postgres.NULL
+	}
+	return postgres.String(*v)
+}
+
+// timePtrArg returns the jet argument expression for a nullable
+// timestamptz column.
+func timePtrArg(v *time.Time) postgres.Expression {
+	if v == nil {
+		return postgres.NULL
+	}
+	return postgres.TimestampzT(v.UTC())
+}

backend/internal/diplomail/translator/libretranslate.go

@@ -0,0 +1,154 @@
+package translator
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+	"time"
+)
+
+// LibreTranslateEngine is the engine identifier persisted in
+// `diplomail_translations.translator` for cache rows produced by the
+// LibreTranslate client.
+const LibreTranslateEngine = "libretranslate"
+
+// LibreTranslateConfig configures the HTTP client. URL is the base
+// of the deployed instance (without `/translate`). Timeout bounds a
+// single HTTP request; the worker layers retry / backoff on top.
+type LibreTranslateConfig struct {
+	URL     string
+	Timeout time.Duration
+}
+
+// ErrUnsupportedLanguagePair classifies a LibreTranslate 400 response
+// that indicates the engine cannot translate between the requested
+// source / target codes. The worker treats this as terminal: no
+// further retries, deliver the original.
+var ErrUnsupportedLanguagePair = errors.New("translator: language pair not supported by libretranslate")
+
+// NewLibreTranslate constructs a Translator that posts to
+// `<URL>/translate`. Returns an error when URL is empty so wiring
+// catches "translator misconfigured" at startup rather than at
+// first-translation-attempt.
+func NewLibreTranslate(cfg LibreTranslateConfig) (Translator, error) {
+	url := strings.TrimRight(strings.TrimSpace(cfg.URL), "/")
+	if url == "" {
+		return nil, errors.New("translator: libretranslate URL must be set")
+	}
+	timeout := cfg.Timeout
+	if timeout <= 0 {
+		timeout = 10 * time.Second
+	}
+	return &libreTranslate{
+		endpoint: url + "/translate",
+		client:   &http.Client{Timeout: timeout},
+	}, nil
+}
+
+type libreTranslate struct {
+	endpoint string
+	client   *http.Client
+}
+
+// requestBody is the LibreTranslate POST /translate input shape.
+// `q` is sent as a two-element array so the engine returns one
+// translation per element in the same call (subject + body).
+type requestBody struct {
+	Q      []string `json:"q"`
+	Source string   `json:"source"`
+	Target string   `json:"target"`
+	Format string   `json:"format"`
+}
+
+// responseBody is the LibreTranslate output shape when `q` is an
+// array. The single-string-q variant is a different shape; we never
+// emit a single-q request so the client always sees the array form.
+type responseBody struct {
+	TranslatedText []string `json:"translatedText"`
+	Error          string   `json:"error,omitempty"`
+}
+
+// Translate posts subject + body to LibreTranslate, normalising the
+// language codes and classifying the response. The 400 / unsupported-
+// pair path is signalled by `ErrUnsupportedLanguagePair`. All other
+// HTTP errors (timeout, 5xx, network failure) come back as wrapped
+// errors so the worker can backoff and retry.
+func (l *libreTranslate) Translate(ctx context.Context, srcLang, dstLang, subject, body string) (Result, error) {
+	src := normaliseLanguageCode(srcLang)
+	dst := normaliseLanguageCode(dstLang)
+	if src == "" || dst == "" {
+		return Result{}, fmt.Errorf("translator: missing source or target language (src=%q dst=%q)", srcLang, dstLang)
+	}
+	if src == dst {
+		return Result{Subject: subject, Body: body, Engine: NoopEngine}, nil
+	}
+
+	reqBody, err := json.Marshal(requestBody{
+		Q:      []string{subject, body},
+		Source: src,
+		Target: dst,
+		Format: "text",
+	})
+	if err != nil {
+		return Result{}, fmt.Errorf("translator: marshal request: %w", err)
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, l.endpoint, bytes.NewReader(reqBody))
+	if err != nil {
+		return Result{}, fmt.Errorf("translator: build request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Accept", "application/json")
+
+	resp, err := l.client.Do(req)
+	if err != nil {
+		return Result{}, fmt.Errorf("translator: do request: %w", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	raw, err := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	if err != nil {
+		return Result{}, fmt.Errorf("translator: read response: %w", err)
+	}
+	if resp.StatusCode == http.StatusBadRequest {
+		return Result{}, fmt.Errorf("%w: %s", ErrUnsupportedLanguagePair, strings.TrimSpace(string(raw)))
+	}
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		return Result{}, fmt.Errorf("translator: libretranslate http %d: %s", resp.StatusCode, strings.TrimSpace(string(raw)))
+	}
+
+	var out responseBody
+	if err := json.Unmarshal(raw, &out); err != nil {
+		return Result{}, fmt.Errorf("translator: unmarshal response: %w", err)
+	}
+	if out.Error != "" {
+		return Result{}, fmt.Errorf("translator: libretranslate error: %s", out.Error)
+	}
+	if len(out.TranslatedText) != 2 {
+		return Result{}, fmt.Errorf("translator: libretranslate returned %d strings, want 2", len(out.TranslatedText))
+	}
+	return Result{
+		Subject: out.TranslatedText[0],
+		Body:    out.TranslatedText[1],
+		Engine:  LibreTranslateEngine,
+	}, nil
+}
+
+// normaliseLanguageCode collapses a BCP 47 tag to the ISO 639-1 base
+// that LibreTranslate expects (`en-US` → `en`, `EN` → `en`). The
+// helper is mirrored on the diplomail service side; both sides need
+// to use the same normalisation so cache keys line up.
+func normaliseLanguageCode(tag string) string {
+	tag = strings.TrimSpace(tag)
+	if tag == "" {
+		return ""
+	}
+	if i := strings.IndexAny(tag, "-_"); i > 0 {
+		tag = tag[:i]
+	}
+	return strings.ToLower(tag)
+}

backend/internal/diplomail/translator/libretranslate_test.go

@@ -0,0 +1,173 @@
+package translator
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestLibreTranslateHappyPath(t *testing.T) {
+	t.Parallel()
+	var (
+		requestSource string
+		requestTarget string
+		requestQ      []string
+		requestFormat string
+	)
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		body, _ := io.ReadAll(r.Body)
+		var in requestBody
+		if err := json.Unmarshal(body, &in); err != nil {
+			t.Errorf("unmarshal: %v", err)
+		}
+		requestSource = in.Source
+		requestTarget = in.Target
+		requestQ = in.Q
+		requestFormat = in.Format
+		_ = json.NewEncoder(w).Encode(responseBody{
+			TranslatedText: []string{"[ru] " + in.Q[0], "[ru] " + in.Q[1]},
+		})
+	}))
+	t.Cleanup(server.Close)
+
+	tr, err := NewLibreTranslate(LibreTranslateConfig{URL: server.URL, Timeout: 2 * time.Second})
+	if err != nil {
+		t.Fatalf("new: %v", err)
+	}
+	res, err := tr.Translate(context.Background(), "en", "ru", "Hello", "World")
+	if err != nil {
+		t.Fatalf("translate: %v", err)
+	}
+	if res.Engine != LibreTranslateEngine {
+		t.Fatalf("engine = %q, want %q", res.Engine, LibreTranslateEngine)
+	}
+	if res.Subject != "[ru] Hello" || res.Body != "[ru] World" {
+		t.Fatalf("result = %+v", res)
+	}
+	if requestSource != "en" || requestTarget != "ru" || requestFormat != "text" {
+		t.Fatalf("request fields: src=%q dst=%q fmt=%q", requestSource, requestTarget, requestFormat)
+	}
+	if len(requestQ) != 2 || requestQ[0] != "Hello" || requestQ[1] != "World" {
+		t.Fatalf("request q = %v", requestQ)
+	}
+}
+
+func TestLibreTranslateNormalisesLanguageCodes(t *testing.T) {
+	t.Parallel()
+	var src, dst string
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		body, _ := io.ReadAll(r.Body)
+		var in requestBody
+		_ = json.Unmarshal(body, &in)
+		src, dst = in.Source, in.Target
+		_ = json.NewEncoder(w).Encode(responseBody{TranslatedText: []string{"a", "b"}})
+	}))
+	t.Cleanup(server.Close)
+
+	tr, _ := NewLibreTranslate(LibreTranslateConfig{URL: server.URL})
+	if _, err := tr.Translate(context.Background(), "EN-US", "ru-RU", "x", "y"); err != nil {
+		t.Fatalf("translate: %v", err)
+	}
+	if src != "en" || dst != "ru" {
+		t.Fatalf("normalised codes src=%q dst=%q, want en/ru", src, dst)
+	}
+}
+
+func TestLibreTranslateUnsupportedPair(t *testing.T) {
+	t.Parallel()
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusBadRequest)
+		_, _ = w.Write([]byte(`{"error":"language not supported"}`))
+	}))
+	t.Cleanup(server.Close)
+
+	tr, _ := NewLibreTranslate(LibreTranslateConfig{URL: server.URL})
+	_, err := tr.Translate(context.Background(), "en", "xx", "subject", "body")
+	if !errors.Is(err, ErrUnsupportedLanguagePair) {
+		t.Fatalf("err = %v, want ErrUnsupportedLanguagePair", err)
+	}
+}
+
+func TestLibreTranslateServerError(t *testing.T) {
+	t.Parallel()
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+		_, _ = w.Write([]byte("kaboom"))
+	}))
+	t.Cleanup(server.Close)
+
+	tr, _ := NewLibreTranslate(LibreTranslateConfig{URL: server.URL})
+	_, err := tr.Translate(context.Background(), "en", "ru", "subject", "body")
+	if err == nil {
+		t.Fatalf("expected error, got nil")
+	}
+	if errors.Is(err, ErrUnsupportedLanguagePair) {
+		t.Fatalf("err mis-classified as unsupported pair: %v", err)
+	}
+	if !strings.Contains(err.Error(), "500") {
+		t.Fatalf("err = %v, want mention of 500", err)
+	}
+}
+
+func TestLibreTranslateSameSourceAndTargetIsNoop(t *testing.T) {
+	t.Parallel()
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		t.Errorf("translator should not call the server for identical src/dst: %s", r.URL.Path)
+	}))
+	t.Cleanup(server.Close)
+
+	tr, _ := NewLibreTranslate(LibreTranslateConfig{URL: server.URL})
+	res, err := tr.Translate(context.Background(), "en", "EN", "x", "y")
+	if err != nil {
+		t.Fatalf("translate: %v", err)
+	}
+	if res.Engine != NoopEngine {
+		t.Fatalf("engine = %q, want %q", res.Engine, NoopEngine)
+	}
+}
+
+func TestLibreTranslateRequiresURL(t *testing.T) {
+	t.Parallel()
+	_, err := NewLibreTranslate(LibreTranslateConfig{URL: ""})
+	if err == nil {
+		t.Fatalf("expected error for empty URL")
+	}
+}
+
+// TestLibreTranslateRejectsMalformedArray defends against a server
+// that returns a partial / unexpected `translatedText` payload. The
+// client must surface an error (not panic, not return a half-empty
+// Result) so the worker can decide between retry and fallback.
+func TestLibreTranslateRejectsMalformedArray(t *testing.T) {
+	t.Parallel()
+	cases := []struct {
+		name string
+		body string
+	}{
+		{"single string", `{"translatedText": "only one"}`},
+		{"array of one", `{"translatedText": ["only one"]}`},
+		{"empty array", `{"translatedText": []}`},
+		{"missing field", `{"foo":"bar"}`},
+	}
+	for _, tc := range cases {
+		body := tc.body
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+				_, _ = w.Write([]byte(body))
+			}))
+			t.Cleanup(server.Close)
+			tr, _ := NewLibreTranslate(LibreTranslateConfig{URL: server.URL})
+			res, err := tr.Translate(context.Background(), "en", "ru", "subject", "body")
+			if err == nil {
+				t.Fatalf("expected error for malformed body %q, got %+v", body, res)
+			}
+		})
+	}
+}

backend/internal/diplomail/translator/translator.go

@@ -0,0 +1,59 @@
+// Package translator wraps the per-language rendering for the
+// diplomail subsystem. The package exposes a narrow `Translator`
+// interface so the actual translation backend (LibreTranslate, an
+// in-process model, a SaaS engine, …) can be swapped without
+// touching the rest of the codebase.
+//
+// Stage D ships a `NoopTranslator` that returns the input unchanged.
+// The diplomail Service treats a `Name == NoopEngine` result as
+// "translation unavailable" and refrains from writing a cache row;
+// the inbox handler then returns the original body with a
+// `translated == false` payload. The contract lets the rest of the
+// system ship without a translation backend; future stages can wire
+// a real `Translator` without code changes elsewhere.
+package translator
+
+import "context"
+
+// NoopEngine is the engine identifier returned by `NoopTranslator`.
+// The diplomail Service checks for this value to decide whether to
+// persist a `diplomail_translations` row.
+const NoopEngine = "noop"
+
+// Result carries one translated rendering plus the engine identifier
+// that produced it. The engine name is persisted as
+// `diplomail_translations.translator` so an operator can see which
+// backend produced each row.
+type Result struct {
+	Subject string
+	Body    string
+	Engine  string
+}
+
+// Translator is the read-only surface diplomail consumes when it
+// needs to render a message for a recipient whose
+// `preferred_language` differs from `body_lang`. Implementations
+// must be safe for concurrent use; `Translate` may be invoked from
+// the async worker on many messages at once.
+type Translator interface {
+	// Translate renders `subject` and `body` from `srcLang` into
+	// `dstLang`. A nil error with `Result.Engine == NoopEngine`
+	// signals that no real rendering happened.
+	Translate(ctx context.Context, srcLang, dstLang, subject, body string) (Result, error)
+}
+
+// NewNoop returns a Translator that always returns the input
+// unchanged with engine name `NoopEngine`.
+func NewNoop() Translator {
+	return noop{}
+}
+
+type noop struct{}
+
+func (noop) Translate(_ context.Context, _, _, subject, body string) (Result, error) {
+	return Result{
+		Subject: subject,
+		Body:    body,
+		Engine:  NoopEngine,
+	}, nil
+}

backend/internal/diplomail/types.go

@@ -0,0 +1,255 @@
+package diplomail
+
+import (
+	"time"
+
+	"github.com/google/uuid"
+)
+
+// Message mirrors a row in `backend.diplomail_messages` enriched with
+// the per-message metadata captured at insert time.
+//
+// SenderUserID and SenderUsername are nullable in the DB so that the
+// CHECK constraint can cover the three legal sender shapes:
+//
+//   - player: SenderUserID set, SenderUsername set
+//   - admin:  SenderUserID nil, SenderUsername set
+//   - system: SenderUserID nil, SenderUsername nil
+type Message struct {
+	MessageID      uuid.UUID
+	GameID         uuid.UUID
+	GameName       string
+	Kind           string
+	SenderKind     string
+	SenderUserID   *uuid.UUID
+	SenderUsername *string
+	SenderIP       string
+	Subject        string
+	Body           string
+	BodyLang       string
+	BroadcastScope string
+	CreatedAt      time.Time
+}
+
+// Recipient mirrors a row in `backend.diplomail_recipients`. The
+// per-recipient state (read/deleted/delivered/notified) lives here.
+// RecipientUserName, RecipientRaceName, and
+// RecipientPreferredLanguage are snapshots taken at insert time so
+// the inbox listing, admin search, and translation worker render
+// correctly even after the source rows are renamed or revoked.
+//
+// AvailableAt encodes the async-translation contract introduced in
+// Stage E:
+//
+//   - non-nil → message is visible to the recipient (in inbox /
+//     unread counts / push events) starting from this timestamp;
+//   - nil → recipient is waiting for the translation worker to fan
+//     out the translated rendering. The translation_attempts counter
+//     tracks the number of failed LibreTranslate calls; the worker
+//     gives up after `MaxTranslationAttempts` and falls back to the
+//     original body, flipping AvailableAt to now().
+type Recipient struct {
+	RecipientID                uuid.UUID
+	MessageID                  uuid.UUID
+	GameID                     uuid.UUID
+	UserID                     uuid.UUID
+	RecipientUserName          string
+	RecipientRaceName          *string
+	RecipientPreferredLanguage string
+	AvailableAt                *time.Time
+	TranslationAttempts        int32
+	NextTranslationAttemptAt   *time.Time
+	DeliveredAt                *time.Time
+	ReadAt                     *time.Time
+	DeletedAt                  *time.Time
+	NotifiedAt                 *time.Time
+}
+
+// InboxEntry is the read-side projection composed of a Message and the
+// caller's own Recipient row. The HTTP layer renders one of these per
+// item in the inbox listing. Translation, when non-nil, carries the
+// per-recipient rendering returned from
+// `Service.GetMessage(ctx, …, targetLang)` and surfaced under the
+// `body_translated` payload field; Stage D ships a noop translator,
+// so this field stays nil until a real backend is wired.
+type InboxEntry struct {
+	Message
+	Recipient   Recipient
+	Translation *Translation
+}
+
+// Translation mirrors a row in `backend.diplomail_translations`. The
+// engine identifier is preserved so an operator can see which
+// backend produced the cached rendering.
+type Translation struct {
+	TranslationID    uuid.UUID
+	MessageID        uuid.UUID
+	TargetLang       string
+	TranslatedSubject string
+	TranslatedBody   string
+	Translator       string
+	TranslatedAt     time.Time
+}
+
+// SendPersonalInput is the request payload for SendPersonal: the
+// caller sending a single-recipient personal message. Validation
+// (active membership, body length, etc.) is performed inside the
+// service.
+type SendPersonalInput struct {
+	GameID          uuid.UUID
+	SenderUserID    uuid.UUID
+	RecipientUserID uuid.UUID
+	Subject         string
+	Body            string
+	SenderIP        string
+}
+
+// CallerKind enumerates the privileged sender roles for admin-kind
+// messages. Owners (`CallerKindOwner`) are players who own a private
+// game; admins (`CallerKindAdmin`) hit the dedicated admin route;
+// `CallerKindSystem` is reserved for internal lifecycle hooks.
+const (
+	CallerKindOwner  = "owner"
+	CallerKindAdmin  = "admin"
+	CallerKindSystem = "system"
+)
+
+// SendAdminPersonalInput is the request payload for an owner /
+// admin / system sending an admin-kind message to a single
+// recipient. Authorization (owner-vs-admin distinction) is enforced
+// by the HTTP layer; the service trusts the caller designation.
+type SendAdminPersonalInput struct {
+	GameID          uuid.UUID
+	CallerKind      string
+	CallerUserID    *uuid.UUID
+	CallerUsername  string
+	RecipientUserID uuid.UUID
+	Subject         string
+	Body            string
+	SenderIP        string
+}
+
+// SendAdminBroadcastInput is the request payload for an owner /
+// admin / system broadcasting an admin-kind message inside a single
+// game. RecipientScope selects the address book; the sender's own
+// recipient row is never created (a broadcast author does not get a
+// copy of their own message).
+type SendAdminBroadcastInput struct {
+	GameID         uuid.UUID
+	CallerKind     string
+	CallerUserID   *uuid.UUID
+	CallerUsername string
+	RecipientScope string
+	Subject        string
+	Body           string
+	SenderIP       string
+}
+
+// LifecycleEventKind enumerates the producer-side intents the lobby
+// emits when a game-state or membership-state transition lands.
+const (
+	LifecycleKindGamePaused          = "game.paused"
+	LifecycleKindGameCancelled       = "game.cancelled"
+	LifecycleKindMembershipRemoved   = "membership.removed"
+	LifecycleKindMembershipBlocked   = "membership.blocked"
+)
+
+// SendPlayerBroadcastInput is the request payload for the paid-tier
+// player broadcast. The sender is a player; recipients are the
+// active members of the game minus the sender. The resulting message
+// is `kind="personal"`, `sender_kind="player"`,
+// `broadcast_scope="game_broadcast"` — recipients may reply as if it
+// were a personal send, but the reply goes back to the broadcaster
+// only.
+type SendPlayerBroadcastInput struct {
+	GameID       uuid.UUID
+	SenderUserID uuid.UUID
+	Subject      string
+	Body         string
+	SenderIP     string
+}
+
+// MultiGameBroadcastScope enumerates the admin multi-game broadcast
+// modes. `selected` requires `GameIDs`; `all_running` enumerates
+// every game whose status is non-terminal through GameLookup.
+const (
+	MultiGameScopeSelected   = "selected"
+	MultiGameScopeAllRunning = "all_running"
+)
+
+// SendMultiGameBroadcastInput is the request payload for the admin
+// multi-game broadcast. The service materialises one message row per
+// addressed game (so a recipient who plays in two games receives two
+// independently-deletable inbox entries), then fan-outs the push
+// events.
+type SendMultiGameBroadcastInput struct {
+	CallerUsername string
+	Scope          string
+	GameIDs        []uuid.UUID
+	RecipientScope string
+	Subject        string
+	Body           string
+	SenderIP       string
+}
+
+// BulkCleanupInput selects messages eligible for purge. OlderThanYears
+// must be >= 1; the service translates the value into a cutoff
+// expressed in years and walks `GameLookup.ListFinishedGamesBefore`.
+type BulkCleanupInput struct {
+	OlderThanYears int
+}
+
+// CleanupResult summarises a bulk-cleanup run for the admin response
+// envelope.
+type CleanupResult struct {
+	GameIDs        []uuid.UUID
+	MessagesDeleted int
+}
+
+// AdminMessageListing is the filter passed to ListMessagesForAdmin.
+// Pagination uses (Page, PageSize) consistent with the rest of the
+// admin surface. Filters are AND-combined; the empty filter returns
+// every persisted row.
+type AdminMessageListing struct {
+	Page     int
+	PageSize int
+	GameID   *uuid.UUID
+	Kind     string
+	SenderKind string
+}
+
+// AdminMessagePage is the canonical pagination envelope.
+type AdminMessagePage struct {
+	Items    []Message
+	Total    int
+	Page     int
+	PageSize int
+}
+
+// LifecycleEvent is the payload lobby hands to PublishLifecycle when
+// a transition needs to be reflected as durable system mail. The
+// recipient set is derived by the service:
+//
+//   - For game.* events the message fans out to every active member
+//     of the game except the actor (the actor sees the action in
+//     their own UI through other channels).
+//   - For membership.* events the message addresses exactly
+//     `TargetUser` (the kicked player), regardless of their current
+//     membership status — this is how a kicked player retains read
+//     access to the explanation of the kick.
+type LifecycleEvent struct {
+	GameID     uuid.UUID
+	Kind       string
+	Actor      string
+	Reason     string
+	TargetUser *uuid.UUID
+}
+
+// UnreadCount carries a per-game unread-count row returned by
+// UnreadCountsForUser. The lobby badge UI consumes the slice plus the
+// derived total.
+type UnreadCount struct {
+	GameID   uuid.UUID
+	GameName string
+	Unread   int
+}

backend/internal/diplomail/worker.go

@@ -0,0 +1,209 @@
+package diplomail
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"galaxy/backend/internal/diplomail/translator"
+
+	"github.com/google/uuid"
+	"go.uber.org/zap"
+)
+
+// translationBackoff returns the sleep applied before retry attempt
+// `attempt`. attempt is 1-indexed (the value the row carries AFTER
+// the failure is recorded). The schedule mirrors the spec —
+// 1s → 2s → 4s → 8s → 16s — so 5 failed attempts span ~31 seconds
+// before the worker falls back to delivering the original.
+func translationBackoff(attempt int32) time.Duration {
+	if attempt <= 0 {
+		return 0
+	}
+	out := time.Second
+	for i := int32(1); i < attempt; i++ {
+		out *= 2
+	}
+	const cap = 60 * time.Second
+	if out > cap {
+		return cap
+	}
+	return out
+}
+
+// Worker drives the async translation pipeline. Each tick picks a
+// single (message_id, target_lang) pair from
+// `diplomail_recipients` where `available_at IS NULL`, asks the
+// configured Translator to render the body, and either delivers the
+// pending recipients (success) or schedules a retry (transient
+// failure) or delivers them with a fallback to the original body
+// (terminal failure / max attempts).
+//
+// The worker is single-threaded by design: one HTTP call to
+// LibreTranslate at a time. This protects the upstream from spikes
+// and keeps the implementation reviewable.
+//
+// Implements `internal/app.Component` so it plugs into the same
+// lifecycle as the mail and notification workers.
+type Worker struct {
+	svc *Service
+}
+
+// NewWorker constructs a Worker bound to svc. Returning a non-nil
+// Worker even when the translator is the noop fallback is
+// intentional — the pickup query still works and falls through to
+// fallback delivery, which is the desired behaviour for setups
+// without LibreTranslate.
+func NewWorker(svc *Service) *Worker { return &Worker{svc: svc} }
+
+// Run drives the worker loop until ctx is cancelled.
+func (w *Worker) Run(ctx context.Context) error {
+	if w == nil || w.svc == nil {
+		return nil
+	}
+	logger := w.svc.deps.Logger.Named("worker")
+	interval := w.svc.deps.Config.WorkerInterval
+	if interval <= 0 {
+		interval = 2 * time.Second
+	}
+	if err := w.tick(ctx); err != nil && !errors.Is(err, context.Canceled) {
+		logger.Warn("diplomail worker initial tick failed", zap.Error(err))
+	}
+	ticker := time.NewTicker(interval)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return nil
+		case <-ticker.C:
+			if err := w.tick(ctx); err != nil && !errors.Is(err, context.Canceled) {
+				logger.Warn("diplomail worker tick failed", zap.Error(err))
+			}
+		}
+	}
+}
+
+// Shutdown is a no-op: every translation outcome is committed inside
+// tick before returning, so cancelling the parent ctx is enough.
+func (w *Worker) Shutdown(_ context.Context) error { return nil }
+
+// Tick exposes the per-tick work for tests so they can drive the
+// worker without depending on the ticker.
+func (w *Worker) Tick(ctx context.Context) error { return w.tick(ctx) }
+
+// tick picks one pair from the queue and applies the result. The
+// per-tick budget is one pair on purpose: the worker is single
+// threaded and we do not want a fast LibreTranslate instance to
+// starve the rest of the backend's I/O behind a long-running batch.
+func (w *Worker) tick(ctx context.Context) error {
+	if ctx.Err() != nil {
+		return ctx.Err()
+	}
+	pair, ok, err := w.svc.deps.Store.PickPendingTranslationPair(ctx, w.svc.nowUTC())
+	if err != nil {
+		return err
+	}
+	if !ok {
+		return nil
+	}
+	return w.processPair(ctx, pair)
+}
+
+// processPair runs the full pipeline for one (message, target_lang).
+// Steps:
+//
+//  1. Load the source message.
+//  2. Check the translation cache. If a row already exists (another
+//     worker pre-populated it, or two pairs converged on the same
+//     target), reuse it and deliver.
+//  3. Otherwise call the configured Translator.
+//  4. Apply the outcome: success → cache + deliver; unsupported
+//     pair → deliver fallback (no cache row); other failure →
+//     schedule retry or deliver fallback after MaxAttempts.
+//  5. Fan out push events for every recipient whose `available_at`
+//     just transitioned.
+func (w *Worker) processPair(ctx context.Context, pair PendingTranslationPair) error {
+	logger := w.svc.deps.Logger.Named("worker").With(
+		zap.String("message_id", pair.MessageID.String()),
+		zap.String("target_lang", pair.TargetLang),
+	)
+	msg, err := w.svc.deps.Store.LoadMessage(ctx, pair.MessageID)
+	if err != nil {
+		return err
+	}
+
+	if cached, err := w.svc.deps.Store.LoadTranslation(ctx, pair.MessageID, pair.TargetLang); err == nil {
+		t := cached
+		return w.deliverPair(ctx, msg, pair.TargetLang, &t, logger)
+	} else if !errors.Is(err, ErrNotFound) {
+		return err
+	}
+
+	result, callErr := w.svc.deps.Translator.Translate(ctx, msg.BodyLang, pair.TargetLang, msg.Subject, msg.Body)
+	if callErr == nil && result.Engine != "" && result.Engine != translator.NoopEngine {
+		tr := Translation{
+			TranslationID:     uuid.New(),
+			MessageID:         msg.MessageID,
+			TargetLang:        pair.TargetLang,
+			TranslatedSubject: result.Subject,
+			TranslatedBody:    result.Body,
+			Translator:        result.Engine,
+		}
+		return w.deliverPair(ctx, msg, pair.TargetLang, &tr, logger)
+	}
+	if callErr == nil {
+		// Noop translator (or engine returned empty). Treat as
+		// "translation unavailable" — deliver fallback so users
+		// see the original.
+		logger.Debug("translator returned noop, delivering fallback")
+		return w.deliverPair(ctx, msg, pair.TargetLang, nil, logger)
+	}
+	if errors.Is(callErr, translator.ErrUnsupportedLanguagePair) {
+		logger.Info("language pair unsupported, delivering fallback", zap.Error(callErr))
+		return w.deliverPair(ctx, msg, pair.TargetLang, nil, logger)
+	}
+
+	// Transient failure — bump the attempts counter and schedule a
+	// retry. The next attempt timestamp is computed from the
+	// post-increment counter so the spec's 1s→2s→4s→8s→16s schedule
+	// applies between retries of the same pair.
+	maxAttempts := w.svc.deps.Config.TranslatorMaxAttempts
+	if maxAttempts <= 0 {
+		maxAttempts = 5
+	}
+	nextAttempt := pair.CurrentAttempts + 1
+	if int(nextAttempt) >= maxAttempts {
+		logger.Warn("translator max attempts reached, delivering fallback",
+			zap.Int32("attempts", nextAttempt), zap.Error(callErr))
+		return w.deliverPair(ctx, msg, pair.TargetLang, nil, logger)
+	}
+	next := w.svc.nowUTC().Add(translationBackoff(nextAttempt + 1))
+	if _, err := w.svc.deps.Store.SchedulePairRetry(ctx, pair.MessageID, pair.TargetLang, next); err != nil {
+		return err
+	}
+	logger.Info("translator attempt failed, scheduled retry",
+		zap.Int32("attempts", nextAttempt),
+		zap.Time("next_attempt_at", next),
+		zap.Error(callErr))
+	return nil
+}
+
+// deliverPair flips every still-pending recipient of (messageID,
+// targetLang) to delivered, optionally inserting the translation row
+// in the same transaction, and emits push events to the recipients
+// who were just unblocked.
+func (w *Worker) deliverPair(ctx context.Context, msg Message, targetLang string, translation *Translation, logger *zap.Logger) error {
+	recipients, err := w.svc.deps.Store.MarkPairDelivered(ctx, msg.MessageID, targetLang, translation, w.svc.nowUTC())
+	if err != nil {
+		return err
+	}
+	if len(recipients) == 0 {
+		logger.Debug("deliver yielded no recipients (already delivered)")
+		return nil
+	}
+	for _, r := range recipients {
+		w.svc.publishMessageReceived(ctx, msg, r)
+	}
+	return nil
+}
+

backend/internal/lobby/cache.go

@@ -117,6 +117,24 @@ func (c *Cache) GetGame(gameID uuid.UUID) (GameRecord, bool) {
 	return g, ok
 }
 
+// ListGames returns a snapshot copy of every cached game. Terminal-
+// state games (finished, cancelled) are evicted from the cache on
+// `PutGame`, so the result reflects the live roster of running /
+// paused / draft / starting / etc. games. The slice is freshly
+// allocated and safe for the caller to mutate.
+func (c *Cache) ListGames() []GameRecord {
+	if c == nil {
+		return nil
+	}
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	out := make([]GameRecord, 0, len(c.games))
+	for _, g := range c.games {
+		out = append(out, g)
+	}
+	return out
+}
+
 // PutGame stores game in the cache when its status is cacheable;
 // terminal statuses (finished, cancelled) cause the entry to be evicted.
 func (c *Cache) PutGame(game GameRecord) {

backend/internal/lobby/deps.go

@@ -51,6 +51,37 @@ type NotificationPublisher interface {
 	PublishLobbyEvent(ctx context.Context, intent LobbyNotification) error
 }
 
+// DiplomailPublisher is the outbound surface the lobby uses to drop a
+// durable system mail entry whenever a game-state or
+// membership-state transition needs to land in the affected players'
+// inboxes. The real implementation in `cmd/backend/main` adapts the
+// `*diplomail.Service.PublishLifecycle` call; tests and partial
+// wiring fall back to `NewNoopDiplomailPublisher`.
+type DiplomailPublisher interface {
+	PublishLifecycle(ctx context.Context, event LifecycleEvent) error
+}
+
+// LifecycleEvent is the open shape carried by a system-mail intent.
+// `Kind` is one of the lobby-internal constants
+// (`LifecycleKindGamePaused`, etc.). `TargetUser` is populated only
+// for membership-scoped events; the publisher derives the game-scoped
+// recipient set itself.
+type LifecycleEvent struct {
+	GameID     uuid.UUID
+	Kind       string
+	Actor      string
+	Reason     string
+	TargetUser *uuid.UUID
+}
+
+// Lifecycle-event kinds the lobby emits.
+const (
+	LifecycleKindGamePaused        = "game.paused"
+	LifecycleKindGameCancelled     = "game.cancelled"
+	LifecycleKindMembershipRemoved = "membership.removed"
+	LifecycleKindMembershipBlocked = "membership.blocked"
+)
+
 // LobbyNotification is the open shape carried by a notification intent.
 // The implementation emits a small set of `Kind` values matching the catalog in
 // `backend/README.md` §10. The `Payload` map is the kind-specific data
@@ -123,3 +154,26 @@ func (p *noopNotificationPublisher) PublishLobbyEvent(_ context.Context, intent
 	)
 	return nil
 }
+
+// NewNoopDiplomailPublisher returns a DiplomailPublisher that logs
+// every call at debug level and returns nil. Used by tests and by
+// the lobby Service factory when the Deps.Diplomail field is left
+// nil.
+func NewNoopDiplomailPublisher(logger *zap.Logger) DiplomailPublisher {
+	if logger == nil {
+		logger = zap.NewNop()
+	}
+	return &noopDiplomailPublisher{logger: logger.Named("lobby.diplomail.noop")}
+}
+
+type noopDiplomailPublisher struct {
+	logger *zap.Logger
+}
+
+func (p *noopDiplomailPublisher) PublishLifecycle(_ context.Context, event LifecycleEvent) error {
+	p.logger.Debug("noop diplomail lifecycle",
+		zap.String("kind", event.Kind),
+		zap.String("game_id", event.GameID.String()),
+	)
+	return nil
+}

backend/internal/lobby/games.go

@@ -10,6 +10,7 @@ import (
 	"galaxy/cronutil"
 
 	"github.com/google/uuid"
+	"go.uber.org/zap"
 )
 
 // CreateGameInput is the parameter struct for Service.CreateGame.
@@ -233,6 +234,41 @@ func (s *Service) ListMyGames(ctx context.Context, userID uuid.UUID) ([]GameReco
 	return s.deps.Store.ListMyGames(ctx, userID)
 }
 
+// ListFinishedGamesBefore returns every game whose status is
+// `finished` or `cancelled` and whose `finished_at` is strictly older
+// than cutoff. The result walks the store through the admin-paged
+// query with a 200-row batch size; the caller is expected to invoke
+// this from rare admin workflows (diplomail bulk cleanup) rather
+// than hot-path reads.
+func (s *Service) ListFinishedGamesBefore(ctx context.Context, cutoff time.Time) ([]GameRecord, error) {
+	const pageSize = 200
+	page := 1
+	var out []GameRecord
+	for {
+		batch, _, err := s.deps.Store.ListAdminGames(ctx, page, pageSize)
+		if err != nil {
+			return nil, fmt.Errorf("lobby: list finished games before %s: %w", cutoff, err)
+		}
+		if len(batch) == 0 {
+			break
+		}
+		for _, g := range batch {
+			if g.Status != GameStatusFinished && g.Status != GameStatusCancelled {
+				continue
+			}
+			if g.FinishedAt == nil || !g.FinishedAt.Before(cutoff) {
+				continue
+			}
+			out = append(out, g)
+		}
+		if len(batch) < pageSize {
+			break
+		}
+		page++
+	}
+	return out, nil
+}
+
 // DeleteGame removes the game and every referencing row (memberships,
 // applications, invites, runtime_records, player_mappings) via the
 // `ON DELETE CASCADE` constraints declared in `00001_init.sql`.
@@ -441,9 +477,43 @@ func (s *Service) transition(ctx context.Context, callerUserID *uuid.UUID, calle
 			return updated, fmt.Errorf("post-commit %s: %w", rule.Reason, err)
 		}
 	}
+	s.emitGameLifecycleMail(ctx, updated, callerIsAdmin, rule)
 	return updated, nil
 }
 
+// emitGameLifecycleMail asks the diplomail publisher to drop a
+// system-mail entry whenever a state change is user-visible. Only
+// the `paused` and `cancelled` transitions emit mail today (the spec
+// names them explicitly); `running`/`finished`/etc. are signalled by
+// other channels and do not need a durable inbox entry.
+func (s *Service) emitGameLifecycleMail(ctx context.Context, game GameRecord, callerIsAdmin bool, rule transitionRule) {
+	var kind string
+	switch rule.To {
+	case GameStatusPaused:
+		kind = LifecycleKindGamePaused
+	case GameStatusCancelled:
+		kind = LifecycleKindGameCancelled
+	default:
+		return
+	}
+	actor := "the game owner"
+	if callerIsAdmin {
+		actor = "an administrator"
+	}
+	ev := LifecycleEvent{
+		GameID: game.GameID,
+		Kind:   kind,
+		Actor:  actor,
+		Reason: rule.Reason,
+	}
+	if err := s.deps.Diplomail.PublishLifecycle(ctx, ev); err != nil {
+		s.deps.Logger.Warn("publish lifecycle mail failed",
+			zap.String("game_id", game.GameID.String()),
+			zap.String("kind", kind),
+			zap.Error(err))
+	}
+}
+
 // checkOwner enforces ownership semantics:
 //
 // - callerIsAdmin == true → always allowed (admin force-start, etc.).

backend/internal/lobby/lobby.go

@@ -124,6 +124,7 @@ type Deps struct {
 	Cache *Cache
 	Runtime RuntimeGateway
 	Notification NotificationPublisher
+	Diplomail DiplomailPublisher
 	Entitlement EntitlementProvider
 	Policy *Policy
 	Config config.LobbyConfig
@@ -156,6 +157,9 @@ func NewService(deps Deps) (*Service, error) {
 	if deps.Notification == nil {
 		deps.Notification = NewNoopNotificationPublisher(deps.Logger)
 	}
+	if deps.Diplomail == nil {
+		deps.Diplomail = NewNoopDiplomailPublisher(deps.Logger)
+	}
 	if deps.Policy == nil {
 		policy, err := NewPolicy()
 		if err != nil {

backend/internal/lobby/memberships.go

@@ -76,6 +76,7 @@ func (s *Service) AdminBanMember(ctx context.Context, gameID, userID uuid.UUID,
 			zap.String("membership_id", updated.MembershipID.String()),
 			zap.Error(pubErr))
 	}
+	s.emitMembershipLifecycleMail(ctx, updated, MembershipStatusBlocked, true, reason)
 	_ = game
 	return updated, nil
 }
@@ -142,9 +143,44 @@ func (s *Service) changeMembershipStatus(
 			zap.String("kind", notificationKind),
 			zap.Error(pubErr))
 	}
+	s.emitMembershipLifecycleMail(ctx, updated, newStatus, callerIsAdmin, "")
 	return updated, nil
 }
 
+// emitMembershipLifecycleMail asks the diplomail publisher to drop a
+// durable explanation into the kicked player's inbox. The mail
+// survives the membership row going to `removed` / `blocked` so the
+// player keeps read access to it (soft-access rule, item 8).
+func (s *Service) emitMembershipLifecycleMail(ctx context.Context, membership Membership, newStatus string, callerIsAdmin bool, reason string) {
+	var kind string
+	switch newStatus {
+	case MembershipStatusRemoved:
+		kind = LifecycleKindMembershipRemoved
+	case MembershipStatusBlocked:
+		kind = LifecycleKindMembershipBlocked
+	default:
+		return
+	}
+	actor := "the game owner"
+	if callerIsAdmin {
+		actor = "an administrator"
+	}
+	target := membership.UserID
+	ev := LifecycleEvent{
+		GameID:     membership.GameID,
+		Kind:       kind,
+		Actor:      actor,
+		Reason:     reason,
+		TargetUser: &target,
+	}
+	if err := s.deps.Diplomail.PublishLifecycle(ctx, ev); err != nil {
+		s.deps.Logger.Warn("publish membership lifecycle mail failed",
+			zap.String("membership_id", membership.MembershipID.String()),
+			zap.String("kind", kind),
+			zap.Error(err))
+	}
+}
+
 func (s *Service) canManageMembership(game GameRecord, membership Membership, callerUserID *uuid.UUID, allowSelf bool) bool {
 	if game.Visibility == VisibilityPublic {
 		// Public-game membership management is admin-only.

backend/internal/notification/catalog.go

@@ -19,6 +19,7 @@ const (
 	KindRuntimeStartConfigInvalid = "runtime.start_config_invalid"
 	KindGameTurnReady = "game.turn.ready"
 	KindGamePaused = "game.paused"
+	KindDiplomailReceived = "diplomail.message.received"
 )
 
 // CatalogEntry describes the per-kind delivery policy: which channels
@@ -103,6 +104,9 @@ var catalog = map[string]CatalogEntry{
 	KindGamePaused: {
 		Channels: []string{ChannelPush},
 	},
+	KindDiplomailReceived: {
+		Channels: []string{ChannelPush},
+	},
 }
 
 // LookupCatalog returns the per-kind policy and a boolean reporting
@@ -133,5 +137,6 @@ func SupportedKinds() []string {
 		KindRuntimeStartConfigInvalid,
 		KindGameTurnReady,
 		KindGamePaused,
+		KindDiplomailReceived,
 	}
 }

backend/internal/notification/catalog_test.go

@@ -41,6 +41,7 @@ func TestCatalogChannels(t *testing.T) {
 		KindRuntimeStartConfigInvalid:   {ChannelEmail},
 		KindGameTurnReady:               {ChannelPush},
 		KindGamePaused:                  {ChannelPush},
+		KindDiplomailReceived:           {ChannelPush},
 	}
 	for kind, want := range expect {
 		entry, ok := LookupCatalog(kind)

backend/internal/notification/events_test.go

@@ -25,9 +25,15 @@ import (
 // payload is `{game_id, turn, reason}` consumed by the same in-game
 // shell layout, so there is no value in dragging a FB schema in for
 // one consumer.
+//
+// `diplomail.message.received` (Stage A) carries the message metadata
+// plus an unread-count snapshot. Stage A intentionally ships the
+// payload as JSON so the diplomail UI can iterate on the contract
+// without a FB schema dance; a later stage can promote it.
 var jsonFriendlyKinds = map[string]bool{
-	KindGameTurnReady: true,
-	KindGamePaused:    true,
+	KindGameTurnReady:     true,
+	KindGamePaused:        true,
+	KindDiplomailReceived: true,
 }
 
 // TestBuildClientPushEventCoversCatalog asserts that every catalog kind
@@ -88,6 +94,17 @@ func TestBuildClientPushEventCoversCatalog(t *testing.T) {
 			"turn":    int32(7),
 			"reason":  "generation_failed",
 		}},
+		{"diplomail message received", KindDiplomailReceived, map[string]any{
+			"message_id":   gameID.String(),
+			"game_id":      gameID.String(),
+			"kind":         "personal",
+			"sender_kind":  "player",
+			"subject":      "Trade deal",
+			"preview":      "Care to talk gas mining?",
+			"preview_lang": "en",
+			"unread_total": 3,
+			"unread_game":  1,
+		}},
 	}
 
 	seenKinds := map[string]bool{}

backend/internal/postgres/jet/backend/model/diplomail_messages.go

@@ -0,0 +1,29 @@
+//
+// Code generated by go-jet DO NOT EDIT.
+//
+// WARNING: Changes to this file may cause incorrect behavior
+// and will be lost if the code is regenerated
+//
+
+package model
+
+import (
+	"github.com/google/uuid"
+	"time"
+)
+
+type DiplomailMessages struct {
+	MessageID      uuid.UUID `sql:"primary_key"`
+	GameID         uuid.UUID
+	GameName       string
+	Kind           string
+	SenderKind     string
+	SenderUserID   *uuid.UUID
+	SenderUsername *string
+	SenderIP       string
+	Subject        string
+	Body           string
+	BodyLang       string
+	BroadcastScope string
+	CreatedAt      time.Time
+}

backend/internal/postgres/jet/backend/model/diplomail_recipients.go

@@ -0,0 +1,30 @@
+//
+// Code generated by go-jet DO NOT EDIT.
+//
+// WARNING: Changes to this file may cause incorrect behavior
+// and will be lost if the code is regenerated
+//
+
+package model
+
+import (
+	"github.com/google/uuid"
+	"time"
+)
+
+type DiplomailRecipients struct {
+	RecipientID                uuid.UUID `sql:"primary_key"`
+	MessageID                  uuid.UUID
+	GameID                     uuid.UUID
+	UserID                     uuid.UUID
+	RecipientUserName          string
+	RecipientRaceName          *string
+	RecipientPreferredLanguage string
+	AvailableAt                *time.Time
+	TranslationAttempts        int32
+	NextTranslationAttemptAt   *time.Time
+	DeliveredAt                *time.Time
+	ReadAt                     *time.Time
+	DeletedAt                  *time.Time
+	NotifiedAt                 *time.Time
+}

backend/internal/postgres/jet/backend/model/diplomail_translations.go

@@ -0,0 +1,23 @@
+//
+// Code generated by go-jet DO NOT EDIT.
+//
+// WARNING: Changes to this file may cause incorrect behavior
+// and will be lost if the code is regenerated
+//
+
+package model
+
+import (
+	"github.com/google/uuid"
+	"time"
+)
+
+type DiplomailTranslations struct {
+	TranslationID     uuid.UUID `sql:"primary_key"`
+	MessageID         uuid.UUID
+	TargetLang        string
+	TranslatedSubject string
+	TranslatedBody    string
+	Translator        string
+	TranslatedAt      time.Time
+}

backend/internal/postgres/jet/backend/table/diplomail_messages.go

@@ -0,0 +1,114 @@
+//
+// Code generated by go-jet DO NOT EDIT.
+//
+// WARNING: Changes to this file may cause incorrect behavior
+// and will be lost if the code is regenerated
+//
+
+package table
+
+import (
+	"github.com/go-jet/jet/v2/postgres"
+)
+
+var DiplomailMessages = newDiplomailMessagesTable("backend", "diplomail_messages", "")
+
+type diplomailMessagesTable struct {
+	postgres.Table
+
+	// Columns
+	MessageID      postgres.ColumnString
+	GameID         postgres.ColumnString
+	GameName       postgres.ColumnString
+	Kind           postgres.ColumnString
+	SenderKind     postgres.ColumnString
+	SenderUserID   postgres.ColumnString
+	SenderUsername postgres.ColumnString
+	SenderIP       postgres.ColumnString
+	Subject        postgres.ColumnString
+	Body           postgres.ColumnString
+	BodyLang       postgres.ColumnString
+	BroadcastScope postgres.ColumnString
+	CreatedAt      postgres.ColumnTimestampz
+
+	AllColumns     postgres.ColumnList
+	MutableColumns postgres.ColumnList
+	DefaultColumns postgres.ColumnList
+}
+
+type DiplomailMessagesTable struct {
+	diplomailMessagesTable
+
+	EXCLUDED diplomailMessagesTable
+}
+
+// AS creates new DiplomailMessagesTable with assigned alias
+func (a DiplomailMessagesTable) AS(alias string) *DiplomailMessagesTable {
+	return newDiplomailMessagesTable(a.SchemaName(), a.TableName(), alias)
+}
+
+// Schema creates new DiplomailMessagesTable with assigned schema name
+func (a DiplomailMessagesTable) FromSchema(schemaName string) *DiplomailMessagesTable {
+	return newDiplomailMessagesTable(schemaName, a.TableName(), a.Alias())
+}
+
+// WithPrefix creates new DiplomailMessagesTable with assigned table prefix
+func (a DiplomailMessagesTable) WithPrefix(prefix string) *DiplomailMessagesTable {
+	return newDiplomailMessagesTable(a.SchemaName(), prefix+a.TableName(), a.TableName())
+}
+
+// WithSuffix creates new DiplomailMessagesTable with assigned table suffix
+func (a DiplomailMessagesTable) WithSuffix(suffix string) *DiplomailMessagesTable {
+	return newDiplomailMessagesTable(a.SchemaName(), a.TableName()+suffix, a.TableName())
+}
+
+func newDiplomailMessagesTable(schemaName, tableName, alias string) *DiplomailMessagesTable {
+	return &DiplomailMessagesTable{
+		diplomailMessagesTable: newDiplomailMessagesTableImpl(schemaName, tableName, alias),
+		EXCLUDED:               newDiplomailMessagesTableImpl("", "excluded", ""),
+	}
+}
+
+func newDiplomailMessagesTableImpl(schemaName, tableName, alias string) diplomailMessagesTable {
+	var (
+		MessageIDColumn      = postgres.StringColumn("message_id")
+		GameIDColumn         = postgres.StringColumn("game_id")
+		GameNameColumn       = postgres.StringColumn("game_name")
+		KindColumn           = postgres.StringColumn("kind")
+		SenderKindColumn     = postgres.StringColumn("sender_kind")
+		SenderUserIDColumn   = postgres.StringColumn("sender_user_id")
+		SenderUsernameColumn = postgres.StringColumn("sender_username")
+		SenderIPColumn       = postgres.StringColumn("sender_ip")
+		SubjectColumn        = postgres.StringColumn("subject")
+		BodyColumn           = postgres.StringColumn("body")
+		BodyLangColumn       = postgres.StringColumn("body_lang")
+		BroadcastScopeColumn = postgres.StringColumn("broadcast_scope")
+		CreatedAtColumn      = postgres.TimestampzColumn("created_at")
+		allColumns           = postgres.ColumnList{MessageIDColumn, GameIDColumn, GameNameColumn, KindColumn, SenderKindColumn, SenderUserIDColumn, SenderUsernameColumn, SenderIPColumn, SubjectColumn, BodyColumn, BodyLangColumn, BroadcastScopeColumn, CreatedAtColumn}
+		mutableColumns       = postgres.ColumnList{GameIDColumn, GameNameColumn, KindColumn, SenderKindColumn, SenderUserIDColumn, SenderUsernameColumn, SenderIPColumn, SubjectColumn, BodyColumn, BodyLangColumn, BroadcastScopeColumn, CreatedAtColumn}
+		defaultColumns       = postgres.ColumnList{SenderIPColumn, SubjectColumn, BodyLangColumn, BroadcastScopeColumn, CreatedAtColumn}
+	)
+
+	return diplomailMessagesTable{
+		Table: postgres.NewTable(schemaName, tableName, alias, allColumns...),
+
+		//Columns
+		MessageID:      MessageIDColumn,
+		GameID:         GameIDColumn,
+		GameName:       GameNameColumn,
+		Kind:           KindColumn,
+		SenderKind:     SenderKindColumn,
+		SenderUserID:   SenderUserIDColumn,
+		SenderUsername: SenderUsernameColumn,
+		SenderIP:       SenderIPColumn,
+		Subject:        SubjectColumn,
+		Body:           BodyColumn,
+		BodyLang:       BodyLangColumn,
+		BroadcastScope: BroadcastScopeColumn,
+		CreatedAt:      CreatedAtColumn,
+
+		AllColumns:     allColumns,
+		MutableColumns: mutableColumns,
+		DefaultColumns: defaultColumns,
+	}
+}

backend/internal/postgres/jet/backend/table/diplomail_recipients.go

@@ -0,0 +1,117 @@
+//
+// Code generated by go-jet DO NOT EDIT.
+//
+// WARNING: Changes to this file may cause incorrect behavior
+// and will be lost if the code is regenerated
+//
+
+package table
+
+import (
+	"github.com/go-jet/jet/v2/postgres"
+)
+
+var DiplomailRecipients = newDiplomailRecipientsTable("backend", "diplomail_recipients", "")
+
+type diplomailRecipientsTable struct {
+	postgres.Table
+
+	// Columns
+	RecipientID                postgres.ColumnString
+	MessageID                  postgres.ColumnString
+	GameID                     postgres.ColumnString
+	UserID                     postgres.ColumnString
+	RecipientUserName          postgres.ColumnString
+	RecipientRaceName          postgres.ColumnString
+	RecipientPreferredLanguage postgres.ColumnString
+	AvailableAt                postgres.ColumnTimestampz
+	TranslationAttempts        postgres.ColumnInteger
+	NextTranslationAttemptAt   postgres.ColumnTimestampz
+	DeliveredAt                postgres.ColumnTimestampz
+	ReadAt                     postgres.ColumnTimestampz
+	DeletedAt                  postgres.ColumnTimestampz
+	NotifiedAt                 postgres.ColumnTimestampz
+
+	AllColumns     postgres.ColumnList
+	MutableColumns postgres.ColumnList
+	DefaultColumns postgres.ColumnList
+}
+
+type DiplomailRecipientsTable struct {
+	diplomailRecipientsTable
+
+	EXCLUDED diplomailRecipientsTable
+}
+
+// AS creates new DiplomailRecipientsTable with assigned alias
+func (a DiplomailRecipientsTable) AS(alias string) *DiplomailRecipientsTable {
+	return newDiplomailRecipientsTable(a.SchemaName(), a.TableName(), alias)
+}
+
+// Schema creates new DiplomailRecipientsTable with assigned schema name
+func (a DiplomailRecipientsTable) FromSchema(schemaName string) *DiplomailRecipientsTable {
+	return newDiplomailRecipientsTable(schemaName, a.TableName(), a.Alias())
+}
+
+// WithPrefix creates new DiplomailRecipientsTable with assigned table prefix
+func (a DiplomailRecipientsTable) WithPrefix(prefix string) *DiplomailRecipientsTable {
+	return newDiplomailRecipientsTable(a.SchemaName(), prefix+a.TableName(), a.TableName())
+}
+
+// WithSuffix creates new DiplomailRecipientsTable with assigned table suffix
+func (a DiplomailRecipientsTable) WithSuffix(suffix string) *DiplomailRecipientsTable {
+	return newDiplomailRecipientsTable(a.SchemaName(), a.TableName()+suffix, a.TableName())
+}
+
+func newDiplomailRecipientsTable(schemaName, tableName, alias string) *DiplomailRecipientsTable {
+	return &DiplomailRecipientsTable{
+		diplomailRecipientsTable: newDiplomailRecipientsTableImpl(schemaName, tableName, alias),
+		EXCLUDED:                 newDiplomailRecipientsTableImpl("", "excluded", ""),
+	}
+}
+
+func newDiplomailRecipientsTableImpl(schemaName, tableName, alias string) diplomailRecipientsTable {
+	var (
+		RecipientIDColumn                = postgres.StringColumn("recipient_id")
+		MessageIDColumn                  = postgres.StringColumn("message_id")
+		GameIDColumn                     = postgres.StringColumn("game_id")
+		UserIDColumn                     = postgres.StringColumn("user_id")
+		RecipientUserNameColumn          = postgres.StringColumn("recipient_user_name")
+		RecipientRaceNameColumn          = postgres.StringColumn("recipient_race_name")
+		RecipientPreferredLanguageColumn = postgres.StringColumn("recipient_preferred_language")
+		AvailableAtColumn                = postgres.TimestampzColumn("available_at")
+		TranslationAttemptsColumn        = postgres.IntegerColumn("translation_attempts")
+		NextTranslationAttemptAtColumn   = postgres.TimestampzColumn("next_translation_attempt_at")
+		DeliveredAtColumn                = postgres.TimestampzColumn("delivered_at")
+		ReadAtColumn                     = postgres.TimestampzColumn("read_at")
+		DeletedAtColumn                  = postgres.TimestampzColumn("deleted_at")
+		NotifiedAtColumn                 = postgres.TimestampzColumn("notified_at")
+		allColumns                       = postgres.ColumnList{RecipientIDColumn, MessageIDColumn, GameIDColumn, UserIDColumn, RecipientUserNameColumn, RecipientRaceNameColumn, RecipientPreferredLanguageColumn, AvailableAtColumn, TranslationAttemptsColumn, NextTranslationAttemptAtColumn, DeliveredAtColumn, ReadAtColumn, DeletedAtColumn, NotifiedAtColumn}
+		mutableColumns                   = postgres.ColumnList{MessageIDColumn, GameIDColumn, UserIDColumn, RecipientUserNameColumn, RecipientRaceNameColumn, RecipientPreferredLanguageColumn, AvailableAtColumn, TranslationAttemptsColumn, NextTranslationAttemptAtColumn, DeliveredAtColumn, ReadAtColumn, DeletedAtColumn, NotifiedAtColumn}
+		defaultColumns                   = postgres.ColumnList{RecipientPreferredLanguageColumn, TranslationAttemptsColumn}
+	)
+
+	return diplomailRecipientsTable{
+		Table: postgres.NewTable(schemaName, tableName, alias, allColumns...),
+
+		//Columns
+		RecipientID:                RecipientIDColumn,
+		MessageID:                  MessageIDColumn,
+		GameID:                     GameIDColumn,
+		UserID:                     UserIDColumn,
+		RecipientUserName:          RecipientUserNameColumn,
+		RecipientRaceName:          RecipientRaceNameColumn,
+		RecipientPreferredLanguage: RecipientPreferredLanguageColumn,
+		AvailableAt:                AvailableAtColumn,
+		TranslationAttempts:        TranslationAttemptsColumn,
+		NextTranslationAttemptAt:   NextTranslationAttemptAtColumn,
+		DeliveredAt:                DeliveredAtColumn,
+		ReadAt:                     ReadAtColumn,
+		DeletedAt:                  DeletedAtColumn,
+		NotifiedAt:                 NotifiedAtColumn,
+
+		AllColumns:     allColumns,
+		MutableColumns: mutableColumns,
+		DefaultColumns: defaultColumns,
+	}
+}

backend/internal/postgres/jet/backend/table/diplomail_translations.go

@@ -0,0 +1,96 @@
+//
+// Code generated by go-jet DO NOT EDIT.
+//
+// WARNING: Changes to this file may cause incorrect behavior
+// and will be lost if the code is regenerated
+//
+
+package table
+
+import (
+	"github.com/go-jet/jet/v2/postgres"
+)
+
+var DiplomailTranslations = newDiplomailTranslationsTable("backend", "diplomail_translations", "")
+
+type diplomailTranslationsTable struct {
+	postgres.Table
+
+	// Columns
+	TranslationID     postgres.ColumnString
+	MessageID         postgres.ColumnString
+	TargetLang        postgres.ColumnString
+	TranslatedSubject postgres.ColumnString
+	TranslatedBody    postgres.ColumnString
+	Translator        postgres.ColumnString
+	TranslatedAt      postgres.ColumnTimestampz
+
+	AllColumns     postgres.ColumnList
+	MutableColumns postgres.ColumnList
+	DefaultColumns postgres.ColumnList
+}
+
+type DiplomailTranslationsTable struct {
+	diplomailTranslationsTable
+
+	EXCLUDED diplomailTranslationsTable
+}
+
+// AS creates new DiplomailTranslationsTable with assigned alias
+func (a DiplomailTranslationsTable) AS(alias string) *DiplomailTranslationsTable {
+	return newDiplomailTranslationsTable(a.SchemaName(), a.TableName(), alias)
+}
+
+// Schema creates new DiplomailTranslationsTable with assigned schema name
+func (a DiplomailTranslationsTable) FromSchema(schemaName string) *DiplomailTranslationsTable {
+	return newDiplomailTranslationsTable(schemaName, a.TableName(), a.Alias())
+}
+
+// WithPrefix creates new DiplomailTranslationsTable with assigned table prefix
+func (a DiplomailTranslationsTable) WithPrefix(prefix string) *DiplomailTranslationsTable {
+	return newDiplomailTranslationsTable(a.SchemaName(), prefix+a.TableName(), a.TableName())
+}
+
+// WithSuffix creates new DiplomailTranslationsTable with assigned table suffix
+func (a DiplomailTranslationsTable) WithSuffix(suffix string) *DiplomailTranslationsTable {
+	return newDiplomailTranslationsTable(a.SchemaName(), a.TableName()+suffix, a.TableName())
+}
+
+func newDiplomailTranslationsTable(schemaName, tableName, alias string) *DiplomailTranslationsTable {
+	return &DiplomailTranslationsTable{
+		diplomailTranslationsTable: newDiplomailTranslationsTableImpl(schemaName, tableName, alias),
+		EXCLUDED:                   newDiplomailTranslationsTableImpl("", "excluded", ""),
+	}
+}
+
+func newDiplomailTranslationsTableImpl(schemaName, tableName, alias string) diplomailTranslationsTable {
+	var (
+		TranslationIDColumn     = postgres.StringColumn("translation_id")
+		MessageIDColumn         = postgres.StringColumn("message_id")
+		TargetLangColumn        = postgres.StringColumn("target_lang")
+		TranslatedSubjectColumn = postgres.StringColumn("translated_subject")
+		TranslatedBodyColumn    = postgres.StringColumn("translated_body")
+		TranslatorColumn        = postgres.StringColumn("translator")
+		TranslatedAtColumn      = postgres.TimestampzColumn("translated_at")
+		allColumns              = postgres.ColumnList{TranslationIDColumn, MessageIDColumn, TargetLangColumn, TranslatedSubjectColumn, TranslatedBodyColumn, TranslatorColumn, TranslatedAtColumn}
+		mutableColumns          = postgres.ColumnList{MessageIDColumn, TargetLangColumn, TranslatedSubjectColumn, TranslatedBodyColumn, TranslatorColumn, TranslatedAtColumn}
+		defaultColumns          = postgres.ColumnList{TranslatedSubjectColumn, TranslatedAtColumn}
+	)
+
+	return diplomailTranslationsTable{
+		Table: postgres.NewTable(schemaName, tableName, alias, allColumns...),
+
+		//Columns
+		TranslationID:     TranslationIDColumn,
+		MessageID:         MessageIDColumn,
+		TargetLang:        TargetLangColumn,
+		TranslatedSubject: TranslatedSubjectColumn,
+		TranslatedBody:    TranslatedBodyColumn,
+		Translator:        TranslatorColumn,
+		TranslatedAt:      TranslatedAtColumn,
+
+		AllColumns:     allColumns,
+		MutableColumns: mutableColumns,
+		DefaultColumns: defaultColumns,
+	}
+}

backend/internal/postgres/jet/backend/table/table_use_schema.go

@@ -16,6 +16,9 @@ func UseSchema(schema string) {
 	AuthChallenges = AuthChallenges.FromSchema(schema)
 	BlockedEmails = BlockedEmails.FromSchema(schema)
 	DeviceSessions = DeviceSessions.FromSchema(schema)
+	DiplomailMessages = DiplomailMessages.FromSchema(schema)
+	DiplomailRecipients = DiplomailRecipients.FromSchema(schema)
+	DiplomailTranslations = DiplomailTranslations.FromSchema(schema)
 	EngineVersions = EngineVersions.FromSchema(schema)
 	EntitlementRecords = EntitlementRecords.FromSchema(schema)
 	EntitlementSnapshots = EntitlementSnapshots.FromSchema(schema)

backend/internal/postgres/migrations/00001_init.sql

@@ -606,7 +606,8 @@ CREATE TABLE notifications (
             'lobby.race_name.expired',
             'runtime.image_pull_failed', 'runtime.container_start_failed',
             'runtime.start_config_invalid',
-            'game.turn.ready', 'game.paused'
+            'game.turn.ready', 'game.paused',
+            'diplomail.message.received'
         ))
 );
 
@@ -662,6 +663,114 @@ CREATE TABLE notification_malformed_intents (
 CREATE INDEX notification_malformed_intents_listing_idx
     ON notification_malformed_intents (received_at DESC);
 
+-- =====================================================================
+-- Diplomail domain
+-- =====================================================================
+
+-- diplomail_messages is the canonical record of every diplomatic-mail
+-- send: one row per personal message, owner/admin send, broadcast, or
+-- system notification. game_name is captured at insert time so the
+-- bulk-purge / rename paths still render correctly. sender_username
+-- carries either accounts.user_name (sender_kind='player') or
+-- admin_accounts.username (sender_kind='admin'); system senders leave
+-- it NULL. body and subject are plain UTF-8; length limits are enforced
+-- in the service layer and may be tuned without a migration.
+CREATE TABLE diplomail_messages (
+    message_id        uuid        PRIMARY KEY,
+    game_id           uuid        NOT NULL REFERENCES games (game_id) ON DELETE CASCADE,
+    game_name         text        NOT NULL,
+    kind              text        NOT NULL,
+    sender_kind       text        NOT NULL,
+    sender_user_id    uuid,
+    sender_username   text,
+    sender_ip         text        NOT NULL DEFAULT '',
+    subject           text        NOT NULL DEFAULT '',
+    body              text        NOT NULL,
+    body_lang         text        NOT NULL DEFAULT 'und',
+    broadcast_scope   text        NOT NULL DEFAULT 'single',
+    created_at        timestamptz NOT NULL DEFAULT now(),
+    CONSTRAINT diplomail_messages_kind_chk
+        CHECK (kind IN ('personal', 'admin')),
+    CONSTRAINT diplomail_messages_sender_kind_chk
+        CHECK (sender_kind IN ('player', 'admin', 'system')),
+    CONSTRAINT diplomail_messages_sender_identity_chk CHECK (
+        (sender_kind = 'player' AND sender_user_id IS NOT NULL AND sender_username IS NOT NULL) OR
+        (sender_kind = 'admin'  AND sender_user_id IS NULL     AND sender_username IS NOT NULL) OR
+        (sender_kind = 'system' AND sender_user_id IS NULL     AND sender_username IS NULL)
+    ),
+    CONSTRAINT diplomail_messages_kind_sender_chk CHECK (
+        (kind = 'personal' AND sender_kind = 'player') OR
+        (kind = 'admin'    AND sender_kind IN ('player', 'admin', 'system'))
+    ),
+    CONSTRAINT diplomail_messages_broadcast_scope_chk
+        CHECK (broadcast_scope IN ('single', 'game_broadcast', 'multi_game_broadcast'))
+);
+
+CREATE INDEX diplomail_messages_game_idx
+    ON diplomail_messages (game_id, created_at DESC);
+
+CREATE INDEX diplomail_messages_sender_user_idx
+    ON diplomail_messages (sender_user_id, created_at DESC)
+    WHERE sender_user_id IS NOT NULL;
+
+-- diplomail_recipients carries one row per (message, recipient). The
+-- per-user read/delete/deliver/notified state lives here. recipient
+-- snapshots (user_name, race_name) are captured at insert time so the
+-- inbox listing and admin search render without joining accounts /
+-- memberships and survive race-name renames, membership revocation,
+-- and account soft-delete. recipient_race_name is nullable for the
+-- rare admin notifications addressed to a player who no longer has an
+-- active membership in the game.
+CREATE TABLE diplomail_recipients (
+    recipient_id                  uuid        PRIMARY KEY,
+    message_id                    uuid        NOT NULL REFERENCES diplomail_messages (message_id) ON DELETE CASCADE,
+    game_id                       uuid        NOT NULL,
+    user_id                       uuid        NOT NULL,
+    recipient_user_name           text        NOT NULL,
+    recipient_race_name           text,
+    recipient_preferred_language  text        NOT NULL DEFAULT '',
+    available_at                  timestamptz,
+    translation_attempts          integer     NOT NULL DEFAULT 0,
+    next_translation_attempt_at   timestamptz,
+    delivered_at                  timestamptz,
+    read_at                       timestamptz,
+    deleted_at                    timestamptz,
+    notified_at                   timestamptz,
+    CONSTRAINT diplomail_recipients_unique UNIQUE (message_id, user_id)
+);
+
+CREATE INDEX diplomail_recipients_inbox_idx
+    ON diplomail_recipients (user_id, game_id, deleted_at, read_at);
+
+CREATE INDEX diplomail_recipients_unread_idx
+    ON diplomail_recipients (user_id, game_id)
+    WHERE read_at IS NULL AND deleted_at IS NULL AND available_at IS NOT NULL;
+
+-- Index drives the translation worker's pending-pair pickup. The
+-- partial filter keeps the scan tight: terminal-state recipients
+-- (with a non-NULL available_at) never appear in this btree. The
+-- composite ordering puts the next-attempt clock first so the
+-- backoff filter (`next_translation_attempt_at <= now()`) seeks
+-- before the secondary cluster on (message_id, lang).
+CREATE INDEX diplomail_recipients_pending_translation_idx
+    ON diplomail_recipients (next_translation_attempt_at, message_id, recipient_preferred_language)
+    WHERE available_at IS NULL;
+
+-- diplomail_translations caches one rendered translation per
+-- (message, target_lang) so a broadcast addressed to many recipients
+-- with the same preferred_language is translated once. translator
+-- identifies the backend that produced the row.
+CREATE TABLE diplomail_translations (
+    translation_id      uuid        PRIMARY KEY,
+    message_id          uuid        NOT NULL REFERENCES diplomail_messages (message_id) ON DELETE CASCADE,
+    target_lang         text        NOT NULL,
+    translated_subject  text        NOT NULL DEFAULT '',
+    translated_body     text        NOT NULL,
+    translator          text        NOT NULL,
+    translated_at       timestamptz NOT NULL DEFAULT now(),
+    CONSTRAINT diplomail_translations_unique UNIQUE (message_id, target_lang)
+);
+
 -- =====================================================================
 -- Geo domain
 -- =====================================================================

backend/internal/postgres/migrations_test.go

@@ -68,6 +68,10 @@ var expectedBackendTables = []string{
 	"notification_malformed_intents",
 	"notification_routes",
 	"notifications",
+	// Diplomail domain.
+	"diplomail_messages",
+	"diplomail_recipients",
+	"diplomail_translations",
 	// Geo domain.
 	"user_country_counters",
 }

backend/internal/server/contract_test.go

@@ -46,6 +46,7 @@ var pathParamStubs = map[string]string{
 	"user_id": "00000000-0000-0000-0000-000000000007",
 	"device_session_id": "00000000-0000-0000-0000-000000000008",
 	"battle_id": "00000000-0000-0000-0000-000000000009",
+	"message_id": "00000000-0000-0000-0000-00000000000a",
 	"id": "1.2.3",
 	"username": "alice",
 	"turn": "42",
@@ -149,6 +150,35 @@ var requestBodyStubs = map[string]map[string]any{
 		"user_id": pathParamStubs["user_id"],
 		"reason": "ToS violation",
 	},
+	"userMailSendPersonal": {
+		"recipient_user_id": pathParamStubs["user_id"],
+		"subject": "Contract test subject",
+		"body": "Contract test body",
+	},
+	"userMailSendAdmin": {
+		"target": "user",
+		"recipient_user_id": pathParamStubs["user_id"],
+		"subject": "Contract test admin subject",
+		"body": "Contract test admin body",
+	},
+	"adminDiplomailSend": {
+		"target": "user",
+		"recipient_user_id": pathParamStubs["user_id"],
+		"subject": "Contract test admin subject",
+		"body": "Contract test admin body",
+	},
+	"userMailSendBroadcast": {
+		"subject": "Contract test paid broadcast",
+		"body": "Contract test paid broadcast body",
+	},
+	"adminDiplomailBroadcast": {
+		"scope": "all_running",
+		"subject": "Contract test multi-game broadcast",
+		"body": "Contract test multi-game broadcast body",
+	},
+	"adminDiplomailCleanup": {
+		"older_than_years": 1,
+	},
 }
 
 // TestOpenAPIContract is the top-level OpenAPI contract test. It

backend/internal/server/handlers_admin_diplomail.go

@@ -0,0 +1,326 @@
+package server
+
+import (
+	"net/http"
+
+	"galaxy/backend/internal/diplomail"
+	"galaxy/backend/internal/server/clientip"
+	"galaxy/backend/internal/server/handlers"
+	"galaxy/backend/internal/server/httperr"
+	"galaxy/backend/internal/server/middleware/basicauth"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+	"go.uber.org/zap"
+)
+
+// AdminDiplomailHandlers groups the diplomatic-mail handlers exposed
+// under `/api/v1/admin/games/{game_id}/mail` (per-game admin send /
+// broadcast). The handler is intentionally separate from
+// `AdminMailHandlers`, which owns the unrelated email outbox surface
+// under `/api/v1/admin/mail/*`.
+type AdminDiplomailHandlers struct {
+	svc    *diplomail.Service
+	logger *zap.Logger
+}
+
+// NewAdminDiplomailHandlers constructs the handler set. svc may be
+// nil — in that case every handler returns 501 not_implemented.
+func NewAdminDiplomailHandlers(svc *diplomail.Service, logger *zap.Logger) *AdminDiplomailHandlers {
+	if logger == nil {
+		logger = zap.NewNop()
+	}
+	return &AdminDiplomailHandlers{svc: svc, logger: logger.Named("http.admin.diplomail")}
+}
+
+// Send handles POST /api/v1/admin/games/{game_id}/mail. The body
+// shape mirrors the owner route: `target="user"` requires
+// `recipient_user_id`; `target="all"` accepts an optional
+// `recipients` scope. The authenticated admin username is captured
+// from the basicauth context and persisted as `sender_username`.
+func (h *AdminDiplomailHandlers) Send() gin.HandlerFunc {
+	if h.svc == nil {
+		return handlers.NotImplemented("adminDiplomailSend")
+	}
+	return func(c *gin.Context) {
+		username, ok := basicauth.UsernameFromContext(c.Request.Context())
+		if !ok || username == "" {
+			httperr.Abort(c, http.StatusUnauthorized, httperr.CodeUnauthorized, "admin authentication is required")
+			return
+		}
+		gameID, ok := parseGameIDParam(c)
+		if !ok {
+			return
+		}
+		var req userMailSendAdminRequestWire
+		if err := c.ShouldBindJSON(&req); err != nil {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "request body must be valid JSON")
+			return
+		}
+		ctx := c.Request.Context()
+		switch req.Target {
+		case "", "user":
+			recipientID, parseErr := uuid.Parse(req.RecipientUserID)
+			if parseErr != nil {
+				httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "recipient_user_id must be a valid UUID")
+				return
+			}
+			msg, rcpt, sendErr := h.svc.SendAdminPersonal(ctx, diplomail.SendAdminPersonalInput{
+				GameID:          gameID,
+				CallerKind:      diplomail.CallerKindAdmin,
+				CallerUsername:  username,
+				RecipientUserID: recipientID,
+				Subject:         req.Subject,
+				Body:            req.Body,
+				SenderIP:        clientip.ExtractSourceIP(c),
+			})
+			if sendErr != nil {
+				respondDiplomailError(c, h.logger, "admin mail send personal", ctx, sendErr)
+				return
+			}
+			c.JSON(http.StatusCreated, mailMessageDetailToWire(diplomail.InboxEntry{Message: msg, Recipient: rcpt}, true))
+		case "all":
+			msg, recipients, sendErr := h.svc.SendAdminBroadcast(ctx, diplomail.SendAdminBroadcastInput{
+				GameID:         gameID,
+				CallerKind:     diplomail.CallerKindAdmin,
+				CallerUsername: username,
+				RecipientScope: req.Recipients,
+				Subject:        req.Subject,
+				Body:           req.Body,
+				SenderIP:       clientip.ExtractSourceIP(c),
+			})
+			if sendErr != nil {
+				respondDiplomailError(c, h.logger, "admin mail send broadcast", ctx, sendErr)
+				return
+			}
+			c.JSON(http.StatusCreated, mailBroadcastReceiptToWire(msg, recipients))
+		default:
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "target must be 'user' or 'all'")
+		}
+	}
+}
+
+// Broadcast handles POST /api/v1/admin/mail/broadcast. Body:
+//
+//	{
+//	  "scope": "selected" | "all_running",
+//	  "game_ids": ["..."],
+//	  "recipients": "active" | "active_and_removed" | "all_members",
+//	  "subject": "...",
+//	  "body": "..."
+//	}
+//
+// The handler routes through SendAdminMultiGameBroadcast and returns
+// a fan-out receipt describing the message ids created and the
+// total recipient count.
+func (h *AdminDiplomailHandlers) Broadcast() gin.HandlerFunc {
+	if h.svc == nil {
+		return handlers.NotImplemented("adminDiplomailBroadcast")
+	}
+	return func(c *gin.Context) {
+		username, ok := basicauth.UsernameFromContext(c.Request.Context())
+		if !ok || username == "" {
+			httperr.Abort(c, http.StatusUnauthorized, httperr.CodeUnauthorized, "admin authentication is required")
+			return
+		}
+		var req adminDiplomailBroadcastRequestWire
+		if err := c.ShouldBindJSON(&req); err != nil {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "request body must be valid JSON")
+			return
+		}
+		gameIDs := make([]uuid.UUID, 0, len(req.GameIDs))
+		for _, raw := range req.GameIDs {
+			parsed, err := uuid.Parse(raw)
+			if err != nil {
+				httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "game_ids must be valid UUIDs")
+				return
+			}
+			gameIDs = append(gameIDs, parsed)
+		}
+		ctx := c.Request.Context()
+		msgs, total, err := h.svc.SendAdminMultiGameBroadcast(ctx, diplomail.SendMultiGameBroadcastInput{
+			CallerUsername: username,
+			Scope:          req.Scope,
+			GameIDs:        gameIDs,
+			RecipientScope: req.Recipients,
+			Subject:        req.Subject,
+			Body:           req.Body,
+			SenderIP:       clientip.ExtractSourceIP(c),
+		})
+		if err != nil {
+			respondDiplomailError(c, h.logger, "admin mail broadcast", ctx, err)
+			return
+		}
+		out := adminDiplomailBroadcastResponseWire{
+			RecipientCount: total,
+			Messages:       make([]adminDiplomailBroadcastMessageWire, 0, len(msgs)),
+		}
+		for _, m := range msgs {
+			out.Messages = append(out.Messages, adminDiplomailBroadcastMessageWire{
+				MessageID: m.MessageID.String(),
+				GameID:    m.GameID.String(),
+				GameName:  m.GameName,
+			})
+		}
+		c.JSON(http.StatusCreated, out)
+	}
+}
+
+// Cleanup handles POST /api/v1/admin/mail/cleanup. Body:
+//
+//	{ "older_than_years": 1 }
+//
+// The endpoint removes every diplomail_messages row whose game
+// finished more than the supplied number of years ago. The cascade
+// on the recipient and translation tables prunes the per-user state
+// in the same transaction. Returns a CleanupResult envelope.
+func (h *AdminDiplomailHandlers) Cleanup() gin.HandlerFunc {
+	if h.svc == nil {
+		return handlers.NotImplemented("adminDiplomailCleanup")
+	}
+	return func(c *gin.Context) {
+		username, ok := basicauth.UsernameFromContext(c.Request.Context())
+		if !ok || username == "" {
+			httperr.Abort(c, http.StatusUnauthorized, httperr.CodeUnauthorized, "admin authentication is required")
+			return
+		}
+		_ = username
+		var req adminDiplomailCleanupRequestWire
+		if err := c.ShouldBindJSON(&req); err != nil {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "request body must be valid JSON")
+			return
+		}
+		ctx := c.Request.Context()
+		result, err := h.svc.BulkCleanup(ctx, diplomail.BulkCleanupInput{OlderThanYears: req.OlderThanYears})
+		if err != nil {
+			respondDiplomailError(c, h.logger, "admin mail cleanup", ctx, err)
+			return
+		}
+		out := adminDiplomailCleanupResponseWire{
+			MessagesDeleted: result.MessagesDeleted,
+			GameIDs:         make([]string, 0, len(result.GameIDs)),
+		}
+		for _, id := range result.GameIDs {
+			out.GameIDs = append(out.GameIDs, id.String())
+		}
+		c.JSON(http.StatusOK, out)
+	}
+}
+
+// List handles GET /api/v1/admin/mail/messages. Supports pagination
+// via `page` and `page_size`, plus optional `game_id`, `kind`, and
+// `sender_kind` filters.
+func (h *AdminDiplomailHandlers) List() gin.HandlerFunc {
+	if h.svc == nil {
+		return handlers.NotImplemented("adminDiplomailList")
+	}
+	return func(c *gin.Context) {
+		username, ok := basicauth.UsernameFromContext(c.Request.Context())
+		if !ok || username == "" {
+			httperr.Abort(c, http.StatusUnauthorized, httperr.CodeUnauthorized, "admin authentication is required")
+			return
+		}
+		filter := diplomail.AdminMessageListing{
+			Page:       parsePositiveQueryInt(c.Query("page"), 1),
+			PageSize:   parsePositiveQueryInt(c.Query("page_size"), 50),
+			Kind:       c.Query("kind"),
+			SenderKind: c.Query("sender_kind"),
+		}
+		if raw := c.Query("game_id"); raw != "" {
+			parsed, err := uuid.Parse(raw)
+			if err != nil {
+				httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "game_id must be a valid UUID")
+				return
+			}
+			filter.GameID = &parsed
+		}
+		ctx := c.Request.Context()
+		page, err := h.svc.ListMessagesForAdmin(ctx, filter)
+		if err != nil {
+			respondDiplomailError(c, h.logger, "admin mail list", ctx, err)
+			return
+		}
+		out := adminDiplomailListResponseWire{
+			Total:    page.Total,
+			Page:     page.Page,
+			PageSize: page.PageSize,
+			Items:    make([]adminDiplomailMessageWire, 0, len(page.Items)),
+		}
+		for _, m := range page.Items {
+			entry := adminDiplomailMessageWire{
+				MessageID:      m.MessageID.String(),
+				GameID:         m.GameID.String(),
+				GameName:       m.GameName,
+				Kind:           m.Kind,
+				SenderKind:     m.SenderKind,
+				SenderIP:       m.SenderIP,
+				Subject:        m.Subject,
+				Body:           m.Body,
+				BodyLang:       m.BodyLang,
+				BroadcastScope: m.BroadcastScope,
+				CreatedAt:      m.CreatedAt.UTC().Format(timestampLayout),
+			}
+			if m.SenderUserID != nil {
+				s := m.SenderUserID.String()
+				entry.SenderUserID = &s
+			}
+			if m.SenderUsername != nil {
+				s := *m.SenderUsername
+				entry.SenderUsername = &s
+			}
+			out.Items = append(out.Items, entry)
+		}
+		c.JSON(http.StatusOK, out)
+	}
+}
+
+type adminDiplomailBroadcastRequestWire struct {
+	Scope      string   `json:"scope"`
+	GameIDs    []string `json:"game_ids,omitempty"`
+	Recipients string   `json:"recipients,omitempty"`
+	Subject    string   `json:"subject,omitempty"`
+	Body       string   `json:"body"`
+}
+
+type adminDiplomailBroadcastMessageWire struct {
+	MessageID string `json:"message_id"`
+	GameID    string `json:"game_id"`
+	GameName  string `json:"game_name,omitempty"`
+}
+
+type adminDiplomailBroadcastResponseWire struct {
+	RecipientCount int                                  `json:"recipient_count"`
+	Messages       []adminDiplomailBroadcastMessageWire `json:"messages"`
+}
+
+type adminDiplomailCleanupRequestWire struct {
+	OlderThanYears int `json:"older_than_years"`
+}
+
+type adminDiplomailCleanupResponseWire struct {
+	MessagesDeleted int      `json:"messages_deleted"`
+	GameIDs         []string `json:"game_ids"`
+}
+
+type adminDiplomailMessageWire struct {
+	MessageID      string  `json:"message_id"`
+	GameID         string  `json:"game_id"`
+	GameName       string  `json:"game_name,omitempty"`
+	Kind           string  `json:"kind"`
+	SenderKind     string  `json:"sender_kind"`
+	SenderUserID   *string `json:"sender_user_id,omitempty"`
+	SenderUsername *string `json:"sender_username,omitempty"`
+	SenderIP       string  `json:"sender_ip,omitempty"`
+	Subject        string  `json:"subject,omitempty"`
+	Body           string  `json:"body"`
+	BodyLang       string  `json:"body_lang"`
+	BroadcastScope string  `json:"broadcast_scope"`
+	CreatedAt      string  `json:"created_at"`
+}
+
+type adminDiplomailListResponseWire struct {
+	Total    int                          `json:"total"`
+	Page     int                          `json:"page"`
+	PageSize int                          `json:"page_size"`
+	Items    []adminDiplomailMessageWire  `json:"items"`
+}

backend/internal/server/handlers_user_mail.go

@@ -0,0 +1,663 @@
+package server
+
+import (
+	"context"
+	"errors"
+	"net/http"
+
+	"galaxy/backend/internal/diplomail"
+	"galaxy/backend/internal/lobby"
+	"galaxy/backend/internal/server/clientip"
+	"galaxy/backend/internal/server/handlers"
+	"galaxy/backend/internal/server/httperr"
+	"galaxy/backend/internal/server/middleware/userid"
+	"galaxy/backend/internal/telemetry"
+	"galaxy/backend/internal/user"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+	"go.uber.org/zap"
+)
+
+// UserMailHandlers groups the diplomatic-mail handlers under
+// `/api/v1/user/games/{game_id}/mail/*` and the lobby-side
+// `/api/v1/user/lobby/mail/unread-counts`. Stage A wires the
+// personal subset; Stage B adds the owner-only admin send path,
+// which needs `*lobby.Service` to confirm ownership and `*user.Service`
+// to resolve the owner's `user_name` for the `sender_username` column.
+type UserMailHandlers struct {
+	svc    *diplomail.Service
+	lobby  *lobby.Service
+	users  *user.Service
+	logger *zap.Logger
+}
+
+// NewUserMailHandlers constructs the handler set. svc may be nil — in
+// that case every handler returns 501 not_implemented. lobby and
+// users are optional: when either is nil the admin-send handler
+// degrades to 501 (the personal-send and read paths stay functional).
+func NewUserMailHandlers(svc *diplomail.Service, lobbySvc *lobby.Service, users *user.Service, logger *zap.Logger) *UserMailHandlers {
+	if logger == nil {
+		logger = zap.NewNop()
+	}
+	return &UserMailHandlers{
+		svc:    svc,
+		lobby:  lobbySvc,
+		users:  users,
+		logger: logger.Named("http.user.mail"),
+	}
+}
+
+// preferredLanguage looks up the caller's `accounts.preferred_language`
+// so the per-message read can attach the cached translation when
+// available. Failures are logged at debug level and the function
+// returns an empty string — translation is best-effort and the
+// caller still receives the original body.
+func (h *UserMailHandlers) preferredLanguage(ctx context.Context, userID uuid.UUID) string {
+	if h.users == nil {
+		return ""
+	}
+	account, err := h.users.GetAccount(ctx, userID)
+	if err != nil {
+		h.logger.Debug("resolve preferred_language failed",
+			zap.String("user_id", userID.String()),
+			zap.Error(err))
+		return ""
+	}
+	return account.PreferredLanguage
+}
+
+// SendPersonal handles POST /api/v1/user/games/{game_id}/mail/messages.
+func (h *UserMailHandlers) SendPersonal() gin.HandlerFunc {
+	if h.svc == nil {
+		return handlers.NotImplemented("userMailSendPersonal")
+	}
+	return func(c *gin.Context) {
+		userID, ok := userid.FromContext(c.Request.Context())
+		if !ok {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "X-User-ID header is required")
+			return
+		}
+		gameID, ok := parseGameIDParam(c)
+		if !ok {
+			return
+		}
+		var req userMailSendRequestWire
+		if err := c.ShouldBindJSON(&req); err != nil {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "request body must be valid JSON")
+			return
+		}
+		recipientID, err := uuid.Parse(req.RecipientUserID)
+		if err != nil {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "recipient_user_id must be a valid UUID")
+			return
+		}
+		ctx := c.Request.Context()
+		msg, rcpt, err := h.svc.SendPersonal(ctx, diplomail.SendPersonalInput{
+			GameID:          gameID,
+			SenderUserID:    userID,
+			RecipientUserID: recipientID,
+			Subject:         req.Subject,
+			Body:            req.Body,
+			SenderIP:        clientip.ExtractSourceIP(c),
+		})
+		if err != nil {
+			respondDiplomailError(c, h.logger, "user mail send personal", ctx, err)
+			return
+		}
+		c.JSON(http.StatusCreated, mailMessageDetailToWire(diplomail.InboxEntry{Message: msg, Recipient: rcpt}, true))
+	}
+}
+
+// Get handles GET /api/v1/user/games/{game_id}/mail/messages/{message_id}.
+func (h *UserMailHandlers) Get() gin.HandlerFunc {
+	if h.svc == nil {
+		return handlers.NotImplemented("userMailGet")
+	}
+	return func(c *gin.Context) {
+		userID, ok := userid.FromContext(c.Request.Context())
+		if !ok {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "X-User-ID header is required")
+			return
+		}
+		if _, ok := parseGameIDParam(c); !ok {
+			return
+		}
+		messageID, ok := parseMessageIDParam(c)
+		if !ok {
+			return
+		}
+		ctx := c.Request.Context()
+		targetLang := h.preferredLanguage(ctx, userID)
+		entry, err := h.svc.GetMessage(ctx, userID, messageID, targetLang)
+		if err != nil {
+			respondDiplomailError(c, h.logger, "user mail get", ctx, err)
+			return
+		}
+		c.JSON(http.StatusOK, mailMessageDetailToWire(entry, false))
+	}
+}
+
+// Inbox handles GET /api/v1/user/games/{game_id}/mail/inbox.
+func (h *UserMailHandlers) Inbox() gin.HandlerFunc {
+	if h.svc == nil {
+		return handlers.NotImplemented("userMailInbox")
+	}
+	return func(c *gin.Context) {
+		userID, ok := userid.FromContext(c.Request.Context())
+		if !ok {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "X-User-ID header is required")
+			return
+		}
+		gameID, ok := parseGameIDParam(c)
+		if !ok {
+			return
+		}
+		ctx := c.Request.Context()
+		targetLang := h.preferredLanguage(ctx, userID)
+		items, err := h.svc.ListInbox(ctx, gameID, userID, targetLang)
+		if err != nil {
+			respondDiplomailError(c, h.logger, "user mail inbox", ctx, err)
+			return
+		}
+		out := userMailInboxListWire{Items: make([]userMailMessageDetailWire, 0, len(items))}
+		for _, e := range items {
+			out.Items = append(out.Items, mailMessageDetailToWire(e, false))
+		}
+		c.JSON(http.StatusOK, out)
+	}
+}
+
+// Sent handles GET /api/v1/user/games/{game_id}/mail/sent.
+func (h *UserMailHandlers) Sent() gin.HandlerFunc {
+	if h.svc == nil {
+		return handlers.NotImplemented("userMailSent")
+	}
+	return func(c *gin.Context) {
+		userID, ok := userid.FromContext(c.Request.Context())
+		if !ok {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "X-User-ID header is required")
+			return
+		}
+		gameID, ok := parseGameIDParam(c)
+		if !ok {
+			return
+		}
+		ctx := c.Request.Context()
+		items, err := h.svc.ListSent(ctx, gameID, userID)
+		if err != nil {
+			respondDiplomailError(c, h.logger, "user mail sent", ctx, err)
+			return
+		}
+		out := userMailSentListWire{Items: make([]userMailSentSummaryWire, 0, len(items))}
+		for _, m := range items {
+			out.Items = append(out.Items, mailMessageSummaryToWire(m))
+		}
+		c.JSON(http.StatusOK, out)
+	}
+}
+
+// MarkRead handles POST /api/v1/user/games/{game_id}/mail/messages/{message_id}/read.
+func (h *UserMailHandlers) MarkRead() gin.HandlerFunc {
+	if h.svc == nil {
+		return handlers.NotImplemented("userMailMarkRead")
+	}
+	return func(c *gin.Context) {
+		userID, ok := userid.FromContext(c.Request.Context())
+		if !ok {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "X-User-ID header is required")
+			return
+		}
+		if _, ok := parseGameIDParam(c); !ok {
+			return
+		}
+		messageID, ok := parseMessageIDParam(c)
+		if !ok {
+			return
+		}
+		ctx := c.Request.Context()
+		rcpt, err := h.svc.MarkRead(ctx, userID, messageID)
+		if err != nil {
+			respondDiplomailError(c, h.logger, "user mail mark read", ctx, err)
+			return
+		}
+		c.JSON(http.StatusOK, mailRecipientStateToWire(rcpt))
+	}
+}
+
+// Delete handles DELETE /api/v1/user/games/{game_id}/mail/messages/{message_id}.
+func (h *UserMailHandlers) Delete() gin.HandlerFunc {
+	if h.svc == nil {
+		return handlers.NotImplemented("userMailDelete")
+	}
+	return func(c *gin.Context) {
+		userID, ok := userid.FromContext(c.Request.Context())
+		if !ok {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "X-User-ID header is required")
+			return
+		}
+		if _, ok := parseGameIDParam(c); !ok {
+			return
+		}
+		messageID, ok := parseMessageIDParam(c)
+		if !ok {
+			return
+		}
+		ctx := c.Request.Context()
+		rcpt, err := h.svc.DeleteMessage(ctx, userID, messageID)
+		if err != nil {
+			respondDiplomailError(c, h.logger, "user mail delete", ctx, err)
+			return
+		}
+		c.JSON(http.StatusOK, mailRecipientStateToWire(rcpt))
+	}
+}
+
+// SendBroadcast handles POST /api/v1/user/games/{game_id}/mail/broadcast.
+//
+// The endpoint is the paid-tier player broadcast: any player on a
+// non-`free` entitlement tier may send one personal message that
+// fans out to every other active member of the game. The result
+// rows carry `kind="personal"`, `sender_kind="player"`,
+// `broadcast_scope="game_broadcast"`. Free-tier callers see a 403.
+func (h *UserMailHandlers) SendBroadcast() gin.HandlerFunc {
+	if h.svc == nil {
+		return handlers.NotImplemented("userMailSendBroadcast")
+	}
+	return func(c *gin.Context) {
+		userID, ok := userid.FromContext(c.Request.Context())
+		if !ok {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "X-User-ID header is required")
+			return
+		}
+		gameID, ok := parseGameIDParam(c)
+		if !ok {
+			return
+		}
+		var req userMailSendBroadcastRequestWire
+		if err := c.ShouldBindJSON(&req); err != nil {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "request body must be valid JSON")
+			return
+		}
+		ctx := c.Request.Context()
+		msg, recipients, err := h.svc.SendPlayerBroadcast(ctx, diplomail.SendPlayerBroadcastInput{
+			GameID:       gameID,
+			SenderUserID: userID,
+			Subject:      req.Subject,
+			Body:         req.Body,
+			SenderIP:     clientip.ExtractSourceIP(c),
+		})
+		if err != nil {
+			respondDiplomailError(c, h.logger, "user mail send broadcast", ctx, err)
+			return
+		}
+		c.JSON(http.StatusCreated, mailBroadcastReceiptToWire(msg, recipients))
+	}
+}
+
+// SendAdmin handles POST /api/v1/user/games/{game_id}/mail/admin.
+//
+// Owner-only: the caller must be the owner of the private game. The
+// handler resolves the owner's `user_name` so the
+// `sender_username` column carries a useful identity, then routes to
+// SendAdminPersonal (for `target="user"`) or SendAdminBroadcast (for
+// `target="all"`). Site administrators use the separate admin route
+// in `handlers_admin_mail_send.go`.
+func (h *UserMailHandlers) SendAdmin() gin.HandlerFunc {
+	if h.svc == nil || h.lobby == nil || h.users == nil {
+		return handlers.NotImplemented("userMailSendAdmin")
+	}
+	return func(c *gin.Context) {
+		userID, ok := userid.FromContext(c.Request.Context())
+		if !ok {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "X-User-ID header is required")
+			return
+		}
+		gameID, ok := parseGameIDParam(c)
+		if !ok {
+			return
+		}
+		var req userMailSendAdminRequestWire
+		if err := c.ShouldBindJSON(&req); err != nil {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "request body must be valid JSON")
+			return
+		}
+		ctx := c.Request.Context()
+
+		game, err := h.lobby.GetGame(ctx, gameID)
+		if err != nil {
+			respondLobbyError(c, h.logger, "user mail send admin: load game", ctx, err)
+			return
+		}
+		if game.OwnerUserID == nil || *game.OwnerUserID != userID {
+			httperr.Abort(c, http.StatusForbidden, httperr.CodeForbidden, "caller is not the owner of this game")
+			return
+		}
+		account, err := h.users.GetAccount(ctx, userID)
+		if err != nil {
+			respondAccountError(c, h.logger, "user mail send admin: resolve user_name", ctx, err)
+			return
+		}
+
+		switch req.Target {
+		case "", "user":
+			recipientID, parseErr := uuid.Parse(req.RecipientUserID)
+			if parseErr != nil {
+				httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "recipient_user_id must be a valid UUID")
+				return
+			}
+			callerUserID := userID
+			msg, rcpt, sendErr := h.svc.SendAdminPersonal(ctx, diplomail.SendAdminPersonalInput{
+				GameID:          gameID,
+				CallerKind:      diplomail.CallerKindOwner,
+				CallerUserID:    &callerUserID,
+				CallerUsername:  account.UserName,
+				RecipientUserID: recipientID,
+				Subject:         req.Subject,
+				Body:            req.Body,
+				SenderIP:        clientip.ExtractSourceIP(c),
+			})
+			if sendErr != nil {
+				respondDiplomailError(c, h.logger, "user mail send admin personal", ctx, sendErr)
+				return
+			}
+			c.JSON(http.StatusCreated, mailMessageDetailToWire(diplomail.InboxEntry{Message: msg, Recipient: rcpt}, true))
+		case "all":
+			callerUserID := userID
+			msg, recipients, sendErr := h.svc.SendAdminBroadcast(ctx, diplomail.SendAdminBroadcastInput{
+				GameID:         gameID,
+				CallerKind:     diplomail.CallerKindOwner,
+				CallerUserID:   &callerUserID,
+				CallerUsername: account.UserName,
+				RecipientScope: req.Recipients,
+				Subject:        req.Subject,
+				Body:           req.Body,
+				SenderIP:       clientip.ExtractSourceIP(c),
+			})
+			if sendErr != nil {
+				respondDiplomailError(c, h.logger, "user mail send admin broadcast", ctx, sendErr)
+				return
+			}
+			c.JSON(http.StatusCreated, mailBroadcastReceiptToWire(msg, recipients))
+		default:
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "target must be 'user' or 'all'")
+		}
+	}
+}
+
+// UnreadCounts handles GET /api/v1/user/lobby/mail/unread-counts.
+func (h *UserMailHandlers) UnreadCounts() gin.HandlerFunc {
+	if h.svc == nil {
+		return handlers.NotImplemented("userMailUnreadCounts")
+	}
+	return func(c *gin.Context) {
+		userID, ok := userid.FromContext(c.Request.Context())
+		if !ok {
+			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "X-User-ID header is required")
+			return
+		}
+		ctx := c.Request.Context()
+		items, err := h.svc.UnreadCountsForUser(ctx, userID)
+		if err != nil {
+			respondDiplomailError(c, h.logger, "user mail unread counts", ctx, err)
+			return
+		}
+		out := userMailUnreadCountsResponseWire{Items: make([]userMailUnreadCountWire, 0, len(items))}
+		total := 0
+		for _, u := range items {
+			out.Items = append(out.Items, userMailUnreadCountWire{
+				GameID:   u.GameID.String(),
+				GameName: u.GameName,
+				Unread:   u.Unread,
+			})
+			total += u.Unread
+		}
+		out.Total = total
+		c.JSON(http.StatusOK, out)
+	}
+}
+
+// respondDiplomailError maps diplomail-package sentinels to the
+// standard JSON error envelope. Unknown errors land on a 500.
+func respondDiplomailError(c *gin.Context, logger *zap.Logger, op string, ctx context.Context, err error) {
+	switch {
+	case errors.Is(err, diplomail.ErrInvalidInput):
+		httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, err.Error())
+	case errors.Is(err, diplomail.ErrNotFound):
+		httperr.Abort(c, http.StatusNotFound, httperr.CodeNotFound, "resource was not found")
+	case errors.Is(err, diplomail.ErrForbidden):
+		httperr.Abort(c, http.StatusForbidden, httperr.CodeForbidden, err.Error())
+	case errors.Is(err, diplomail.ErrConflict):
+		httperr.Abort(c, http.StatusConflict, httperr.CodeConflict, err.Error())
+	default:
+		logger.Error(op+" failed",
+			append(telemetry.TraceFieldsFromContext(ctx), zap.Error(err))...,
+		)
+		httperr.Abort(c, http.StatusInternalServerError, httperr.CodeInternalError, "service error")
+	}
+}
+
+// parseMessageIDParam reads `message_id` from the path. Writes a 400
+// envelope on invalid input and returns false in that case.
+func parseMessageIDParam(c *gin.Context) (uuid.UUID, bool) {
+	parsed, err := uuid.Parse(c.Param("message_id"))
+	if err != nil {
+		httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "message_id must be a valid UUID")
+		return uuid.Nil, false
+	}
+	return parsed, true
+}
+
+// userMailSendRequestWire mirrors the request body for SendPersonal.
+type userMailSendRequestWire struct {
+	RecipientUserID string `json:"recipient_user_id"`
+	Subject         string `json:"subject,omitempty"`
+	Body            string `json:"body"`
+}
+
+// userMailSendBroadcastRequestWire mirrors the request body for the
+// paid-tier player broadcast. There is no `target` discriminator —
+// the recipient set is always "every other active member".
+type userMailSendBroadcastRequestWire struct {
+	Subject string `json:"subject,omitempty"`
+	Body    string `json:"body"`
+}
+
+// userMailSendAdminRequestWire mirrors the request body for the
+// owner-only admin send. `target="user"` requires
+// `recipient_user_id`; `target="all"` accepts the optional
+// `recipients` scope (default `active`).
+type userMailSendAdminRequestWire struct {
+	Target          string `json:"target"`
+	RecipientUserID string `json:"recipient_user_id,omitempty"`
+	Recipients      string `json:"recipients,omitempty"`
+	Subject         string `json:"subject,omitempty"`
+	Body            string `json:"body"`
+}
+
+// userMailBroadcastReceiptWire is the response shape returned after a
+// successful broadcast. It carries the canonical message metadata
+// together with the count of materialised recipient rows so the
+// caller (UI, admin tool) can confirm the fan-out happened.
+type userMailBroadcastReceiptWire struct {
+	MessageID      string `json:"message_id"`
+	GameID         string `json:"game_id"`
+	GameName       string `json:"game_name,omitempty"`
+	Kind           string `json:"kind"`
+	SenderKind     string `json:"sender_kind"`
+	Subject        string `json:"subject,omitempty"`
+	Body           string `json:"body"`
+	BodyLang       string `json:"body_lang"`
+	BroadcastScope string `json:"broadcast_scope"`
+	CreatedAt      string `json:"created_at"`
+	RecipientCount int    `json:"recipient_count"`
+}
+
+func mailBroadcastReceiptToWire(m diplomail.Message, recipients []diplomail.Recipient) userMailBroadcastReceiptWire {
+	return userMailBroadcastReceiptWire{
+		MessageID:      m.MessageID.String(),
+		GameID:         m.GameID.String(),
+		GameName:       m.GameName,
+		Kind:           m.Kind,
+		SenderKind:     m.SenderKind,
+		Subject:        m.Subject,
+		Body:           m.Body,
+		BodyLang:       m.BodyLang,
+		BroadcastScope: m.BroadcastScope,
+		CreatedAt:      m.CreatedAt.UTC().Format(timestampLayout),
+		RecipientCount: len(recipients),
+	}
+}
+
+// userMailMessageDetailWire mirrors the unified response shape for
+// inbox listings and per-message reads. Sender identifiers are
+// optional: system messages carry neither user id nor username.
+// Translation fields are populated when a cached rendering exists
+// for the caller's `preferred_language`; the UI renders
+// `body_translated` and surfaces the original through a
+// "show original" toggle.
+type userMailMessageDetailWire struct {
+	MessageID         string  `json:"message_id"`
+	GameID            string  `json:"game_id"`
+	GameName          string  `json:"game_name,omitempty"`
+	Kind              string  `json:"kind"`
+	SenderKind        string  `json:"sender_kind"`
+	SenderUserID      *string `json:"sender_user_id,omitempty"`
+	SenderUsername    *string `json:"sender_username,omitempty"`
+	Subject           string  `json:"subject,omitempty"`
+	Body              string  `json:"body"`
+	BodyLang          string  `json:"body_lang"`
+	BroadcastScope    string  `json:"broadcast_scope"`
+	CreatedAt         string  `json:"created_at"`
+	RecipientUserID   string  `json:"recipient_user_id"`
+	RecipientUserName string  `json:"recipient_user_name,omitempty"`
+	RecipientRaceName *string `json:"recipient_race_name,omitempty"`
+	ReadAt            *string `json:"read_at,omitempty"`
+	DeletedAt         *string `json:"deleted_at,omitempty"`
+	TranslatedSubject *string `json:"translated_subject,omitempty"`
+	TranslatedBody    *string `json:"translated_body,omitempty"`
+	TranslationLang   *string `json:"translation_lang,omitempty"`
+	Translator        *string `json:"translator,omitempty"`
+}
+
+// userMailSentSummaryWire mirrors the response shape for the
+// sender-side listing. Recipient state is intentionally omitted (one
+// author may have N recipients per broadcast in later stages).
+type userMailSentSummaryWire struct {
+	MessageID      string `json:"message_id"`
+	GameID         string `json:"game_id"`
+	GameName       string `json:"game_name,omitempty"`
+	Kind           string `json:"kind"`
+	Subject        string `json:"subject,omitempty"`
+	Body           string `json:"body"`
+	BodyLang       string `json:"body_lang"`
+	BroadcastScope string `json:"broadcast_scope"`
+	CreatedAt      string `json:"created_at"`
+}
+
+type userMailInboxListWire struct {
+	Items []userMailMessageDetailWire `json:"items"`
+}
+
+type userMailSentListWire struct {
+	Items []userMailSentSummaryWire `json:"items"`
+}
+
+type userMailUnreadCountWire struct {
+	GameID   string `json:"game_id"`
+	GameName string `json:"game_name,omitempty"`
+	Unread   int    `json:"unread"`
+}
+
+type userMailUnreadCountsResponseWire struct {
+	Total int                       `json:"total"`
+	Items []userMailUnreadCountWire `json:"items"`
+}
+
+func mailMessageDetailToWire(entry diplomail.InboxEntry, justCreated bool) userMailMessageDetailWire {
+	out := userMailMessageDetailWire{
+		MessageID:         entry.MessageID.String(),
+		GameID:            entry.GameID.String(),
+		GameName:          entry.GameName,
+		Kind:              entry.Kind,
+		SenderKind:        entry.SenderKind,
+		Subject:           entry.Subject,
+		Body:              entry.Body,
+		BodyLang:          entry.BodyLang,
+		BroadcastScope:    entry.BroadcastScope,
+		CreatedAt:         entry.CreatedAt.UTC().Format(timestampLayout),
+		RecipientUserID:   entry.Recipient.UserID.String(),
+		RecipientUserName: entry.Recipient.RecipientUserName,
+	}
+	if entry.SenderUserID != nil {
+		s := entry.SenderUserID.String()
+		out.SenderUserID = &s
+	}
+	if entry.SenderUsername != nil {
+		s := *entry.SenderUsername
+		out.SenderUsername = &s
+	}
+	if entry.Recipient.RecipientRaceName != nil {
+		s := *entry.Recipient.RecipientRaceName
+		out.RecipientRaceName = &s
+	}
+	if entry.Recipient.ReadAt != nil {
+		s := entry.Recipient.ReadAt.UTC().Format(timestampLayout)
+		out.ReadAt = &s
+	}
+	if entry.Recipient.DeletedAt != nil {
+		s := entry.Recipient.DeletedAt.UTC().Format(timestampLayout)
+		out.DeletedAt = &s
+	}
+	if entry.Translation != nil {
+		tr := entry.Translation
+		subj := tr.TranslatedSubject
+		body := tr.TranslatedBody
+		lang := tr.TargetLang
+		engine := tr.Translator
+		out.TranslatedSubject = &subj
+		out.TranslatedBody = &body
+		out.TranslationLang = &lang
+		out.Translator = &engine
+	}
+	_ = justCreated
+	return out
+}
+
+func mailMessageSummaryToWire(m diplomail.Message) userMailSentSummaryWire {
+	return userMailSentSummaryWire{
+		MessageID:      m.MessageID.String(),
+		GameID:         m.GameID.String(),
+		GameName:       m.GameName,
+		Kind:           m.Kind,
+		Subject:        m.Subject,
+		Body:           m.Body,
+		BodyLang:       m.BodyLang,
+		BroadcastScope: m.BroadcastScope,
+		CreatedAt:      m.CreatedAt.UTC().Format(timestampLayout),
+	}
+}
+
+// mailRecipientStateToWire renders the recipient row after a
+// mark-read or soft-delete call. The caller only needs the per-user
+// state, not the full message body again.
+func mailRecipientStateToWire(r diplomail.Recipient) userMailRecipientStateWire {
+	out := userMailRecipientStateWire{
+		MessageID: r.MessageID.String(),
+	}
+	if r.ReadAt != nil {
+		s := r.ReadAt.UTC().Format(timestampLayout)
+		out.ReadAt = &s
+	}
+	if r.DeletedAt != nil {
+		s := r.DeletedAt.UTC().Format(timestampLayout)
+		out.DeletedAt = &s
+	}
+	return out
+}
+
+type userMailRecipientStateWire struct {
+	MessageID string  `json:"message_id"`
+	ReadAt    *string `json:"read_at,omitempty"`
+	DeletedAt *string `json:"deleted_at,omitempty"`
+}

backend/internal/server/router.go

@@ -68,6 +68,7 @@ type RouterDependencies struct {
 	UserLobbyMy *UserLobbyMyHandlers
 	UserLobbyRaceNames *UserLobbyRaceNamesHandlers
 	UserGames *UserGamesHandlers
+	UserMail *UserMailHandlers
 	UserSessions *UserSessionsHandlers
 	AdminAdminAccounts *AdminAdminAccountsHandlers
 	AdminUsers *AdminUsersHandlers
@@ -75,6 +76,7 @@ type RouterDependencies struct {
 	AdminRuntimes *AdminRuntimesHandlers
 	AdminEngineVersions *AdminEngineVersionsHandlers
 	AdminMail *AdminMailHandlers
+	AdminDiplomail *AdminDiplomailHandlers
 	AdminNotifications *AdminNotificationsHandlers
 	AdminGeo *AdminGeoHandlers
 	InternalSessions *InternalSessionsHandlers
@@ -163,6 +165,9 @@ func withDefaultHandlers(deps RouterDependencies) RouterDependencies {
 	if deps.UserGames == nil {
 		deps.UserGames = NewUserGamesHandlers(nil, nil, deps.Logger)
 	}
+	if deps.UserMail == nil {
+		deps.UserMail = NewUserMailHandlers(nil, nil, nil, deps.Logger)
+	}
 	if deps.UserSessions == nil {
 		deps.UserSessions = NewUserSessionsHandlers(nil, deps.Logger)
 	}
@@ -184,6 +189,9 @@ func withDefaultHandlers(deps RouterDependencies) RouterDependencies {
 	if deps.AdminMail == nil {
 		deps.AdminMail = NewAdminMailHandlers(nil, deps.Logger)
 	}
+	if deps.AdminDiplomail == nil {
+		deps.AdminDiplomail = NewAdminDiplomailHandlers(nil, deps.Logger)
+	}
 	if deps.AdminNotifications == nil {
 		deps.AdminNotifications = NewAdminNotificationsHandlers(nil, deps.Logger)
 	}
@@ -255,6 +263,9 @@ func registerUserRoutes(router *gin.Engine, instruments *metrics.Instruments, de
 	my.GET("/invites", deps.UserLobbyMy.Invites())
 	my.GET("/race-names", deps.UserLobbyMy.RaceNames())
 
+	lobbyMail := lobbyGroup.Group("/mail")
+	lobbyMail.GET("/unread-counts", deps.UserMail.UnreadCounts())
+
 	raceNames := lobbyGroup.Group("/race-names")
 	raceNames.POST("/register", deps.UserLobbyRaceNames.Register())
 
@@ -265,6 +276,16 @@ func registerUserRoutes(router *gin.Engine, instruments *metrics.Instruments, de
 	userGames.GET("/:game_id/reports/:turn", deps.UserGames.Report())
 	userGames.GET("/:game_id/battles/:turn/:battle_id", deps.UserGames.Battle())
 
+	userMail := userGames.Group("/:game_id/mail")
+	userMail.POST("/messages", deps.UserMail.SendPersonal())
+	userMail.POST("/broadcast", deps.UserMail.SendBroadcast())
+	userMail.POST("/admin", deps.UserMail.SendAdmin())
+	userMail.GET("/messages/:message_id", deps.UserMail.Get())
+	userMail.POST("/messages/:message_id/read", deps.UserMail.MarkRead())
+	userMail.DELETE("/messages/:message_id", deps.UserMail.Delete())
+	userMail.GET("/inbox", deps.UserMail.Inbox())
+	userMail.GET("/sent", deps.UserMail.Sent())
+
 	userSessions := group.Group("/sessions")
 	userSessions.GET("", deps.UserSessions.List())
 	userSessions.POST("/revoke-all", deps.UserSessions.RevokeAll())
@@ -299,6 +320,7 @@ func registerAdminRoutes(router *gin.Engine, instruments *metrics.Instruments, d
 	games.POST("/:game_id/force-start", deps.AdminGames.ForceStart())
 	games.POST("/:game_id/force-stop", deps.AdminGames.ForceStop())
 	games.POST("/:game_id/ban-member", deps.AdminGames.BanMember())
+	games.POST("/:game_id/mail", deps.AdminDiplomail.Send())
 
 	runtimes := group.Group("/runtimes")
 	runtimes.GET("/:game_id", deps.AdminRuntimes.Get())
@@ -318,6 +340,9 @@ func registerAdminRoutes(router *gin.Engine, instruments *metrics.Instruments, d
 	mail.GET("/deliveries/:delivery_id/attempts", deps.AdminMail.ListDeliveryAttempts())
 	mail.POST("/deliveries/:delivery_id/resend", deps.AdminMail.ResendDelivery())
 	mail.GET("/dead-letters", deps.AdminMail.ListDeadLetters())
+	mail.GET("/messages", deps.AdminDiplomail.List())
+	mail.POST("/broadcast", deps.AdminDiplomail.Broadcast())
+	mail.POST("/cleanup", deps.AdminDiplomail.Cleanup())
 
 	notifications := group.Group("/notifications")
 	notifications.GET("", deps.AdminNotifications.List())

backend/openapi.yaml

@@ -1144,6 +1144,295 @@ paths:
           $ref: "#/components/responses/NotImplementedError"
         "500":
           $ref: "#/components/responses/InternalError"
+  /api/v1/user/games/{game_id}/mail/messages:
+    post:
+      tags: [User]
+      operationId: userMailSendPersonal
+      summary: Send a personal diplomatic mail message
+      description: |
+        Sends a replyable personal message from the authenticated user
+        to another active member of the same game. Both sender and
+        recipient must be active members. Body is plain UTF-8 text
+        (no HTML processing on the server); `subject` is optional.
+        Body length is capped at `BACKEND_DIPLOMAIL_MAX_BODY_BYTES`
+        (default 4096) and subject length at
+        `BACKEND_DIPLOMAIL_MAX_SUBJECT_BYTES` (default 256).
+      security:
+        - UserHeader: []
+      parameters:
+        - $ref: "#/components/parameters/XUserID"
+        - $ref: "#/components/parameters/GameID"
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/UserMailSendRequest"
+      responses:
+        "201":
+          description: Personal message accepted and persisted.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/UserMailMessageDetail"
+        "400":
+          $ref: "#/components/responses/InvalidRequestError"
+        "403":
+          $ref: "#/components/responses/ForbiddenError"
+        "501":
+          $ref: "#/components/responses/NotImplementedError"
+        "500":
+          $ref: "#/components/responses/InternalError"
+  /api/v1/user/games/{game_id}/mail/broadcast:
+    post:
+      tags: [User]
+      operationId: userMailSendBroadcast
+      summary: Send a paid-tier personal broadcast to a game's active members
+      description: |
+        Paid-tier players (`entitlement.is_paid == true`) may send one
+        personal message that fans out to every other active member of
+        the game. Free-tier callers receive 403. The resulting rows
+        carry `kind="personal"`, `sender_kind="player"`,
+        `broadcast_scope="game_broadcast"`. Recipients reply through
+        the regular personal-send endpoint; the reply targets the
+        broadcaster only.
+      security:
+        - UserHeader: []
+      parameters:
+        - $ref: "#/components/parameters/XUserID"
+        - $ref: "#/components/parameters/GameID"
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/UserMailSendBroadcastRequest"
+      responses:
+        "201":
+          description: Personal broadcast accepted; receipt carries the recipient count.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/UserMailBroadcastReceipt"
+        "400":
+          $ref: "#/components/responses/InvalidRequestError"
+        "403":
+          $ref: "#/components/responses/ForbiddenError"
+        "501":
+          $ref: "#/components/responses/NotImplementedError"
+        "500":
+          $ref: "#/components/responses/InternalError"
+  /api/v1/user/games/{game_id}/mail/admin:
+    post:
+      tags: [User]
+      operationId: userMailSendAdmin
+      summary: Send a non-replyable admin notification (owner only)
+      description: |
+        Owner-only: the caller must be the owner of the private game.
+        `target="user"` requires `recipient_user_id`; `target="all"`
+        accepts an optional `recipients` scope (`active` by default,
+        plus `active_and_removed` and `all_members`). The message
+        carries `kind="admin"` and is therefore non-replyable.
+      security:
+        - UserHeader: []
+      parameters:
+        - $ref: "#/components/parameters/XUserID"
+        - $ref: "#/components/parameters/GameID"
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/UserMailSendAdminRequest"
+      responses:
+        "201":
+          description: Admin message persisted; broadcasts return a fan-out receipt.
+          content:
+            application/json:
+              schema:
+                oneOf:
+                  - $ref: "#/components/schemas/UserMailMessageDetail"
+                  - $ref: "#/components/schemas/UserMailBroadcastReceipt"
+        "400":
+          $ref: "#/components/responses/InvalidRequestError"
+        "403":
+          $ref: "#/components/responses/ForbiddenError"
+        "404":
+          $ref: "#/components/responses/NotFoundError"
+        "501":
+          $ref: "#/components/responses/NotImplementedError"
+        "500":
+          $ref: "#/components/responses/InternalError"
+  /api/v1/user/games/{game_id}/mail/messages/{message_id}:
+    get:
+      tags: [User]
+      operationId: userMailGet
+      summary: Read one diplomatic mail message
+      security:
+        - UserHeader: []
+      parameters:
+        - $ref: "#/components/parameters/XUserID"
+        - $ref: "#/components/parameters/GameID"
+        - $ref: "#/components/parameters/MessageID"
+      responses:
+        "200":
+          description: Message addressed to the caller.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/UserMailMessageDetail"
+        "400":
+          $ref: "#/components/responses/InvalidRequestError"
+        "404":
+          $ref: "#/components/responses/NotFoundError"
+        "501":
+          $ref: "#/components/responses/NotImplementedError"
+        "500":
+          $ref: "#/components/responses/InternalError"
+    delete:
+      tags: [User]
+      operationId: userMailDelete
+      summary: Soft-delete a previously-read message
+      description: |
+        Marks the caller's recipient row for the message as deleted.
+        The underlying message stays persisted (admin / system mail is
+        retained for the lifetime of the game). The recipient row must
+        have `read_at` set first; otherwise the call returns 409.
+      security:
+        - UserHeader: []
+      parameters:
+        - $ref: "#/components/parameters/XUserID"
+        - $ref: "#/components/parameters/GameID"
+        - $ref: "#/components/parameters/MessageID"
+      responses:
+        "200":
+          description: Message soft-deleted for the caller.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/UserMailRecipientState"
+        "400":
+          $ref: "#/components/responses/InvalidRequestError"
+        "404":
+          $ref: "#/components/responses/NotFoundError"
+        "409":
+          $ref: "#/components/responses/ConflictError"
+        "501":
+          $ref: "#/components/responses/NotImplementedError"
+        "500":
+          $ref: "#/components/responses/InternalError"
+  /api/v1/user/games/{game_id}/mail/messages/{message_id}/read:
+    post:
+      tags: [User]
+      operationId: userMailMarkRead
+      summary: Mark a diplomatic mail message as read
+      description: |
+        Idempotent. Sets `read_at` on the caller's recipient row when
+        it is still unread; a second call on an already-read row is a
+        no-op and the existing state is returned.
+      security:
+        - UserHeader: []
+      parameters:
+        - $ref: "#/components/parameters/XUserID"
+        - $ref: "#/components/parameters/GameID"
+        - $ref: "#/components/parameters/MessageID"
+      responses:
+        "200":
+          description: Recipient state after the mark-read.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/UserMailRecipientState"
+        "400":
+          $ref: "#/components/responses/InvalidRequestError"
+        "404":
+          $ref: "#/components/responses/NotFoundError"
+        "501":
+          $ref: "#/components/responses/NotImplementedError"
+        "500":
+          $ref: "#/components/responses/InternalError"
+  /api/v1/user/games/{game_id}/mail/inbox:
+    get:
+      tags: [User]
+      operationId: userMailInbox
+      summary: List the caller's inbox for a game
+      description: |
+        Returns every non-soft-deleted mail row addressed to the
+        caller in the given game, newest first. Includes the
+        per-recipient read state. Soft access: the caller may not be
+        an active member if every visible row carries
+        `kind="admin"`.
+      security:
+        - UserHeader: []
+      parameters:
+        - $ref: "#/components/parameters/XUserID"
+        - $ref: "#/components/parameters/GameID"
+      responses:
+        "200":
+          description: Inbox entries for the caller in the given game.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/UserMailInboxList"
+        "400":
+          $ref: "#/components/responses/InvalidRequestError"
+        "501":
+          $ref: "#/components/responses/NotImplementedError"
+        "500":
+          $ref: "#/components/responses/InternalError"
+  /api/v1/user/games/{game_id}/mail/sent:
+    get:
+      tags: [User]
+      operationId: userMailSent
+      summary: List the caller's sent personal messages in a game
+      description: |
+        Returns personal messages authored by the caller in the given
+        game, newest first. Admin / system messages are not listed
+        (they have no `sender_user_id`).
+      security:
+        - UserHeader: []
+      parameters:
+        - $ref: "#/components/parameters/XUserID"
+        - $ref: "#/components/parameters/GameID"
+      responses:
+        "200":
+          description: Sent personal messages by the caller.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/UserMailSentList"
+        "400":
+          $ref: "#/components/responses/InvalidRequestError"
+        "501":
+          $ref: "#/components/responses/NotImplementedError"
+        "500":
+          $ref: "#/components/responses/InternalError"
+  /api/v1/user/lobby/mail/unread-counts:
+    get:
+      tags: [User]
+      operationId: userMailUnreadCounts
+      summary: Per-game and total unread mail counts for the caller
+      description: |
+        Drives the lobby badge: returns one entry per game the caller
+        has any unread mail in, plus the global total. The response
+        is empty (and `total == 0`) when there is nothing unread.
+      security:
+        - UserHeader: []
+      parameters:
+        - $ref: "#/components/parameters/XUserID"
+      responses:
+        "200":
+          description: Per-game unread counts addressed to the caller.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/UserMailUnreadCountsResponse"
+        "400":
+          $ref: "#/components/responses/InvalidRequestError"
+        "501":
+          $ref: "#/components/responses/NotImplementedError"
+        "500":
+          $ref: "#/components/responses/InternalError"
   /api/v1/user/sessions:
     get:
       tags: [User]
@@ -1704,6 +1993,176 @@ paths:
           $ref: "#/components/responses/NotImplementedError"
         "500":
           $ref: "#/components/responses/InternalError"
+  /api/v1/admin/mail/broadcast:
+    post:
+      tags: [Admin]
+      operationId: adminDiplomailBroadcast
+      summary: Multi-game admin broadcast
+      description: |
+        Fans out one admin-kind broadcast across the games selected
+        by `scope`. `scope="selected"` requires `game_ids`;
+        `scope="all_running"` enumerates every game whose status is
+        non-terminal. Recipients are resolved per-game via the same
+        scope vocabulary as the per-game admin send. A recipient
+        appearing in multiple addressed games receives one
+        independently-deletable inbox entry per game.
+      security:
+        - AdminBasicAuth: []
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/AdminDiplomailBroadcastRequest"
+      responses:
+        "201":
+          description: Broadcast accepted; per-game message ids and total recipient count.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/AdminDiplomailBroadcastResponse"
+        "400":
+          $ref: "#/components/responses/InvalidRequestError"
+        "401":
+          $ref: "#/components/responses/UnauthorizedError"
+        "501":
+          $ref: "#/components/responses/NotImplementedError"
+        "500":
+          $ref: "#/components/responses/InternalError"
+  /api/v1/admin/mail/cleanup:
+    post:
+      tags: [Admin]
+      operationId: adminDiplomailCleanup
+      summary: Bulk-purge diplomail messages from old finished games
+      description: |
+        Removes every `diplomail_messages` row whose game finished
+        more than `older_than_years` years ago. Cascading FKs prune
+        the recipient and translation tables in the same transaction.
+        `older_than_years` must be >= 1.
+      security:
+        - AdminBasicAuth: []
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/AdminDiplomailCleanupRequest"
+      responses:
+        "200":
+          description: Cleanup result.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/AdminDiplomailCleanupResponse"
+        "400":
+          $ref: "#/components/responses/InvalidRequestError"
+        "401":
+          $ref: "#/components/responses/UnauthorizedError"
+        "501":
+          $ref: "#/components/responses/NotImplementedError"
+        "500":
+          $ref: "#/components/responses/InternalError"
+  /api/v1/admin/mail/messages:
+    get:
+      tags: [Admin]
+      operationId: adminDiplomailList
+      summary: Paginated admin view of diplomail messages
+      description: |
+        Returns the canonical message rows for admin observability.
+        Optional filters: `game_id`, `kind` (personal / admin),
+        `sender_kind` (player / admin / system). Pagination via
+        `page` and `page_size`.
+      security:
+        - AdminBasicAuth: []
+      parameters:
+        - name: page
+          in: query
+          required: false
+          schema:
+            type: integer
+            minimum: 1
+        - name: page_size
+          in: query
+          required: false
+          schema:
+            type: integer
+            minimum: 1
+        - name: game_id
+          in: query
+          required: false
+          schema:
+            type: string
+            format: uuid
+        - name: kind
+          in: query
+          required: false
+          schema:
+            type: string
+            enum: [personal, admin]
+        - name: sender_kind
+          in: query
+          required: false
+          schema:
+            type: string
+            enum: [player, admin, system]
+      responses:
+        "200":
+          description: Paginated diplomail messages.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/AdminDiplomailListResponse"
+        "400":
+          $ref: "#/components/responses/InvalidRequestError"
+        "401":
+          $ref: "#/components/responses/UnauthorizedError"
+        "501":
+          $ref: "#/components/responses/NotImplementedError"
+        "500":
+          $ref: "#/components/responses/InternalError"
+  /api/v1/admin/games/{game_id}/mail:
+    post:
+      tags: [Admin]
+      operationId: adminDiplomailSend
+      summary: Send a diplomatic-mail admin notification to one game
+      description: |
+        Site-admin send for the diplomatic-mail subsystem. Body shape
+        mirrors the owner-only `POST /api/v1/user/games/{game_id}/mail/admin`
+        endpoint. `target="user"` requires `recipient_user_id`;
+        `target="all"` accepts an optional `recipients` scope
+        (`active` / `active_and_removed` / `all_members`). The
+        authenticated admin username is persisted as `sender_username`.
+      security:
+        - AdminBasicAuth: []
+      parameters:
+        - $ref: "#/components/parameters/GameID"
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/UserMailSendAdminRequest"
+      responses:
+        "201":
+          description: Admin message persisted; broadcasts return a fan-out receipt.
+          content:
+            application/json:
+              schema:
+                oneOf:
+                  - $ref: "#/components/schemas/UserMailMessageDetail"
+                  - $ref: "#/components/schemas/UserMailBroadcastReceipt"
+        "400":
+          $ref: "#/components/responses/InvalidRequestError"
+        "401":
+          $ref: "#/components/responses/UnauthorizedError"
+        "403":
+          $ref: "#/components/responses/ForbiddenError"
+        "404":
+          $ref: "#/components/responses/NotFoundError"
+        "501":
+          $ref: "#/components/responses/NotImplementedError"
+        "500":
+          $ref: "#/components/responses/InternalError"
   /api/v1/admin/runtimes/{game_id}:
     get:
       tags: [Admin]
@@ -2247,6 +2706,13 @@ components:
       schema:
         type: string
         format: uuid
+    MessageID:
+      name: message_id
+      in: path
+      required: true
+      schema:
+        type: string
+        format: uuid
     NotificationID:
       name: notification_id
       in: path
@@ -3599,6 +4065,405 @@ components:
           type: array
           items:
             $ref: "#/components/schemas/DeviceSession"
+    UserMailSendRequest:
+      type: object
+      additionalProperties: false
+      required: [recipient_user_id, body]
+      properties:
+        recipient_user_id:
+          type: string
+          format: uuid
+        subject:
+          type: string
+          description: |
+            Optional subject. Empty string and missing field are
+            treated the same.
+        body:
+          type: string
+          description: Plain UTF-8 body. HTML is not parsed on the server.
+    UserMailSendAdminRequest:
+      type: object
+      additionalProperties: false
+      required: [target, body]
+      properties:
+        target:
+          type: string
+          enum: [user, all]
+        recipient_user_id:
+          type: string
+          format: uuid
+          description: |
+            Required when `target="user"`. Identifies the recipient
+            of the personal admin message; the recipient may be in
+            any membership status (admin notifications can reach
+            kicked players).
+        recipients:
+          type: string
+          enum: [active, active_and_removed, all_members]
+          description: |
+            Optional scope when `target="all"`. Defaults to `active`.
+        subject:
+          type: string
+        body:
+          type: string
+    UserMailBroadcastReceipt:
+      type: object
+      additionalProperties: false
+      required:
+        - message_id
+        - game_id
+        - kind
+        - sender_kind
+        - body
+        - body_lang
+        - broadcast_scope
+        - created_at
+        - recipient_count
+      properties:
+        message_id:
+          type: string
+          format: uuid
+        game_id:
+          type: string
+          format: uuid
+        game_name:
+          type: string
+        kind:
+          type: string
+          enum: [personal, admin]
+        sender_kind:
+          type: string
+          enum: [player, admin, system]
+        subject:
+          type: string
+        body:
+          type: string
+        body_lang:
+          type: string
+        broadcast_scope:
+          type: string
+          enum: [single, game_broadcast, multi_game_broadcast]
+        created_at:
+          type: string
+          format: date-time
+        recipient_count:
+          type: integer
+          minimum: 0
+    UserMailSendBroadcastRequest:
+      type: object
+      additionalProperties: false
+      required: [body]
+      properties:
+        subject:
+          type: string
+        body:
+          type: string
+    AdminDiplomailBroadcastRequest:
+      type: object
+      additionalProperties: false
+      required: [scope, body]
+      properties:
+        scope:
+          type: string
+          enum: [selected, all_running]
+        game_ids:
+          type: array
+          items:
+            type: string
+            format: uuid
+        recipients:
+          type: string
+          enum: [active, active_and_removed, all_members]
+        subject:
+          type: string
+        body:
+          type: string
+    AdminDiplomailBroadcastResponse:
+      type: object
+      additionalProperties: false
+      required: [recipient_count, messages]
+      properties:
+        recipient_count:
+          type: integer
+          minimum: 0
+        messages:
+          type: array
+          items:
+            type: object
+            additionalProperties: false
+            required: [message_id, game_id]
+            properties:
+              message_id:
+                type: string
+                format: uuid
+              game_id:
+                type: string
+                format: uuid
+              game_name:
+                type: string
+    AdminDiplomailCleanupRequest:
+      type: object
+      additionalProperties: false
+      required: [older_than_years]
+      properties:
+        older_than_years:
+          type: integer
+          minimum: 1
+    AdminDiplomailCleanupResponse:
+      type: object
+      additionalProperties: false
+      required: [messages_deleted, game_ids]
+      properties:
+        messages_deleted:
+          type: integer
+          minimum: 0
+        game_ids:
+          type: array
+          items:
+            type: string
+            format: uuid
+    AdminDiplomailMessage:
+      type: object
+      additionalProperties: false
+      required:
+        - message_id
+        - game_id
+        - kind
+        - sender_kind
+        - body
+        - body_lang
+        - broadcast_scope
+        - created_at
+      properties:
+        message_id:
+          type: string
+          format: uuid
+        game_id:
+          type: string
+          format: uuid
+        game_name:
+          type: string
+        kind:
+          type: string
+          enum: [personal, admin]
+        sender_kind:
+          type: string
+          enum: [player, admin, system]
+        sender_user_id:
+          type: string
+          format: uuid
+          nullable: true
+        sender_username:
+          type: string
+          nullable: true
+        sender_ip:
+          type: string
+        subject:
+          type: string
+        body:
+          type: string
+        body_lang:
+          type: string
+        broadcast_scope:
+          type: string
+          enum: [single, game_broadcast, multi_game_broadcast]
+        created_at:
+          type: string
+          format: date-time
+    AdminDiplomailListResponse:
+      type: object
+      additionalProperties: false
+      required: [total, page, page_size, items]
+      properties:
+        total:
+          type: integer
+          minimum: 0
+        page:
+          type: integer
+          minimum: 1
+        page_size:
+          type: integer
+          minimum: 1
+        items:
+          type: array
+          items:
+            $ref: "#/components/schemas/AdminDiplomailMessage"
+    UserMailMessageDetail:
+      type: object
+      additionalProperties: false
+      required:
+        - message_id
+        - game_id
+        - kind
+        - sender_kind
+        - body
+        - body_lang
+        - broadcast_scope
+        - created_at
+        - recipient_user_id
+      properties:
+        message_id:
+          type: string
+          format: uuid
+        game_id:
+          type: string
+          format: uuid
+        game_name:
+          type: string
+        kind:
+          type: string
+          enum: [personal, admin]
+        sender_kind:
+          type: string
+          enum: [player, admin, system]
+        sender_user_id:
+          type: string
+          format: uuid
+          nullable: true
+        sender_username:
+          type: string
+          nullable: true
+        subject:
+          type: string
+        body:
+          type: string
+        body_lang:
+          type: string
+          description: BCP 47 tag. `und` until Stage D adds detection.
+        broadcast_scope:
+          type: string
+          enum: [single, game_broadcast, multi_game_broadcast]
+        created_at:
+          type: string
+          format: date-time
+        recipient_user_id:
+          type: string
+          format: uuid
+        recipient_user_name:
+          type: string
+        recipient_race_name:
+          type: string
+          nullable: true
+        read_at:
+          type: string
+          format: date-time
+          nullable: true
+        deleted_at:
+          type: string
+          format: date-time
+          nullable: true
+        translated_subject:
+          type: string
+          description: |
+            Subject rendered into the caller's preferred_language by
+            the translation cache. Absent when the caller's language
+            matches `body_lang` or the translator could not produce
+            a rendering.
+        translated_body:
+          type: string
+          description: |
+            Body rendered into the caller's preferred_language. Same
+            absence semantics as `translated_subject`.
+        translation_lang:
+          type: string
+          description: BCP 47 tag of the rendered translation.
+        translator:
+          type: string
+          description: Identifier of the translation engine that produced the cached row.
+    UserMailSentSummary:
+      type: object
+      additionalProperties: false
+      required:
+        - message_id
+        - game_id
+        - kind
+        - body
+        - body_lang
+        - broadcast_scope
+        - created_at
+      properties:
+        message_id:
+          type: string
+          format: uuid
+        game_id:
+          type: string
+          format: uuid
+        game_name:
+          type: string
+        kind:
+          type: string
+          enum: [personal, admin]
+        subject:
+          type: string
+        body:
+          type: string
+        body_lang:
+          type: string
+        broadcast_scope:
+          type: string
+          enum: [single, game_broadcast, multi_game_broadcast]
+        created_at:
+          type: string
+          format: date-time
+    UserMailInboxList:
+      type: object
+      additionalProperties: false
+      required: [items]
+      properties:
+        items:
+          type: array
+          items:
+            $ref: "#/components/schemas/UserMailMessageDetail"
+    UserMailSentList:
+      type: object
+      additionalProperties: false
+      required: [items]
+      properties:
+        items:
+          type: array
+          items:
+            $ref: "#/components/schemas/UserMailSentSummary"
+    UserMailUnreadCount:
+      type: object
+      additionalProperties: false
+      required: [game_id, unread]
+      properties:
+        game_id:
+          type: string
+          format: uuid
+        game_name:
+          type: string
+        unread:
+          type: integer
+          minimum: 0
+    UserMailUnreadCountsResponse:
+      type: object
+      additionalProperties: false
+      required: [total, items]
+      properties:
+        total:
+          type: integer
+          minimum: 0
+        items:
+          type: array
+          items:
+            $ref: "#/components/schemas/UserMailUnreadCount"
+    UserMailRecipientState:
+      type: object
+      additionalProperties: false
+      required: [message_id]
+      properties:
+        message_id:
+          type: string
+          format: uuid
+        read_at:
+          type: string
+          format: date-time
+          nullable: true
+        deleted_at:
+          type: string
+          format: date-time
+          nullable: true
   responses:
     NotImplementedError:
       description: Endpoint is documented but not implemented yet.

docs/ARCHITECTURE.md

@@ -192,10 +192,12 @@ because they cross domain boundaries:
   `race_name`) remain `text`.
 - Foreign keys are intra-domain only: `accounts → entitlement_*` /
   `sanction_*` / `limit_*`; `games → applications` / `invites` /
-  `memberships` (with `ON DELETE CASCADE`); `mail_payloads →
-  mail_deliveries → mail_recipients` / `mail_attempts` /
-  `mail_dead_letters`; `notifications → notification_routes` /
-  `notification_dead_letters`. Cross-domain references
+  `memberships` / `diplomail_messages` (each with
+  `ON DELETE CASCADE`); `mail_payloads → mail_deliveries →
+  mail_recipients` / `mail_attempts` / `mail_dead_letters`;
+  `notifications → notification_routes` / `notification_dead_letters`;
+  `diplomail_messages → diplomail_recipients` /
+  `diplomail_translations`. Cross-domain references
   (`memberships.user_id`, `games.owner_user_id`, etc.) are kept as
   opaque `uuid` columns because each domain runs its own cleanup
   through the in-process cascade described in [§7](#7-in-process-async-patterns). Adding a database
@@ -456,12 +458,15 @@ committed; SMTP completion is asynchronous to the auth request.
 
 Notifications are an in-process pipeline. The closed catalog is
 defined in `backend/internal/notification/catalog.go` and currently
-covers 13 kinds: 10 lobby kinds (invite received/revoked, application
+covers 16 kinds: 10 lobby kinds (invite received/revoked, application
 submitted/approved/rejected, membership removed/blocked, race name
-registered/pending/expired) and 3 admin-recipient runtime kinds
-(image pull failed, container start failed, start config invalid).
-Per-kind delivery channels (push, email, or both) and the admin-vs-
-per-user recipient routing live in the same file.
+registered/pending/expired), 3 admin-recipient runtime kinds (image
+pull failed, container start failed, start config invalid), 2 game
+lifecycle kinds (turn ready, game paused), and the
+`diplomail.message.received` kind that fans diplomatic-mail send
+events out to the recipient's push stream. Per-kind delivery channels
+(push, email, or both) and the admin-vs-per-user recipient routing
+live in the same file.
 
 For every intent, `notification.Submit` performs:
 
@@ -490,6 +495,34 @@ Notification persistence is the auditable record of "we tried to tell
 this user about this thing"; clients still derive their actual game
 state through normal user-facing reads.
 
+### 12.1 Diplomatic mail subsystem
+
+`backend/internal/diplomail` owns the player-to-player message channel
+that the in-game mail view consumes. The data lives in three tables:
+
+- `diplomail_messages` — one canonical row per send. Captures the
+  game name and the sender IP at insert time so audit rendering
+  survives game renames and bulk purges. `kind` is `personal` (a
+  replyable player→player message) or `admin` (a non-replyable
+  notification produced by an administrator or the system).
+  `sender_kind` distinguishes `player`, `admin`, and `system` senders.
+  `broadcast_scope` carries `single`, `game_broadcast`, or
+  `multi_game_broadcast`.
+- `diplomail_recipients` — one row per (message, recipient). Holds
+  the per-user `read_at`, `deleted_at`, `delivered_at`, `notified_at`
+  state plus snapshot fields (`recipient_user_name`,
+  `recipient_race_name`) so admin search and the inbox listing render
+  correctly even after the source rows are renamed or revoked.
+- `diplomail_translations` — cached per-language rendering shared
+  across every recipient with the same `accounts.preferred_language`.
+
+Stage A wires the personal subset (single recipient, no language
+detection). Lifecycle hooks (paused / cancelled / kicked), paid-tier
+player broadcasts, multi-game admin broadcasts, bulk purge, and the
+detection / translation cache land in later stages. The package is
+the only place that constructs `diplomail.message.received` push
+intents; the notification pipeline takes it from there.
+
 ## 13. Container Lifecycle (in-process)
 
 `backend/internal/runtime` owns the lifecycle of game-engine containers

docs/FUNCTIONAL.md

@@ -47,6 +47,7 @@ same scenario when they participate in the same business flow.
 8. [Notifications and mail](#8-notifications-and-mail)
 9. [Geo signal](#9-geo-signal)
 10. [Administration](#10-administration)
+11. [Diplomatic mail](#11-diplomatic-mail)
 
 ---
 
@@ -1153,3 +1154,223 @@ counters are populated by the runtime, and operators can only read.
 - Mail outbox and notification dispatcher:
   [ARCHITECTURE.md §11](ARCHITECTURE.md#11-mail-outbox),
   [§12](ARCHITECTURE.md#12-notification-pipeline) and [Section 8](#8-notifications-and-mail).
+
+---
+
+## 11. Diplomatic mail
+
+This scenario covers the player-to-player and admin-to-player
+messaging system exposed inside a game. The system is conceptually
+part of the lobby (messages outlive game runtime restarts), but
+they are surfaced exclusively inside the in-game UI; the lobby
+surfaces only an unread counter.
+
+### 11.1 Scope
+
+In scope: sending personal mail between active members of the same
+game; replying to personal mail; reading and marking-read /
+soft-deleting one's own incoming mail; admin / owner notifications
+addressed to one player or broadcast to a game; paid-tier player
+broadcasts; site-admin multi-game broadcasts; bulk purge of
+messages tied to terminated games; auto-translation of the body
+into the recipient's `preferred_language` with a cached rendering.
+
+Out of scope: out-of-game chat, group chats spanning multiple
+games, file attachments, message editing or unsend, end-to-end
+encryption.
+
+### 11.2 The message model
+
+Every send produces exactly one row in `diplomail_messages` plus
+one row per recipient in `diplomail_recipients`. A broadcast to N
+recipients is one message + N recipient rows; the translation row,
+when materialised, is shared across every recipient with the same
+target language.
+
+`diplomail_messages.kind` is the closed set
+`{personal, admin}`. Personal messages are replyable (the
+recipient sends back a new personal message); admin messages are
+non-replyable acknowledgements of a state change or operator
+action. `sender_kind` is `{player, admin, system}` and identifies
+the originator's role: a player owns the game (admin notification
+from owner), a site administrator pushed it (admin notification
+from operator), or the lobby state machine produced it
+(`game.paused`, `game.cancelled`, `membership.removed`,
+`membership.blocked`).
+
+`broadcast_scope` records whether the send was a single-recipient
+delivery (`single`), a one-game broadcast (`game_broadcast`), or a
+cross-game admin broadcast (`multi_game_broadcast`). Recipients of
+a multi-game broadcast see one independently-deletable inbox entry
+per game they were addressed in.
+
+Per-row snapshots travel with each message: `game_name`,
+`sender_username`, `sender_ip`, plus on the recipient row
+`recipient_user_name`, `recipient_race_name`, and
+`recipient_preferred_language`. These survive game-name changes,
+membership revocation, account soft-delete, and the eventual
+bulk-purge cascade — they let the admin observability surface
+render correctly long after the live rows have moved on.
+
+Bodies and subjects are plain UTF-8 text. The server does not
+parse, sanitise, or escape HTML; the client renders bodies through
+`textContent`. Maximum body size is
+`BACKEND_DIPLOMAIL_MAX_BODY_BYTES` (default `4096`); maximum
+subject size is `BACKEND_DIPLOMAIL_MAX_SUBJECT_BYTES` (default
+`256`).
+
+### 11.3 Sending mail
+
+Personal sends require active membership in the game for both the
+sender and the recipient. Free-tier players send one personal
+message per request. Paid-tier players additionally have access to
+a game-scoped broadcast that addresses every other active member
+in one call; replies fan back to the broadcast author.
+
+Game owners (of private games) and site administrators send admin
+notifications. The owner endpoint lives under the user surface
+(authenticated by `X-User-ID`, owner check enforced); the admin
+endpoint lives under the admin surface (HTTP Basic). Both accept
+`target=user` (single recipient) or `target=all` (game broadcast).
+Site administrators additionally have a multi-game endpoint that
+accepts `scope=selected` with a list of game ids or
+`scope=all_running` that enumerates every game with non-terminal
+status.
+
+Broadcast composition is parameterised by `recipients`: `active`
+(default), `active_and_removed`, or `all_members` (includes
+blocked rows for audit-style mail). The broadcast author's own
+recipient row is never created.
+
+A paid-tier broadcast is rejected with `403 forbidden` when the
+caller's entitlement tier is `free`.
+
+### 11.4 Receiving mail
+
+The recipient sees the message in their in-game inbox once the
+async translation worker has finished processing it (see
+[§11.6](#116-translation)). Until then the row stays invisible:
+absent from the inbox listing, not counted in the unread badge, no
+push event delivered. This avoids a surprise where the inbox shows
+a row with no translation and an outdated unread count.
+
+The unread badge in the lobby aggregates by game. The
+`/api/v1/user/lobby/mail/unread-counts` endpoint returns one entry
+per game with non-zero unread plus the global total; the lobby UI
+renders the total badge and a per-game tile counter without
+exposing the messages themselves.
+
+Marking a message as read is idempotent. Soft-deletion requires the
+message to already be marked read — a client cannot erase an
+unopened message. Soft-deletion is per-recipient: the underlying
+message row survives until the admin bulk-purge endpoint removes
+the entire game's mail tree.
+
+The message detail response includes both the original body and,
+when available, the cached translation; the client UI defaults to
+the translated text and offers a "show original" toggle.
+
+### 11.5 Lifecycle hooks
+
+Three lobby transitions land as system mail in the affected
+players' inboxes:
+
+- **Game paused / cancelled.** When the game state machine moves
+  through `paused` or `cancelled`, the lobby emits a system mail
+  addressed to every active member. The message explains the
+  transition with a server-rendered template, so even an offline
+  player finds the context the next time they open the inbox.
+- **Membership removed / blocked.** Manual self-leave, owner-driven
+  removal, and admin ban each emit a system mail addressed to the
+  affected player only. This mail survives the membership going
+  to `removed` / `blocked`, so a kicked player keeps read access
+  to the explanation forever (soft-access rule).
+
+Future inactivity-driven removal must call the same publisher so
+the explanation reaches the affected player; the lobby package
+README pins this contract for the next implementer.
+
+### 11.6 Translation
+
+`diplomail_messages.body_lang` is filled at send time by an
+in-process language detector that operates on the body only.
+Subject inherits the body's detected language for the translation
+cache lookup. When detection cannot confidently label the body
+(too short, empty, mixed scripts) the value is the BCP 47
+`und` ("undetermined") sentinel and the translation pipeline is
+short-circuited — recipients receive the original.
+
+Translation happens asynchronously. Every recipient row stores a
+snapshot of the addressee's `preferred_language` plus an
+`available_at` timestamp. A recipient whose language matches the
+detected `body_lang` (or whose preferred language is empty / the
+body language is `und`) gets `available_at = now()` on insert and
+the push event fires immediately. A recipient whose language
+differs is inserted with `available_at IS NULL` and waits for the
+translation worker.
+
+The worker (`internal/diplomail.Worker`) ticks every
+`BACKEND_DIPLOMAIL_WORKER_INTERVAL` (default `2s`) and processes
+one `(message_id, target_lang)` pair per tick. It consults the
+translation cache first; on miss it asks the configured
+`Translator`. The default deployment ships the LibreTranslate HTTP
+client; an empty `BACKEND_DIPLOMAIL_TRANSLATOR_URL` falls back to
+the noop translator that delivers every message in the original
+language.
+
+Translation outcomes:
+
+- **Success.** A row in `diplomail_translations` is inserted (or
+  reused if another worker won the race), every pending recipient
+  of the pair is flipped to `available_at = now()`, and one push
+  event per recipient is published.
+- **Unsupported language pair** (HTTP 400 from LibreTranslate).
+  No translation row is persisted; recipients are delivered with
+  the original body. Subsequent reads return the original.
+- **Transient failure** (timeout, 5xx, network error). The
+  attempt counter is bumped and the next attempt is scheduled via
+  exponential backoff `1s → 2s → 4s → 8s → 16s` (capped at 60s).
+  After `BACKEND_DIPLOMAIL_TRANSLATOR_MAX_ATTEMPTS` (default `5`)
+  the worker falls back to delivering the original body. A
+  prolonged translator outage therefore stalls delivery by at
+  most ~30 seconds per pair before the receiver sees the
+  original.
+
+The translation cache is shared: a broadcast to N recipients with
+the same preferred language produces one cache row and one
+translator call, not N.
+
+### 11.7 Storage and purge
+
+Messages live in `diplomail_messages`; per-recipient state lives
+in `diplomail_recipients` with a foreign-key cascade to the
+message; translations live in `diplomail_translations` also with a
+cascade. The sender IP is captured at insert time from
+`X-Forwarded-For` (forwarded by gateway) for evidence preservation.
+
+There is no automatic retention. The admin bulk-purge endpoint
+removes every message whose game finished more than
+`older_than_years` years ago (minimum `1`); the cascade drops the
+recipient and translation rows in the same transaction.
+
+### 11.8 Operator visibility
+
+The admin surface exposes a paginated listing of every persisted
+message (`/api/v1/admin/mail/messages`) filterable by `game_id`,
+`kind`, and `sender_kind`. The bulk-purge endpoint
+(`/api/v1/admin/mail/cleanup`) accepts the `older_than_years`
+threshold. Per-game admin sends and multi-game broadcasts live
+under `/api/v1/admin/games/{game_id}/mail` and
+`/api/v1/admin/mail/broadcast`.
+
+### 11.9 Cross-references
+
+- Package overview and stage map:
+  [`backend/internal/diplomail/README.md`](../backend/internal/diplomail/README.md).
+- LibreTranslate setup recipe for local development:
+  [`backend/docs/diplomail-translator-setup.md`](../backend/docs/diplomail-translator-setup.md).
+- Storage detail:
+  [ARCHITECTURE.md §12.1](ARCHITECTURE.md#121-diplomatic-mail-subsystem).
+- Push transport for delivery events: [Section 7](#7-push-channel).
+- Notification catalog kind `diplomail.message.received`:
+  [`backend/README.md` §10](../backend/README.md#10-notification-catalog).

docs/FUNCTIONAL_ru.md

@@ -47,6 +47,7 @@ field-level-валидация — всё это лежит в нижнеуро
 8. [Уведомления и почта](#8-уведомления-и-почта)
 9. [Гео-сигнал](#9-гео-сигнал)
 10. [Администрирование](#10-администрирование)
+11. [Дипломатическая почта](#11-дипломатическая-почта)
 
 ---
 
@@ -1193,3 +1194,220 @@ dead-letters и malformed notification-намерения. Они также м
   [ARCHITECTURE.md §11](ARCHITECTURE.md#11-mail-outbox),
   [§12](ARCHITECTURE.md#12-notification-pipeline) и
   [Раздел 8](#8-уведомления-и-почта).
+
+---
+
+## 11. Дипломатическая почта
+
+Сценарий описывает обмен сообщениями между игроками одной партии и
+адресные / широковещательные уведомления от администрации и
+владельца партии. Подсистема концептуально часть лобби (сообщения
+переживают рестарты движка), но видна только внутри игрового UI;
+в лобби виден лишь счётчик непрочитанного.
+
+### 11.1 Состав
+
+В составе: отправка персональной почты между активными участниками
+одной партии; ответы на персональную почту; чтение, отметка
+«прочитано» и soft-удаление своей входящей почты; адресные и
+широковещательные уведомления от админов и владельцев; платный
+broadcast от игроков; мультигеймовая admin-рассылка; ручная
+массовая чистка почты завершённых партий; авто-перевод тела
+сообщения на `preferred_language` получателя с кэшированием.
+
+Вне состава: чат вне партии, групповые чаты с участниками разных
+партий, вложения, редактирование / отзыв сообщения,
+end-to-end-шифрование.
+
+### 11.2 Модель сообщения
+
+Каждая отправка порождает ровно одну строку в `diplomail_messages`
+плюс по одной строке на получателя в `diplomail_recipients`.
+Broadcast на N получателей — одно сообщение и N recipient-строк;
+строка перевода, если материализована, общая для всех получателей
+с одинаковым целевым языком.
+
+`diplomail_messages.kind` — закрытое множество
+`{personal, admin}`. Персональные сообщения допускают ответ
+(получатель отправляет новое персональное сообщение);
+admin-сообщения не предполагают ответа — это уведомления о смене
+состояния или операторском действии. `sender_kind` — это
+`{player, admin, system}` и определяет роль отправителя: игрок-
+владелец партии (admin-уведомление от owner), site-администратор
+(admin-уведомление от оператора) или собственно автомат лобби
+(`game.paused`, `game.cancelled`, `membership.removed`,
+`membership.blocked`).
+
+`broadcast_scope` фиксирует тип отправки: одному получателю
+(`single`), рассылка по одной партии (`game_broadcast`) или
+admin-рассылка по нескольким партиям (`multi_game_broadcast`).
+Получатели multi_game-рассылки видят отдельную, независимо
+удаляемую запись inbox в каждой адресованной партии.
+
+Снимки сохраняются прямо в строках сообщения и получателя:
+`game_name`, `sender_username`, `sender_ip` и на стороне
+получателя — `recipient_user_name`, `recipient_race_name` и
+`recipient_preferred_language`. Они переживают переименование
+партии, отзыв членства, soft-delete аккаунта и итоговый
+bulk-purge — admin observability отрисовывается корректно даже
+после исчезновения «живых» строк.
+
+Тела и subject — plain UTF-8 текст. Сервер не парсит, не санитайзит
+и не экранирует HTML; клиент рендерит тело через `textContent`.
+Максимум размера тела — `BACKEND_DIPLOMAIL_MAX_BODY_BYTES`
+(по умолчанию `4096`); максимум для subject —
+`BACKEND_DIPLOMAIL_MAX_SUBJECT_BYTES` (по умолчанию `256`).
+
+### 11.3 Отправка почты
+
+Персональная отправка требует активного членства в партии и от
+отправителя, и от получателя. Игроки free-tier отправляют одно
+персональное сообщение за запрос. Игрокам платных тиров доступен
+и игровой broadcast — одна отправка на всех остальных активных
+участников партии; ответы возвращаются автору broadcast.
+
+Владельцы (приватных партий) и site-администраторы отправляют
+admin-уведомления. Endpoint владельца находится на user-поверхности
+(аутентификация по `X-User-ID`, проверка владельца в обработчике);
+endpoint администратора — на admin-поверхности (HTTP Basic). Оба
+принимают `target=user` (один получатель) или `target=all`
+(broadcast в одной партии). Site-администратору доступен
+дополнительный multi-game endpoint, принимающий
+`scope=selected` со списком game_id или `scope=all_running` —
+перебор всех партий в нетерминальных состояниях.
+
+Состав получателей broadcast параметризуется полем `recipients`:
+`active` (по умолчанию), `active_and_removed` или `all_members`
+(включает блокированных, для аудит-уведомлений). Собственная
+recipient-строка автора broadcast не создаётся.
+
+Player-broadcast от free-tier пользователя отклоняется кодом
+`403 forbidden`.
+
+### 11.4 Получение почты
+
+Получатель видит сообщение в своём inbox только после того, как
+асинхронный worker перевода обработал его (см.
+[§11.6](#116-перевод)). До этого строка невидима: не выводится в
+inbox-листинге, не учитывается в badge непрочитанного, push-событие
+не доставляется. Это исключает ситуацию «строка появилась, перевод
+не подъехал, badge мигает».
+
+Badge непрочитанного в лобби агрегируется по партиям. Endpoint
+`/api/v1/user/lobby/mail/unread-counts` возвращает по одной записи
+на каждую партию с ненулевым unread плюс общий total; UI лобби
+отображает общий badge и плитки по партиям, не раскрывая самих
+сообщений.
+
+Mark-read идемпотентен. Soft-удаление требует, чтобы сообщение уже
+было помечено прочитанным — клиент не может стереть неоткрытое
+сообщение. Soft-удаление действует только для одного получателя:
+строка самого сообщения переживает удаление вплоть до admin
+bulk-purge всей почты соответствующей партии.
+
+Ответ message-detail содержит и оригинальное тело, и (если есть
+кэш) перевод; UI по умолчанию показывает перевод и предлагает
+переключение «показать оригинал».
+
+### 11.5 Хуки жизненного цикла
+
+Три транзитных перехода в лобби порождают system mail в inbox
+затронутых игроков:
+
+- **Пауза / отмена игры.** Когда автомат партии проходит через
+  `paused` или `cancelled`, лобби эмитит system-сообщение всем
+  активным членам. Текст рендерится сервером по шаблону, чтобы
+  игрок, открывший inbox позже, нашёл объяснение даже без
+  одновременной push-сессии.
+- **Удаление / блокировка членства.** Сам-выход, удаление
+  владельцем и admin-бан порождают system-сообщение только для
+  затронутого игрока. Это письмо переживает переход членства в
+  `removed` / `blocked` — игрок сохраняет к нему read-доступ
+  навсегда (правило soft-доступа).
+
+Будущее удаление по неактивности должно вызывать тот же publisher,
+чтобы объяснение дошло до затронутого игрока; README пакета
+прибивает этот контракт для следующего реализатора.
+
+### 11.6 Перевод
+
+`diplomail_messages.body_lang` заполняется на стороне сервера в
+момент отправки внутрипроцессным детектором языка, работающим
+только по телу. Subject наследует язык тела для ключа кэша
+перевода. Когда детектор не может уверенно классифицировать тело
+(слишком короткое, пустое, смешанные скрипты), значение —
+плейсхолдер BCP 47 `und` ("неопределённый"), и pipeline перевода
+обходится стороной — получатели видят оригинал.
+
+Перевод выполняется асинхронно. Каждая recipient-строка содержит
+снимок `preferred_language` получателя плюс метку `available_at`.
+Получатель, чей язык совпадает с детектированным `body_lang` (или
+чей preferred_language пуст / язык тела — `und`), получает
+`available_at = now()` сразу при вставке, и push-событие
+отправляется в момент `POST`. Получатель с отличающимся языком
+вставляется с `available_at IS NULL` и ждёт worker.
+
+Worker (`internal/diplomail.Worker`) тикает каждые
+`BACKEND_DIPLOMAIL_WORKER_INTERVAL` (по умолчанию `2s`) и
+обрабатывает по одной паре `(message_id, target_lang)` за тик. Он
+сначала смотрит в кэш переводов; на miss дёргает настроенный
+`Translator`. Дефолт production-сборки — LibreTranslate HTTP
+клиент; пустой `BACKEND_DIPLOMAIL_TRANSLATOR_URL` оставляет
+noop-translator, который доставляет сообщение в оригинале.
+
+Исходы перевода:
+
+- **Успех.** Строка в `diplomail_translations` создаётся (или
+  переиспользуется, если параллельная попытка успела раньше),
+  все pending-получатели пары переключаются на
+  `available_at = now()`, и по каждому отправляется push.
+- **Неподдерживаемая пара языков** (HTTP 400 от LibreTranslate).
+  Строка перевода не сохраняется; получатели доставляются с
+  оригинальным телом. Последующие чтения возвращают оригинал.
+- **Транзитный сбой** (timeout, 5xx, network error). Счётчик
+  попыток увеличивается, следующая попытка планируется по
+  экспоненциальному backoff `1s → 2s → 4s → 8s → 16s`
+  (с потолком 60s). После
+  `BACKEND_DIPLOMAIL_TRANSLATOR_MAX_ATTEMPTS` (по умолчанию `5`)
+  worker fallback'ит на оригинальное тело. Длительный отказ
+  переводчика тормозит доставку максимум на ~30 секунд на пару
+  до того, как получатель увидит оригинал.
+
+Кэш переводов общий: broadcast на N получателей с одинаковым
+preferred_language порождает одну строку кэша и один вызов
+переводчика, не N.
+
+### 11.7 Хранение и purge
+
+Сообщения живут в `diplomail_messages`; per-recipient state — в
+`diplomail_recipients` с FK-каскадом на сообщение; переводы — в
+`diplomail_translations` тоже с каскадом. IP-адрес отправителя
+снимается из `X-Forwarded-For` (форвардит gateway) и хранится в
+сообщении для сохранения доказательств.
+
+Автоматического retention нет. Admin bulk-purge endpoint удаляет
+все сообщения, чья партия завершилась более `older_than_years`
+лет назад (минимум `1`); каскад удаляет recipient- и
+translation-строки той же транзакцией.
+
+### 11.8 Видимость для оператора
+
+Admin-поверхность экспонирует постраничный листинг всех сообщений
+(`/api/v1/admin/mail/messages`) с фильтрами по `game_id`, `kind`
+и `sender_kind`. Bulk-purge endpoint
+(`/api/v1/admin/mail/cleanup`) принимает порог
+`older_than_years`. Per-game admin-отправки и multi-game
+broadcast'ы доступны через `/api/v1/admin/games/{game_id}/mail`
+и `/api/v1/admin/mail/broadcast`.
+
+### 11.9 Перекрёстные ссылки
+
+- Обзор пакета и карта стадий:
+  [`backend/internal/diplomail/README.md`](../backend/internal/diplomail/README.md).
+- Рецепт развёртывания LibreTranslate для локальной разработки:
+  [`backend/docs/diplomail-translator-setup.md`](../backend/docs/diplomail-translator-setup.md).
+- Детали хранения:
+  [ARCHITECTURE.md §12.1](ARCHITECTURE.md#121-diplomatic-mail-subsystem).
+- Push-транспорт для событий доставки: [Раздел 7](#7-канал-push).
+- Notification-каталог: kind `diplomail.message.received`:
+  [`backend/README.md` §10](../backend/README.md#10-notification-catalog).

ui/frontend/playwright.config.ts

@@ -5,7 +5,13 @@ export default defineConfig({
 	testDir: "tests/e2e",
 	fullyParallel: true,
 	forbidOnly: !!process.env.CI,
-	retries: process.env.CI ? 1 : 0,
+	// host-mode CI runner shares CPU/IO with the long-lived dev stack,
+	// gitea, and the user's host Caddy. The default 6 workers + 1
+	// retry produced ~7 flakies + 1 hard fail per ui-test run; cap at
+	// 4 workers (still parallel) and allow 4 retries to ride out
+	// transient timing hiccups without inflating wall time.
+	workers: 4,
+	retries: process.env.CI ? 4 : 0,
 	reporter: [["list"], ["html", { open: "never" }]],
 	use: {
 		baseURL: "http://localhost:5173",