feat(export): server-rendered artifacts behind one signed download URL

The finished-game export now works identically on every platform: the
client mints a signed relative URL (game.export_url) carrying its date
locale, IANA time zone and localized non-play labels, resolves it
against its own origin and hands it to the platform's native download —
Telegram downloadFile, VKWebAppDownloadFile, or a plain browser anchor
(also the desktop VK iframe). Both artifacts ride the route: the .gcg
text (no more clipboard mode, except the legacy pre-8.0 Telegram
fallback) and the PNG of the final position.

The PNG is rasterized by a new internal 'renderer' sidecar (node:22-slim
+ skia-canvas + baked Liberation/Noto Color Emoji fonts) executing the
SAME ui/src/lib/gameimage.ts the web project unit-tests, bundled at
image build time — one renderer, no drift; the browser no longer draws
or delivers bytes itself. The backend rebuilds the render payload from
the journal + engine.AlphabetTable, verifies the HMAC (10-minute TTL,
BACKEND_EXPORT_SIGN_KEY, constant-time, uniform 404s) on its public
group, and streams the artifact as a named attachment; the gateway
forwards /dl/* behind the per-IP public rate limiter (caddy @gateway
matcher extended — the landing catch-all trap).

Deploy: renderer service (compose + prod overlay + roll before backend
+ prod push list), EXPORT_SIGN_KEY env (TEST_/PROD_ secrets), CI runs
the sidecar smoke in the ui job. Docs: ARCHITECTURE export-delivery
section, FUNCTIONAL(+_ru), UI_DESIGN, TESTING, deploy/README.

.gitea/workflows/ci.yaml

@@ -73,6 +73,9 @@ jobs:
             go=false; ui=false
             if echo "$files" | grep -qE '^(backend/|pkg/|gateway/|platform/|loadtest/|go\.work)'; then go=true; fi
             if echo "$files" | grep -qE '^ui/'; then ui=true; fi
+            # The render sidecar bundles ui/src/lib, so its dir rides the ui lane (the
+            # deploy's compose build picks it up either way).
+            if echo "$files" | grep -qE '^renderer/'; then ui=true; fi
             # A workflow or deploy change re-runs everything as a safety net.
             if echo "$files" | grep -qE '^(\.gitea/workflows/|deploy/)'; then go=true; ui=true; fi
           else
@@ -199,6 +202,14 @@ jobs:
       - name: Bundle-size budget
         run: node scripts/bundle-size.mjs
 
+      # The render sidecar executes the shared ui/src/lib/gameimage.ts on skia-canvas;
+      # its smoke test guards the bundling + skia seam (docs/TESTING.md).
+      - name: Render sidecar test
+        working-directory: renderer
+        run: |
+          pnpm install --frozen-lockfile
+          pnpm test
+
       - name: Install Playwright browsers
         run: pnpm exec playwright install chromium webkit
         timeout-minutes: 5
@@ -319,6 +330,8 @@ jobs:
           # VK Mini App protected key (offline HMAC for the launch-param signature); empty
           # leaves the VK auth path (auth.vk) disabled until the operator sets the secret.
           GATEWAY_VK_APP_SECRET: ${{ secrets.TEST_GATEWAY_VK_APP_SECRET }}
+          # Signs the finished-game export download URLs (backend + compose interpolation).
+          EXPORT_SIGN_KEY: ${{ secrets.TEST_EXPORT_SIGN_KEY }}
           GM_BASICAUTH_USER: ${{ vars.TEST_GM_BASICAUTH_USER }}
           GRAFANA_ROOT_URL: ${{ vars.TEST_GRAFANA_ROOT_URL }}
           CADDY_SITE_ADDRESS: ${{ vars.TEST_CADDY_SITE_ADDRESS }}

.gitea/workflows/prod-deploy.yaml

@@ -59,10 +59,10 @@ jobs:
         working-directory: deploy
         run: |
           export TAG="${{ steps.ver.outputs.tag }}" APP_VERSION="${{ steps.ver.outputs.tag }}" SCRABBLE_CONFIG_DIR=.
-          # The four main-stack images via compose (reuses the build args, incl. VERSION);
+          # The main-stack images via compose (reuses the build args, incl. VERSION);
           # the bot separately, since it is profiled out of the prod compose.
           docker compose -f docker-compose.yml -f docker-compose.prod.yml build
-          docker compose -f docker-compose.yml -f docker-compose.prod.yml push backend gateway landing validator
+          docker compose -f docker-compose.yml -f docker-compose.prod.yml push backend gateway landing validator renderer
           docker build -f ../platform/telegram/Dockerfile --target bot --build-arg VERSION="$TAG" -t "$REGISTRY/scrabble-telegram-bot:$TAG" ..
           docker push "$REGISTRY/scrabble-telegram-bot:$TAG"
 
@@ -84,6 +84,8 @@ jobs:
       GRAFANA_ADMIN_PASSWORD: ${{ secrets.PROD_GRAFANA_ADMIN_PASSWORD }}
       TELEGRAM_BOT_TOKEN: ${{ secrets.PROD_TELEGRAM_BOT_TOKEN }}
       GATEWAY_VK_APP_SECRET: ${{ secrets.PROD_GATEWAY_VK_APP_SECRET }}
+      # Signs the finished-game export download URLs (backend BACKEND_EXPORT_SIGN_KEY).
+      EXPORT_SIGN_KEY: ${{ secrets.PROD_EXPORT_SIGN_KEY }}
       PROD_BOTLINK_CA: ${{ secrets.PROD_BOTLINK_CA }}
       PROD_BOTLINK_GATEWAY_CERT: ${{ secrets.PROD_BOTLINK_GATEWAY_CERT }}
       PROD_BOTLINK_GATEWAY_KEY: ${{ secrets.PROD_BOTLINK_GATEWAY_KEY }}
@@ -139,6 +141,7 @@ jobs:
           export TELEGRAM_BOT_TOKEN='$TELEGRAM_BOT_TOKEN'
           export TELEGRAM_MINIAPP_URL='$TELEGRAM_MINIAPP_URL'
           export GATEWAY_VK_APP_SECRET='$GATEWAY_VK_APP_SECRET'
+          export EXPORT_SIGN_KEY='$EXPORT_SIGN_KEY'
           export GATEWAY_ABUSE_BAN_ENABLED='true'
           EOF
           printf '%s\n' "$PROD_BOTLINK_CA"           > stage/certs-main/ca.crt

CLAUDE.md

@@ -125,6 +125,7 @@ gateway/                     # module scrabble/gateway: Connect-RPC edge, embeds
 ui/                          # Svelte + Vite SPA + landing (Node project, not in go.work)
 pkg/                         # shared: telemetry, version, wire/FlatBuffers, proto, mtls
 platform/telegram/           # Telegram side-service: cmd/validator (HMAC, no VPN) + cmd/bot (Bot API; dials gateway over reverse mTLS bot-link)
+renderer/                    # image-render sidecar (Node + skia-canvas): runs ui/src/lib/gameimage.ts server-side for the finished-game PNG export
 loadtest/                    # module scrabble/loadtest: the load/stress harness
 docs/  .gitea/workflows/  CLAUDE.md  README.md
 backend/Dockerfile gateway/Dockerfile platform/telegram/Dockerfile loadtest/Dockerfile  # multi-stage distroless; gateway/Dockerfile has the `landing` target, platform/telegram/Dockerfile has `validator`+`bot` targets

backend/cmd/backend/main.go

@@ -33,6 +33,7 @@ import (
 	"scrabble/backend/internal/postgres"
 	"scrabble/backend/internal/pushgrpc"
 	"scrabble/backend/internal/ratewatch"
+	"scrabble/backend/internal/render"
 	"scrabble/backend/internal/robot"
 	"scrabble/backend/internal/server"
 	"scrabble/backend/internal/session"
@@ -232,6 +233,13 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 	// block and the banner admin console section.
 	adsSvc := ads.NewService(ads.NewStore(db))
 
+	// The image-render sidecar client for the PNG export artifact; nil (PNG
+	// download answers 404) when BACKEND_RENDERER_URL is unset.
+	var renderer *render.Client
+	if cfg.RendererURL != "" {
+		renderer = render.New(cfg.RendererURL)
+	}
+
 	srv := server.New(cfg.HTTPAddr, server.Deps{
 		Logger:        logger,
 		DB:            db,
@@ -253,6 +261,8 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 		BanView:       banView,
 		Ads:           adsSvc,
 		Notifier:      hub,
+		ExportSignKey: cfg.ExportSignKey,
+		Renderer:      renderer,
 	})
 	pushSrv := pushgrpc.NewServer(cfg.GRPCAddr, hub, logger)
 

backend/internal/config/config.go

@@ -51,6 +51,12 @@ type Config struct {
 	// GuestRetention is the account age past which an unused guest (no game seat)
 	// is eligible for deletion by the reaper.
 	GuestRetention time.Duration
+	// ExportSignKey signs the finished-game export download URLs. Empty leaves
+	// the export-URL endpoints disabled (503 on mint, 404 on download).
+	ExportSignKey string
+	// RendererURL is the base URL of the internal image-render sidecar (e.g.
+	// http://renderer:8090). Empty disables the PNG export artifact.
+	RendererURL string
 }
 
 // Defaults applied when the corresponding environment variable is unset.
@@ -151,6 +157,8 @@ func Load() (Config, error) {
 		ConnectorAddr:     os.Getenv("BACKEND_CONNECTOR_ADDR"),
 		GuestReapInterval: guestReapInterval,
 		GuestRetention:    guestRetention,
+		ExportSignKey:     os.Getenv("BACKEND_EXPORT_SIGN_KEY"),
+		RendererURL:       os.Getenv("BACKEND_RENDERER_URL"),
 	}
 	if err := c.validate(); err != nil {
 		return Config{}, err

backend/internal/game/service.go

@@ -1363,30 +1363,53 @@ func (svc *Service) SetupDraws(ctx context.Context, gameID uuid.UUID) ([]SetupDr
 	return svc.store.SetupDraws(ctx, gameID)
 }
 
-// ExportGCG renders a game as GCG text from the journal alone (no dictionary). It
+// ExportView returns a finished game with its journal and per-seat display names —
-// is allowed only on a finished game: exporting an in-progress game would leak the
+// the material every export artifact (the GCG text, the PNG render payload) is built
-// full move journal mid-play, so an active game yields ErrGameActive.
+// from. It is allowed only on a finished game: exporting an in-progress game would
-func (svc *Service) ExportGCG(ctx context.Context, gameID uuid.UUID) (string, error) {
+// leak the full move journal mid-play, so an active game yields ErrGameActive. In an
+// honest-AI game the robot seat is labelled "AI", not its pool name.
+func (svc *Service) ExportView(ctx context.Context, gameID uuid.UUID) (Game, []HistoryMove, []string, error) {
 	g, err := svc.store.GetGame(ctx, gameID)
 	if err != nil {
-		return "", err
+		return Game{}, nil, nil, err
 	}
 	if g.Status != StatusFinished {
-		return "", ErrGameActive
+		return Game{}, nil, nil, ErrGameActive
 	}
 	moves, err := svc.store.GetJournal(ctx, gameID)
 	if err != nil {
-		return "", err
+		return Game{}, nil, nil, err
 	}
 	names := svc.seatNames(ctx, g)
 	if g.VsAI {
-		// Label the robot seat "AI" in an honest-AI game's export, not its pool name.
 		for _, s := range g.Seats {
 			if robot, err := svc.accounts.IsRobot(ctx, s.AccountID); err == nil && robot {
 				names[s.Seat] = aiPlayerName
 			}
 		}
 	}
+	return g, moves, names, nil
+}
+
+// EnsureExportable reports whether a game may be exported (it exists and is
+// finished) without loading the journal — the export-URL mint check.
+func (svc *Service) EnsureExportable(ctx context.Context, gameID uuid.UUID) error {
+	g, err := svc.store.GetGame(ctx, gameID)
+	if err != nil {
+		return err
+	}
+	if g.Status != StatusFinished {
+		return ErrGameActive
+	}
+	return nil
+}
+
+// ExportGCG renders a game as GCG text from the journal alone (no dictionary).
+func (svc *Service) ExportGCG(ctx context.Context, gameID uuid.UUID) (string, error) {
+	g, moves, names, err := svc.ExportView(ctx, gameID)
+	if err != nil {
+		return "", err
+	}
 	return writeGCG(g, names, moves), nil
 }
 

backend/internal/render/render.go

@@ -0,0 +1,61 @@
+// Package render is the backend's client for the internal image-render sidecar: it POSTs
+// a finished game's export payload and receives the rasterized PNG. The sidecar runs the
+// same drawing code the web client unit-tests (ui/src/lib/gameimage.ts on skia-canvas);
+// authentication and the signed public URL live in the server layer — this client only
+// carries bytes.
+package render
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+)
+
+// maxPNG caps a render response; a scale-2 export of the largest plausible game is well
+// under 2 MiB, so anything bigger is a sidecar malfunction, not a valid image.
+const maxPNG = 8 << 20
+
+// Client calls the render sidecar over the internal network.
+type Client struct {
+	base string
+	http *http.Client
+}
+
+// New returns a client for the sidecar at baseURL (e.g. http://renderer:8090). A render
+// of a full game takes well under a second; the timeout leaves room for a cold start.
+func New(baseURL string) *Client {
+	return &Client{base: baseURL, http: &http.Client{Timeout: 15 * time.Second}}
+}
+
+// Render posts payload (the JSON request shape the sidecar consumes) and returns the PNG.
+func (c *Client) Render(ctx context.Context, payload any) ([]byte, error) {
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return nil, fmt.Errorf("render: marshal payload: %w", err)
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.base+"/render", bytes.NewReader(body))
+	if err != nil {
+		return nil, fmt.Errorf("render: build request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+	resp, err := c.http.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("render: %w", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("render: sidecar status %d", resp.StatusCode)
+	}
+	png, err := io.ReadAll(io.LimitReader(resp.Body, maxPNG+1))
+	if err != nil {
+		return nil, fmt.Errorf("render: read response: %w", err)
+	}
+	if len(png) > maxPNG {
+		return nil, fmt.Errorf("render: response exceeds %d bytes", maxPNG)
+	}
+	return png, nil
+}

backend/internal/server/export.go

@@ -0,0 +1,306 @@
+// Finished-game export downloads: a signed, short-lived, relative URL minted for a
+// participant and later fetched with no credentials at all — the platforms' native
+// download calls (Telegram downloadFile, VKWebAppDownloadFile, a plain browser
+// anchor) strip cookies and headers, so the HMAC in the URL is the whole grant.
+// The client resolves the relative path against its own origin; the edge routes
+// /dl/* to the gateway, which forwards it here (/api/v1/public/dl/...).
+package server
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/base64"
+	"fmt"
+	"net/http"
+	"net/url"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+	"go.uber.org/zap"
+
+	"scrabble/backend/internal/engine"
+	"scrabble/backend/internal/game"
+)
+
+// exportURLTTL is how long a minted download URL stays valid. Long enough for the
+// platform's download dialog and a retry, short enough that a leaked link dies fast.
+const exportURLTTL = 10 * time.Minute
+
+// Query/label size caps: the presentation params ride the signed URL, so they are
+// bounded defensively (they only ever hold a BCP-47 tag and four short UI words).
+const (
+	maxDateLocaleLen = 35
+	maxLabelsLen     = 120
+	maxTimeZoneLen   = 50
+)
+
+// exportActionOrder fixes the position of each non-play move label in the `t` CSV.
+var exportActionOrder = [4]string{"pass", "exchange", "resign", "timeout"}
+
+// signExport computes the URL signature over the canonical parameter string. The
+// canonical form is independent of the public path prefix, so the gateway may mount
+// the route anywhere.
+func (s *Server) signExport(gameID, kind, exp, dateLocale, timeZone, labels string) string {
+	mac := hmac.New(sha256.New, s.exportKey)
+	fmt.Fprintf(mac, "%s|%s|%s|%s|%s|%s", gameID, kind, exp, dateLocale, timeZone, labels)
+	return base64.RawURLEncoding.EncodeToString(mac.Sum(nil))
+}
+
+// exportURLDTO is the minted link: a relative signed path plus the download filename.
+type exportURLDTO struct {
+	Path     string `json:"path"`
+	Filename string `json:"filename"`
+}
+
+// handleExportURL mints the signed download path for a finished game's artifact.
+// GET /api/v1/user/games/:id/export-url?kind=png|gcg&dl=<date-locale>&tz=<IANA zone>&t=<labels CSV>
+func (s *Server) handleExportURL(c *gin.Context) {
+	if len(s.exportKey) == 0 {
+		c.AbortWithStatusJSON(http.StatusServiceUnavailable,
+			errorResponse{Error: errorBody{Code: "export_unavailable", Message: "export signing is not configured"}})
+		return
+	}
+	_, gameID, ok := s.userGame(c)
+	if !ok {
+		return
+	}
+	kind := c.Query("kind")
+	if kind != "png" && kind != "gcg" {
+		abortBadRequest(c, "invalid kind")
+		return
+	}
+	dateLocale := c.Query("dl")
+	timeZone := c.Query("tz")
+	labels := c.Query("t")
+	if len(dateLocale) > maxDateLocaleLen || len(labels) > maxLabelsLen || len(timeZone) > maxTimeZoneLen {
+		abortBadRequest(c, "presentation params too long")
+		return
+	}
+	if err := s.games.EnsureExportable(c.Request.Context(), gameID); err != nil {
+		s.abortErr(c, err)
+		return
+	}
+	exp := strconv.FormatInt(time.Now().Add(exportURLTTL).Unix(), 10)
+	sig := s.signExport(gameID.String(), kind, exp, dateLocale, timeZone, labels)
+	q := url.Values{"e": {exp}, "s": {sig}}
+	if dateLocale != "" {
+		q.Set("l", dateLocale)
+	}
+	if timeZone != "" {
+		q.Set("z", timeZone)
+	}
+	if labels != "" {
+		q.Set("t", labels)
+	}
+	c.JSON(http.StatusOK, exportURLDTO{
+		Path:     "/dl/" + gameID.String() + "/" + kind + "?" + q.Encode(),
+		Filename: exportFilename(gameID, kind),
+	})
+}
+
+func exportFilename(gameID uuid.UUID, kind string) string {
+	return "game-" + gameID.String()[:8] + "." + kind
+}
+
+// handleExportDownload serves a minted artifact. It is a public route: the signature
+// and expiry are the only authorization (see the package comment). Every failure is
+// a plain 404 so the endpoint is not a validity oracle.
+// GET /api/v1/public/dl/:id/:kind?e=&l=&z=&t=&s=
+func (s *Server) handleExportDownload(c *gin.Context) {
+	if len(s.exportKey) == 0 {
+		c.String(http.StatusNotFound, "not found")
+		return
+	}
+	gameID, err := uuid.Parse(c.Param("id"))
+	kind := c.Param("kind")
+	exp := c.Query("e")
+	dateLocale := c.Query("l")
+	timeZone := c.Query("z")
+	labels := c.Query("t")
+	sig := c.Query("s")
+	if err != nil || (kind != "png" && kind != "gcg") ||
+		len(dateLocale) > maxDateLocaleLen || len(labels) > maxLabelsLen || len(timeZone) > maxTimeZoneLen {
+		c.String(http.StatusNotFound, "not found")
+		return
+	}
+	want := s.signExport(gameID.String(), kind, exp, dateLocale, timeZone, labels)
+	if subtleNeq(sig, want) {
+		c.String(http.StatusNotFound, "not found")
+		return
+	}
+	if unix, err := strconv.ParseInt(exp, 10, 64); err != nil || time.Now().Unix() > unix {
+		c.String(http.StatusNotFound, "not found")
+		return
+	}
+
+	filename := exportFilename(gameID, kind)
+	if kind == "gcg" {
+		gcg, err := s.games.ExportGCG(c.Request.Context(), gameID)
+		if err != nil {
+			c.String(http.StatusNotFound, "not found")
+			return
+		}
+		serveAttachment(c, filename, "text/plain; charset=utf-8", []byte(gcg))
+		return
+	}
+
+	if s.renderer == nil {
+		c.String(http.StatusNotFound, "not found")
+		return
+	}
+	g, moves, names, err := s.games.ExportView(c.Request.Context(), gameID)
+	if err != nil {
+		c.String(http.StatusNotFound, "not found")
+		return
+	}
+	payload, err := renderPayload(g, moves, names, dateLocale, timeZone, labels, c.GetHeader("X-Public-Host"))
+	if err != nil {
+		s.log.Warn("export render payload", zap.Error(err))
+		c.String(http.StatusNotFound, "not found")
+		return
+	}
+	png, err := s.renderer.Render(c.Request.Context(), payload)
+	if err != nil {
+		s.log.Warn("export render", zap.Error(err))
+		c.String(http.StatusServiceUnavailable, "render unavailable")
+		return
+	}
+	serveAttachment(c, filename, "image/png", png)
+}
+
+// subtleNeq compares two signature strings in constant time.
+func subtleNeq(got, want string) bool {
+	return !hmac.Equal([]byte(got), []byte(want))
+}
+
+// serveAttachment writes bytes as a named file download.
+func serveAttachment(c *gin.Context, filename, contentType string, data []byte) {
+	c.Header("X-Content-Type-Options", "nosniff")
+	c.Header("Content-Disposition", `attachment; filename="`+sanitizeFilename(filename)+`"`)
+	c.Header("Cache-Control", "private, max-age=0")
+	c.Data(http.StatusOK, contentType, data)
+}
+
+// --- the render-sidecar request payload (the ui-model shapes drawGameImage consumes) ---
+
+type renderSeatJSON struct {
+	Seat        int    `json:"seat"`
+	AccountID   string `json:"accountId"`
+	DisplayName string `json:"displayName"`
+	Score       int    `json:"score"`
+	HintsUsed   int    `json:"hintsUsed"`
+	IsWinner    bool   `json:"isWinner"`
+}
+
+type renderGameJSON struct {
+	ID               string           `json:"id"`
+	Variant          string           `json:"variant"`
+	Status           string           `json:"status"`
+	Players          int              `json:"players"`
+	LastActivityUnix int64            `json:"lastActivityUnix"`
+	Seats            []renderSeatJSON `json:"seats"`
+}
+
+type renderTileJSON struct {
+	Row    int    `json:"row"`
+	Col    int    `json:"col"`
+	Letter string `json:"letter"`
+	Blank  bool   `json:"blank"`
+}
+
+type renderMoveJSON struct {
+	Player  int              `json:"player"`
+	Action  string           `json:"action"`
+	Dir     string           `json:"dir"`
+	MainRow int              `json:"mainRow"`
+	MainCol int              `json:"mainCol"`
+	Tiles   []renderTileJSON `json:"tiles"`
+	Words   []string         `json:"words"`
+	Count   int              `json:"count"`
+	Score   int              `json:"score"`
+	Total   int              `json:"total"`
+}
+
+type renderAlphaJSON struct {
+	Index  int    `json:"index"`
+	Letter string `json:"letter"`
+	Value  int    `json:"value"`
+}
+
+type renderRequestJSON struct {
+	Game       renderGameJSON    `json:"game"`
+	Moves      []renderMoveJSON  `json:"moves"`
+	Alphabet   []renderAlphaJSON `json:"alphabet"`
+	Labels     map[string]string `json:"labels"`
+	DateLocale string            `json:"dateLocale"`
+	TimeZone   string            `json:"timeZone"`
+	Hostname   string            `json:"hostname"`
+}
+
+// renderPayload assembles the sidecar request from the export view. Letters are
+// upper-cased for display exactly as the client codec does; the localized non-play
+// labels arrive as a positional CSV (see exportActionOrder) minted into the URL.
+func renderPayload(g game.Game, moves []game.HistoryMove, names []string, dateLocale, timeZone, labelsCSV, host string) (renderRequestJSON, error) {
+	alpha, err := engine.AlphabetTable(g.Variant)
+	if err != nil {
+		return renderRequestJSON{}, fmt.Errorf("alphabet for %s: %w", g.Variant, err)
+	}
+	req := renderRequestJSON{
+		Game: renderGameJSON{
+			ID:      g.ID.String(),
+			Variant: g.Variant.String(),
+			Status:  g.Status,
+			Players: g.Players,
+		},
+		Labels:     map[string]string{},
+		DateLocale: dateLocale,
+		TimeZone:   timeZone,
+		Hostname:   host,
+	}
+	finished := g.UpdatedAt
+	if g.FinishedAt != nil {
+		finished = *g.FinishedAt
+	}
+	req.Game.LastActivityUnix = finished.Unix()
+	for _, st := range g.Seats {
+		name := st.DisplayName
+		if st.Seat < len(names) {
+			name = names[st.Seat]
+		}
+		req.Game.Seats = append(req.Game.Seats, renderSeatJSON{
+			Seat: st.Seat, AccountID: st.AccountID.String(), DisplayName: name,
+			Score: st.Score, HintsUsed: st.HintsUsed, IsWinner: st.IsWinner,
+		})
+	}
+	for _, m := range moves {
+		mv := renderMoveJSON{
+			Player: m.Seat, Action: m.Action, Dir: m.Dir,
+			MainRow: m.MainRow, MainCol: m.MainCol,
+			Words: make([]string, 0, len(m.Words)),
+			Count: len(m.Exchanged), Score: m.Score, Total: m.RunningTotal,
+			Tiles: make([]renderTileJSON, 0, len(m.Tiles)),
+		}
+		for _, w := range m.Words {
+			mv.Words = append(mv.Words, strings.ToUpper(w))
+		}
+		for _, t := range m.Tiles {
+			mv.Tiles = append(mv.Tiles, renderTileJSON{Row: t.Row, Col: t.Col, Letter: strings.ToUpper(t.Letter), Blank: t.Blank})
+		}
+		req.Moves = append(req.Moves, mv)
+	}
+	for _, a := range alpha {
+		req.Alphabet = append(req.Alphabet, renderAlphaJSON{Index: int(a.Index), Letter: strings.ToUpper(a.Letter), Value: a.Value})
+	}
+	if labelsCSV != "" {
+		parts := strings.Split(labelsCSV, ",")
+		for i, action := range exportActionOrder {
+			if i < len(parts) && parts[i] != "" {
+				req.Labels[action] = parts[i]
+			}
+		}
+	}
+	return req, nil
+}

backend/internal/server/export_test.go

@@ -0,0 +1,148 @@
+package server
+
+import (
+	"net/http"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/google/uuid"
+
+	"scrabble/backend/internal/account"
+	"scrabble/backend/internal/engine"
+	"scrabble/backend/internal/game"
+	"scrabble/backend/internal/session"
+)
+
+// newExportServer is the routing harness with a signing key installed, so the
+// pre-service branches of the export endpoints are reachable.
+func newExportServer() *Server {
+	return New(":0", Deps{
+		Sessions:      &session.Service{},
+		Accounts:      &account.Store{},
+		Games:         &game.Service{},
+		ExportSignKey: "test-key",
+	})
+}
+
+func TestSignExportIsDeterministicAndTamperEvident(t *testing.T) {
+	s := newExportServer()
+	sig := s.signExport("g1", "png", "123", "ru", "Europe/Moscow", "пас,обмен")
+	if sig != s.signExport("g1", "png", "123", "ru", "Europe/Moscow", "пас,обмен") {
+		t.Fatal("same inputs produced different signatures")
+	}
+	for _, tampered := range []string{
+		s.signExport("g2", "png", "123", "ru", "Europe/Moscow", "пас,обмен"),
+		s.signExport("g1", "gcg", "123", "ru", "Europe/Moscow", "пас,обмен"),
+		s.signExport("g1", "png", "124", "ru", "Europe/Moscow", "пас,обмен"),
+		s.signExport("g1", "png", "123", "en", "Europe/Moscow", "пас,обмен"),
+		s.signExport("g1", "png", "123", "ru", "UTC", "пас,обмен"),
+		s.signExport("g1", "png", "123", "ru", "Europe/Moscow", "пас"),
+	} {
+		if tampered == sig {
+			t.Fatal("tampered input produced the same signature")
+		}
+	}
+}
+
+func TestExportURLWithoutKeyIs503(t *testing.T) {
+	s := New(":0", Deps{Sessions: &session.Service{}, Accounts: &account.Store{}, Games: &game.Service{}})
+	rec := do(t, s, http.MethodGet, "/api/v1/user/games/"+uuid.NewString()+"/export-url?kind=png", "",
+		map[string]string{"X-User-ID": uuid.NewString()})
+	if rec.Code != http.StatusServiceUnavailable {
+		t.Fatalf("mint without key = %d, want 503", rec.Code)
+	}
+}
+
+func TestExportURLRejectsBadParams(t *testing.T) {
+	s := newExportServer()
+	uid := map[string]string{"X-User-ID": uuid.NewString()}
+	gid := uuid.NewString()
+
+	if rec := do(t, s, http.MethodGet, "/api/v1/user/games/"+gid+"/export-url?kind=exe", "", uid); rec.Code != http.StatusBadRequest {
+		t.Fatalf("bad kind = %d, want 400", rec.Code)
+	}
+	long := strings.Repeat("x", maxLabelsLen+1)
+	if rec := do(t, s, http.MethodGet, "/api/v1/user/games/"+gid+"/export-url?kind=png&t="+long, "", uid); rec.Code != http.StatusBadRequest {
+		t.Fatalf("oversized labels = %d, want 400", rec.Code)
+	}
+}
+
+func TestExportDownloadRejectsBadSignatures(t *testing.T) {
+	s := newExportServer()
+	gid := uuid.NewString()
+	exp := strconv.FormatInt(time.Now().Add(time.Minute).Unix(), 10)
+
+	// A wrong signature never reaches the domain (404 before any service call).
+	url := "/api/v1/public/dl/" + gid + "/png?e=" + exp + "&s=forged"
+	if rec := do(t, s, http.MethodGet, url, "", nil); rec.Code != http.StatusNotFound {
+		t.Fatalf("forged signature = %d, want 404", rec.Code)
+	}
+
+	// A valid signature over an EXPIRED timestamp is refused the same way.
+	old := strconv.FormatInt(time.Now().Add(-time.Minute).Unix(), 10)
+	url = "/api/v1/public/dl/" + gid + "/png?e=" + old + "&s=" + s.signExport(gid, "png", old, "", "", "")
+	if rec := do(t, s, http.MethodGet, url, "", nil); rec.Code != http.StatusNotFound {
+		t.Fatalf("expired link = %d, want 404", rec.Code)
+	}
+
+	// An unknown kind is refused before signature checks.
+	url = "/api/v1/public/dl/" + gid + "/exe?e=" + exp + "&s=x"
+	if rec := do(t, s, http.MethodGet, url, "", nil); rec.Code != http.StatusNotFound {
+		t.Fatalf("bad kind = %d, want 404", rec.Code)
+	}
+}
+
+func TestRenderPayloadMapsTheExportView(t *testing.T) {
+	gid := uuid.New()
+	finished := time.Unix(1_782_997_629, 0)
+	g := game.Game{
+		ID:         gid,
+		Variant:    engine.VariantRussianScrabble,
+		Status:     game.StatusFinished,
+		Players:    2,
+		FinishedAt: &finished,
+		Seats: []game.Seat{
+			{Seat: 0, Score: 42, IsWinner: true, DisplayName: "snapshot"},
+			{Seat: 1, Score: 30},
+		},
+	}
+	moves := []game.HistoryMove{
+		{
+			Seat: 0, Action: "play", Dir: "H", MainRow: 7, MainCol: 4,
+			Tiles: []engine.TileRecord{{Row: 7, Col: 4, Letter: "ч", Blank: false}},
+			Words: []string{"чика"}, Score: 9, RunningTotal: 9,
+		},
+		{Seat: 1, Action: "exchange", Exchanged: []string{"а", "б"}, RunningTotal: 0},
+	}
+	names := []string{"Аня", "Боб"}
+
+	p, err := renderPayload(g, moves, names, "ru", "Europe/Moscow", "пас,обмен,сдался,таймаут", "erudit-game.ru")
+	if err != nil {
+		t.Fatalf("renderPayload: %v", err)
+	}
+	if p.Game.LastActivityUnix != finished.Unix() {
+		t.Fatalf("lastActivityUnix = %d, want %d", p.Game.LastActivityUnix, finished.Unix())
+	}
+	if p.Game.Seats[0].DisplayName != "Аня" || !p.Game.Seats[0].IsWinner {
+		t.Fatalf("seat 0 = %+v, want the resolved name and the winner flag", p.Game.Seats[0])
+	}
+	if p.Moves[0].Words[0] != "ЧИКА" || p.Moves[0].Tiles[0].Letter != "Ч" {
+		t.Fatalf("letters not upper-cased: %+v", p.Moves[0])
+	}
+	if p.Moves[1].Count != 2 {
+		t.Fatalf("exchange count = %d, want 2", p.Moves[1].Count)
+	}
+	if p.Labels["pass"] != "пас" || p.Labels["timeout"] != "таймаут" {
+		t.Fatalf("labels not mapped positionally: %v", p.Labels)
+	}
+	if len(p.Alphabet) == 0 || p.Hostname != "erudit-game.ru" || p.TimeZone != "Europe/Moscow" {
+		t.Fatalf("alphabet/hostname/zone missing: %d entries, host %q, tz %q", len(p.Alphabet), p.Hostname, p.TimeZone)
+	}
+	for _, a := range p.Alphabet {
+		if a.Letter != strings.ToUpper(a.Letter) {
+			t.Fatalf("alphabet letter %q not upper-cased", a.Letter)
+		}
+	}
+}

backend/internal/server/handlers.go

@@ -87,12 +87,17 @@ func (s *Server) registerRoutes() {
 		u.POST("/games/:id/complaint", s.handleComplaint)
 		u.GET("/games/:id/history", s.handleHistory)
 		u.GET("/games/:id/gcg", s.handleExportGCG)
+		u.GET("/games/:id/export-url", s.handleExportURL)
 		u.GET("/games/:id/draft", s.handleGetDraft)
 		u.PUT("/games/:id/draft", s.handleSaveDraft)
 		u.POST("/games/:id/hide", s.handleHideGame)
 		// Raw dictionary download for the client-side local move preview, keyed by
 		// the game's pinned (variant, version); immutable, so cached hard.
 		u.GET("/dict/:variant/:version", s.handleDictBytes)
+		// The signed finished-game export download — the only public data route:
+		// the URL's HMAC + expiry are the whole grant (export.go), because the
+		// platforms' native download calls carry no credentials.
+		s.public.GET("/dl/:id/:kind", s.handleExportDownload)
 	}
 	if s.feedback != nil {
 		u.POST("/feedback", s.handleFeedbackSubmit)

backend/internal/server/server.go

@@ -29,6 +29,7 @@ import (
 	"scrabble/backend/internal/lobby"
 	"scrabble/backend/internal/notify"
 	"scrabble/backend/internal/ratewatch"
+	"scrabble/backend/internal/render"
 	"scrabble/backend/internal/session"
 	"scrabble/backend/internal/social"
 	"scrabble/backend/internal/telemetry"
@@ -96,6 +97,12 @@ type Deps struct {
 	// signal the banner/hint/role console actions emit. A nil Notifier discards
 	// them (notify.Nop).
 	Notifier notify.Publisher
+	// ExportSignKey signs the finished-game export download URLs (export.go). An
+	// empty key leaves the export-URL endpoints answering 503/404.
+	ExportSignKey string
+	// Renderer is the image-render sidecar client for the PNG export artifact. A
+	// nil Renderer makes the PNG download answer 404 (the GCG artifact still works).
+	Renderer *render.Client
 }
 
 // Server owns the gin engine, the underlying HTTP server and the readiness
@@ -124,6 +131,8 @@ type Server struct {
 	ads         *ads.Service
 	notifier    notify.Publisher
 	console     *adminconsole.Renderer
+	exportKey   []byte
+	renderer    *render.Client
 
 	public   *gin.RouterGroup
 	user     *gin.RouterGroup
@@ -173,8 +182,12 @@ func New(addr string, deps Deps) *Server {
 		banview:       deps.BanView,
 		ads:           deps.Ads,
 		notifier:      notifier,
+		renderer:      deps.Renderer,
 		http:          &http.Server{Addr: addr, Handler: engine},
 	}
+	if deps.ExportSignKey != "" {
+		s.exportKey = []byte(deps.ExportSignKey)
+	}
 	s.registerProbes(engine)
 	s.registerAPIGroups(engine)
 	s.registerRoutes()

deploy/.env.example

@@ -21,6 +21,11 @@ DICT_VERSION=v1.3.0
 # --- Logging ----------------------------------------------------------------
 LOG_LEVEL=info
 
+# --- Finished-game export ----------------------------------------------------
+# HMAC key signing the public export download URLs (/dl/*). Required; generate a
+# real contour value with `openssl rand -base64 32` (Gitea TEST_/PROD_EXPORT_SIGN_KEY).
+EXPORT_SIGN_KEY=dev-export-sign-key
+
 # --- Edge / caddy -----------------------------------------------------------
 # Test: ":80" (the host caddy terminates TLS and forwards to scrabble:80 on the
 # external `edge` network). Prod: a domain so caddy does its own ACME.

deploy/README.md

@@ -16,6 +16,7 @@ operational reference for **every environment variable**.
 | `landing` | built (`gateway/Dockerfile`, target `landing`) | Static landing page at `/` (caddy:2-alpine + the shared Vite build, `deploy/landing/Caddyfile`); absorbs stray public paths. |
 | `backend` | built (`backend/Dockerfile`) | Domain service; bakes in the DAWG dictionaries; runs migrations at boot. |
 | `postgres` | `postgres:17-alpine` | Database (named volume, `pg_isready` healthcheck). |
+| `renderer` | built (`renderer/Dockerfile`) | Finished-game image-render sidecar (Node + skia-canvas running the shared `ui/src/lib/gameimage.ts`); internal-only HTTP at `renderer:8090`, called by the backend for the PNG export artifact. |
 | `validator` | built (`platform/telegram/Dockerfile`, target `validator`) | Telegram HMAC validator (no VPN, no Bot API); internal gRPC at `validator:9091`. Game login depends only on this. |
 | `vpn` + `bot` | sidecar + built (`platform/telegram/Dockerfile`, target `bot`) | Telegram bot, gated to the **`telegram-local`** profile; egresses through the AmneziaWG sidecar and dials the gateway bot-link (mTLS) at `gateway:9443`. The test contour activates the profile; the prod **main** host omits it and runs the bot standalone on its **own host** (`docker-compose.bot.yml`, no VPN — native Bot API egress). |
 | `otelcol` | `otel/opentelemetry-collector-contrib` | OTLP/gRPC `:4317` → Prometheus scrape (`:9464`) + Tempo. |
@@ -62,6 +63,7 @@ compose binds from this directory.
 | `POSTGRES_PASSWORD` | secret | Postgres password (also embedded in `BACKEND_POSTGRES_DSN`). |
 | `GM_BASICAUTH_HASH` | secret | bcrypt hash gating `/_gm` (admin console + Grafana). Generate with `docker run --rm caddy:2-alpine caddy hash-password --plaintext '<pw>'`. |
 | `TELEGRAM_MINIAPP_URL` | variable | The Mini App URL the bot hands out in deep links / buttons. |
+| `EXPORT_SIGN_KEY` | secret | HMAC key signing the public finished-game export download URLs (`/dl/*`). Generate with `openssl rand -base64 32`. |
 
 **Plus the bot token** — `TELEGRAM_BOT_TOKEN` (secret), shared by the validator (HMAC
 secret) and the bot (Bot API). It defaults to empty in compose, but both **fail at
@@ -106,7 +108,8 @@ at each other on the `internal` network — listed here so they are not mistaken
 missing config: `BACKEND_POSTGRES_DSN` (→ `postgres`, `search_path=backend`),
 `GATEWAY_BACKEND_HTTP_URL`/`_GRPC_ADDR` (→ `backend`),
 `GATEWAY_VALIDATOR_ADDR` (→ `validator:9091`), `BACKEND_CONNECTOR_ADDR` (→ the gateway
-bot-link relay `gateway:9092`), the bot's `TELEGRAM_GATEWAY_ADDR` (→ `gateway:9443`,
+bot-link relay `gateway:9092`), `BACKEND_RENDERER_URL` (→ `renderer:8090`, the image-render
+sidecar), the bot's `TELEGRAM_GATEWAY_ADDR` (→ `gateway:9443`,
 mTLS) with the `GATEWAY_BOTLINK_*` / `TELEGRAM_BOTLINK_*` cert paths under `/certs` (the
 mTLS material is generated by `deploy/gen-certs.sh`, gitignored, regenerated each
 deploy), and all services' `*_OTEL_*_EXPORTER=otlp` →
@@ -194,7 +197,7 @@ players arrive.
 
 **`PROD_` Gitea set** (mirrors `TEST_`, mapped onto the unprefixed names above) — secrets:
 `PROD_{POSTGRES_PASSWORD, GM_BASICAUTH_HASH, GRAFANA_ADMIN_PASSWORD, TELEGRAM_BOT_TOKEN,
-TELEGRAM_PROMO_BOT_TOKEN, REGISTRY_PASSWORD, SSH_KEY, SSH_KNOWN_HOSTS, BOTLINK_CA,
+TELEGRAM_PROMO_BOT_TOKEN, EXPORT_SIGN_KEY, REGISTRY_PASSWORD, SSH_KEY, SSH_KNOWN_HOSTS, BOTLINK_CA,
 BOTLINK_GATEWAY_CERT, BOTLINK_GATEWAY_KEY, BOTLINK_BOT_CERT, BOTLINK_BOT_KEY}`; variables:
 `PROD_{REGISTRY_USER, MAIN_HOST, TG_HOST, CADDY_SITE_ADDRESS, GM_BASICAUTH_USER,
 GRAFANA_ROOT_URL, LOG_LEVEL, DICT_VERSION, TELEGRAM_MINIAPP_URL, TELEGRAM_GAME_CHANNEL_ID,

deploy/caddy/Caddyfile

@@ -53,7 +53,7 @@
 	# The game SPA and the Connect edge are served by the gateway. Strip any
 	# client-supplied X-Scrabble-Honeypot here so the gateway only ever honours the
 	# tag the honeypot block sets below (a client cannot self-tag a real request).
-	@gateway path /app /app/* /telegram /telegram/* /vk /vk/* /dict/* /metrics/* /scrabble.edge.v1.Gateway/*
+	@gateway path /app /app/* /telegram /telegram/* /vk /vk/* /dict/* /dl/* /metrics/* /scrabble.edge.v1.Gateway/*
 	handle @gateway {
 		reverse_proxy gateway:8081 {
 			header_up -X-Scrabble-Honeypot

deploy/docker-compose.prod.yml

@@ -50,6 +50,13 @@ services:
         limits:
           memory: 384M
 
+  renderer:
+    image: ${REGISTRY:?set REGISTRY}/scrabble-renderer:${TAG:?set TAG}
+    deploy:
+      resources:
+        limits:
+          memory: 160M
+
   validator:
     image: ${REGISTRY:?set REGISTRY}/scrabble-telegram-validator:${TAG:?set TAG}
     deploy:

deploy/docker-compose.yml

@@ -61,6 +61,36 @@ services:
           memory: 512M
     networks: [internal]
 
+  # The finished-game image-render sidecar: internal-only, called by the backend for the
+  # PNG export artifact. It runs the same ui/src/lib/gameimage.ts the web client
+  # unit-tests, on skia-canvas (renderer/README.md). node:22-slim carries a shell, so —
+  # uniquely among the built services — it has a real container healthcheck the backend's
+  # depends_on gates on.
+  renderer:
+    container_name: scrabble-renderer
+    image: scrabble-renderer:latest
+    build:
+      context: ..
+      dockerfile: renderer/Dockerfile
+      args:
+        VERSION: ${APP_VERSION:-dev}
+    restart: unless-stopped
+    logging: *default-logging
+    environment:
+      RENDERER_PORT: "8090"
+    healthcheck:
+      test: ["CMD", "node", "-e", "fetch('http://127.0.0.1:8090/healthz').then((r)=>process.exit(r.ok?0:1)).catch(()=>process.exit(1))"]
+      interval: 10s
+      timeout: 3s
+      retries: 12
+    # A render peaks well under 100 MiB (a 2-MP canvas + skia); idle sits near 60 MiB.
+    deploy:
+      resources:
+        limits:
+          cpus: "1.0"
+          memory: 192M
+    networks: [internal]
+
   backend:
     container_name: scrabble-backend
     image: scrabble-backend:latest
@@ -80,9 +110,15 @@ services:
     depends_on:
       postgres:
         condition: service_healthy
+      renderer:
+        condition: service_healthy
     environment:
       # search_path=backend matches the migrations (00001 creates the schema).
       BACKEND_POSTGRES_DSN: postgres://${POSTGRES_USER:-scrabble}:${POSTGRES_PASSWORD}@postgres:5432/${POSTGRES_DB:-scrabble}?sslmode=disable&search_path=backend
+      # The finished-game export: the render sidecar address + the HMAC key signing the
+      # public download URLs (deploy env: TEST_/PROD_EXPORT_SIGN_KEY).
+      BACKEND_RENDERER_URL: http://renderer:8090
+      BACKEND_EXPORT_SIGN_KEY: ${EXPORT_SIGN_KEY:?set EXPORT_SIGN_KEY — the export download URL signing secret}
       # The pool caps at 25 conns (~28 backends) around 500 players; 40 gives headroom
       # for bursts. Postgres (2 cores / 512 MiB) handles it.
       BACKEND_POSTGRES_MAX_OPEN_CONNS: "40"

deploy/prod-deploy.sh

@@ -134,6 +134,7 @@ fi
 
 # Roll one service at a time, least -> most dependent; any failure rolls everything back.
 roll postgres  health_postgres                              || { rollback; exit 1; }
+roll renderer  health_running scrabble-renderer             || { rollback; exit 1; }
 roll backend   health_backend                               || { rollback; exit 1; }
 roll gateway   health_running scrabble-gateway              || { rollback; exit 1; }
 roll landing   health_landing                               || { rollback; exit 1; }

docs/ARCHITECTURE.md

@@ -785,11 +785,32 @@ the same rows and is likewise self-contained — we ship our own writer (the sol
 exposes none): the standard Poslfit dialect (UTF-8, `#player`/`#lexicon`
 pragmas, `8G`/`H8` coordinates, lower-case blanks, `.` pass-throughs, `-TILES`
 exchanges), plus `#note` lines for resignations and timeouts, which the standard
-does not cover. **GCG export is offered only on a finished game** (`game.ErrGameActive`
+does not cover. **Export is offered only on a finished game** (`game.ErrGameActive`
-otherwise), so an in-progress journal is never leaked mid-play; the client
+otherwise), so an in-progress journal is never leaked mid-play.
-shares the `.gcg` file via the Web Share API where available; an Android in-app WebView
+
-(Telegram / VK) has no Web Share and silently ignores an `<a download>`, so there it copies the GCG
+**Export delivery — the signed download URL.** Both export artifacts — the `.gcg` text
-text to the clipboard instead (the payload is tiny), and a plain desktop browser downloads the file.
+and the rendered **PNG of the final position** — travel one uniform route on every
+platform: the client calls the authenticated `game.export_url` op, the backend mints a
+**relative, HMAC-signed, short-lived path**
+(`/dl/{game}/{kind}?e=<expiry>&…&s=<HMAC-SHA256>`, 10-minute TTL,
+`BACKEND_EXPORT_SIGN_KEY`), and the client resolves it against its **own origin** (no
+service ever needs to know the public host) and hands it to the platform's native
+download: Telegram `downloadFile` (Bot API 8.0), `VKWebAppDownloadFile`, or a plain
+browser anchor elsewhere (including the desktop VK iframe). The GET is the gateway's
+**only unauthenticated data route** (`/dl/*` — in the caddy `@gateway` matcher and the
+per-IP public rate limiter): the native download calls carry no cookies or headers, so
+the URL's signature — verified by the backend on its `/api/v1/public` group in constant
+time, every failure a uniform 404 — is the whole grant, and minting requires an
+authenticated caller on a finished game. The PNG is rasterized on demand by the
+**`renderer` sidecar** (internal-only Node + skia-canvas running the same
+`ui/src/lib/gameimage.ts` the web project unit-tests — one renderer, no drift;
+`renderer/README.md`); the backend rebuilds the render payload from the journal +
+`engine.AlphabetTable`, and the client's date locale plus its UI-localized non-play
+labels ride the signed URL so the server render matches the player's presentation.
+Nothing is stored: the artifact is re-derived from the immutable finished journal on
+each GET. The only remaining platform branch is a legacy Telegram client predating
+`downloadFile`, where the GCG falls back to the old clipboard copy and the image option
+is not offered.
 
 The alphabet-on-the-wire transport does **not** touch this invariant: the live edge
 exchanges alphabet indices, but the persisted journal (and everything derived from it —

docs/FUNCTIONAL.md

@@ -326,29 +326,29 @@ journal; an AI game is throwaway). The format chooser is always the app's **own
 modal** — deliberately not Telegram's native popup, whose callback runs without
 user activation and silently breaks the share/clipboard delivery it leads to.
 
-The **image** is rendered on the client (Canvas 2D, always the light theme): the
+The **image** is rendered on the server (the internal render sidecar runs the same
-final board with classic coordinate axes A..O / 1..15 on the left — premium squares
+drawing module the web client tests; always the light theme): the final board with
-as plain colour fills, no text labels — and a compact per-seat scoresheet on the
+classic coordinate axes A..O / 1..15 on the left — premium squares as plain colour
-right: each seat's name and final score in the header (🏆 by the winner), then one
+fills, no text labels — and a compact per-seat scoresheet on the right: each seat's
-row per move carrying the main word's classic coordinate (an across play is
+name and final score in the header (🏆 by the winner), then one row per move
-row-first, `8G`; a down play column-first, `H8` — the GCG convention), the word and
+carrying the main word's classic coordinate (an across play is row-first, `8G`; a
-its points; extra words of a multi-word play ride a smaller second line, non-play
+down play column-first, `H8` — the GCG convention), the word and its points; extra
-moves show as localized notes (pass/exchange/resign/timeout), and a closing ± row
+words of a multi-word play ride a smaller second line, non-play moves show as
-shows the endgame rack settlement when there was one (the final scores are
+localized notes (pass/exchange/resign/timeout), and a closing ± row shows the
-authoritative — running totals alone do not include it). The footer stamps the site
+endgame rack settlement when there was one (the final scores are authoritative —
-host and the finish date in the device locale. The scoresheet typography is fixed;
+running totals alone do not include it). The footer stamps the site host and the
-a long game stretches the board (never below its minimum) so the image carries no
+finish date in the device locale. The scoresheet typography is fixed; a long game
-dead space.
+stretches the board (never below its minimum) so the image carries no dead space.
 
-Delivery per format: the **GCG** file is Web-Shared where the platform supports it;
+Delivery is **one route for both formats on every platform**: the app requests a
-on an Android in-app client (Telegram / VK), which has neither Web Share nor a
+signed, short-lived download link and hands it to the platform's native download —
-working file download, it copies the GCG text to the clipboard (with a confirming
+Telegram's download dialog, VK's `VKWebAppDownloadFile`, or an ordinary browser
-toast); otherwise it downloads the file. The **PNG** is Web-Shared or downloaded the
+file download elsewhere (including the desktop VK iframe). The link needs no login
-same way, but a binary image has no clipboard-text fallback at all — so the image
+to fetch (the platforms' download calls carry none), is valid for minutes, and
-option is currently **withheld inside the in-app webviews** (Telegram / VK) and
+serves the artifact as a named file attachment. The single exception is a legacy
-offered on the plain web and mobile browsers only; it returns there with the
+Telegram client without the download dialog (pre-Bot API 8.0): there the GCG falls
-server-rendered signed-URL delivery (Telegram `downloadFile` /
+back to the old clipboard copy (with the confirming toast) and the image option is
-`VKWebAppDownloadFile`). Statistics (durable accounts only):
+not offered. Statistics (durable accounts only):
 wins, losses, draws, max points in a game, and max points for a single move (the
 best play, which already includes every word it formed plus the all-tiles bonus). It
 also shows the player's **move count** (their plays — passes and exchanges do not

docs/FUNCTIONAL_ru.md

@@ -335,7 +335,8 @@ Telegram.
 сознательно не нативный попап Telegram: его коллбек приходит без user activation и
 молча ломает доставку через share/буфер, к которой ведёт выбор.
 
-**Картинка** рендерится на клиенте (Canvas 2D, всегда светлая тема): финальная
+**Картинка** рендерится на сервере (внутренний рендер-сайдкар исполняет тот же
+модуль отрисовки, что тестирует веб-клиент; всегда светлая тема): финальная
 доска с классическими осями координат A..O / 1..15 слева — бонус-клетки чистой
 цветовой заливкой, без текстовых подписей — и компактная таблица ходов по местам
 справа: в шапке имя и финальный счёт каждого места (🏆 у победителя), далее по
@@ -348,15 +349,15 @@ Telegram.
 и дата завершения в локали устройства. Типографика таблицы фиксирована; длинная
 партия растягивает доску (не ниже минимума), так что пустот на картинке нет.
 
-Доставка по форматам: файлом **GCG** клиент делится через Web Share там, где
+Доставка — **один путь для обоих форматов на любой платформе**: приложение
-платформа это поддерживает; в Android-приложении (Telegram / VK), где нет ни Web
+запрашивает подписанную короткоживущую ссылку на скачивание и передаёт её родному
-Share, ни рабочей загрузки файла, копирует текст GCG в буфер обмена (с
+механизму платформы — диалогу загрузки Telegram, `VKWebAppDownloadFile` у VK или
-подтверждающим тостом); иначе скачивает файл. **PNG** делится и скачивается так же,
+обычному браузерному скачиванию файла в остальных случаях (включая десктопный
-но у бинарной картинки нет текстового фолбэка через буфер вовсе — поэтому пункт
+iframe VK). Ссылка не требует логина при скачивании (родные загрузчики платформ его
-«картинка» пока **скрыт во встроенных webview** (Telegram / VK) и предлагается
+не несут), живёт минуты и отдаёт артефакт именованным файлом. Единственное
-только в обычном вебе и мобильных браузерах; туда он вернётся с серверным рендером
+исключение — устаревший клиент Telegram без диалога загрузки (до Bot API 8.0): там
-и доставкой по подписанному URL (Telegram `downloadFile` /
+GCG откатывается на прежнее копирование в буфер (с подтверждающим тостом), а пункт
-`VKWebAppDownloadFile`). Статистика (только у постоянных аккаунтов):
+«картинка» не предлагается. Статистика (только у постоянных аккаунтов):
 победы, поражения, ничьи, макс. очков за партию и макс. очков за один ход (лучший
 ход, уже включающий все образованные им слова и бонус за все фишки). Также
 показываются **число ходов** игрока (его выкладки — пасы и обмены не считаются) и

docs/TESTING.md

@@ -19,8 +19,15 @@ tests or touching CI.
   the FlatBuffers codecs (friend list, invitation, stats), the win-rate
   derivation and the GCG share/copy/download choice, plus Playwright specs against the
   mock for the friends screen (code issue/redeem, accept a request), the lobby
-  invitations section, the stats screen, profile editing, and the GCG export's
+  invitations section, the stats screen, profile editing, and the export chooser's
-  finished-only visibility.
+  finished-only visibility + its signed-URL download flow (route-intercepted).
+- **Render sidecar** — `renderer/` (Node + skia-canvas executing the shared
+  `ui/src/lib/gameimage.ts`) carries a `node --test` smoke: the committed fixture (a
+  real self-played 35-move game) must rasterize to a plausible PNG
+  (`pnpm -C renderer test`). The drawing module's pure parts (scoresheet, layout,
+  notation) stay unit-tested in `ui/` — the sidecar test guards only the
+  skia/bundling seam. Pixel goldens are deliberately avoided (fonts differ across
+  hosts).
 - **Local-eval conformance** — the client's on-device move preview (the ported
   dawg reader + validator, `ui/src/lib/dict`) is checked byte-for-byte against the
   authoritative Go engine. `backend/cmd/dictgen` and `backend/cmd/validategen` emit

docs/UI_DESIGN.md

@@ -407,28 +407,29 @@ enabled on the first, uncached load) and flip in place when an event refreshes t
   (the word(s) and the move score, no running total); the 📤 in the history header appears
   only once the game is finished — never in an honest-AI game (throwaway practice) — and
   opens the **format chooser**: always the app's own modal, never Telegram's native popup
-  (a `showPopup` callback carries no user activation, which silently breaks the
+  (a `showPopup` callback carries no user activation, which silently breaks gesture-gated
-  `navigator.share` / clipboard delivery it leads to — on-device finding). The accent button
+  delivery APIs — on-device finding). The accent button leads with the image, the GCG file
-  leads with the image where offered, the GCG file is the quiet alternative (GCG needs the
+  is the quiet alternative; both need the connection. Both formats travel the same
-  connection, the image renders locally). The GCG file goes by Web Share where available, a
+  signed-URL route: the app mints a relative link (`game.export_url`), resolves it against
-  clipboard copy in an Android in-app WebView (Telegram / VK, which has neither Web Share nor
+  its own origin and hands it to the platform's native download — Telegram `downloadFile`,
-  a working download), else a Blob download. The image option shows **only outside the in-app
+  `VKWebAppDownloadFile`, else a plain anchor download (also the desktop VK iframe, where
-  WebViews** for now (a binary PNG has no working route there — no Web Share, a dead
+  the bridge method is absent and the anchor works). A legacy Telegram client without
-  `<a download>`, a text-only clipboard, and the long-press menu mangles data: URLs); it
+  `downloadFile` keeps the old GCG clipboard copy and hides the image option. Confirming a
-  returns there with the server-rendered signed-URL delivery. Confirming a resign reveals
+  resign reveals the full board: it closes the history drawer (portrait) and zooms the
-  the full board: it closes the history drawer (portrait) and zooms the board out.
+  board out.
-- **Export image** (`lib/gameimage.ts`, Canvas 2D, dynamically imported): always the light
+- **Export image** (`lib/gameimage.ts` — the shared drawing module the render sidecar
-  palette (pinned constants mirroring `app.css`), the final board with classic axes A..O /
+  executes; the browser app no longer draws it): always the light palette (pinned constants
-  1..15, premium squares as plain colour fills (no text labels), tiles in the in-game style
+  mirroring `app.css`), the final board with classic axes A..O / 1..15, premium squares as
-  (bevel, letter top-left, value bottom-right, ✻ for an Erudit blank), no last-move
+  plain colour fills (no text labels), tiles in the in-game style (bevel, letter top-left,
-  highlight. The right column is the scoresheet: per-seat name over the final score (🏆 by
+  value bottom-right, ✻ for an Erudit blank), no last-move highlight. The right column is
-  the winner), one fixed-typography row per move — muted classic coordinate (across =
+  the scoresheet: per-seat name over the final score (🏆 by the winner), one
-  row-first `8G`, down = column-first `H8`), the main word, points right-aligned; extra
+  fixed-typography row per move — muted classic coordinate (across = row-first `8G`, down =
-  words of a multi-word play on a smaller second line; italic localized notes for
+  column-first `H8`), the main word, points right-aligned; extra words of a multi-word play
-  pass/exchange/resign/timeout; a closing muted ± row for the endgame rack settlement when
+  on a smaller second line; italic localized notes for pass/exchange/resign/timeout; a
-  present. Footer: `hostname · finish date` in the **device** locale. The scoresheet's
+  closing muted ± row for the endgame rack settlement when present. Footer:
-  height drives the board side (never below its minimum): a long game stretches the board,
+  `hostname · finish date` in the **device** locale. The scoresheet's height drives the
-  never the typography, so the image has no dead space.
+  board side (never below its minimum): a long game stretches the board, never the
+  typography, so the image has no dead space.
 - **Finished game**: the board keeps no last-word highlight and no zoom; the history header
   offers *Export game* (not *Drop game*; an AI game offers neither) and the comms hub hides the 🔎 *Dictionary* tab — and a **finished AI game has no comms at all** (no chat, dictionary closed), so its 💬 entry is dropped from the header too; and
   the footer (rack + tab bar) is **drawn but inert** (greyed, non-interactive) rather than

gateway/internal/backendclient/api_social.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"net/http"
 	"net/url"
+	"strings"
 )
 
 // The response structs and client methods mirror the backend's social,
@@ -347,3 +348,28 @@ func (c *Client) ExportGCG(ctx context.Context, userID, gameID string) (GcgResp,
 	err := c.do(ctx, http.MethodGet, c.gamePath(gameID, "/gcg"), userID, "", nil, &out)
 	return out, err
 }
+
+// ExportURLResp is the minted signed download link for an export artifact.
+type ExportURLResp struct {
+	Path     string `json:"path"`
+	Filename string `json:"filename"`
+}
+
+// ExportURL mints a signed download URL for a finished game's artifact (kind
+// "png" or "gcg"). dateLocale and the localized non-play labels ride the URL so
+// the server render matches the player's presentation.
+func (c *Client) ExportURL(ctx context.Context, userID, gameID, kind, dateLocale, timeZone string, labels []string) (ExportURLResp, error) {
+	q := url.Values{"kind": {kind}}
+	if dateLocale != "" {
+		q.Set("dl", dateLocale)
+	}
+	if timeZone != "" {
+		q.Set("tz", timeZone)
+	}
+	if len(labels) > 0 {
+		q.Set("t", strings.Join(labels, ","))
+	}
+	var out ExportURLResp
+	err := c.do(ctx, http.MethodGet, c.gamePath(gameID, "/export-url")+"?"+q.Encode(), userID, "", nil, &out)
+	return out, err
+}

gateway/internal/backendclient/client.go

@@ -39,10 +39,18 @@ const backendMaxIdleConns = 512
 type Client struct {
 	baseURL string
 	http    *http.Client
-	conn    *grpc.ClientConn
+	// dl serves the export downloads: the backend may wait on the render sidecar
-	push    pushv1.PushClient
+	// for several seconds, so these calls get their own, longer deadline than the
+	// ordinary REST budget.
+	dl   *http.Client
+	conn *grpc.ClientConn
+	push pushv1.PushClient
 }
 
+// exportDownloadTimeout bounds one export-download fetch end to end (the backend's
+// own sidecar budget is 15s).
+const exportDownloadTimeout = 30 * time.Second
+
 // New dials the backend push gRPC endpoint and prepares the REST client. The
 // backend lives on a trusted network segment, so the gRPC connection uses
 // insecure (plaintext) transport credentials (ARCHITECTURE.md §12).
@@ -62,11 +70,39 @@ func New(httpURL, grpcAddr string, timeout time.Duration) (*Client, error) {
 	return &Client{
 		baseURL: strings.TrimRight(httpURL, "/"),
 		http:    &http.Client{Timeout: timeout, Transport: transport},
+		dl:      &http.Client{Timeout: exportDownloadTimeout, Transport: transport},
 		conn:    conn,
 		push:    pushv1.NewPushClient(conn),
 	}, nil
 }
 
+// ExportDownload fetches a signed finished-game export artifact from the backend's
+// public group, forwarding the caller's public Host for the image footer. It returns
+// the bytes with the backend's Content-Type and Content-Disposition. rest is the
+// public path suffix after /dl (e.g. "/<game>/<kind>?e=…&s=…").
+func (c *Client) ExportDownload(ctx context.Context, rest, publicHost string) ([]byte, string, string, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, c.baseURL+"/api/v1/public/dl"+rest, nil)
+	if err != nil {
+		return nil, "", "", fmt.Errorf("backendclient: new request: %w", err)
+	}
+	if publicHost != "" {
+		req.Header.Set("X-Public-Host", publicHost)
+	}
+	resp, err := c.dl.Do(req)
+	if err != nil {
+		return nil, "", "", fmt.Errorf("backendclient: GET export: %w", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+	data, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, "", "", fmt.Errorf("backendclient: read export: %w", err)
+	}
+	if resp.StatusCode >= http.StatusMultipleChoices {
+		return nil, "", "", parseAPIError(resp.StatusCode, data)
+	}
+	return data, resp.Header.Get("Content-Type"), resp.Header.Get("Content-Disposition"), nil
+}
+
 // Close releases the gRPC connection.
 func (c *Client) Close() error { return c.conn.Close() }
 

gateway/internal/connectsrv/server.go

@@ -193,6 +193,7 @@ func (s *Server) HTTPHandler() http.Handler {
 	// The client-side local move preview pulls each game's pinned dictionary blob
 	// through this session-gated route (not public); see dictBytesHandler.
 	mux.Handle("/dict/", s.dictBytesHandler())
+	mux.Handle("/dl/", s.exportDownloadHandler())
 	// The client posts its local-move-preview adoption telemetry here (session-gated).
 	mux.Handle("/metrics/local-eval", s.localEvalMetricsHandler())
 	// The embedded UI: the game SPA under /app/ (web), /telegram/ (the Telegram Mini
@@ -415,6 +416,59 @@ func (s *Server) limitAdmin(next http.Handler) http.Handler {
 // user-class limiter, and forwards the backend's immutable Cache-Control so the
 // browser caches the blob hard. Only GET is allowed; the path is
 // /dict/{variant}/{version}.
+// exportDownloadHandler serves the signed finished-game export downloads (/dl/*).
+// It is the gateway's only unauthenticated data route: the platforms' native
+// download calls (Telegram downloadFile, VKWebAppDownloadFile, a plain anchor)
+// carry no session, so the URL's HMAC — verified by the backend — is the whole
+// grant. The gateway only rate-limits by IP and forwards, passing the public Host
+// along for the image footer.
+func (s *Server) exportDownloadHandler() http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if s.backend == nil {
+			http.NotFound(w, r)
+			return
+		}
+		if r.Method != http.MethodGet {
+			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+			return
+		}
+		ip := peerIP(r.RemoteAddr, r.Header)
+		if !s.limiter.Allow("public:"+ip, s.publicPolicy) {
+			s.noteRateLimited(r.Context(), classPublic, ip, "export-dl")
+			http.Error(w, "rate limited", http.StatusTooManyRequests)
+			return
+		}
+		rest := strings.TrimPrefix(r.URL.Path, "/dl")
+		if rest == "" || rest == "/" {
+			http.NotFound(w, r)
+			return
+		}
+		if r.URL.RawQuery != "" {
+			rest += "?" + r.URL.RawQuery
+		}
+		data, contentType, disposition, err := s.backend.ExportDownload(r.Context(), rest, r.Host)
+		if err != nil {
+			var apiErr *backendclient.APIError
+			if errors.As(err, &apiErr) && apiErr.Status < http.StatusInternalServerError {
+				http.NotFound(w, r) // invalid, expired or unknown link
+				return
+			}
+			s.log.Warn("export download failed", zap.Error(err))
+			http.Error(w, "bad gateway", http.StatusBadGateway)
+			return
+		}
+		if contentType != "" {
+			w.Header().Set("Content-Type", contentType)
+		}
+		if disposition != "" {
+			w.Header().Set("Content-Disposition", disposition)
+		}
+		w.Header().Set("X-Content-Type-Options", "nosniff")
+		w.Header().Set("Cache-Control", "private, max-age=0")
+		_, _ = w.Write(data)
+	})
+}
+
 func (s *Server) dictBytesHandler() http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if s.backend == nil {

gateway/internal/transcode/encode_social.go

@@ -251,6 +251,18 @@ func encodeInvitationList(r backendclient.InvitationListResp) []byte {
 	return b.FinishedBytes()
 }
 
+// encodeExportURL builds an ExportUrl payload.
+func encodeExportURL(r backendclient.ExportURLResp) []byte {
+	b := flatbuffers.NewBuilder(256)
+	path := b.CreateString(r.Path)
+	fn := b.CreateString(r.Filename)
+	fb.ExportUrlStart(b)
+	fb.ExportUrlAddPath(b, path)
+	fb.ExportUrlAddFilename(b, fn)
+	b.Finish(fb.ExportUrlEnd(b))
+	return b.FinishedBytes()
+}
+
 // encodeGcg builds a GcgExport payload.
 func encodeGcg(r backendclient.GcgResp) []byte {
 	b := flatbuffers.NewBuilder(1024)

gateway/internal/transcode/transcode_social.go

@@ -31,6 +31,7 @@ const (
 	MsgProfileUpdate     = "profile.update"
 	MsgStatsGet          = "stats.get"
 	MsgGameGCG           = "game.gcg"
+	MsgGameExportURL     = "game.export_url"
 )
 
 // registerSocialOps adds the social, account and history operations to the
@@ -56,6 +57,7 @@ func registerSocialOps(r *Registry, backend *backendclient.Client) {
 	r.ops[MsgProfileUpdate] = Op{Handler: profileUpdateHandler(backend), Auth: true}
 	r.ops[MsgStatsGet] = Op{Handler: statsHandler(backend), Auth: true}
 	r.ops[MsgGameGCG] = Op{Handler: gcgHandler(backend), Auth: true}
+	r.ops[MsgGameExportURL] = Op{Handler: exportURLHandler(backend), Auth: true}
 }
 
 // --- friends ---
@@ -290,6 +292,21 @@ func gcgHandler(backend *backendclient.Client) Handler {
 	}
 }
 
+func exportURLHandler(backend *backendclient.Client) Handler {
+	return func(ctx context.Context, req Request) ([]byte, error) {
+		in := fb.GetRootAsExportUrlRequest(req.Payload, 0)
+		labels := make([]string, 0, in.ActionLabelsLength())
+		for i := range in.ActionLabelsLength() {
+			labels = append(labels, string(in.ActionLabels(i)))
+		}
+		res, err := backend.ExportURL(ctx, req.UserID, string(in.GameId()), string(in.Kind()), string(in.DateLocale()), string(in.TimeZone()), labels)
+		if err != nil {
+			return nil, err
+		}
+		return encodeExportURL(res), nil
+	}
+}
+
 // decodeInviteeIDs reads the invitee id vector from a CreateInvitationRequest.
 func decodeInviteeIDs(in *fb.CreateInvitationRequest) []string {
 	n := in.InviteeIdsLength()

gateway/internal/transcode/transcode_social_test.go

@@ -263,6 +263,54 @@ func TestGcgRoundTrip(t *testing.T) {
 	}
 }
 
+func TestExportURLRoundTrip(t *testing.T) {
+	backend, cleanup := fakeBackend(t, func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/v1/user/games/g-1/export-url" {
+			t.Errorf("unexpected path %q", r.URL.Path)
+		}
+		q := r.URL.Query()
+		if q.Get("kind") != "png" || q.Get("dl") != "ru-RU" || q.Get("tz") != "Europe/Moscow" || q.Get("t") != "пас,обмен,сдался,таймаут" {
+			t.Errorf("unexpected query %q", r.URL.RawQuery)
+		}
+		_, _ = w.Write([]byte(`{"path":"/dl/g-1/png?e=1&s=x","filename":"game-g-1.png"}`))
+	})
+	defer cleanup()
+
+	reg := transcode.NewRegistry(backend, nil)
+	op, _ := reg.Lookup(transcode.MsgGameExportURL)
+
+	b := flatbuffers.NewBuilder(256)
+	gid := b.CreateString("g-1")
+	kind := b.CreateString("png")
+	dl := b.CreateString("ru-RU")
+	tz := b.CreateString("Europe/Moscow")
+	labels := make([]flatbuffers.UOffsetT, 0, 4)
+	for _, s := range []string{"пас", "обмен", "сдался", "таймаут"} {
+		labels = append(labels, b.CreateString(s))
+	}
+	fb.ExportUrlRequestStartActionLabelsVector(b, len(labels))
+	for i := len(labels) - 1; i >= 0; i-- {
+		b.PrependUOffsetT(labels[i])
+	}
+	vec := b.EndVector(len(labels))
+	fb.ExportUrlRequestStart(b)
+	fb.ExportUrlRequestAddGameId(b, gid)
+	fb.ExportUrlRequestAddKind(b, kind)
+	fb.ExportUrlRequestAddDateLocale(b, dl)
+	fb.ExportUrlRequestAddActionLabels(b, vec)
+	fb.ExportUrlRequestAddTimeZone(b, tz)
+	b.Finish(fb.ExportUrlRequestEnd(b))
+
+	payload, err := op.Handler(context.Background(), transcode.Request{UserID: "u-1", Payload: b.FinishedBytes()})
+	if err != nil {
+		t.Fatalf("handler: %v", err)
+	}
+	res := fb.GetRootAsExportUrl(payload, 0)
+	if string(res.Path()) != "/dl/g-1/png?e=1&s=x" || string(res.Filename()) != "game-g-1.png" {
+		t.Fatalf("export url decoded wrong: path=%q filename=%q", res.Path(), res.Filename())
+	}
+}
+
 func TestProfileUpdateRoundTripAway(t *testing.T) {
 	var gotBody map[string]any
 	backend, cleanup := fakeBackend(t, func(w http.ResponseWriter, r *http.Request) {

pkg/fbs/scrabble.fbs

@@ -658,6 +658,27 @@ table GcgExport {
   content:string;
 }
 
+// ExportUrlRequest asks for a signed download URL of a finished game's export artifact.
+// kind is "png" or "gcg". For the PNG the client passes its presentation context — the
+// UI-localized non-play move labels (pass, exchange, resign, timeout, in that order),
+// the device date locale and the device IANA time zone — which ride the signed URL so
+// the server render matches what the player would have seen locally.
+table ExportUrlRequest {
+  game_id:string;
+  kind:string;
+  date_locale:string;
+  action_labels:[string];
+  time_zone:string;
+}
+
+// ExportUrl is the minted download link: a relative, signed, short-lived path the client
+// resolves against its own origin (the SPA and the gateway share it), plus the filename
+// the download will carry.
+table ExportUrl {
+  path:string;
+  filename:string;
+}
+
 // --- push event payloads ---
 
 // YourTurnEvent signals that it is now the recipient's turn. The trailing fields enrich the

pkg/fbs/scrabblefb/ExportUrl.go

@@ -0,0 +1,71 @@
+// Code generated by the FlatBuffers compiler. DO NOT EDIT.
+
+package scrabblefb
+
+import (
+	flatbuffers "github.com/google/flatbuffers/go"
+)
+
+type ExportUrl struct {
+	_tab flatbuffers.Table
+}
+
+func GetRootAsExportUrl(buf []byte, offset flatbuffers.UOffsetT) *ExportUrl {
+	n := flatbuffers.GetUOffsetT(buf[offset:])
+	x := &ExportUrl{}
+	x.Init(buf, n+offset)
+	return x
+}
+
+func FinishExportUrlBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.Finish(offset)
+}
+
+func GetSizePrefixedRootAsExportUrl(buf []byte, offset flatbuffers.UOffsetT) *ExportUrl {
+	n := flatbuffers.GetUOffsetT(buf[offset+flatbuffers.SizeUint32:])
+	x := &ExportUrl{}
+	x.Init(buf, n+offset+flatbuffers.SizeUint32)
+	return x
+}
+
+func FinishSizePrefixedExportUrlBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.FinishSizePrefixed(offset)
+}
+
+func (rcv *ExportUrl) Init(buf []byte, i flatbuffers.UOffsetT) {
+	rcv._tab.Bytes = buf
+	rcv._tab.Pos = i
+}
+
+func (rcv *ExportUrl) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
+func (rcv *ExportUrl) Path() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *ExportUrl) Filename() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func ExportUrlStart(builder *flatbuffers.Builder) {
+	builder.StartObject(2)
+}
+func ExportUrlAddPath(builder *flatbuffers.Builder, path flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(path), 0)
+}
+func ExportUrlAddFilename(builder *flatbuffers.Builder, filename flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(1, flatbuffers.UOffsetT(filename), 0)
+}
+func ExportUrlEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	return builder.EndObject()
+}

pkg/fbs/scrabblefb/ExportUrlRequest.go

@@ -0,0 +1,116 @@
+// Code generated by the FlatBuffers compiler. DO NOT EDIT.
+
+package scrabblefb
+
+import (
+	flatbuffers "github.com/google/flatbuffers/go"
+)
+
+type ExportUrlRequest struct {
+	_tab flatbuffers.Table
+}
+
+func GetRootAsExportUrlRequest(buf []byte, offset flatbuffers.UOffsetT) *ExportUrlRequest {
+	n := flatbuffers.GetUOffsetT(buf[offset:])
+	x := &ExportUrlRequest{}
+	x.Init(buf, n+offset)
+	return x
+}
+
+func FinishExportUrlRequestBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.Finish(offset)
+}
+
+func GetSizePrefixedRootAsExportUrlRequest(buf []byte, offset flatbuffers.UOffsetT) *ExportUrlRequest {
+	n := flatbuffers.GetUOffsetT(buf[offset+flatbuffers.SizeUint32:])
+	x := &ExportUrlRequest{}
+	x.Init(buf, n+offset+flatbuffers.SizeUint32)
+	return x
+}
+
+func FinishSizePrefixedExportUrlRequestBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.FinishSizePrefixed(offset)
+}
+
+func (rcv *ExportUrlRequest) Init(buf []byte, i flatbuffers.UOffsetT) {
+	rcv._tab.Bytes = buf
+	rcv._tab.Pos = i
+}
+
+func (rcv *ExportUrlRequest) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
+func (rcv *ExportUrlRequest) GameId() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *ExportUrlRequest) Kind() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *ExportUrlRequest) DateLocale() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(8))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *ExportUrlRequest) ActionLabels(j int) []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(10))
+	if o != 0 {
+		a := rcv._tab.Vector(o)
+		return rcv._tab.ByteVector(a + flatbuffers.UOffsetT(j*4))
+	}
+	return nil
+}
+
+func (rcv *ExportUrlRequest) ActionLabelsLength() int {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(10))
+	if o != 0 {
+		return rcv._tab.VectorLen(o)
+	}
+	return 0
+}
+
+func (rcv *ExportUrlRequest) TimeZone() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(12))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func ExportUrlRequestStart(builder *flatbuffers.Builder) {
+	builder.StartObject(5)
+}
+func ExportUrlRequestAddGameId(builder *flatbuffers.Builder, gameId flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(gameId), 0)
+}
+func ExportUrlRequestAddKind(builder *flatbuffers.Builder, kind flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(1, flatbuffers.UOffsetT(kind), 0)
+}
+func ExportUrlRequestAddDateLocale(builder *flatbuffers.Builder, dateLocale flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(2, flatbuffers.UOffsetT(dateLocale), 0)
+}
+func ExportUrlRequestAddActionLabels(builder *flatbuffers.Builder, actionLabels flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(3, flatbuffers.UOffsetT(actionLabels), 0)
+}
+func ExportUrlRequestStartActionLabelsVector(builder *flatbuffers.Builder, numElems int) flatbuffers.UOffsetT {
+	return builder.StartVector(4, numElems, 4)
+}
+func ExportUrlRequestAddTimeZone(builder *flatbuffers.Builder, timeZone flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(4, flatbuffers.UOffsetT(timeZone), 0)
+}
+func ExportUrlRequestEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	return builder.EndObject()
+}

renderer/.gitignore

@@ -0,0 +1,2 @@
+node_modules/
+dist/

renderer/Dockerfile

@@ -0,0 +1,29 @@
+# renderer — the finished-game image-render sidecar: Node + skia-canvas running the SAME
+# ui/src/lib/gameimage.ts the web client unit-tests, bundled at build time (renderer/README.md).
+# Debian slim, not the repo's usual alpine/distroless: skia-canvas ships prebuilt glibc
+# binaries and resolves fonts through fontconfig, and the runtime fonts are baked into the
+# image — Liberation Sans (the UI font stack's Linux face) + Noto Color Emoji (the 🏆).
+FROM node:22-slim AS build
+WORKDIR /src/renderer
+RUN corepack enable && corepack prepare pnpm@11.0.9 --activate
+COPY renderer/package.json renderer/pnpm-lock.yaml renderer/pnpm-workspace.yaml ./
+RUN pnpm install --frozen-lockfile
+COPY renderer/build.mjs ./
+COPY renderer/src ./src
+COPY ui/src/lib /src/ui/src/lib
+RUN pnpm run bundle
+
+FROM node:22-slim
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends fonts-liberation fonts-noto-color-emoji \
+    && rm -rf /var/lib/apt/lists/*
+ENV NODE_ENV=production
+ARG VERSION=dev
+ENV APP_VERSION=${VERSION}
+WORKDIR /app
+COPY --from=build /src/renderer/node_modules ./node_modules
+COPY --from=build /src/renderer/dist ./dist
+COPY renderer/src/server.mjs renderer/src/render.mjs ./src/
+USER node
+EXPOSE 8090
+CMD ["node", "src/server.mjs"]

renderer/README.md

@@ -0,0 +1,34 @@
+# renderer — the finished-game image-render sidecar
+
+An internal-only Node service that rasterizes the finished-game export PNG. It runs the
+**same** `ui/src/lib/gameimage.ts` the web project unit-tests — bundled verbatim at image
+build time (`src/entry.ts` → esbuild → `dist/gameimage.mjs`) — on
+[skia-canvas](https://github.com/samizdatco/skia-canvas), so the server render is
+pixel-identical to the design the owner signed off in the browser.
+
+## Interface
+
+- `POST /render` — `{game, moves, alphabet, labels, dateLocale, hostname, scale?}` →
+  `image/png`. `game`/`moves` are the ui-model shapes (`GameView` / `MoveRecord[]`);
+  `alphabet` is the per-variant `(index, letter, value)` table tile values are drawn
+  from; `labels` localizes the non-play moves (pass/exchange/resign/timeout);
+  `hostname` + `dateLocale` feed the footer.
+- `GET /healthz` — liveness (the compose healthcheck the backend's `depends_on` gates on).
+
+The service draws and nothing else: authentication, the participant check and the signed
+public download URL all live in the backend (`backend/internal/server/export.go`); the
+network path is client → gateway `/dl/*` → backend → this sidecar.
+
+## Development
+
+```sh
+pnpm install          # skia-canvas + esbuild MUST stay approved in pnpm-workspace.yaml
+                      # (allowBuilds) or the native binary is silently never fetched
+pnpm test             # bundles, then node --test against testdata/request.json
+node src/server.mjs   # local run on :8090 (RENDERER_PORT overrides)
+```
+
+The runtime image (`renderer/Dockerfile`, `node:22-slim`) bakes in Liberation Sans (the
+UI font stack's Linux face) and Noto Color Emoji (the scoresheet 🏆); skia-canvas picks
+both up through fontconfig. The fixture `testdata/request.json` is a real 35-move
+self-played Russian Scrabble game.

renderer/build.mjs

@@ -0,0 +1,13 @@
+// Bundles the shared ui/src/lib game-image renderer (see src/entry.ts) into
+// dist/gameimage.mjs for the sidecar runtime. Uses the esbuild JS API — the CLI shim is
+// unreliable under pnpm's bin wrapper (it re-runs the native binary through node).
+import { build } from 'esbuild';
+
+await build({
+  entryPoints: ['src/entry.ts'],
+  bundle: true,
+  format: 'esm',
+  platform: 'node',
+  outfile: 'dist/gameimage.mjs',
+  logLevel: 'info',
+});

renderer/package.json

@@ -0,0 +1,23 @@
+{
+  "name": "scrabble-renderer",
+  "private": true,
+  "version": "0.0.0",
+  "type": "module",
+  "description": "Internal sidecar that renders the finished-game export PNG with the same ui/src/lib/gameimage.ts the browser build tests, on skia-canvas.",
+  "scripts": {
+    "bundle": "node build.mjs",
+    "test": "pnpm run bundle && node --test test/*.test.mjs"
+  },
+  "dependencies": {
+    "skia-canvas": "^3.0.6"
+  },
+  "devDependencies": {
+    "esbuild": "^0.25.0"
+  },
+  "pnpm": {
+    "onlyBuiltDependencies": [
+      "esbuild",
+      "skia-canvas"
+    ]
+  }
+}

renderer/pnpm-lock.yaml

@@ -0,0 +1,366 @@
+lockfileVersion: '9.0'
+
+settings:
+  autoInstallPeers: true
+  excludeLinksFromLockfile: false
+
+importers:
+
+  .:
+    dependencies:
+      skia-canvas:
+        specifier: ^3.0.6
+        version: 3.0.8
+    devDependencies:
+      esbuild:
+        specifier: ^0.25.0
+        version: 0.25.12
+
+packages:
+
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+    cpu: [ppc64]
+    os: [aix]
+
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+    cpu: [arm64]
+    os: [android]
+
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+    os: [android]
+
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+    cpu: [x64]
+    os: [android]
+
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+
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+    os: [win32]
+
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+
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+    peerDependencies:
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+    peerDependenciesMeta:
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+        optional: true
+
+  detect-libc@2.1.2:
+    resolution: {integrity: sha512-Btj2BOOO83o3WyH59e8MgXsxEQVcarkUOpEYrubB0urwnN10yQ364rsiByU11nZlqWYZm05i/of7io4mzihBtQ==}
+    engines: {node: '>=8'}
+
+  esbuild@0.25.12:
+    resolution: {integrity: sha512-bbPBYYrtZbkt6Os6FiTLCTFxvq4tt3JKall1vRwshA3fdVztsLAatFaZobhkBC8/BrPetoa0oksYoKXoG4ryJg==}
+    engines: {node: '>=18'}
+    hasBin: true
+
+  follow-redirects@1.16.0:
+    resolution: {integrity: sha512-y5rN/uOsadFT/JfYwhxRS5R7Qce+g3zG97+JrtFZlC9klX/W5hD7iiLzScI4nZqUS7DNUdhPgw4xI8W2LuXlUw==}
+    engines: {node: '>=4.0'}
+    peerDependencies:
+      debug: '*'
+    peerDependenciesMeta:
+      debug:
+        optional: true
+
+  https-proxy-agent@7.0.6:
+    resolution: {integrity: sha512-vK9P5/iUfdl95AI+JVyUuIcVtd4ofvtrOr3HNtM2yxC9bnMbEdp3x01OhQNnjb8IJYi38VlTE3mBXwcfvywuSw==}
+    engines: {node: '>= 14'}
+
+  ms@2.1.3:
+    resolution: {integrity: sha512-6FlzubTLZG3J2a/NVCAleEhjzq5oxgHyaCU9yYXvcLsvoVaHJq/s5xXI6/XXP6tz7R9xAOtHnSO/tXtF3WRTlA==}
+
+  parenthesis@3.1.8:
+    resolution: {integrity: sha512-KF/U8tk54BgQewkJPvB4s/US3VQY68BRDpH638+7O/n58TpnwiwnOtGIOsT2/i+M78s61BBpeC83STB88d8sqw==}
+
+  skia-canvas@3.0.8:
+    resolution: {integrity: sha512-FSYKxp8Ng2vOeeOBiyPhnn6ui6FirPJXMyjk4PKl8N/OWzVrkMawUgY9zubIWHMdYtyWFn0gfX3QlRwg6HBmdg==}
+
+  string-split-by@1.0.0:
+    resolution: {integrity: sha512-KaJKY+hfpzNyet/emP81PJA9hTVSfxNLS9SFTWxdCnnW1/zOOwiV248+EfoX7IQFcBaOp4G5YE6xTJMF+pLg6A==}
+
+snapshots:
+
+  '@esbuild/aix-ppc64@0.25.12':
+    optional: true
+
+  '@esbuild/android-arm64@0.25.12':
+    optional: true
+
+  '@esbuild/android-arm@0.25.12':
+    optional: true
+
+  '@esbuild/android-x64@0.25.12':
+    optional: true
+
+  '@esbuild/darwin-arm64@0.25.12':
+    optional: true
+
+  '@esbuild/darwin-x64@0.25.12':
+    optional: true
+
+  '@esbuild/freebsd-arm64@0.25.12':
+    optional: true
+
+  '@esbuild/freebsd-x64@0.25.12':
+    optional: true
+
+  '@esbuild/linux-arm64@0.25.12':
+    optional: true
+
+  '@esbuild/linux-arm@0.25.12':
+    optional: true
+
+  '@esbuild/linux-ia32@0.25.12':
+    optional: true
+
+  '@esbuild/linux-loong64@0.25.12':
+    optional: true
+
+  '@esbuild/linux-mips64el@0.25.12':
+    optional: true
+
+  '@esbuild/linux-ppc64@0.25.12':
+    optional: true
+
+  '@esbuild/linux-riscv64@0.25.12':
+    optional: true
+
+  '@esbuild/linux-s390x@0.25.12':
+    optional: true
+
+  '@esbuild/linux-x64@0.25.12':
+    optional: true
+
+  '@esbuild/netbsd-arm64@0.25.12':
+    optional: true
+
+  '@esbuild/netbsd-x64@0.25.12':
+    optional: true
+
+  '@esbuild/openbsd-arm64@0.25.12':
+    optional: true
+
+  '@esbuild/openbsd-x64@0.25.12':
+    optional: true
+
+  '@esbuild/openharmony-arm64@0.25.12':
+    optional: true
+
+  '@esbuild/sunos-x64@0.25.12':
+    optional: true
+
+  '@esbuild/win32-arm64@0.25.12':
+    optional: true
+
+  '@esbuild/win32-ia32@0.25.12':
+    optional: true
+
+  '@esbuild/win32-x64@0.25.12':
+    optional: true
+
+  agent-base@7.1.4: {}
+
+  debug@4.4.3:
+    dependencies:
+      ms: 2.1.3
+
+  detect-libc@2.1.2: {}
+
+  esbuild@0.25.12:
+    optionalDependencies:
+      '@esbuild/aix-ppc64': 0.25.12
+      '@esbuild/android-arm': 0.25.12
+      '@esbuild/android-arm64': 0.25.12
+      '@esbuild/android-x64': 0.25.12
+      '@esbuild/darwin-arm64': 0.25.12
+      '@esbuild/darwin-x64': 0.25.12
+      '@esbuild/freebsd-arm64': 0.25.12
+      '@esbuild/freebsd-x64': 0.25.12
+      '@esbuild/linux-arm': 0.25.12
+      '@esbuild/linux-arm64': 0.25.12
+      '@esbuild/linux-ia32': 0.25.12
+      '@esbuild/linux-loong64': 0.25.12
+      '@esbuild/linux-mips64el': 0.25.12
+      '@esbuild/linux-ppc64': 0.25.12
+      '@esbuild/linux-riscv64': 0.25.12
+      '@esbuild/linux-s390x': 0.25.12
+      '@esbuild/linux-x64': 0.25.12
+      '@esbuild/netbsd-arm64': 0.25.12
+      '@esbuild/netbsd-x64': 0.25.12
+      '@esbuild/openbsd-arm64': 0.25.12
+      '@esbuild/openbsd-x64': 0.25.12
+      '@esbuild/openharmony-arm64': 0.25.12
+      '@esbuild/sunos-x64': 0.25.12
+      '@esbuild/win32-arm64': 0.25.12
+      '@esbuild/win32-ia32': 0.25.12
+      '@esbuild/win32-x64': 0.25.12
+
+  follow-redirects@1.16.0: {}
+
+  https-proxy-agent@7.0.6:
+    dependencies:
+      agent-base: 7.1.4
+      debug: 4.4.3
+    transitivePeerDependencies:
+      - supports-color
+
+  ms@2.1.3: {}
+
+  parenthesis@3.1.8: {}
+
+  skia-canvas@3.0.8:
+    dependencies:
+      detect-libc: 2.1.2
+      follow-redirects: 1.16.0
+      https-proxy-agent: 7.0.6
+      string-split-by: 1.0.0
+    transitivePeerDependencies:
+      - debug
+      - supports-color
+
+  string-split-by@1.0.0:
+    dependencies:
+      parenthesis: 3.1.8

renderer/pnpm-workspace.yaml

@@ -0,0 +1,6 @@
+# pnpm 11 records build-script approval here. esbuild's postinstall materialises its CLI
+# shim; skia-canvas's postinstall downloads the prebuilt native .node binary — without the
+# approval it is silently skipped and the service fails at boot.
+allowBuilds:
+  esbuild: true
+  skia-canvas: true

renderer/src/entry.ts

@@ -0,0 +1,6 @@
+// The esbuild bundle entry: re-exports the SHARED game-image renderer from ui/src/lib —
+// the exact module the browser build unit-tests — plus the alphabet cache seeder the
+// server fills from the backend-supplied per-variant table. Bundled by `pnpm run bundle`
+// into dist/gameimage.mjs (type erasure only; the ui project type-checks the source).
+export { drawGameImage, type RenderOptions } from '../../ui/src/lib/gameimage';
+export { setAlphabet } from '../../ui/src/lib/alphabet';

renderer/src/render.mjs

@@ -0,0 +1,24 @@
+// The render core, separated from the HTTP wiring so the node test can call it directly.
+import { Canvas } from 'skia-canvas';
+import { drawGameImage, setAlphabet } from '../dist/gameimage.mjs';
+
+/**
+ * renderRequest rasterizes one export request — the JSON shape the backend sends:
+ * { game, moves, alphabet, labels, dateLocale, hostname, scale? } — into a PNG buffer.
+ * game/moves are the ui-model shapes (GameView / MoveRecord[]) the shared drawGameImage
+ * consumes; alphabet is the per-variant (index, letter, value) table it scores tiles with.
+ */
+export async function renderRequest(payload) {
+  const { game, moves, alphabet, labels, dateLocale, timeZone, hostname, scale } = payload;
+  if (!game || !Array.isArray(moves)) throw Object.assign(new Error('bad payload'), { status: 400 });
+  setAlphabet(game.variant, alphabet ?? []);
+  const canvas = new Canvas(1, 1);
+  drawGameImage(canvas, game, moves, {
+    actionLabel: (a) => (labels && labels[a]) || a,
+    hostname: hostname || '',
+    dateLocale: dateLocale || undefined,
+    timeZone: timeZone || undefined,
+    scale: scale || 2,
+  });
+  return canvas.toBuffer('png');
+}

renderer/src/server.mjs

@@ -0,0 +1,55 @@
+// The render sidecar: a minimal internal HTTP service the backend calls to rasterize the
+// finished-game export image. It runs the same drawGameImage the browser build ships
+// (bundled from ui/src/lib at image build time) on skia-canvas, with system fonts from
+// the image (Liberation Sans + Noto Color Emoji via fontconfig).
+//
+//   POST /render  {game, moves, alphabet, labels, dateLocale, hostname, scale?} → image/png
+//   GET  /healthz → 200
+//
+// The service is internal-only (docker network `internal`); authentication, participant
+// checks and the signed public URL all live in the backend — this process only draws.
+import { createServer } from 'node:http';
+import { renderRequest } from './render.mjs';
+
+const PORT = Number(process.env.RENDERER_PORT || 8090);
+// A render request is a finished game's journal — generously capped.
+const MAX_BODY = 2 * 1024 * 1024;
+
+function readBody(req) {
+  return new Promise((resolve, reject) => {
+    const chunks = [];
+    let size = 0;
+    req.on('data', (c) => {
+      size += c.length;
+      if (size > MAX_BODY) {
+        reject(Object.assign(new Error('body too large'), { status: 413 }));
+        req.destroy();
+        return;
+      }
+      chunks.push(c);
+    });
+    req.on('end', () => resolve(Buffer.concat(chunks)));
+    req.on('error', reject);
+  });
+}
+
+const server = createServer(async (req, res) => {
+  try {
+    if (req.method === 'GET' && req.url === '/healthz') {
+      res.writeHead(200, { 'content-type': 'text/plain' }).end('ok');
+      return;
+    }
+    if (req.method === 'POST' && req.url === '/render') {
+      const png = await renderRequest(JSON.parse(await readBody(req)));
+      res.writeHead(200, { 'content-type': 'image/png', 'content-length': png.length }).end(png);
+      return;
+    }
+    res.writeHead(404).end();
+  } catch (err) {
+    const status = err.status || (err instanceof SyntaxError ? 400 : 500);
+    console.error(`render error: ${err.message}`);
+    res.writeHead(status, { 'content-type': 'text/plain' }).end('render failed');
+  }
+});
+
+server.listen(PORT, () => console.log(`renderer listening on :${PORT}`));

renderer/test/render.test.mjs

@@ -0,0 +1,37 @@
+// Smoke test for the render core: feeds the committed fixture (a real 35-move self-played
+// Russian Scrabble game) through renderRequest and asserts a sane PNG comes back. Pixel
+// goldens are deliberately avoided — font rasterization differs across hosts; the shared
+// drawing logic itself is unit-tested in ui/ (gameimage.test.ts).
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
+import { dirname, join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { renderRequest } from '../src/render.mjs';
+
+const here = dirname(fileURLToPath(import.meta.url));
+const fixture = () => JSON.parse(readFileSync(join(here, '../testdata/request.json'), 'utf8'));
+
+function pngSize(buf) {
+  // IHDR is the first chunk: width/height are big-endian u32 at offsets 16/20.
+  return { w: buf.readUInt32BE(16), h: buf.readUInt32BE(20) };
+}
+
+test('renders the fixture game to a plausible PNG', async () => {
+  const png = await renderRequest(fixture());
+  assert.ok(png.length > 50_000, `png too small: ${png.length}`);
+  assert.deepEqual([...png.subarray(0, 8)], [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]);
+  const { w, h } = pngSize(png);
+  // scale 2 over a MIN_SIDE 620 board + two seat columns: sanity bounds, not a golden.
+  assert.ok(w > 1600 && w < 3000, `unexpected width ${w}`);
+  assert.ok(h > 1000 && h < 3000, `unexpected height ${h}`);
+});
+
+test('rejects a payload without a game', async () => {
+  await assert.rejects(() => renderRequest({ moves: [] }), /bad payload/);
+});
+
+test('renders concurrently without cross-talk', async () => {
+  const [a, b] = await Promise.all([renderRequest(fixture()), renderRequest(fixture())]);
+  assert.equal(a.length, b.length);
+});

ui/e2e/export.spec.ts

@@ -1,18 +1,31 @@
 import { expect, test, type Page } from './fixtures';
 
 // The finished-game export: the history header's 📤 button opens the app's own format
-// chooser modal — never Telegram's native popup, whose callback runs without user
+// chooser (never Telegram's native popup — its callback carries no user activation),
-// activation and so kills navigator.share / clipboard writes (verified on-device).
+// and BOTH formats travel the same unified route on every platform: the client mints a
-// The PNG option is offered only outside the in-app WebViews (no working binary
+// signed relative URL (game.export_url), resolves it against its own origin and hands
-// delivery there until the server-rendered signed-URL path lands); the GCG file is
+// it to the platform's native download — Telegram downloadFile / VKWebAppDownloadFile —
-// always offered. g3 ("vs Rick") is the seeded finished game. Web Share is
+// or a plain anchor download in a browser. g3 ("vs Rick") is the seeded finished game.
-// force-disabled per test so both engines deterministically exercise the download
+// The mock gateway returns a shape-faithful /dl/... path; the tests intercept that
-// branch.
+// route and serve bytes, so the download itself is exercised end to end.
 
-async function disableWebShare(page: Page): Promise<void> {
+// A minimal valid 1×1 PNG, hex-decoded without node typings (the e2e tsconfig has none).
-  await page.addInitScript(() => {
+const PNG_HEX =
-    Object.defineProperty(navigator, 'canShare', { value: () => false, configurable: true });
+  '89504e470d0a1a0a0000000d49484452000000010000000108060000001f15c489' +
-    Object.defineProperty(navigator, 'share', { value: undefined, configurable: true });
+  '0000000a49444154789c6360000000020001e221bc330000000049454e44ae426082';
+const PNG_BYTES = Uint8Array.from({ length: PNG_HEX.length / 2 }, (_, i) =>
+  parseInt(PNG_HEX.slice(i * 2, i * 2 + 2), 16),
+);
+
+async function routeDl(page: Page): Promise<void> {
+  await page.route('**/dl/**', (route) => {
+    const png = route.request().url().includes('/png');
+    return route.fulfill({
+      status: 200,
+      contentType: png ? 'image/png' : 'text/plain; charset=utf-8',
+      headers: { 'Content-Disposition': 'attachment' },
+      body: png ? PNG_BYTES : '#character-encoding UTF-8\n',
+    });
   });
 }
 
@@ -25,20 +38,18 @@ async function openFinishedHistory(page: Page): Promise<void> {
   await expect(page.getByRole('button', { name: 'Export game' })).toBeVisible();
 }
 
-test('the export chooser downloads the PNG image on a plain browser', async ({ page }) => {
+test('the chooser downloads the PNG through the signed URL on a plain browser', async ({ page }) => {
-  await disableWebShare(page);
+  await routeDl(page);
   await openFinishedHistory(page);
   await page.getByRole('button', { name: 'Export game' }).click();
 
-  // The app's own chooser modal offers both formats on the plain web.
-  await expect(page.getByRole('button', { name: 'GCG file' })).toBeVisible();
   const download = page.waitForEvent('download');
   await page.getByRole('button', { name: 'Image (PNG)' }).click();
   expect((await download).suggestedFilename()).toMatch(/^game-.+\.png$/);
 });
 
-test('the export chooser downloads the GCG file on a plain browser', async ({ page }) => {
+test('the chooser downloads the GCG through the same signed-URL route', async ({ page }) => {
-  await disableWebShare(page);
+  await routeDl(page);
   await openFinishedHistory(page);
   await page.getByRole('button', { name: 'Export game' }).click();
 
@@ -47,13 +58,9 @@ test('the export chooser downloads the GCG file on a plain browser', async ({ pa
   expect((await download).suggestedFilename()).toMatch(/^game-.+\.gcg$/);
 });
 
-test('inside Telegram the chooser is the app modal and withholds the image option', async ({
+test('inside Telegram both formats go through the native downloadFile dialog', async ({ page }) => {
-  page,
+  // A Telegram stub with downloadFile present (Bot API 8.0): the image option is offered
-}) => {
+  // and the artifact is handed to the native download — never an in-webview anchor.
-  await disableWebShare(page);
-  // A Telegram WebApp stub with showPopup present: were the chooser still native, it would
-  // be called — the spy locks the regression (its activation-less callback breaks share and
-  // clipboard delivery on real devices).
   await page.addInitScript(() => {
     Object.assign(window, {
       Telegram: {
@@ -62,9 +69,9 @@ test('inside Telegram the chooser is the app modal and withholds the image optio
           initDataUnsafe: {},
           ready() {},
           expand() {},
-          showPopup(_params: unknown, cb: (id: string) => void) {
+          downloadFile(params: { url: string; file_name: string }) {
-            (window as unknown as { __popupCalled?: boolean }).__popupCalled = true;
+            const w = window as unknown as { __downloads?: { url: string; file_name: string }[] };
-            setTimeout(() => cb(''), 0);
+            (w.__downloads ??= []).push(params);
           },
         },
       },
@@ -77,11 +84,49 @@ test('inside Telegram the chooser is the app modal and withholds the image optio
   await page.locator('.scoreboard').click();
   await page.getByRole('button', { name: 'Export game' }).click();
 
-  // The app's own modal opened with the GCG option only — no PNG in an in-app WebView…
+  await page.getByRole('button', { name: 'Image (PNG)' }).click();
+  await expect
+    .poll(() =>
+      page.evaluate(() => (window as unknown as { __downloads?: { url: string; file_name: string }[] }).__downloads),
+    )
+    .toHaveLength(1);
+  const dl = await page.evaluate(
+    () => (window as unknown as { __downloads: { url: string; file_name: string }[] }).__downloads[0],
+  );
+  // The relative signed path was resolved against the app's own origin — absolute for TG.
+  expect(dl.url).toMatch(/^http.+\/dl\/.+\/png\?/);
+  expect(dl.file_name).toMatch(/^game-.+\.png$/);
+});
+
+test('a legacy Telegram client (no downloadFile) hides the image and copies the GCG', async ({ page }) => {
+  await page.addInitScript(() => {
+    // Headless engines deny the real clipboard; a permissive stub keeps the legacy
+    // copy path deterministic in both browsers.
+    Object.defineProperty(navigator, 'clipboard', {
+      value: { writeText: async () => {} },
+      configurable: true,
+    });
+    Object.assign(window, {
+      Telegram: {
+        WebApp: {
+          initData: 'query_id=test&user=%7B%22id%22%3A1%7D&auth_date=1&hash=deadbeef',
+          initDataUnsafe: {},
+          ready() {},
+          expand() {},
+        },
+      },
+    });
+  });
+  await page.goto('/');
+  await expect(page.getByText('Your turn')).toBeVisible();
+  await page.getByRole('button', { name: /Rick/ }).click();
+  await expect(page.locator('[data-cell]').first()).toBeVisible();
+  await page.locator('.scoreboard').click();
+  await page.getByRole('button', { name: 'Export game' }).click();
+
+  // No image option without the native download; the GCG stays available (clipboard path).
   await expect(page.getByRole('button', { name: 'GCG file' })).toBeVisible();
   await expect(page.getByRole('button', { name: 'Image (PNG)' })).toHaveCount(0);
-  // …and the native popup was never used for the chooser.
+  await page.getByRole('button', { name: 'GCG file' }).click();
-  expect(
+  await expect(page.getByText('GCG copied to the clipboard.')).toBeVisible();
-    await page.evaluate(() => (window as unknown as { __popupCalled?: boolean }).__popupCalled),
-  ).toBeFalsy();
 });

ui/src/game/Game.svelte

@@ -22,12 +22,12 @@
   import { variantNameKey, usesStarBlank, BLANK_STAR } from '../lib/variants';
   import { alphabetLetters, hasAlphabet } from '../lib/alphabet';
   import { hintsLeft } from '../lib/hints';
-  import { shareOrDownloadGcg, shareOrDownloadImage } from '../lib/share';
+  import { downloadUrl, shareOrDownloadGcg } from '../lib/share';
-  import { insideVK, vkCopyText } from '../lib/vk';
+  import { insideVK, vkCopyText, vkDownloadFile } from '../lib/vk';
   import { getCachedGame, setCachedGame, setCachedDraft, type CachedGame } from '../lib/gamecache';
   import { patchLobbyGame } from '../lib/lobbycache';
   import { applyGameOver, applyMoveDelta, applyOpponentJoined, type DeltaResult } from '../lib/gamedelta';
-  import { insideTelegram, telegramDialogsAvailable, telegramShowConfirm } from '../lib/telegram';
+  import { insideTelegram, telegramCanDownloadFile, telegramDialogsAvailable, telegramDownloadFile, telegramShowConfirm } from '../lib/telegram';
   import { haptic } from '../lib/haptics';
   import {
     BLANK,
@@ -931,26 +931,30 @@
     return view.game.seats.some((s) => s.isWinner) ? t('game.lost') : t('game.tied');
   }
 
-  // The finished-game export offers two formats — the GCG file and the rendered PNG image —
+  // The finished-game export offers two formats — the GCG file and the server-rendered PNG
-  // behind one 📤 button, always through the app's own modal. Never Telegram's native popup
+  // image — behind one 📤 button, always through the app's own modal. Never Telegram's
-  // here: its callback runs with NO user activation, so navigator.share / clipboard writes
+  // native popup here: its callback runs with NO user activation, which breaks the
-  // silently fail from it (verified on-device, TG iOS + Android). A real DOM button click in
+  // gesture-gated delivery APIs (verified on-device). Both formats travel the SAME route on
-  // the modal keeps the gesture alive for the delivery APIs.
+  // every platform: mint a signed relative URL, resolve it against our origin, then hand it
+  // to the platform's native download call — Telegram downloadFile / VKWebAppDownloadFile —
+  // or a plain browser anchor download elsewhere (including the desktop VK iframe, where
+  // the bridge method is unavailable and vkDownloadFile falls through).
   let exportOpen = $state(false);
-  // The PNG option is withheld in an in-app WebView (Telegram / VK) for now: a binary image
+  // The only platform without the URL delivery is a legacy Telegram client predating
-  // has no working delivery there (no Web Share, a dead <a download>, text-only clipboard,
+  // Bot API 8.0 downloadFile: the GCG falls back to the old clipboard copy there, and
-  // and the long-press menu mangles data: URLs). It returns with the server-rendered
+  // the image option is not offered.
-  // signed-URL delivery (Telegram downloadFile / VKWebAppDownloadFile).
+  const exportImageAvailable = $derived(!insideTelegram() || telegramCanDownloadFile());
-  const exportImageAvailable = $derived(!(insideTelegram() || insideVK()));
 
   function onExportClick() {
     exportOpen = true;
   }
 
-  async function exportGcg() {
+  // Legacy-Telegram GCG delivery (no downloadFile): fetch the text and copy it to the
+  // clipboard, as before the unified URL route.
+  async function exportGcgLegacy() {
     try {
       const gcg = await gateway.exportGcg(id);
-      const outcome = await shareOrDownloadGcg(gcg, insideTelegram() || insideVK(), copyGcgText);
+      const outcome = await shareOrDownloadGcg(gcg, true, copyGcgText);
       if (outcome === 'copied') showToast(t('game.gcgCopied'), 'info');
       else if (outcome === 'failed') showToast(t('error.generic'), 'error');
     } catch (e) {
@@ -958,17 +962,24 @@
     }
   }
 
-  // exportImage renders the finished game as a PNG (lib/gameimage, dynamically imported so the
+  // exportArtifact delivers a finished game's artifact by the unified signed-URL route.
-  // renderer stays out of the startup bundle) and delivers it — Web Share where the platform
+  // The device date locale and the UI-localized non-play labels ride the URL so the
-  // supports it, else a download (only reachable outside the in-app WebViews, see
+  // server-rendered image matches what the player would have seen locally.
-  // exportImageAvailable).
+  const EXPORT_ACTIONS = ['pass', 'exchange', 'resign', 'timeout'] as const;
-  async function exportImage() {
+  async function exportArtifact(kind: 'png' | 'gcg') {
-    if (!view) return;
+    if (insideTelegram() && !telegramCanDownloadFile()) {
+      void exportGcgLegacy();
+      return;
+    }
     try {
-      const { renderGameImage } = await import('../lib/gameimage');
+      const labels = EXPORT_ACTIONS.map((a) => t(`move.${a}` as MessageKey));
-      const blob = await renderGameImage(view.game, moves, { actionLabel: moveActionLabel });
+      const dateLocale = typeof navigator !== 'undefined' ? (navigator.language ?? '') : '';
-      const file = new File([blob], `game-${id.slice(0, 8)}.png`, { type: 'image/png' });
+      const timeZone = Intl.DateTimeFormat().resolvedOptions().timeZone ?? '';
-      await shareOrDownloadImage(file);
+      const { path, filename } = await gateway.exportUrl(id, kind, dateLocale, labels, timeZone);
+      const url = new URL(path, location.origin).href;
+      if (insideTelegram() && telegramDownloadFile(url, filename)) return;
+      if (insideVK() && (await vkDownloadFile(url, filename))) return;
+      downloadUrl(url, filename);
     } catch (e) {
       handleError(e);
     }
@@ -1492,13 +1503,17 @@
   <Modal title={t('game.exportGcg')} onclose={() => (exportOpen = false)}>
     <div class="export-opts">
       {#if exportImageAvailable}
-        <button class="confirm" onclick={() => { exportOpen = false; void exportImage(); }}>
+        <button
+          class="confirm"
+          onclick={() => { exportOpen = false; void exportArtifact('png'); }}
+          disabled={!connection.online}
+        >
           {t('game.exportImageOpt')}
         </button>
       {/if}
       <button
         class={exportImageAvailable ? 'export-alt' : 'confirm'}
-        onclick={() => { exportOpen = false; void exportGcg(); }}
+        onclick={() => { exportOpen = false; void exportArtifact('gcg'); }}
         disabled={!connection.online}
       >
         {t('game.exportGcgOpt')}

ui/src/gen/fbs/scrabblefb.ts

@@ -23,6 +23,8 @@ export { EnqueueRequest } from './scrabblefb/enqueue-request.js';
 export { EvalRequest } from './scrabblefb/eval-request.js';
 export { EvalResult } from './scrabblefb/eval-result.js';
 export { ExchangeRequest } from './scrabblefb/exchange-request.js';
+export { ExportUrl } from './scrabblefb/export-url.js';
+export { ExportUrlRequest } from './scrabblefb/export-url-request.js';
 export { FeedbackReply } from './scrabblefb/feedback-reply.js';
 export { FeedbackState } from './scrabblefb/feedback-state.js';
 export { FeedbackSubmitRequest } from './scrabblefb/feedback-submit-request.js';

ui/src/gen/fbs/scrabblefb/export-url-request.ts

@@ -0,0 +1,113 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import * as flatbuffers from 'flatbuffers';
+
+export class ExportUrlRequest {
+  bb: flatbuffers.ByteBuffer|null = null;
+  bb_pos = 0;
+  __init(i:number, bb:flatbuffers.ByteBuffer):ExportUrlRequest {
+  this.bb_pos = i;
+  this.bb = bb;
+  return this;
+}
+
+static getRootAsExportUrlRequest(bb:flatbuffers.ByteBuffer, obj?:ExportUrlRequest):ExportUrlRequest {
+  return (obj || new ExportUrlRequest()).__init(bb.readInt32(bb.position()) + bb.position(), bb);
+}
+
+static getSizePrefixedRootAsExportUrlRequest(bb:flatbuffers.ByteBuffer, obj?:ExportUrlRequest):ExportUrlRequest {
+  bb.setPosition(bb.position() + flatbuffers.SIZE_PREFIX_LENGTH);
+  return (obj || new ExportUrlRequest()).__init(bb.readInt32(bb.position()) + bb.position(), bb);
+}
+
+gameId():string|null
+gameId(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+gameId(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 4);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+kind():string|null
+kind(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+kind(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 6);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+dateLocale():string|null
+dateLocale(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+dateLocale(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 8);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+actionLabels(index: number):string
+actionLabels(index: number,optionalEncoding:flatbuffers.Encoding):string|Uint8Array
+actionLabels(index: number,optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 10);
+  return offset ? this.bb!.__string(this.bb!.__vector(this.bb_pos + offset) + index * 4, optionalEncoding) : null;
+}
+
+actionLabelsLength():number {
+  const offset = this.bb!.__offset(this.bb_pos, 10);
+  return offset ? this.bb!.__vector_len(this.bb_pos + offset) : 0;
+}
+
+timeZone():string|null
+timeZone(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+timeZone(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 12);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+static startExportUrlRequest(builder:flatbuffers.Builder) {
+  builder.startObject(5);
+}
+
+static addGameId(builder:flatbuffers.Builder, gameIdOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(0, gameIdOffset, 0);
+}
+
+static addKind(builder:flatbuffers.Builder, kindOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(1, kindOffset, 0);
+}
+
+static addDateLocale(builder:flatbuffers.Builder, dateLocaleOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(2, dateLocaleOffset, 0);
+}
+
+static addActionLabels(builder:flatbuffers.Builder, actionLabelsOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(3, actionLabelsOffset, 0);
+}
+
+static createActionLabelsVector(builder:flatbuffers.Builder, data:flatbuffers.Offset[]):flatbuffers.Offset {
+  builder.startVector(4, data.length, 4);
+  for (let i = data.length - 1; i >= 0; i--) {
+    builder.addOffset(data[i]!);
+  }
+  return builder.endVector();
+}
+
+static startActionLabelsVector(builder:flatbuffers.Builder, numElems:number) {
+  builder.startVector(4, numElems, 4);
+}
+
+static addTimeZone(builder:flatbuffers.Builder, timeZoneOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(4, timeZoneOffset, 0);
+}
+
+static endExportUrlRequest(builder:flatbuffers.Builder):flatbuffers.Offset {
+  const offset = builder.endObject();
+  return offset;
+}
+
+static createExportUrlRequest(builder:flatbuffers.Builder, gameIdOffset:flatbuffers.Offset, kindOffset:flatbuffers.Offset, dateLocaleOffset:flatbuffers.Offset, actionLabelsOffset:flatbuffers.Offset, timeZoneOffset:flatbuffers.Offset):flatbuffers.Offset {
+  ExportUrlRequest.startExportUrlRequest(builder);
+  ExportUrlRequest.addGameId(builder, gameIdOffset);
+  ExportUrlRequest.addKind(builder, kindOffset);
+  ExportUrlRequest.addDateLocale(builder, dateLocaleOffset);
+  ExportUrlRequest.addActionLabels(builder, actionLabelsOffset);
+  ExportUrlRequest.addTimeZone(builder, timeZoneOffset);
+  return ExportUrlRequest.endExportUrlRequest(builder);
+}
+}

ui/src/gen/fbs/scrabblefb/export-url.ts

@@ -0,0 +1,60 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import * as flatbuffers from 'flatbuffers';
+
+export class ExportUrl {
+  bb: flatbuffers.ByteBuffer|null = null;
+  bb_pos = 0;
+  __init(i:number, bb:flatbuffers.ByteBuffer):ExportUrl {
+  this.bb_pos = i;
+  this.bb = bb;
+  return this;
+}
+
+static getRootAsExportUrl(bb:flatbuffers.ByteBuffer, obj?:ExportUrl):ExportUrl {
+  return (obj || new ExportUrl()).__init(bb.readInt32(bb.position()) + bb.position(), bb);
+}
+
+static getSizePrefixedRootAsExportUrl(bb:flatbuffers.ByteBuffer, obj?:ExportUrl):ExportUrl {
+  bb.setPosition(bb.position() + flatbuffers.SIZE_PREFIX_LENGTH);
+  return (obj || new ExportUrl()).__init(bb.readInt32(bb.position()) + bb.position(), bb);
+}
+
+path():string|null
+path(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+path(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 4);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+filename():string|null
+filename(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+filename(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 6);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+static startExportUrl(builder:flatbuffers.Builder) {
+  builder.startObject(2);
+}
+
+static addPath(builder:flatbuffers.Builder, pathOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(0, pathOffset, 0);
+}
+
+static addFilename(builder:flatbuffers.Builder, filenameOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(1, filenameOffset, 0);
+}
+
+static endExportUrl(builder:flatbuffers.Builder):flatbuffers.Offset {
+  const offset = builder.endObject();
+  return offset;
+}
+
+static createExportUrl(builder:flatbuffers.Builder, pathOffset:flatbuffers.Offset, filenameOffset:flatbuffers.Offset):flatbuffers.Offset {
+  ExportUrl.startExportUrl(builder);
+  ExportUrl.addPath(builder, pathOffset);
+  ExportUrl.addFilename(builder, filenameOffset);
+  return ExportUrl.endExportUrl(builder);
+}
+}

ui/src/lib/client.ts

@@ -14,6 +14,7 @@ import type {
   FriendCode,
   GameList,
   GameView,
+  ExportUrl,
   GcgExport,
   History,
   HintResult,
@@ -161,6 +162,10 @@ export interface GatewayClient {
   profileUpdate(p: ProfileUpdate): Promise<Profile>;
   statsGet(): Promise<Stats>;
   exportGcg(gameId: string): Promise<GcgExport>;
+  /** Mints a signed download URL for a finished game's artifact. dateLocale and the
+   *  localized non-play labels (pass/exchange/resign/timeout, in that order) ride the
+   *  URL so the server-rendered image matches the player's presentation. */
+  exportUrl(gameId: string, kind: 'png' | 'gcg', dateLocale: string, actionLabels: string[], timeZone: string): Promise<ExportUrl>;
 
   // --- account linking & merge ---
   linkEmailRequest(email: string): Promise<void>;

ui/src/lib/codec.test.ts

@@ -6,6 +6,7 @@ import {
   decodeBlockStatus,
   decodeDraftView,
   decodeEvent,
+  decodeExportUrl,
   decodeFriendList,
   decodeGameList,
   decodeInvitation,
@@ -24,6 +25,7 @@ import {
   encodeDraftSave,
   encodeEnqueue,
   encodeExchange,
+  encodeExportUrlRequest,
   encodeGuestLogin,
   encodeStateRequest,
   encodeSubmitPlay,
@@ -34,6 +36,30 @@ import {
 } from './codec';
 
 describe('codec', () => {
+  it('round-trips the export-url request and response', () => {
+    const req = fb.ExportUrlRequest.getRootAsExportUrlRequest(
+      new ByteBuffer(
+        encodeExportUrlRequest('g-1', 'png', 'ru-RU', ['пас', 'обмен', 'сдался', 'таймаут'], 'Europe/Moscow'),
+      ),
+    );
+    expect(req.gameId()).toBe('g-1');
+    expect(req.kind()).toBe('png');
+    expect(req.dateLocale()).toBe('ru-RU');
+    expect(req.timeZone()).toBe('Europe/Moscow');
+    expect(req.actionLabelsLength()).toBe(4);
+    expect(req.actionLabels(1)).toBe('обмен');
+
+    const b = new Builder(128);
+    const path = b.createString('/dl/g-1/png?e=1&s=x');
+    const fn = b.createString('game-g-1.png');
+    fb.ExportUrl.startExportUrl(b);
+    fb.ExportUrl.addPath(b, path);
+    fb.ExportUrl.addFilename(b, fn);
+    b.finish(fb.ExportUrl.endExportUrl(b));
+    const out = decodeExportUrl(b.asUint8Array());
+    expect(out).toEqual({ path: '/dl/g-1/png?e=1&s=x', filename: 'game-g-1.png' });
+  });
+
   it('encodes an enqueue request carrying the variant, word rule and vs_ai flag', () => {
     for (const vsAi of [false, true]) {
       const req = fb.EnqueueRequest.getRootAsEnqueueRequest(

ui/src/lib/codec.ts

@@ -22,6 +22,7 @@ import type {
   EvalResult,
   FeedbackState,
   FriendCode,
+  ExportUrl,
   GameList,
   GameView,
   GcgExport,
@@ -882,6 +883,36 @@ export function decodeGcg(buf: Uint8Array): GcgExport {
   return { gameId: s(g.gameId()), filename: s(g.filename()), content: s(g.content()) };
 }
 
+export function encodeExportUrlRequest(
+  gameId: string,
+  kind: 'png' | 'gcg',
+  dateLocale: string,
+  actionLabels: string[],
+  timeZone: string,
+): Uint8Array {
+  const b = new Builder(256);
+  const gid = b.createString(gameId);
+  const k = b.createString(kind);
+  const dl = b.createString(dateLocale);
+  const tz = b.createString(timeZone);
+  const labels = fb.ExportUrlRequest.createActionLabelsVector(
+    b,
+    actionLabels.map((l) => b.createString(l)),
+  );
+  fb.ExportUrlRequest.startExportUrlRequest(b);
+  fb.ExportUrlRequest.addGameId(b, gid);
+  fb.ExportUrlRequest.addKind(b, k);
+  fb.ExportUrlRequest.addDateLocale(b, dl);
+  fb.ExportUrlRequest.addActionLabels(b, labels);
+  fb.ExportUrlRequest.addTimeZone(b, tz);
+  return finish(b, fb.ExportUrlRequest.endExportUrlRequest(b));
+}
+
+export function decodeExportUrl(buf: Uint8Array): ExportUrl {
+  const e = fb.ExportUrl.getRootAsExportUrl(new ByteBuffer(buf));
+  return { path: s(e.path()), filename: s(e.filename()) };
+}
+
 function emptyGame(): GameView {
   return {
     id: '',

ui/src/lib/gameimage.ts

@@ -1,12 +1,12 @@
 // Finished-game PNG export: a light-theme snapshot of the final board (classic A..O / 1..15
 // axes) with a compact per-seat scoresheet beside it. Everything is drawn by hand on a
-// Canvas 2D — no dependencies — and the module is reached only through a dynamic import, so
+// Canvas 2D — no dependencies. The module is the SHARED source of truth for the export
-// it stays out of the startup bundle. The scoresheet typography is fixed; the board instead
+// image: the render sidecar bundles it (renderer/src/entry.ts) and rasterizes on
-// stretches to the scoresheet's height (never below MIN_SIDE), so a long game grows the
+// skia-canvas, while this ui project keeps the pure parts unit-tested (the browser app
-// board rather than leaving a hole under it.
+// itself no longer imports it — delivery is the server's signed URL).
 //
-// buildScoresheet and layoutImage are pure (vitest-covered); renderGameImage is the thin
+// buildScoresheet and layoutImage are pure (vitest-covered); drawGameImage is the thin
-// canvas pass exercised by the Playwright e2e.
+// canvas pass exercised by the sidecar's node test.
 
 import type { GameView, MoveRecord, Variant } from './model';
 import { replay } from './board';
@@ -56,16 +56,22 @@ export interface Scoresheet {
 }
 
 /** formatFinishedDate renders the game's finish time for the footer in the DEVICE locale
- *  (regional date conventions, not the UI language) — e.g. "3 июля 2026 г., 16:23".
+ *  and time zone (regional conventions, not the UI language) — e.g. "3 июля 2026 г., 16:23".
- *  dateLocale is for tests; production passes undefined = the system default. */
+ *  Both ride in from the client on a server render; an invalid zone falls back to the
-export function formatFinishedDate(unixSec: number, dateLocale?: string): string {
+ *  process default rather than failing the whole image. */
-  return new Intl.DateTimeFormat(dateLocale, {
+export function formatFinishedDate(unixSec: number, dateLocale?: string, timeZone?: string): string {
+  const opts: Intl.DateTimeFormatOptions = {
     year: 'numeric',
     month: 'long',
     day: 'numeric',
     hour: '2-digit',
     minute: '2-digit',
-  }).format(new Date(unixSec * 1000));
+  };
+  try {
+    return new Intl.DateTimeFormat(dateLocale, { ...opts, timeZone }).format(new Date(unixSec * 1000));
+  } catch {
+    return new Intl.DateTimeFormat(dateLocale, opts).format(new Date(unixSec * 1000));
+  }
 }
 
 /**
@@ -78,7 +84,7 @@ export function buildScoresheet(
   game: GameView,
   moves: MoveRecord[],
   actionLabel: (action: string) => string,
-  opts?: { hostname?: string; dateLocale?: string },
+  opts?: { hostname?: string; dateLocale?: string; timeZone?: string },
 ): Scoresheet {
   const seats = game.seats;
   const grid = historyGrid(moves, seats.length, null);
@@ -106,7 +112,7 @@ export function buildScoresheet(
     rows,
     adjustments,
     hasAdjustments: adjustments.some((a) => a !== 0),
-    footer: `${host} · ${formatFinishedDate(game.lastActivityUnix, opts?.dateLocale)}`,
+    footer: `${host} · ${formatFinishedDate(game.lastActivityUnix, opts?.dateLocale, opts?.timeZone)}`,
   };
 }
 
@@ -190,27 +196,36 @@ export interface RenderOptions {
   hostname?: string;
   /** Footer date locale override (defaults to the device locale) — for tests. */
   dateLocale?: string;
+  /** Footer IANA time zone (the device zone on a server render; defaults to local). */
+  timeZone?: string;
   /** Canvas pixel scale (default 2 — crisp on hi-dpi screens and in chats). */
   scale?: number;
 }
 
+/** CanvasLike is the minimal canvas surface drawGameImage needs — satisfied by both the
+ *  browser HTMLCanvasElement and the render sidecar's skia-canvas Canvas, so the drawing
+ *  code is shared verbatim between the two runtimes. */
+export interface CanvasLike {
+  width: number;
+  height: number;
+  getContext(contextId: '2d'): CanvasRenderingContext2D | null;
+}
+
 /**
- * renderGameImage draws the finished game as a PNG blob: final board with classic axes on
+ * drawGameImage sizes the canvas and draws the finished game onto it: final board with
- * the left, the scoresheet on the right, the site + finish date at the bottom. Light theme
+ * classic axes on the left, the scoresheet on the right, the site + finish date at the
- * always; no last-move highlight (an archival artifact, not a live frame).
+ * bottom. Light theme always; no last-move highlight (an archival artifact, not a live
+ * frame). The caller owns the canvas and its PNG encoding (toBlob in the browser,
+ * toBuffer in the sidecar).
  */
-export async function renderGameImage(
+export function drawGameImage(canvas: CanvasLike, game: GameView, moves: MoveRecord[], opts: RenderOptions): void {
-  game: GameView,
-  moves: MoveRecord[],
-  opts: RenderOptions,
-): Promise<Blob> {
   const sheet = buildScoresheet(game, moves, opts.actionLabel, {
     hostname: opts.hostname,
     dateLocale: opts.dateLocale,
+    timeZone: opts.timeZone,
   });
   const layout = layoutImage(sheet);
   const scale = opts.scale ?? 2;
-  const canvas = document.createElement('canvas');
   canvas.width = Math.round(layout.w * scale);
   canvas.height = Math.round(layout.h * scale);
   const ctx = canvas.getContext('2d');
@@ -228,12 +243,9 @@ export async function renderGameImage(
   ctx.textAlign = 'left';
   ctx.textBaseline = 'alphabetic';
   ctx.fillText(sheet.footer, layout.margin, layout.h - layout.margin - 6);
-
-  return new Promise<Blob>((resolve, reject) => {
-    canvas.toBlob((b) => (b ? resolve(b) : reject(new Error('gameimage: toBlob failed'))), 'image/png');
-  });
 }
 
+
 function drawAxes(ctx: CanvasRenderingContext2D, l: ImageLayout): void {
   const { x, y, cell } = l.board;
   ctx.fillStyle = C.muted;

ui/src/lib/mock/client.ts

@@ -21,6 +21,7 @@ import type {
   FeedbackState,
   FriendCode,
   GameList,
+  ExportUrl,
   GcgExport,
   History,
   HintResult,
@@ -677,6 +678,12 @@ export class MockGateway implements GatewayClient {
       content: `#character-encoding UTF-8\n#player1 p1 You\n#player2 p2 Opp\n`,
     };
   }
+  async exportUrl(gameId: string, kind: 'png' | 'gcg'): Promise<ExportUrl> {
+    const g = this.game(gameId);
+    if (g.view.status !== 'finished') throw new GatewayError('game_active');
+    // A shape-faithful signed path; the e2e intercepts the route and serves bytes.
+    return { path: `/dl/${gameId}/${kind}?e=9999999999&s=mock`, filename: `game-${gameId}.${kind}` };
+  }
 
   // --- live stream ---
   subscribe(onEvent: (e: PushEvent) => void): Unsubscribe {

ui/src/lib/model.ts

@@ -326,6 +326,14 @@ export interface GcgExport {
   content: string;
 }
 
+/** A minted signed download link for a finished game's export artifact. path is
+ *  relative — the client resolves it against its own origin (the SPA and the
+ *  gateway edge share it), so the server never needs to know the public host. */
+export interface ExportUrl {
+  path: string;
+  filename: string;
+}
+
 export interface Session {
   token: string;
   userId: string;

ui/src/lib/retry.ts

@@ -47,6 +47,7 @@ export const READ_OPS: ReadonlySet<string> = new Set([
   'game.state',
   'game.history',
   'game.gcg',
+  'game.export_url',
   'game.evaluate',
   'game.check_word',
   'stats.get',

ui/src/lib/share.test.ts

@@ -1,5 +1,5 @@
 import { afterEach, describe, expect, it, vi } from 'vitest';
-import { pickGcgDelivery, pickImageDelivery, pickTextShare, shareOrDownloadGcg, shareOrDownloadImage, shareText } from './share';
+import { downloadUrl, pickGcgDelivery, pickTextShare, shareOrDownloadGcg, shareText } from './share';
 import type { GcgExport } from './model';
 
 const file = {} as File;
@@ -83,52 +83,21 @@ describe('shareOrDownloadGcg', () => {
   });
 });
 
-describe('pickImageDelivery', () => {
+describe('downloadUrl', () => {
-  const canShareNav = { canShare: () => true, share: async () => {} };
-  const noShareNav = { canShare: () => false, share: async () => {} };
-
-  it('shares when the platform can share files', () => {
-    expect(pickImageDelivery(canShareNav, file)).toBe('share');
-  });
-
-  it('downloads on a plain browser without Web Share (desktop)', () => {
-    expect(pickImageDelivery(noShareNav, file)).toBe('download');
-    expect(pickImageDelivery(undefined, file)).toBe('download');
-  });
-});
-
-describe('shareOrDownloadImage', () => {
   afterEach(() => vi.unstubAllGlobals());
 
-  function stubEnv(canShare: boolean, share: () => Promise<void>) {
+  it('clicks a temporary anchor carrying the URL and the filename', () => {
     const anchor = { href: '', download: '', click: vi.fn(), remove: vi.fn() };
     const createElement = vi.fn(() => anchor);
-    vi.stubGlobal('navigator', { canShare: () => canShare, share });
     vi.stubGlobal('document', { createElement, body: { appendChild: vi.fn() } });
-    vi.stubGlobal('URL', { createObjectURL: vi.fn(() => 'blob:x'), revokeObjectURL: vi.fn() });
-    return { anchor, createElement };
-  }
 
-  const png = () => ({ name: 'game-1.png', type: 'image/png' }) as File;
+    downloadUrl('https://example.test/dl/g-1/png?e=1&s=x', 'game-1.png');
-
-  it('never falls back to the navigating Blob download when a share is cancelled', async () => {
-    const share = vi.fn().mockRejectedValue(new DOMException('cancelled', 'AbortError'));
-    const { createElement } = stubEnv(true, share);
-
-    expect(await shareOrDownloadImage(png())).toBe('shared');
-
-    expect(share).toHaveBeenCalledOnce();
-    expect(createElement).not.toHaveBeenCalled();
-  });
-
-  it('downloads via an anchor on a desktop browser that cannot share files', async () => {
-    const { anchor, createElement } = stubEnv(false, vi.fn());
-
-    expect(await shareOrDownloadImage(png())).toBe('downloaded');
 
     expect(createElement).toHaveBeenCalledWith('a');
-    expect(anchor.click).toHaveBeenCalledOnce();
+    expect(anchor.href).toBe('https://example.test/dl/g-1/png?e=1&s=x');
     expect(anchor.download).toBe('game-1.png');
+    expect(anchor.click).toHaveBeenCalledOnce();
+    expect(anchor.remove).toHaveBeenCalledOnce();
   });
 });
 

ui/src/lib/share.ts

@@ -81,43 +81,20 @@ function downloadFile(content: Blob | string, filename: string, type = 'applicat
 }
 
 /**
- * pickImageDelivery decides how to deliver the PNG game image: Web Share (with the file)
+ * downloadUrl saves a same-origin signed export URL as a file through a temporary
- * wherever it exists — mobile browsers and the iOS Telegram Mini App — else a Blob download.
+ * anchor: the server names it via Content-Disposition, the download attribute is the
- * The image option is not offered inside the in-app WebViews at all (Android Telegram/VK, the
+ * same-origin hint. This is the browser leg of the unified export delivery; the in-app
- * desktop VK iframe): a binary PNG has no working route there until the server-rendered
+ * WebViews never reach it (they use the platform's native download call instead), so
- * signed-URL delivery lands, so this decision never sees them. Pure, unit-tested with a mock
+ * the iOS blob-URL navigation trap does not apply — this is a real https URL.
- * navigator.
  */
-export function pickImageDelivery(nav: ShareNav | undefined, file: File): 'share' | 'download' {
+export function downloadUrl(url: string, filename: string): void {
-  if (
+  if (typeof document === 'undefined') return;
-    nav &&
+  const a = document.createElement('a');
-    typeof nav.canShare === 'function' &&
+  a.href = url;
-    typeof nav.share === 'function' &&
+  a.download = filename;
-    nav.canShare({ files: [file] })
+  document.body.appendChild(a);
-  ) {
+  a.click();
-    return 'share';
+  a.remove();
-  }
-  return 'download';
-}
-
-/**
- * shareOrDownloadImage delivers the rendered game image and reports the route taken. The Web
- * Share invariant matches shareOrDownloadGcg: a cancelled or failed share is a deliberate
- * no-op, never a Blob-download fallback (an <a download> strands the iOS WKWebView on the
- * blob: URL).
- */
-export async function shareOrDownloadImage(file: File): Promise<'shared' | 'downloaded'> {
-  const nav = typeof navigator !== 'undefined' ? navigator : undefined;
-  if (pickImageDelivery(nav, file) === 'share' && nav) {
-    try {
-      await nav.share({ files: [file], title: file.name });
-    } catch {
-      /* cancelled or failed — intentionally a no-op (see shareOrDownloadGcg) */
-    }
-    return 'shared';
-  }
-  downloadFile(file, file.name, file.type);
-  return 'downloaded';
 }
 
 type TextShareNav = Pick<Navigator, 'share'> & { canShare?: Navigator['canShare'] };

ui/src/lib/telegram.ts

@@ -67,6 +67,7 @@ interface TelegramWebApp {
   };
   showConfirm?: (message: string, cb?: (ok: boolean) => void) => void;
   showPopup?: (params: TelegramPopupParams, cb?: (buttonId: string) => void) => void;
+  downloadFile?: (params: { url: string; file_name: string }, cb?: (accepted: boolean) => void) => void;
 }
 
 function webApp(): TelegramWebApp | undefined {
@@ -372,7 +373,8 @@ export function telegramShowConfirm(message: string): Promise<boolean> {
 /**
  * telegramShowPopup shows Telegram's native popup and resolves the pressed button id (the empty
  * string when dismissed without pressing a button). Resolves null outside Telegram or on a client
- * predating the popup, so callers can fall back to their own modal.
+ * predating the popup, so callers can fall back to their own modal. NOTE: the callback runs with
+ * no user activation — never lead from it into navigator.share or a clipboard write.
  */
 export function telegramShowPopup(params: TelegramPopupParams): Promise<string | null> {
   const w = webApp();
@@ -380,6 +382,23 @@ export function telegramShowPopup(params: TelegramPopupParams): Promise<string |
   return new Promise((resolve) => w.showPopup!(params, (id) => resolve(id ?? '')));
 }
 
+/** telegramCanDownloadFile reports whether the native download dialog exists (Bot API 8.0). */
+export function telegramCanDownloadFile(): boolean {
+  return !!webApp()?.downloadFile;
+}
+
+/**
+ * telegramDownloadFile asks Telegram to download url as fileName through its native
+ * dialog — the Mini App file delivery that works on every Telegram platform (a webview
+ * <a download> does not). Returns false outside Telegram or on a client predating it.
+ */
+export function telegramDownloadFile(url: string, fileName: string): boolean {
+  const w = webApp();
+  if (!w?.downloadFile) return false;
+  w.downloadFile({ url, file_name: fileName });
+  return true;
+}
+
 /** Haptic is the set of feedbacks the app triggers. */
 export type Haptic = 'select' | 'success' | 'error' | 'warning' | 'light' | 'medium' | 'heavy';
 

ui/src/lib/transport.ts

@@ -271,6 +271,11 @@ export function createTransport(baseUrl: string): GatewayClient {
     async exportGcg(gameId) {
       return codec.decodeGcg(await exec('game.gcg', codec.encodeGameAction(gameId)));
     },
+    async exportUrl(gameId, kind, dateLocale, actionLabels, timeZone) {
+      return codec.decodeExportUrl(
+        await exec('game.export_url', codec.encodeExportUrlRequest(gameId, kind, dateLocale, actionLabels, timeZone)),
+      );
+    },
 
     subscribe(onEvent, onError) {
       const ctrl = new AbortController();

ui/src/lib/vk.ts

@@ -155,6 +155,21 @@ export async function vkShare(link: string): Promise<boolean> {
   }
 }
 
+/**
+ * vkDownloadFile downloads url as filename through the VK client (VKWebAppDownloadFile) —
+ * the mobile in-app file delivery, where the webview ignores <a download>. Resolves false
+ * on any failure or where the method is unavailable (notably the desktop iframe), so the
+ * caller falls back to a plain browser download of the same URL.
+ */
+export async function vkDownloadFile(url: string, filename: string): Promise<boolean> {
+  try {
+    await (await bridge()).send('VKWebAppDownloadFile', { url, filename });
+    return true;
+  } catch {
+    return false;
+  }
+}
+
 /**
  * vkCopyText copies text to the clipboard via VKWebAppCopyText — which works inside the VK iframe,
  * where navigator.clipboard is blocked. Resolves true on success, false on any failure or outside VK.