feat(export): server-rendered artifacts behind one signed download URL (#160)

The finished-game export (GCG + a new PNG of the final position) is one
signed, short-lived relative URL (game.export_url; HMAC-SHA256, 10-min
TTL, BACKEND_EXPORT_SIGN_KEY) resolved against the client's own origin
and delivered by the best affordance each platform has (five on-device
review rounds):

- TG Android/desktop: native showPopup chooser -> native downloadFile
  dialog (bridge-only chain, activation-safe).
- TG iOS: app-modal chooser -> OS share sheet with the fetched file
  (a popup callback cannot supply the activation the sheet needs).
- VK iOS: VKWebAppDownloadFile for both formats.
- VK Android: the PNG opens in VK's native image viewer, the GCG copies
  to the clipboard (the VK Android downloader hangs on any download,
  Content-Length/Range notwithstanding).
- VK desktop iframe / desktop browsers: plain anchor downloads.
- Mobile browsers: the OS share sheet (fetch-then-share).
- Legacy TG (< Bot API 8.0): app modal + GCG clipboard, no image option.

The PNG is rasterized on demand by the new internal `renderer` sidecar
(node:22-slim + skia-canvas + baked Liberation/Noto Color Emoji fonts)
executing the SAME ui/src/lib/gameimage.ts the ui project unit-tests;
the backend rebuilds the render payload from the journal +
engine.AlphabetTable, and the device date locale, IANA time zone and
localized non-play labels ride the signed URL. Nothing is stored — the
artifact re-derives from the immutable journal on each GET. The gateway
forwards /dl/* (caddy @gateway matcher extended) behind the per-IP
public rate limiter and serves bytes via http.ServeContent.

Deploy: renderer service in compose + prod overlay + rolling order +
prod push list; TEST_/PROD_EXPORT_SIGN_KEY secrets; the sidecar smoke
runs in the ui CI job. Docs: ARCHITECTURE, FUNCTIONAL(+_ru), UI_DESIGN,
TESTING, deploy/README, renderer/README.

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);
+}
+}