feat: "multiple words per turn" rule for Russian games

Add a per-game rule chosen on New Game for Russian variants (default off = the
single-word rule; on = standard Scrabble). Off, only the main word along the play
direction is validated and scored; perpendicular cross-words are ignored,
including in robot move generation. The rule rides every create and enqueue
request and joins the matchmaking key, so games and auto-match stay one uniform
path; "Russian-only" is a UI affordance (English always sends standard and shows
no toggle).

- Engine: consume scrabble-solver v1.1.0's PlayOptions{IgnoreCrossWords}, threaded
  through engine.Options.MultipleWordsPerTurn -> playOpts() into validate, score
  and generate.
- Backend: thread the flag through game CreateParams/Game + store (games column),
  lobby InvitationSettings + invitation row, and the matchmaker queue key (variant
  + rule); persisted, so a rebuilt-from-journal game keeps it. Baseline migration
  gains multiple_words_per_turn (DB not versioned); jet regenerated.
- Edge: multiple_words_per_turn added to the EnqueueRequest / CreateInvitationRequest
  FlatBuffers tables (Go + TS regenerated) and threaded through the gateway.
- UI: a "Multiple words per turn" toggle on New Game, shown for Russian variants
  only (auto-match and friend invite), default off; English silently sends standard.
- Tests: backend engine/matchmaker; UI unit (gating) + Playwright e2e (solver
  corner-case + GCG fixtures ship in v1.1.0). Docs + PRERELEASE tracker updated.

ui/src/gen/fbs/scrabblefb/create-invitation-request.ts

@@ -61,8 +61,13 @@ dropoutTiles(optionalEncoding?:any):string|Uint8Array|null {
   return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
 }
 
+multipleWordsPerTurn():boolean {
+  const offset = this.bb!.__offset(this.bb_pos, 16);
+  return offset ? !!this.bb!.readInt8(this.bb_pos + offset) : false;
+}
+
 static startCreateInvitationRequest(builder:flatbuffers.Builder) {
-  builder.startObject(6);
+  builder.startObject(7);
 }
 
 static addInviteeIds(builder:flatbuffers.Builder, inviteeIdsOffset:flatbuffers.Offset) {
@@ -101,12 +106,16 @@ static addDropoutTiles(builder:flatbuffers.Builder, dropoutTilesOffset:flatbuffe
   builder.addFieldOffset(5, dropoutTilesOffset, 0);
 }
 
+static addMultipleWordsPerTurn(builder:flatbuffers.Builder, multipleWordsPerTurn:boolean) {
+  builder.addFieldInt8(6, +multipleWordsPerTurn, +false);
+}
+
 static endCreateInvitationRequest(builder:flatbuffers.Builder):flatbuffers.Offset {
   const offset = builder.endObject();
   return offset;
 }
 
-static createCreateInvitationRequest(builder:flatbuffers.Builder, inviteeIdsOffset:flatbuffers.Offset, variantOffset:flatbuffers.Offset, turnTimeoutSecs:number, hintsAllowed:boolean, hintsPerPlayer:number, dropoutTilesOffset:flatbuffers.Offset):flatbuffers.Offset {
+static createCreateInvitationRequest(builder:flatbuffers.Builder, inviteeIdsOffset:flatbuffers.Offset, variantOffset:flatbuffers.Offset, turnTimeoutSecs:number, hintsAllowed:boolean, hintsPerPlayer:number, dropoutTilesOffset:flatbuffers.Offset, multipleWordsPerTurn:boolean):flatbuffers.Offset {
   CreateInvitationRequest.startCreateInvitationRequest(builder);
   CreateInvitationRequest.addInviteeIds(builder, inviteeIdsOffset);
   CreateInvitationRequest.addVariant(builder, variantOffset);
@@ -114,6 +123,7 @@ static createCreateInvitationRequest(builder:flatbuffers.Builder, inviteeIdsOffs
   CreateInvitationRequest.addHintsAllowed(builder, hintsAllowed);
   CreateInvitationRequest.addHintsPerPlayer(builder, hintsPerPlayer);
   CreateInvitationRequest.addDropoutTiles(builder, dropoutTilesOffset);
+  CreateInvitationRequest.addMultipleWordsPerTurn(builder, multipleWordsPerTurn);
   return CreateInvitationRequest.endCreateInvitationRequest(builder);
 }
 }

ui/src/gen/fbs/scrabblefb/enqueue-request.ts

@@ -27,22 +27,32 @@ variant(optionalEncoding?:any):string|Uint8Array|null {
   return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
 }
 
+multipleWordsPerTurn():boolean {
+  const offset = this.bb!.__offset(this.bb_pos, 6);
+  return offset ? !!this.bb!.readInt8(this.bb_pos + offset) : false;
+}
+
 static startEnqueueRequest(builder:flatbuffers.Builder) {
-  builder.startObject(1);
+  builder.startObject(2);
 }
 
 static addVariant(builder:flatbuffers.Builder, variantOffset:flatbuffers.Offset) {
   builder.addFieldOffset(0, variantOffset, 0);
 }
 
+static addMultipleWordsPerTurn(builder:flatbuffers.Builder, multipleWordsPerTurn:boolean) {
+  builder.addFieldInt8(1, +multipleWordsPerTurn, +false);
+}
+
 static endEnqueueRequest(builder:flatbuffers.Builder):flatbuffers.Offset {
   const offset = builder.endObject();
   return offset;
 }
 
-static createEnqueueRequest(builder:flatbuffers.Builder, variantOffset:flatbuffers.Offset):flatbuffers.Offset {
+static createEnqueueRequest(builder:flatbuffers.Builder, variantOffset:flatbuffers.Offset, multipleWordsPerTurn:boolean):flatbuffers.Offset {
   EnqueueRequest.startEnqueueRequest(builder);
   EnqueueRequest.addVariant(builder, variantOffset);
+  EnqueueRequest.addMultipleWordsPerTurn(builder, multipleWordsPerTurn);
   return EnqueueRequest.endEnqueueRequest(builder);
 }
 }

ui/src/lib/client.ts

@@ -63,7 +63,7 @@ export interface GatewayClient {
   gamesList(): Promise<GameList>;
 
   // --- lobby ---
-  lobbyEnqueue(variant: Variant): Promise<MatchResult>;
+  lobbyEnqueue(variant: Variant, multipleWords: boolean): Promise<MatchResult>;
   lobbyPoll(): Promise<MatchResult>;
   /** Leave the auto-match pool (idempotent); a cancelled quick-match must not stay queued. */
   lobbyCancel(): Promise<void>;

ui/src/lib/codec.ts

@@ -149,11 +149,12 @@ export function encodeComplaint(gameId: string, word: string, note: string): Uin
   return finish(b, fb.ComplaintRequest.endComplaintRequest(b));
 }
 
-export function encodeEnqueue(variant: Variant): Uint8Array {
+export function encodeEnqueue(variant: Variant, multipleWords: boolean): Uint8Array {
   const b = new Builder(64);
   const v = b.createString(variant);
   fb.EnqueueRequest.startEnqueueRequest(b);
   fb.EnqueueRequest.addVariant(b, v);
+  fb.EnqueueRequest.addMultipleWordsPerTurn(b, multipleWords);
   return finish(b, fb.EnqueueRequest.endEnqueueRequest(b));
 }
 
@@ -523,6 +524,7 @@ export function encodeCreateInvitation(inviteeIds: string[], st: InvitationSetti
   fb.CreateInvitationRequest.addHintsAllowed(b, st.hintsAllowed);
   fb.CreateInvitationRequest.addHintsPerPlayer(b, st.hintsPerPlayer);
   fb.CreateInvitationRequest.addDropoutTiles(b, dropout);
+  fb.CreateInvitationRequest.addMultipleWordsPerTurn(b, st.multipleWordsPerTurn);
   return finish(b, fb.CreateInvitationRequest.endCreateInvitationRequest(b));
 }
 

ui/src/lib/i18n/en.ts

@@ -232,6 +232,7 @@ export const en = {
   'new.invite': 'Send invitation',
   'new.moveTime': 'Move time',
   'new.hintsPerPlayer': 'Hints per player',
+  'new.multipleWordsPerTurn': 'Multiple words per turn',
   'new.invited': 'Invitation sent.',
   'new.noFriends': 'Add friends first to invite them.',
 

ui/src/lib/i18n/ru.ts

@@ -233,6 +233,7 @@ export const ru: Record<MessageKey, string> = {
   'new.invite': 'Отправить приглашение',
   'new.moveTime': 'Время на ход',
   'new.hintsPerPlayer': 'Подсказок на игрока',
+  'new.multipleWordsPerTurn': 'Несколько слов за ход',
   'new.invited': 'Приглашение отправлено.',
   'new.noFriends': 'Сначала добавьте друзей, чтобы пригласить их.',
 

ui/src/lib/mock/client.ts

@@ -142,7 +142,7 @@ export class MockGateway implements GatewayClient {
   }
 
   // --- lobby ---
-  async lobbyEnqueue(variant: Variant): Promise<MatchResult> {
+  async lobbyEnqueue(variant: Variant, _multipleWords: boolean): Promise<MatchResult> {
     // Simulate a 10s-style robot substitution, sped up: match found shortly.
     const id = crypto.randomUUID();
     const g: MockGame = {

ui/src/lib/model.ts

@@ -158,6 +158,8 @@ export interface InvitationSettings {
   hintsAllowed: boolean;
   hintsPerPlayer: number;
   dropoutTiles: 'remove' | 'return';
+  /** true = standard Scrabble; false = the single-word rule (Russian games). */
+  multipleWordsPerTurn: boolean;
 }
 
 export interface InvitationInvitee {

ui/src/lib/transport.ts

@@ -81,8 +81,8 @@ export function createTransport(baseUrl: string): GatewayClient {
       return codec.decodeGameList(await exec('games.list', codec.empty()));
     },
 
-    async lobbyEnqueue(variant) {
-      return codec.decodeMatchResult(await exec('lobby.enqueue', codec.encodeEnqueue(variant)));
+    async lobbyEnqueue(variant, multipleWords) {
+      return codec.decodeMatchResult(await exec('lobby.enqueue', codec.encodeEnqueue(variant, multipleWords)));
     },
     async lobbyPoll() {
       return codec.decodeMatchResult(await exec('lobby.poll', codec.empty()));

ui/src/lib/variants.test.ts

@@ -1,6 +1,11 @@
 import { describe, it, expect } from 'vitest';
 
-import { ALL_VARIANTS, availableVariants } from './variants';
+import {
+  ALL_VARIANTS,
+  availableVariants,
+  supportsMultipleWordsToggle,
+  multipleWordsForRequest,
+} from './variants';
 
 describe('availableVariants', () => {
   it('is ungated (all variants) for an empty or absent set', () => {
@@ -20,3 +25,24 @@ describe('availableVariants', () => {
     expect(availableVariants(['en', 'ru']).map((v) => v.id)).toEqual(['scrabble_en', 'scrabble_ru', 'erudit_ru']);
   });
 });
+
+describe('supportsMultipleWordsToggle', () => {
+  it('is true for Russian variants only', () => {
+    expect(supportsMultipleWordsToggle('scrabble_ru')).toBe(true);
+    expect(supportsMultipleWordsToggle('erudit_ru')).toBe(true);
+    expect(supportsMultipleWordsToggle('scrabble_en')).toBe(false);
+  });
+});
+
+describe('multipleWordsForRequest', () => {
+  it('carries the toggle for Russian games', () => {
+    expect(multipleWordsForRequest('scrabble_ru', false)).toBe(false);
+    expect(multipleWordsForRequest('scrabble_ru', true)).toBe(true);
+    expect(multipleWordsForRequest('erudit_ru', false)).toBe(false);
+  });
+
+  it('forces standard (true) for English whatever the toggle', () => {
+    expect(multipleWordsForRequest('scrabble_en', false)).toBe(true);
+    expect(multipleWordsForRequest('scrabble_en', true)).toBe(true);
+  });
+});

ui/src/lib/variants.ts

@@ -55,3 +55,17 @@ export function availableVariants(supportedLanguages: string[] | undefined): Var
   if (langs.length === 0) return ALL_VARIANTS;
   return ALL_VARIANTS.filter((v) => langs.includes(VARIANT_LANGUAGE[v.id]));
 }
+
+// supportsMultipleWordsToggle reports whether the New Game "multiple words per turn" toggle
+// applies to a variant. Only Russian games choose the rule; English is always standard, so
+// its toggle is not shown.
+export function supportsMultipleWordsToggle(v: Variant): boolean {
+  return VARIANT_LANGUAGE[v] === 'ru';
+}
+
+// multipleWordsForRequest resolves the per-turn word rule sent when starting a game of the
+// variant: Russian games carry the toggle's value, English games are silently standard
+// (true), so matchmaking and game creation stay one uniform path.
+export function multipleWordsForRequest(v: Variant, toggle: boolean): boolean {
+  return supportsMultipleWordsToggle(v) ? toggle : true;
+}

ui/src/screens/NewGame.svelte

@@ -7,7 +7,13 @@
   import { navigate } from '../lib/router.svelte';
   import { t, type MessageKey } from '../lib/i18n/index.svelte';
   import type { AccountRef, Variant } from '../lib/model';
-  import { availableVariants, VARIANT_FLAG, VARIANT_RULES } from '../lib/variants';
+  import {
+    availableVariants,
+    VARIANT_FLAG,
+    VARIANT_RULES,
+    supportsMultipleWordsToggle,
+    multipleWordsForRequest,
+  } from '../lib/variants';
 
   // The auto-match move clock (mirrors backend game.DefaultTurnTimeout = 24h).
   const AUTO_MATCH_HOURS = 24;
@@ -15,6 +21,10 @@
   // The offered variants are gated by the languages the sign-in service supports;
   // the auto-match list and the friend-invite picker both use this.
   const variants = $derived(availableVariants(app.session?.supportedLanguages));
+  // "Multiple words per turn" off is the single-word rule; it is offered for Russian games
+  // only (English is always standard and shows no toggle). Shared by both flows.
+  let multipleWords = $state(false);
+  const autoHasRussian = $derived(variants.some((v) => supportsMultipleWordsToggle(v.id)));
   const timeouts = [
     { secs: 300, key: 'time.minutes' as MessageKey, n: 5 },
     { secs: 1800, key: 'time.minutes' as MessageKey, n: 30 },
@@ -70,7 +80,7 @@
     searching = true;
     matched = false;
     try {
-      const r = await gateway.lobbyEnqueue(v);
+      const r = await gateway.lobbyEnqueue(v, multipleWordsForRequest(v, multipleWords));
       if (r.matched && r.game) {
         matched = true;
         searching = false;
@@ -137,6 +147,7 @@
         hintsAllowed: hints > 0,
         hintsPerPlayer: hints,
         dropoutTiles: 'remove',
+        multipleWordsPerTurn: multipleWordsForRequest(inviteVariant, multipleWords),
       });
       showToast(t('new.invited'));
       navigate('/');
@@ -171,6 +182,12 @@
 
       {#if mode === 'auto'}
         <p class="subtitle">{t('new.subtitle')}</p>
+        {#if autoHasRussian}
+          <label class="toggle">
+            <span>{t('new.multipleWordsPerTurn')}</span>
+            <input type="checkbox" bind:checked={multipleWords} />
+          </label>
+        {/if}
         <div class="variants">
           {#each variants as v (v.id)}
             <button class="variant" onclick={() => find(v.id)} disabled={!connection.online}>
@@ -225,6 +242,12 @@
               </select>
             </label>
           </div>
+          {#if inviteVariant && supportsMultipleWordsToggle(inviteVariant)}
+            <label class="toggle">
+              <span>{t('new.multipleWordsPerTurn')}</span>
+              <input type="checkbox" bind:checked={multipleWords} />
+            </label>
+          {/if}
           <button class="invite" disabled={selected.length === 0 || !inviteVariant || !connection.online} onclick={sendInvite}>{t('new.invite')}</button>
         </div>
       {/if}
@@ -385,6 +408,21 @@
   .field select.placeholder {
     color: var(--text-muted);
   }
+  .toggle {
+    display: flex;
+    align-items: center;
+    justify-content: space-between;
+    gap: 8px;
+    padding: 11px;
+    border: 1px solid var(--border);
+    background: var(--surface);
+    border-radius: var(--radius-sm);
+    user-select: none;
+  }
+  .toggle span {
+    font-size: 0.85rem;
+    color: var(--text);
+  }
   .muted {
     color: var(--text-muted);
     margin: 0;