feat(variants): default a registered account to Erudit + Russian Scrabble

New Game opened on a single variant for everyone, which reads poorly on VK
where Russian Scrabble is the familiar game. A registered account now starts
with both Russian-alphabet games, so the picker offers a real choice with no
pre-selection.

A guest stays on Erudit alone and is invited to register for the rest: the
device-local guest has no profile at all, so the client-side fallback has to
keep matching the server. Registering promotes the set, but only while the
guest still carries the untouched guest default. Existing accounts are not
backfilled — the set they carry may be a deliberate choice.

The Telegram promo start-param becomes additive rather than a replacement,
with English Scrabble withheld from a Russian-speaking arrival; otherwise the
English campaign link would have taken Russian Scrabble away from every
account it onboarded.

docs/ARCHITECTURE.md

@@ -245,9 +245,15 @@ arrive from a platform rather than completing a mandatory registration).
   than stranding a user who never opened Settings on the creation-time seed.
 - **Variant preferences (New Game gating).** Which variants a player may be matched into is a
   per-user **profile** setting — `variant_preferences`, a set of `engine.Variant` labels
-  (`scrabble_en`, `scrabble_ru`, `erudit_ru`) edited on the Settings/Profile screen. New
-  accounts default to **Erudit only** (a DB column default); at least one variant must stay
-  selected. The picker is ordered **Erudit-first** everywhere. The preference gates the New
+  (`scrabble_en`, `scrabble_ru`, `erudit_ru`) edited on the Settings/Profile screen. A newly
+  **registered** account defaults to the two Russian-alphabet games — **Erudit + Russian
+  Scrabble** (a DB column default); a **guest** is deliberately narrower and starts on
+  **Erudit only** (`account.ProvisionGuest` writes the set explicitly), with New Game inviting
+  the guest to register for the rest. Registering promotes the set to the registered default
+  (`account.ClearGuest`), but only while the guest still carries the untouched guest set —
+  a player who chose their own set is never overruled, and **existing accounts are not
+  backfilled** when the default moves. At least one variant must stay selected. The picker is
+  ordered **Erudit-first** everywhere. The preference gates the New
   Game picker on every create path the player **initiates** — auto-match, vs-AI and a friend
   invitation the player **creates** — and the backend **enforces** it on those paths (a chosen
   variant outside the caller's preferences is rejected with HTTP 400). An **invited** friend
@@ -316,6 +322,18 @@ arrive from a platform rather than completing a mandatory registration).
 > `service_language`/`supported_languages` and the push `language` routing field, and
 > gained `variant_preferences` on Profile/UpdateProfile.
 
+> **Decision (2026-07-27) — registered accounts start on both Russian games.** The
+> Erudit-only default was too narrow a first impression on VK, where Russian Scrabble is the
+> familiar game: a **registered** account is now created with `erudit_ru + scrabble_ru`, so
+> New Game opens with a real choice (and therefore no pre-selected variant). A **guest**
+> stays on Erudit alone and is invited to register for the rest, which keeps the offline
+> device-local guest — who has no profile at all — matching the server. **Existing accounts
+> are not backfilled**: the set a player already carries may be a deliberate choice, and the
+> two are indistinguishable in the data. The Telegram promo `start_param` correspondingly
+> became **additive** rather than a replacement (it can only widen a set), with English
+> Scrabble withheld from a Russian-speaking arrival — otherwise the English campaign link
+> would have quietly taken Russian Scrabble away from every account it onboarded.
+
 ## 4. Accounts, identities, linking & merge
 
 - One internal account may carry several **platform identities**
@@ -883,7 +901,8 @@ in either direction (the enqueue excludes the caller's `BlockedWith` set);
 - **Profile**: `preferred_language` (en/ru; tracks the interface language — §4), display name, email
   (confirm-code binding, see §4), **timezone**, the daily **away window**, the
   **variant preferences** (`variant_preferences`, the matchable-variant set that gates New
-  Game — §3, defaulting to Erudit only, at least one enforced) and the
+  Game — §3, defaulting to Erudit + Russian Scrabble for a registered account and Erudit
+  alone for a guest, at least one enforced) and the
   block toggles — all editable through `account.UpdateProfile`, which validates them:
   a display name is Unicode letters joined by single ` `/`.`/`_`
   separators (no leading/trailing/adjacent separators, ≤ 32 runes); the timezone is a

docs/FUNCTIONAL.md

@@ -174,7 +174,8 @@ resigning or by letting it lapse to the 7-day timeout — drops from your *finis
 automatically, with no swipe needed; a normally finished AI game stays until you remove it, and
 no other game type is auto-removed. The game types offered on **New Game** are
 limited to the player's chosen **variant preferences** (see *Profile & settings*) —
-Erudite-first, defaulting to Erudite only. Variants are shown by their **display name** — both Scrabble variants read
+Erudite-first, defaulting to Erudite + Russian Scrabble for a registered player and to Erudite
+alone for a guest. Variants are shown by their **display name** — both Scrabble variants read
 "Scrabble"/"Скрэббл" and Erudit reads "Erudite"/"Эрудит" (by the interface language), and
 the same name titles the in-game screen. This gates only **starting** a new game you initiate —
 auto-match, a vs-AI game and a friend invitation **you create** — so a player still sees and plays
@@ -451,8 +452,11 @@ per-device preference and is hidden on desktop, where the board already fits and
 
 **Preferences (which variants you can be matched into).** A profile setting picks the game
 variants — Erudite, Russian Scrabble and English Scrabble, shown **Erudite-first** — you allow
-yourself to be matched into; a **new account starts with Erudite only** — unless it was created
-through the **promo bot's deep link**, which also enables **English Scrabble** — and you must keep
+yourself to be matched into; a **newly registered account starts with Erudite + Russian
+Scrabble**, and arriving through the **promo bot's deep link** also enables **English Scrabble**
+when your Telegram language is not Russian. A **guest** starts with **Erudite only** and New Game
+invites them to register for the rest; registering widens the account to the registered default.
+Changing the defaults never rewrites accounts that already exist. You must keep
 **at least one** selected. This list is exactly what **New Game** offers when you start a game
 (auto-match, an AI game, or a friend invitation you create) — a variant you have not enabled is
 not offered, and the server refuses it. It does not restrict games you are **invited** to: an

docs/FUNCTIONAL_ru.md

@@ -177,7 +177,8 @@ e-mail) либо ввод фразы. Активные игры форфейтя
 уберёшь её, и никакие другие типы партий автоматически не убираются. Типы партий
 на экране **Новая игра**
 ограничены выбранными игроком **предпочтениями вариантов** (см. «Профиль и
-настройки») — сначала Эрудит, по умолчанию только Эрудит. Варианты показываются под **отображаемым именем** — оба варианта Scrabble
+настройки») — сначала Эрудит, по умолчанию Эрудит и русский Scrabble у зарегистрированного игрока
+и только Эрудит у гостя. Варианты показываются под **отображаемым именем** — оба варианта Scrabble
 читаются как «Scrabble»/«Скрэббл», а Erudit — «Erudite»/«Эрудит» (по языку интерфейса),
 и это же имя выносится в заголовок экрана игры. Это ограничивает только **старт** игры, которую ты
 инициируешь, — авто-подбор, игру с ИИ и приглашение друга, которое ты **создаёшь**, — поэтому игрок
@@ -458,9 +459,12 @@ Telegram. Внутри VK Mini App те же настройки — и язык
 
 **Предпочтения (в какие варианты тебя можно подбирать).** Настройка профиля задаёт варианты
 игры — Эрудит, русский Scrabble и английский Scrabble, показанные **сначала Эрудит**, — в
-которые ты разрешаешь себя подбирать; **новый аккаунт стартует только с Эрудитом** — если только
-он не создан по **диплинку промо-бота**, который дополнительно включает **английский Scrabble**, —
-и нужно оставить выбранным **хотя бы один**. Именно этот список предлагает **Новая игра**, когда ты
+которые ты разрешаешь себя подбирать; **новый зарегистрированный аккаунт стартует с Эрудитом и
+русским Scrabble**, а вход по **диплинку промо-бота** дополнительно включает **английский
+Scrabble**, если язык Telegram не русский. **Гость** стартует **только с Эрудитом**, и «Новая игра»
+предлагает ему зарегистрироваться ради остальных; регистрация расширяет аккаунт до набора
+зарегистрированного. Смена набора по умолчанию никогда не переписывает уже существующие аккаунты.
+Нужно оставить выбранным **хотя бы один**. Именно этот список предлагает **Новая игра**, когда ты
 запускаешь партию (авто-подбор, игра с ИИ или приглашение друга, которое ты создаёшь), — не
 включённый вариант не предлагается, и сервер его отклоняет. На партии, в которые тебя
 **приглашают**, это не влияет: приглашённый друг может принять приглашение в **любом** варианте,