Stage 15: dual Telegram bots & language-gated variants

Service-agnostic refinement of the owner's idea: the sign-in service returns a
set of supported game languages with the user identity, and the lobby gates the
New Game variant choice by it (en -> English; ru -> Russian + Эрудит).

- Connector hosts two bots in one container (one per service language, each its
  own token + game channel; the same telegram_id spans both). ValidateInitData
  tries each token and returns the validating bot's service_language +
  supported_languages. Per-language config (TELEGRAM_BOT_TOKEN_EN/_RU, channels).
- supported_languages rides the Session (fbs, session-scoped, not persisted); the
  UI offers only the matching variants on New Game — gating only the START of a
  new game (auto-match + friend invite), not accept/open/play; backend does not
  enforce.
- service_language persisted (accounts.service_language, migration 00010, written
  every login, last-login-wins) and routes the user-facing Notify push back
  through the right bot (push-target coalesces with preferred_language).
- Admin SendToUser/SendToGameChannel gain an operator-chosen language selector in
  the console (unrelated to ValidateInitData).
- Non-Telegram logins carry the gateway default set
  (GATEWAY_DEFAULT_SUPPORTED_LANGUAGES, all variants).

Wire (committed regen): ValidateInitDataResponse +service_language
+supported_languages; Session +supported_languages; SendToUser/SendToGameChannel
+language. Docs (ARCHITECTURE/FUNCTIONAL/_ru/READMEs) + PLAN updated; stage marked done.

pkg/proto/telegram/v1/telegram.pb.go

@@ -79,15 +79,22 @@ func (x *ValidateInitDataRequest) GetInitData() string {
 
 // ValidateInitDataResponse is the validated identity. external_id is the Telegram
 // user id used as the identities external_id; language_code seeds a new account's
-// preferred language.
+// preferred (interface) language. service_language (en/ru) is the language tag of
+// the bot that validated the launch data; it is persisted per account and routes
+// the user's out-of-app push back through the right bot (it is NOT the game's
+// language). supported_languages is that bot's set of offered game languages
+// (subset of {en, ru}, at least one — a singleton for a single-language bot); the
+// UI gates the New Game variant choice by it.
 type ValidateInitDataResponse struct {
-	state         protoimpl.MessageState `protogen:"open.v1"`
-	ExternalId    string                 `protobuf:"bytes,1,opt,name=external_id,json=externalId,proto3" json:"external_id,omitempty"`
-	Username      string                 `protobuf:"bytes,2,opt,name=username,proto3" json:"username,omitempty"`
-	FirstName     string                 `protobuf:"bytes,3,opt,name=first_name,json=firstName,proto3" json:"first_name,omitempty"`
-	LanguageCode  string                 `protobuf:"bytes,4,opt,name=language_code,json=languageCode,proto3" json:"language_code,omitempty"`
-	unknownFields protoimpl.UnknownFields
-	sizeCache     protoimpl.SizeCache
+	state              protoimpl.MessageState `protogen:"open.v1"`
+	ExternalId         string                 `protobuf:"bytes,1,opt,name=external_id,json=externalId,proto3" json:"external_id,omitempty"`
+	Username           string                 `protobuf:"bytes,2,opt,name=username,proto3" json:"username,omitempty"`
+	FirstName          string                 `protobuf:"bytes,3,opt,name=first_name,json=firstName,proto3" json:"first_name,omitempty"`
+	LanguageCode       string                 `protobuf:"bytes,4,opt,name=language_code,json=languageCode,proto3" json:"language_code,omitempty"`
+	ServiceLanguage    string                 `protobuf:"bytes,5,opt,name=service_language,json=serviceLanguage,proto3" json:"service_language,omitempty"`
+	SupportedLanguages []string               `protobuf:"bytes,6,rep,name=supported_languages,json=supportedLanguages,proto3" json:"supported_languages,omitempty"`
+	unknownFields      protoimpl.UnknownFields
+	sizeCache          protoimpl.SizeCache
 }
 
 func (x *ValidateInitDataResponse) Reset() {
@@ -148,6 +155,20 @@ func (x *ValidateInitDataResponse) GetLanguageCode() string {
 	return ""
 }
 
+func (x *ValidateInitDataResponse) GetServiceLanguage() string {
+	if x != nil {
+		return x.ServiceLanguage
+	}
+	return ""
+}
+
+func (x *ValidateInitDataResponse) GetSupportedLanguages() []string {
+	if x != nil {
+		return x.SupportedLanguages
+	}
+	return nil
+}
+
 // ValidateLoginWidgetRequest carries the Login Widget result serialized as a URL
 // query string (the widget fields plus the hash, e.g. "auth_date=...&id=...&hash=...").
 type ValidateLoginWidgetRequest struct {
@@ -259,7 +280,9 @@ func (x *ValidateLoginWidgetResponse) GetFirstName() string {
 
 // NotifyRequest addresses a push event to one recipient. kind is the backend push
 // catalog kind (your_turn, nudge, match_found, notify); payload is the FlatBuffers
-// scrabblefb.* body for that kind; language (en/ru) selects the message template.
+// scrabblefb.* body for that kind; language (en/ru) is the recipient's service
+// language (from their last ValidateInitData) — it both selects the delivering bot
+// and the message template.
 type NotifyRequest struct {
 	state         protoimpl.MessageState `protogen:"open.v1"`
 	ExternalId    string                 `protobuf:"bytes,1,opt,name=external_id,json=externalId,proto3" json:"external_id,omitempty"`
@@ -374,11 +397,14 @@ func (x *NotifyResponse) GetDelivered() bool {
 	return false
 }
 
-// SendToUserRequest is an admin text message to one user by external_id.
+// SendToUserRequest is an admin text message to one user by external_id. language
+// (en/ru) selects which bot delivers it — an operator choice in the admin console,
+// unrelated to the user's service language.
 type SendToUserRequest struct {
 	state         protoimpl.MessageState `protogen:"open.v1"`
 	ExternalId    string                 `protobuf:"bytes,1,opt,name=external_id,json=externalId,proto3" json:"external_id,omitempty"`
 	Text          string                 `protobuf:"bytes,2,opt,name=text,proto3" json:"text,omitempty"`
+	Language      string                 `protobuf:"bytes,3,opt,name=language,proto3" json:"language,omitempty"`
 	unknownFields protoimpl.UnknownFields
 	sizeCache     protoimpl.SizeCache
 }
@@ -427,10 +453,20 @@ func (x *SendToUserRequest) GetText() string {
 	return ""
 }
 
-// SendToGameChannelRequest is an admin text message to the configured game channel.
+func (x *SendToUserRequest) GetLanguage() string {
+	if x != nil {
+		return x.Language
+	}
+	return ""
+}
+
+// SendToGameChannelRequest is an admin text message to a game channel. language
+// (en/ru) selects which bot's configured channel receives it — an operator choice
+// in the admin console.
 type SendToGameChannelRequest struct {
 	state         protoimpl.MessageState `protogen:"open.v1"`
 	Text          string                 `protobuf:"bytes,1,opt,name=text,proto3" json:"text,omitempty"`
+	Language      string                 `protobuf:"bytes,2,opt,name=language,proto3" json:"language,omitempty"`
 	unknownFields protoimpl.UnknownFields
 	sizeCache     protoimpl.SizeCache
 }
@@ -472,6 +508,13 @@ func (x *SendToGameChannelRequest) GetText() string {
 	return ""
 }
 
+func (x *SendToGameChannelRequest) GetLanguage() string {
+	if x != nil {
+		return x.Language
+	}
+	return ""
+}
+
 // SendResponse reports whether the message was sent.
 type SendResponse struct {
 	state         protoimpl.MessageState `protogen:"open.v1"`
@@ -523,14 +566,16 @@ const file_telegram_v1_telegram_proto_rawDesc = "" +
 	"\n" +
 	"\x1atelegram/v1/telegram.proto\x12\x14scrabble.telegram.v1\"6\n" +
 	"\x17ValidateInitDataRequest\x12\x1b\n" +
-	"\tinit_data\x18\x01 \x01(\tR\binitData\"\x9b\x01\n" +
+	"\tinit_data\x18\x01 \x01(\tR\binitData\"\xf7\x01\n" +
 	"\x18ValidateInitDataResponse\x12\x1f\n" +
 	"\vexternal_id\x18\x01 \x01(\tR\n" +
 	"externalId\x12\x1a\n" +
 	"\busername\x18\x02 \x01(\tR\busername\x12\x1d\n" +
 	"\n" +
 	"first_name\x18\x03 \x01(\tR\tfirstName\x12#\n" +
-	"\rlanguage_code\x18\x04 \x01(\tR\flanguageCode\"0\n" +
+	"\rlanguage_code\x18\x04 \x01(\tR\flanguageCode\x12)\n" +
+	"\x10service_language\x18\x05 \x01(\tR\x0fserviceLanguage\x12/\n" +
+	"\x13supported_languages\x18\x06 \x03(\tR\x12supportedLanguages\"0\n" +
 	"\x1aValidateLoginWidgetRequest\x12\x12\n" +
 	"\x04data\x18\x01 \x01(\tR\x04data\"y\n" +
 	"\x1bValidateLoginWidgetResponse\x12\x1f\n" +
@@ -546,13 +591,15 @@ const file_telegram_v1_telegram_proto_rawDesc = "" +
 	"\apayload\x18\x03 \x01(\fR\apayload\x12\x1a\n" +
 	"\blanguage\x18\x04 \x01(\tR\blanguage\".\n" +
 	"\x0eNotifyResponse\x12\x1c\n" +
-	"\tdelivered\x18\x01 \x01(\bR\tdelivered\"H\n" +
+	"\tdelivered\x18\x01 \x01(\bR\tdelivered\"d\n" +
 	"\x11SendToUserRequest\x12\x1f\n" +
 	"\vexternal_id\x18\x01 \x01(\tR\n" +
 	"externalId\x12\x12\n" +
-	"\x04text\x18\x02 \x01(\tR\x04text\".\n" +
+	"\x04text\x18\x02 \x01(\tR\x04text\x12\x1a\n" +
+	"\blanguage\x18\x03 \x01(\tR\blanguage\"J\n" +
 	"\x18SendToGameChannelRequest\x12\x12\n" +
-	"\x04text\x18\x01 \x01(\tR\x04text\",\n" +
+	"\x04text\x18\x01 \x01(\tR\x04text\x12\x1a\n" +
+	"\blanguage\x18\x02 \x01(\tR\blanguage\",\n" +
 	"\fSendResponse\x12\x1c\n" +
 	"\tdelivered\x18\x01 \x01(\bR\tdelivered2\x92\x04\n" +
 	"\bTelegram\x12q\n" +

pkg/proto/telegram/v1/telegram.proto

@@ -31,12 +31,13 @@ service Telegram {
   // localized message with a Mini App deep-link button from the FlatBuffers
   // payload; unrenderable kinds are skipped (delivered=false).
   rpc Notify(NotifyRequest) returns (NotifyResponse);
-  // SendToUser sends an arbitrary text message to one user (admin use, wired in
-  // Stage 10). delivered is false when the user has not started the bot.
+  // SendToUser sends an arbitrary text message to one user through the bot the
+  // request selects by language (admin use, wired in Stage 10). delivered is false
+  // when the user has not started that bot.
   rpc SendToUser(SendToUserRequest) returns (SendResponse);
-  // SendToGameChannel posts an arbitrary text message to the bot's configured
-  // game channel (admin use, wired in Stage 10); the channel id lives only in the
-  // connector configuration.
+  // SendToGameChannel posts an arbitrary text message to the game channel of the
+  // bot the request selects by language (admin use, wired in Stage 10); the channel
+  // ids live only in the connector configuration.
   rpc SendToGameChannel(SendToGameChannelRequest) returns (SendResponse);
 }
 
@@ -47,12 +48,19 @@ message ValidateInitDataRequest {
 
 // ValidateInitDataResponse is the validated identity. external_id is the Telegram
 // user id used as the identities external_id; language_code seeds a new account's
-// preferred language.
+// preferred (interface) language. service_language (en/ru) is the language tag of
+// the bot that validated the launch data; it is persisted per account and routes
+// the user's out-of-app push back through the right bot (it is NOT the game's
+// language). supported_languages is that bot's set of offered game languages
+// (subset of {en, ru}, at least one — a singleton for a single-language bot); the
+// UI gates the New Game variant choice by it.
 message ValidateInitDataResponse {
   string external_id = 1;
   string username = 2;
   string first_name = 3;
   string language_code = 4;
+  string service_language = 5;
+  repeated string supported_languages = 6;
 }
 
 // ValidateLoginWidgetRequest carries the Login Widget result serialized as a URL
@@ -72,7 +80,9 @@ message ValidateLoginWidgetResponse {
 
 // NotifyRequest addresses a push event to one recipient. kind is the backend push
 // catalog kind (your_turn, nudge, match_found, notify); payload is the FlatBuffers
-// scrabblefb.* body for that kind; language (en/ru) selects the message template.
+// scrabblefb.* body for that kind; language (en/ru) is the recipient's service
+// language (from their last ValidateInitData) — it both selects the delivering bot
+// and the message template.
 message NotifyRequest {
   string external_id = 1;
   string kind = 2;
@@ -86,15 +96,21 @@ message NotifyResponse {
   bool delivered = 1;
 }
 
-// SendToUserRequest is an admin text message to one user by external_id.
+// SendToUserRequest is an admin text message to one user by external_id. language
+// (en/ru) selects which bot delivers it — an operator choice in the admin console,
+// unrelated to the user's service language.
 message SendToUserRequest {
   string external_id = 1;
   string text = 2;
+  string language = 3;
 }
 
-// SendToGameChannelRequest is an admin text message to the configured game channel.
+// SendToGameChannelRequest is an admin text message to a game channel. language
+// (en/ru) selects which bot's configured channel receives it — an operator choice
+// in the admin console.
 message SendToGameChannelRequest {
   string text = 1;
+  string language = 2;
 }
 
 // SendResponse reports whether the message was sent.

pkg/proto/telegram/v1/telegram_grpc.pb.go

@@ -58,12 +58,13 @@ type TelegramClient interface {
 	// localized message with a Mini App deep-link button from the FlatBuffers
 	// payload; unrenderable kinds are skipped (delivered=false).
 	Notify(ctx context.Context, in *NotifyRequest, opts ...grpc.CallOption) (*NotifyResponse, error)
-	// SendToUser sends an arbitrary text message to one user (admin use, wired in
-	// Stage 10). delivered is false when the user has not started the bot.
+	// SendToUser sends an arbitrary text message to one user through the bot the
+	// request selects by language (admin use, wired in Stage 10). delivered is false
+	// when the user has not started that bot.
 	SendToUser(ctx context.Context, in *SendToUserRequest, opts ...grpc.CallOption) (*SendResponse, error)
-	// SendToGameChannel posts an arbitrary text message to the bot's configured
-	// game channel (admin use, wired in Stage 10); the channel id lives only in the
-	// connector configuration.
+	// SendToGameChannel posts an arbitrary text message to the game channel of the
+	// bot the request selects by language (admin use, wired in Stage 10); the channel
+	// ids live only in the connector configuration.
 	SendToGameChannel(ctx context.Context, in *SendToGameChannelRequest, opts ...grpc.CallOption) (*SendResponse, error)
 }
 
@@ -146,12 +147,13 @@ type TelegramServer interface {
 	// localized message with a Mini App deep-link button from the FlatBuffers
 	// payload; unrenderable kinds are skipped (delivered=false).
 	Notify(context.Context, *NotifyRequest) (*NotifyResponse, error)
-	// SendToUser sends an arbitrary text message to one user (admin use, wired in
-	// Stage 10). delivered is false when the user has not started the bot.
+	// SendToUser sends an arbitrary text message to one user through the bot the
+	// request selects by language (admin use, wired in Stage 10). delivered is false
+	// when the user has not started that bot.
 	SendToUser(context.Context, *SendToUserRequest) (*SendResponse, error)
-	// SendToGameChannel posts an arbitrary text message to the bot's configured
-	// game channel (admin use, wired in Stage 10); the channel id lives only in the
-	// connector configuration.
+	// SendToGameChannel posts an arbitrary text message to the game channel of the
+	// bot the request selects by language (admin use, wired in Stage 10); the channel
+	// ids live only in the connector configuration.
 	SendToGameChannel(context.Context, *SendToGameChannelRequest) (*SendResponse, error)
 	mustEmbedUnimplementedTelegramServer()
 }