diff --git a/.gitea/workflows/deploy.yml b/.gitea/workflows/deploy.yml
index ec20fd7..866ed7d 100644
--- a/.gitea/workflows/deploy.yml
+++ b/.gitea/workflows/deploy.yml
@@ -6,7 +6,7 @@ on:
       - main 
 
 env:
-  VERSION: 2.4.0
+  VERSION: 2.5.0
 
 jobs:
   # ЧАСТЬ 1: Собираем образы и кладем в Gitea (чтобы делиться с ребятами)
diff --git a/Directory.Build.props b/Directory.Build.props
index e36cb8b..1e9ffab 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -1,6 +1,6 @@
 <Project>
   <PropertyGroup>
-    <Version>2.4.0</Version>
+    <Version>2.5.0</Version>
     <TargetFramework>net10.0</TargetFramework>
     <LangVersion>preview</LangVersion>
     <Nullable>enable</Nullable>
diff --git a/README.md b/README.md
index fcfe606..b6a2d2a 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@
 
 Проект разработан с упором на производительность, архитектуру Vertical Slice, Native AOT (для бота) и удобство развертывания с использованием .NET Aspire.
 
-**Текущая версия:** `v2.2.0`.
+**Текущая версия:** `v2.5.0`.
 
 ---
 
@@ -24,6 +24,11 @@
 - **⬆️ Управление очередью**: Веб-интерфейс показывает заполненность, лист ожидания и позволяет ГМу поднять первого игрока из очереди.
 - **🔄 Автоматическая синхронизация**: Любые изменения в веб-интерфейсе мгновенно обновляют сообщения с расписанием в Telegram-чатах игроков.
 
+### Discord Bot
+- **Slash-команды расписания**: GM создаёт сессию через `/newsession` и публикует актуальное расписание через `/listsessions`.
+- **Кнопки записи и выхода**: игроки нажимают Join/Leave в Discord-сообщении; бот отвечает ephemeral-сообщением и обновляет schedule message.
+- **Лимиты и waitlist**: при заполненном составе игрок попадает в waitlist, а при выходе участника первый ожидающий автоматически продвигается в основной состав.
+
 ### 🌐 Web Dashboard (Blazor Server)
 - **🔐 Авторизация через Telegram**: Telegram Login Widget с HMAC-SHA256 валидацией.
 - **📱 Telegram Mini App Dashboard**: Мобильная панель открывается из Telegram, проверяет `initData` на сервере, учитывает safe-area телефона и верхнюю панель Telegram.
@@ -108,6 +113,8 @@ docker compose up -d
 1. Напишите боту `/start`.
 2. Создайте группу через `/newgroup`.
 3. Откройте Mini App или Web Dashboard для расширенного управления.
+4. Для Discord пригласите application bot на сервер с правами `bot` и `applications.commands`.
+5. В Discord создайте сессию через `/newsession` или опубликуйте расписание через `/listsessions`; игроки записываются и выходят кнопками в опубликованном сообщении.
 
 ## 💾 Backup и восстановление
 
diff --git a/compose.yaml b/compose.yaml
index 9b27593..c75a26c 100644
--- a/compose.yaml
+++ b/compose.yaml
@@ -49,7 +49,7 @@ services:
         crond -f
 
   bot:
-    image: git.codeanddice.ru/toutsu/gmrelay-bot:2.4.0
+    image: git.codeanddice.ru/toutsu/gmrelay-bot:2.5.0
     restart: always
     depends_on:
       db:
@@ -67,7 +67,7 @@ services:
       retries: 3
 
   discord:
-    image: git.codeanddice.ru/toutsu/gmrelay-discord-bot:2.4.0
+    image: git.codeanddice.ru/toutsu/gmrelay-discord-bot:2.5.0
     restart: always
     depends_on:
       db:
@@ -79,7 +79,7 @@ services:
       - gmrelay
 
   web:
-    image: git.codeanddice.ru/toutsu/gmrelay-web:2.4.0
+    image: git.codeanddice.ru/toutsu/gmrelay-web:2.5.0
     restart: always
     depends_on:
       db:
diff --git a/docs/c4-system-context.md b/docs/c4-system-context.md
index c16acfb..2030035 100644
--- a/docs/c4-system-context.md
+++ b/docs/c4-system-context.md
@@ -1,4 +1,4 @@
-# GM-Relay — C4 Model
+# GM-Relay - C4 Model
 
 ## Level 1: System Context
 
@@ -6,19 +6,24 @@
 C4Context
     title GM-Relay System Context
 
-    Person(gm, "Game Master", "Создаёт сессии, управляет расписанием игр")
-    Person(player, "Player", "Подтверждает участие через inline-кнопки")
+    Person(gm, "Game Master", "Creates sessions and manages schedules")
+    Person(player, "Player", "Joins, leaves, confirms, and receives reminders")
 
-    System(gmrelay, "GM-Relay Bot", "Telegram Worker Service на Raspberry Pi. Управляет подтверждениями, рассылает напоминания и ссылки.")
+    System(gmrelay, "GM-Relay", "Telegram bot, Discord worker, web dashboard, and shared scheduling logic")
 
-    System_Ext(telegram, "Telegram Bot API", "Long Polling. Сообщения, inline keyboards, callback queries.")
-    SystemDb_Ext(postgres, "PostgreSQL", "Сессии, игроки, RSVP-статусы")
+    System_Ext(telegram, "Telegram Bot API", "Commands, inline keyboards, callback queries, Mini App entry points")
+    System_Ext(discord, "Discord Gateway and REST API", "Slash commands, button interactions, message edits, ephemeral replies")
+    SystemDb_Ext(postgres, "PostgreSQL", "Sessions, players, participants, groups, platform identities")
 
-    Rel(gm, telegram, "Команды бота (/newsession)")
-    Rel(player, telegram, "Нажимает кнопки (✅ Буду / ❌ Не смогу)")
-    Rel(telegram, gmrelay, "Updates (Long Polling)")
+    Rel(gm, telegram, "Creates and manages sessions")
+    Rel(gm, discord, "Uses /newsession and /listsessions")
+    Rel(player, telegram, "Uses inline buttons")
+    Rel(player, discord, "Uses Join/Leave buttons")
+    Rel(telegram, gmrelay, "Updates via long polling")
+    Rel(discord, gmrelay, "Gateway events and component interactions")
     Rel(gmrelay, telegram, "SendMessage, EditMessage, AnswerCallbackQuery")
-    Rel(gmrelay, postgres, "SQL (Npgsql + Dapper)")
+    Rel(gmrelay, discord, "Send/edit schedule messages and ephemeral interaction replies")
+    Rel(gmrelay, postgres, "SQL via Npgsql and Dapper")
 ```
 
 ## Level 2: Container
@@ -30,49 +35,76 @@ C4Container
     Person(gm, "Game Master")
     Person(player, "Player")
 
-    System_Boundary(pi, "Raspberry Pi 5") {
-        Container(bot, "GmRelay.Bot", "Worker Service, .NET 10 AOT", "Long polling, обработка команд и callback queries, планировщик")
-        ContainerDb(db, "PostgreSQL 16", "Database", "sessions, players, session_participants, game_groups")
+    System_Boundary(runtime, "Docker Compose / Aspire runtime") {
+        Container(bot, "GmRelay.Bot", "Worker Service, .NET 10 AOT", "Telegram long polling, commands, callback routing, reminders")
+        Container(discordBot, "GmRelay.DiscordBot", "Worker Service, .NET 10", "NetCord Gateway, slash commands, Join/Leave button interactions")
+        Container(web, "GmRelay.Web", "Blazor Server", "Dashboard, Mini App pages, editing and stats")
+        Container(shared, "GmRelay.Shared", ".NET library", "Shared domain models, rendering, and platform-neutral join/leave handlers")
+        ContainerDb(db, "PostgreSQL", "Database", "sessions, players, session_participants, game_groups, platform identities")
     }
 
     System_Ext(telegram, "Telegram Bot API")
+    System_Ext(discord, "Discord Gateway and REST API")
 
     Rel(gm, telegram, "Commands")
-    Rel(player, telegram, "Callback Queries")
-    Rel(telegram, bot, "GetUpdates (Long Polling)")
+    Rel(gm, discord, "Slash commands")
+    Rel(player, telegram, "Callback queries")
+    Rel(player, discord, "Button interactions")
+    Rel(telegram, bot, "GetUpdates")
+    Rel(discord, discordBot, "Gateway events")
     Rel(bot, telegram, "Bot API calls")
+    Rel(discordBot, discord, "REST send/edit/reply calls")
+    Rel(bot, shared, "Uses shared renderers and join/leave handlers")
+    Rel(discordBot, shared, "Uses shared renderers and join/leave handlers")
+    Rel(web, shared, "Uses shared domain and rendering models")
     Rel(bot, db, "Npgsql + Dapper.AOT")
+    Rel(discordBot, db, "Npgsql + Dapper")
+    Rel(web, db, "Npgsql + Dapper")
 ```
 
-## Level 3: Component (GmRelay.Bot)
+## Level 3: Component - Session Interactions
 
 ```mermaid
 C4Component
-    title GmRelay.Bot Components
+    title Platform-Neutral Session Interactions
 
-    Container_Boundary(bot, "GmRelay.Bot") {
-        Component(polling, "TelegramBotService", "BackgroundService", "Long polling loop, получает Updates")
-        Component(router, "UpdateRouter", "C#", "Маршрутизирует Update → Handler по типу")
-        Component(scheduler, "SessionSchedulerService", "BackgroundService", "PeriodicTimer(60s): T-24ч и T-5мин триггеры")
-        Component(migrator, "DbMigrator", "DbUp", "SQL миграции при старте")
-
-        Component(confirm, "SendConfirmationHandler", "Feature", "Отправляет inline keyboard за 24ч")
-        Component(rsvp, "HandleRsvpHandler", "Feature", "Обрабатывает ✅/❌, проверяет all-confirmed")
-        Component(link, "SendJoinLinkHandler", "Feature", "Отправляет join link за 5 мин")
+    Container_Boundary(shared, "GmRelay.Shared") {
+        Component(join, "JoinSessionHandler", "Feature handler", "Adds players as Active or Waitlisted with session row locking")
+        Component(leave, "LeaveSessionHandler", "Feature handler", "Removes players and promotes the first waitlisted player when capacity allows")
+        Component(updateLock, "ScheduleMessageUpdateLock", "In-memory keyed lock", "Serializes DB changes and schedule message edits per platform message")
+        Component(renderer, "SessionBatchViewBuilder", "Renderer model builder", "Builds platform-neutral schedule views and actions")
     }
 
-    System_Ext(telegram, "Telegram Bot API")
-    ContainerDb(db, "PostgreSQL")
+    Container_Boundary(discordBot, "GmRelay.DiscordBot") {
+        Component(discordModule, "DiscordSessionInteractionModule", "NetCord component module", "Maps join_session/leave_session buttons to neutral commands")
+        Component(discordMessenger, "DiscordPlatformMessenger", "IPlatformMessenger", "Edits Discord schedule messages and stores interaction replies")
+    }
 
-    Rel(polling, router, "Update")
-    Rel(router, rsvp, "CallbackQuery rsvp:*")
-    Rel(scheduler, confirm, "T-24h trigger")
-    Rel(scheduler, link, "T-5min trigger")
-    Rel(confirm, telegram, "SendMessage + InlineKeyboard")
-    Rel(rsvp, telegram, "EditMessage + AnswerCallback")
-    Rel(link, telegram, "SendMessage + user mentions")
-    Rel(confirm, db, "SELECT/UPDATE sessions")
-    Rel(rsvp, db, "UPDATE participants, SELECT counts")
-    Rel(link, db, "SELECT confirmed players")
-    Rel(migrator, db, "DDL migrations")
+    Container_Boundary(bot, "GmRelay.Bot") {
+        Component(updateRouter, "UpdateRouter", "Telegram adapter", "Maps callback queries to neutral commands")
+        Component(telegramMessenger, "TelegramPlatformMessenger", "IPlatformMessenger", "Edits Telegram schedule messages and answers callback queries")
+    }
+
+    ContainerDb(db, "PostgreSQL")
+    System_Ext(telegram, "Telegram Bot API")
+    System_Ext(discord, "Discord Gateway and REST API")
+
+    Rel(discord, discordModule, "Button interaction")
+    Rel(discordModule, join, "JoinSessionCommand")
+    Rel(discordModule, leave, "LeaveSessionCommand")
+    Rel(discordModule, discord, "Deferred ephemeral reply, then modify response")
+    Rel(updateRouter, join, "JoinSessionCommand")
+    Rel(updateRouter, leave, "LeaveSessionCommand")
+    Rel(join, updateLock, "Acquire by PlatformMessageRef")
+    Rel(leave, updateLock, "Acquire by PlatformMessageRef")
+    Rel(join, db, "SELECT FOR UPDATE, INSERT participant")
+    Rel(leave, db, "SELECT FOR UPDATE, DELETE/promote participant")
+    Rel(join, renderer, "Build updated schedule view")
+    Rel(leave, renderer, "Build updated schedule view")
+    Rel(join, discordMessenger, "Update Discord schedule when command is Discord")
+    Rel(leave, discordMessenger, "Update Discord schedule when command is Discord")
+    Rel(join, telegramMessenger, "Update Telegram schedule when command is Telegram")
+    Rel(leave, telegramMessenger, "Update Telegram schedule when command is Telegram")
+    Rel(discordMessenger, discord, "ModifyMessage + ephemeral text")
+    Rel(telegramMessenger, telegram, "EditMessage + AnswerCallbackQuery")
 ```
diff --git a/src/GmRelay.Bot/Infrastructure/Telegram/UpdateRouter.cs b/src/GmRelay.Bot/Infrastructure/Telegram/UpdateRouter.cs
index 1491842..ec5f8d9 100644
--- a/src/GmRelay.Bot/Infrastructure/Telegram/UpdateRouter.cs
+++ b/src/GmRelay.Bot/Infrastructure/Telegram/UpdateRouter.cs
@@ -1,5 +1,6 @@
 // ... UpdateRouter will have CancelSessionHandler and cancel_session route instead of close_recruitment
 using GmRelay.Shared.Domain;
+using GmRelay.Shared.Features.Sessions.CreateSession;
 using GmRelay.Shared.Rendering;
 using GmRelay.Bot.Features.Confirmation.HandleRsvp;
 using GmRelay.Bot.Features.Sessions.CreateSession;
diff --git a/src/GmRelay.Bot/Program.cs b/src/GmRelay.Bot/Program.cs
index 9db67ef..38abc3e 100644
--- a/src/GmRelay.Bot/Program.cs
+++ b/src/GmRelay.Bot/Program.cs
@@ -10,6 +10,7 @@ using GmRelay.Bot.Infrastructure.Health;
 using GmRelay.Bot.Infrastructure.Logging;
 using GmRelay.Bot.Infrastructure.Scheduling;
 using GmRelay.Bot.Infrastructure.Telegram;
+using GmRelay.Shared.Features.Sessions.CreateSession;
 using GmRelay.Shared.Platform;
 using Npgsql;
 using Telegram.Bot;
@@ -63,6 +64,7 @@ builder.Services.AddSingleton<ISendJoinLinkHandler>(sp => sp.GetRequiredService<
 builder.Services.AddSingleton<SendOneHourReminderHandler>();
 builder.Services.AddSingleton<ISendOneHourReminderHandler>(sp => sp.GetRequiredService<SendOneHourReminderHandler>());
 builder.Services.AddSingleton<CreateSessionHandler>();
+builder.Services.AddSingleton<IScheduleMessageUpdateLock, ScheduleMessageUpdateLock>();
 builder.Services.AddSingleton<JoinSessionHandler>();
 builder.Services.AddSingleton<LeaveSessionHandler>();
 builder.Services.AddSingleton<PromoteWaitlistedPlayerHandler>();
diff --git a/src/GmRelay.Bot/packages.lock.json b/src/GmRelay.Bot/packages.lock.json
index 2b3b5c5..af21e45 100644
--- a/src/GmRelay.Bot/packages.lock.json
+++ b/src/GmRelay.Bot/packages.lock.json
@@ -661,7 +661,12 @@
         }
       },
       "gmrelay.shared": {
-        "type": "Project"
+        "type": "Project",
+        "dependencies": {
+          "Dapper": "[2.1.72, )",
+          "Microsoft.Extensions.Logging.Abstractions": "[10.0.5, )",
+          "Npgsql": "[10.0.2, )"
+        }
       }
     },
     "net10.0/win-x64": {
diff --git a/src/GmRelay.DiscordBot/Features/Sessions/DiscordSessionInteractionMapper.cs b/src/GmRelay.DiscordBot/Features/Sessions/DiscordSessionInteractionMapper.cs
new file mode 100644
index 0000000..c8a5e98
--- /dev/null
+++ b/src/GmRelay.DiscordBot/Features/Sessions/DiscordSessionInteractionMapper.cs
@@ -0,0 +1,64 @@
+using GmRelay.Shared.Features.Sessions.CreateSession;
+using GmRelay.Shared.Platform;
+
+namespace GmRelay.DiscordBot.Features.Sessions;
+
+public sealed record DiscordSessionInteractionInput(
+    Guid SessionId,
+    string InteractionId,
+    string GuildId,
+    string ChannelId,
+    string MessageId,
+    ulong UserId,
+    string Username,
+    string? DisplayName);
+
+public static class DiscordSessionInteractionMapper
+{
+    public static bool TryParseCustomId(string customId, string expectedAction, out Guid sessionId)
+    {
+        sessionId = default;
+
+        var parts = customId.Split(':', 2);
+        return parts.Length == 2
+            && string.Equals(parts[0], expectedAction, StringComparison.Ordinal)
+            && Guid.TryParse(parts[1], out sessionId);
+    }
+
+    public static JoinSessionCommand CreateJoinCommand(DiscordSessionInteractionInput input) =>
+        new(
+            SessionId: input.SessionId,
+            User: CreateUser(input),
+            InteractionId: input.InteractionId,
+            Group: CreateGroup(input),
+            ScheduleMessage: CreateMessageRef(input));
+
+    public static LeaveSessionCommand CreateLeaveCommand(DiscordSessionInteractionInput input) =>
+        new(
+            SessionId: input.SessionId,
+            User: CreateUser(input),
+            InteractionId: input.InteractionId,
+            Group: CreateGroup(input),
+            ScheduleMessage: CreateMessageRef(input));
+
+    private static PlatformUser CreateUser(DiscordSessionInteractionInput input) =>
+        new(
+            PlatformKind.Discord,
+            input.UserId.ToString(System.Globalization.CultureInfo.InvariantCulture),
+            string.IsNullOrWhiteSpace(input.DisplayName) ? input.Username : input.DisplayName,
+            input.Username);
+
+    private static PlatformGroup CreateGroup(DiscordSessionInteractionInput input) =>
+        new(
+            PlatformKind.Discord,
+            input.GuildId,
+            input.GuildId,
+            input.ChannelId);
+
+    private static PlatformMessageRef CreateMessageRef(DiscordSessionInteractionInput input) =>
+        new(
+            PlatformKind.Discord,
+            input.GuildId,
+            null,
+            input.MessageId);
+}
diff --git a/src/GmRelay.DiscordBot/Features/Sessions/DiscordSessionInteractionModule.cs b/src/GmRelay.DiscordBot/Features/Sessions/DiscordSessionInteractionModule.cs
new file mode 100644
index 0000000..11f46d1
--- /dev/null
+++ b/src/GmRelay.DiscordBot/Features/Sessions/DiscordSessionInteractionModule.cs
@@ -0,0 +1,101 @@
+using GmRelay.DiscordBot.Infrastructure.Discord;
+using GmRelay.Shared.Features.Sessions.CreateSession;
+using NetCord;
+using NetCord.Rest;
+using NetCord.Services.ComponentInteractions;
+
+namespace GmRelay.DiscordBot.Features.Sessions;
+
+public sealed class DiscordSessionInteractionModule(
+    JoinSessionHandler joinSessionHandler,
+    LeaveSessionHandler leaveSessionHandler,
+    DiscordInteractionReplyCache interactionReplies,
+    ILogger<DiscordSessionInteractionModule> logger) : ComponentInteractionModule<ButtonInteractionContext>
+{
+    [ComponentInteraction("join_session")]
+    public async Task JoinAsync(string sessionId)
+    {
+        if (!Guid.TryParse(sessionId, out var parsedSessionId))
+        {
+            await RespondAsync(CreateEphemeralReply("Session button is outdated."));
+            return;
+        }
+
+        var input = CreateInput(parsedSessionId);
+        await RespondAsync(InteractionCallback.DeferredMessage(MessageFlags.Ephemeral));
+        try
+        {
+            await joinSessionHandler.HandleAsync(
+                DiscordSessionInteractionMapper.CreateJoinCommand(input),
+                CancellationToken.None);
+        }
+        catch (Exception ex)
+        {
+            logger.LogError(ex, "Failed to handle Discord join interaction for session {SessionId}", parsedSessionId);
+            await CompleteResponseAsync("Не удалось обработать кнопку.");
+            return;
+        }
+
+        await CompleteWithStoredReplyAsync(input.InteractionId);
+    }
+
+    [ComponentInteraction("leave_session")]
+    public async Task LeaveAsync(string sessionId)
+    {
+        if (!Guid.TryParse(sessionId, out var parsedSessionId))
+        {
+            await RespondAsync(CreateEphemeralReply("Session button is outdated."));
+            return;
+        }
+
+        var input = CreateInput(parsedSessionId);
+        await RespondAsync(InteractionCallback.DeferredMessage(MessageFlags.Ephemeral));
+        try
+        {
+            await leaveSessionHandler.HandleAsync(
+                DiscordSessionInteractionMapper.CreateLeaveCommand(input),
+                CancellationToken.None);
+        }
+        catch (Exception ex)
+        {
+            logger.LogError(ex, "Failed to handle Discord leave interaction for session {SessionId}", parsedSessionId);
+            await CompleteResponseAsync("Не удалось обработать кнопку.");
+            return;
+        }
+
+        await CompleteWithStoredReplyAsync(input.InteractionId);
+    }
+
+    private DiscordSessionInteractionInput CreateInput(Guid sessionId)
+    {
+        var guild = Context.Guild
+            ?? throw new InvalidOperationException("Session buttons can only be used in a guild.");
+        var message = Context.Interaction.Message
+            ?? throw new InvalidOperationException("Session button interaction must include a message.");
+
+        return new DiscordSessionInteractionInput(
+            SessionId: sessionId,
+            InteractionId: Context.Interaction.Id.ToString(System.Globalization.CultureInfo.InvariantCulture),
+            GuildId: guild.Id.ToString(System.Globalization.CultureInfo.InvariantCulture),
+            ChannelId: Context.Channel.Id.ToString(System.Globalization.CultureInfo.InvariantCulture),
+            MessageId: message.Id.ToString(System.Globalization.CultureInfo.InvariantCulture),
+            UserId: Context.User.Id,
+            Username: Context.User.Username,
+            DisplayName: Context.User.GlobalName);
+    }
+
+    private async Task CompleteWithStoredReplyAsync(string interactionId)
+    {
+        var reply = interactionReplies.Take(interactionId);
+        await CompleteResponseAsync(reply?.Text ?? "Session updated.");
+    }
+
+    private Task CompleteResponseAsync(string text) =>
+        ModifyResponseAsync(options => options.Content = text);
+
+    private static InteractionCallbackProperties CreateEphemeralReply(string text) =>
+        InteractionCallback.Message(
+            new InteractionMessageProperties()
+                .WithContent(text)
+                .WithFlags(MessageFlags.Ephemeral));
+}
diff --git a/src/GmRelay.DiscordBot/Infrastructure/Discord/DiscordInteractionReplyCache.cs b/src/GmRelay.DiscordBot/Infrastructure/Discord/DiscordInteractionReplyCache.cs
new file mode 100644
index 0000000..5a80d9b
--- /dev/null
+++ b/src/GmRelay.DiscordBot/Infrastructure/Discord/DiscordInteractionReplyCache.cs
@@ -0,0 +1,17 @@
+using System.Collections.Concurrent;
+using GmRelay.Shared.Platform;
+
+namespace GmRelay.DiscordBot.Infrastructure.Discord;
+
+public sealed class DiscordInteractionReplyCache
+{
+    private readonly ConcurrentDictionary<string, PlatformInteractionReply> replies = new(StringComparer.Ordinal);
+
+    public void Store(PlatformInteractionReply reply) =>
+        replies[reply.InteractionId] = reply;
+
+    public PlatformInteractionReply? Take(string interactionId) =>
+        replies.TryRemove(interactionId, out var reply)
+            ? reply
+            : null;
+}
diff --git a/src/GmRelay.DiscordBot/Infrastructure/Discord/DiscordPlatformMessenger.cs b/src/GmRelay.DiscordBot/Infrastructure/Discord/DiscordPlatformMessenger.cs
index bc435bc..3d68f36 100644
--- a/src/GmRelay.DiscordBot/Infrastructure/Discord/DiscordPlatformMessenger.cs
+++ b/src/GmRelay.DiscordBot/Infrastructure/Discord/DiscordPlatformMessenger.cs
@@ -6,7 +6,9 @@ using NetCord.Rest;
 
 namespace GmRelay.DiscordBot.Infrastructure.Discord;
 
-public sealed class DiscordPlatformMessenger(RestClient restClient) : IPlatformMessenger
+public sealed class DiscordPlatformMessenger(
+    RestClient restClient,
+    DiscordInteractionReplyCache interactionReplies) : IPlatformMessenger
 {
     public async Task<PlatformMessageRef> SendScheduleAsync(PlatformScheduleMessage message, CancellationToken ct)
     {
@@ -61,6 +63,7 @@ public sealed class DiscordPlatformMessenger(RestClient restClient) : IPlatformM
 
     public Task AnswerInteractionAsync(PlatformInteractionReply reply, CancellationToken ct)
     {
+        interactionReplies.Store(reply);
         return Task.CompletedTask;
     }
 
diff --git a/src/GmRelay.DiscordBot/Program.cs b/src/GmRelay.DiscordBot/Program.cs
index 172ec82..79ddff8 100644
--- a/src/GmRelay.DiscordBot/Program.cs
+++ b/src/GmRelay.DiscordBot/Program.cs
@@ -2,6 +2,7 @@ using GmRelay.DiscordBot;
 using GmRelay.DiscordBot.Features.Sessions;
 using GmRelay.DiscordBot.Infrastructure.Discord;
 using GmRelay.DiscordBot.Infrastructure.Logging;
+using GmRelay.Shared.Features.Sessions.CreateSession;
 using GmRelay.Shared.Platform;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
@@ -43,6 +44,10 @@ builder.Services.AddSingleton<NpgsqlDataSource>(sp =>
 builder.Services.AddSingleton<DiscordPermissionChecker>();
 builder.Services.AddSingleton<DiscordListSessionsHandler>();
 builder.Services.AddSingleton<DiscordNewSessionHandler>();
+builder.Services.AddSingleton<IScheduleMessageUpdateLock, ScheduleMessageUpdateLock>();
+builder.Services.AddSingleton<JoinSessionHandler>();
+builder.Services.AddSingleton<LeaveSessionHandler>();
+builder.Services.AddSingleton<DiscordInteractionReplyCache>();
 builder.Services.AddSingleton<IPlatformMessenger, DiscordPlatformMessenger>();
 
 builder.Services
diff --git a/src/GmRelay.DiscordBot/packages.lock.json b/src/GmRelay.DiscordBot/packages.lock.json
index b96db0c..cd04943 100644
--- a/src/GmRelay.DiscordBot/packages.lock.json
+++ b/src/GmRelay.DiscordBot/packages.lock.json
@@ -666,7 +666,12 @@
         }
       },
       "gmrelay.shared": {
-        "type": "Project"
+        "type": "Project",
+        "dependencies": {
+          "Dapper": "[2.1.72, )",
+          "Microsoft.Extensions.Logging.Abstractions": "[10.0.5, )",
+          "Npgsql": "[10.0.2, )"
+        }
       }
     }
   }
diff --git a/src/GmRelay.Bot/Features/Sessions/CreateSession/JoinSessionHandler.cs b/src/GmRelay.Shared/Features/Sessions/CreateSession/JoinSessionHandler.cs
similarity index 92%
rename from src/GmRelay.Bot/Features/Sessions/CreateSession/JoinSessionHandler.cs
rename to src/GmRelay.Shared/Features/Sessions/CreateSession/JoinSessionHandler.cs
index 8301f8d..0486b11 100644
--- a/src/GmRelay.Bot/Features/Sessions/CreateSession/JoinSessionHandler.cs
+++ b/src/GmRelay.Shared/Features/Sessions/CreateSession/JoinSessionHandler.cs
@@ -4,8 +4,9 @@ using Npgsql;
 using GmRelay.Shared.Domain;
 using GmRelay.Shared.Platform;
 using GmRelay.Shared.Rendering;
+using Microsoft.Extensions.Logging;
 
-namespace GmRelay.Bot.Features.Sessions.CreateSession;
+namespace GmRelay.Shared.Features.Sessions.CreateSession;
 
 public sealed record JoinSessionCommand(
     Guid SessionId,
@@ -15,15 +16,17 @@ public sealed record JoinSessionCommand(
     PlatformMessageRef ScheduleMessage);
 
 // DTOs for AOT compilation
-internal sealed record JoinSessionBatchDto(Guid BatchId, string Title, int? MaxPlayers);
+internal sealed record JoinSessionBatchDto(Guid BatchId, string Title, string Status, int? MaxPlayers);
 
 public sealed class JoinSessionHandler(
     NpgsqlDataSource dataSource,
     IPlatformMessenger messenger,
+    IScheduleMessageUpdateLock scheduleUpdateLock,
     ILogger<JoinSessionHandler> logger)
 {
     public async Task HandleAsync(JoinSessionCommand command, CancellationToken ct)
     {
+        await using var updateLock = await scheduleUpdateLock.AcquireAsync(command.ScheduleMessage, ct);
         await using var connection = await dataSource.OpenConnectionAsync(ct);
         await using var transaction = await connection.BeginTransactionAsync(ct);
         var transactionCommitted = false;
@@ -64,7 +67,7 @@ public sealed class JoinSessionHandler(
 
             // 2. Блокируем сессию на время расчета мест, чтобы параллельные нажатия не переполнили состав.
             var batchInfo = await connection.QuerySingleOrDefaultAsync<JoinSessionBatchDto>(
-                @"SELECT batch_id as BatchId, title as Title, max_players as MaxPlayers
+                @"SELECT batch_id as BatchId, title as Title, status as Status, max_players as MaxPlayers
                   FROM sessions
                   WHERE id = @SessionId
                   FOR UPDATE",
@@ -78,6 +81,13 @@ public sealed class JoinSessionHandler(
                 return;
             }
 
+            if (SessionStatus.IsCancelled(batchInfo.Status))
+            {
+                await transaction.RollbackAsync(ct);
+                await AnswerAsync(command.InteractionId, "Сессия уже отменена.", ct);
+                return;
+            }
+
             var existingRegistrationStatus = await connection.ExecuteScalarAsync<string?>(
                 """
                 SELECT sp.registration_status
diff --git a/src/GmRelay.Bot/Features/Sessions/CreateSession/LeaveSessionHandler.cs b/src/GmRelay.Shared/Features/Sessions/CreateSession/LeaveSessionHandler.cs
similarity index 97%
rename from src/GmRelay.Bot/Features/Sessions/CreateSession/LeaveSessionHandler.cs
rename to src/GmRelay.Shared/Features/Sessions/CreateSession/LeaveSessionHandler.cs
index 872c5b9..d58325b 100644
--- a/src/GmRelay.Bot/Features/Sessions/CreateSession/LeaveSessionHandler.cs
+++ b/src/GmRelay.Shared/Features/Sessions/CreateSession/LeaveSessionHandler.cs
@@ -2,9 +2,10 @@ using Dapper;
 using GmRelay.Shared.Domain;
 using GmRelay.Shared.Platform;
 using GmRelay.Shared.Rendering;
+using Microsoft.Extensions.Logging;
 using Npgsql;
 
-namespace GmRelay.Bot.Features.Sessions.CreateSession;
+namespace GmRelay.Shared.Features.Sessions.CreateSession;
 
 public sealed record LeaveSessionCommand(
     Guid SessionId,
@@ -20,10 +21,12 @@ internal sealed record LeaveSessionPromotionDto(Guid ParticipantRowId, string Di
 public sealed class LeaveSessionHandler(
     NpgsqlDataSource dataSource,
     IPlatformMessenger messenger,
+    IScheduleMessageUpdateLock scheduleUpdateLock,
     ILogger<LeaveSessionHandler> logger)
 {
     public async Task HandleAsync(LeaveSessionCommand command, CancellationToken ct)
     {
+        await using var updateLock = await scheduleUpdateLock.AcquireAsync(command.ScheduleMessage, ct);
         await using var connection = await dataSource.OpenConnectionAsync(ct);
         await using var transaction = await connection.BeginTransactionAsync(ct);
         var transactionCommitted = false;
diff --git a/src/GmRelay.Shared/Features/Sessions/CreateSession/ScheduleMessageUpdateLock.cs b/src/GmRelay.Shared/Features/Sessions/CreateSession/ScheduleMessageUpdateLock.cs
new file mode 100644
index 0000000..4fd546e
--- /dev/null
+++ b/src/GmRelay.Shared/Features/Sessions/CreateSession/ScheduleMessageUpdateLock.cs
@@ -0,0 +1,39 @@
+using System.Collections.Concurrent;
+using GmRelay.Shared.Platform;
+
+namespace GmRelay.Shared.Features.Sessions.CreateSession;
+
+public interface IScheduleMessageUpdateLock
+{
+    ValueTask<IAsyncDisposable> AcquireAsync(PlatformMessageRef scheduleMessage, CancellationToken ct);
+}
+
+public sealed class ScheduleMessageUpdateLock : IScheduleMessageUpdateLock
+{
+    private readonly ConcurrentDictionary<string, SemaphoreSlim> locks = new(StringComparer.Ordinal);
+
+    public async ValueTask<IAsyncDisposable> AcquireAsync(PlatformMessageRef scheduleMessage, CancellationToken ct)
+    {
+        var key = CreateKey(scheduleMessage);
+        var semaphore = locks.GetOrAdd(key, _ => new SemaphoreSlim(1, 1));
+        await semaphore.WaitAsync(ct);
+        return new Releaser(semaphore);
+    }
+
+    private static string CreateKey(PlatformMessageRef scheduleMessage) =>
+        string.Join(
+            '\u001F',
+            scheduleMessage.Platform.ToString(),
+            scheduleMessage.ExternalGroupId,
+            scheduleMessage.ExternalThreadId ?? string.Empty,
+            scheduleMessage.ExternalMessageId);
+
+    private sealed class Releaser(SemaphoreSlim semaphore) : IAsyncDisposable
+    {
+        public ValueTask DisposeAsync()
+        {
+            semaphore.Release();
+            return ValueTask.CompletedTask;
+        }
+    }
+}
diff --git a/src/GmRelay.Shared/GmRelay.Shared.csproj b/src/GmRelay.Shared/GmRelay.Shared.csproj
index 97acdba..e9d03bc 100644
--- a/src/GmRelay.Shared/GmRelay.Shared.csproj
+++ b/src/GmRelay.Shared/GmRelay.Shared.csproj
@@ -7,4 +7,10 @@
     <LangVersion>preview</LangVersion>
   </PropertyGroup>
 
+  <ItemGroup>
+    <PackageReference Include="Dapper" Version="2.1.72" />
+    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.5" />
+    <PackageReference Include="Npgsql" Version="10.0.2" />
+  </ItemGroup>
+
 </Project>
diff --git a/src/GmRelay.Shared/packages.lock.json b/src/GmRelay.Shared/packages.lock.json
index 36d6a25..e4562f5 100644
--- a/src/GmRelay.Shared/packages.lock.json
+++ b/src/GmRelay.Shared/packages.lock.json
@@ -2,11 +2,40 @@
   "version": 1,
   "dependencies": {
     "net10.0": {
+      "Dapper": {
+        "type": "Direct",
+        "requested": "[2.1.72, )",
+        "resolved": "2.1.72",
+        "contentHash": "ns4mGqQd9a/MhP8m6w556vVlZIa0/MfUu03zrxjZC/jlr1uVCsUac8bkdB+Fs98Llbd56rRSo1eZH5VVmeGZyw=="
+      },
+      "Microsoft.Extensions.Logging.Abstractions": {
+        "type": "Direct",
+        "requested": "[10.0.5, )",
+        "resolved": "10.0.5",
+        "contentHash": "9HOdqlDtPptVcmKAjsQ/Nr5Rxfq6FMYLdhvZh1lVmeKR738qeYecQD7+ldooXf+u2KzzR1kafSphWngIM3C6ug==",
+        "dependencies": {
+          "Microsoft.Extensions.DependencyInjection.Abstractions": "10.0.5"
+        }
+      },
+      "Npgsql": {
+        "type": "Direct",
+        "requested": "[10.0.2, )",
+        "resolved": "10.0.2",
+        "contentHash": "q5RfBI+wywJSFUNDE1L4ZbHEHCFTblo8Uf6A6oe4feOUFYiUQXyAf9GBh5qEZpvJaHiEbpBPkQumjEhXCJxdrg==",
+        "dependencies": {
+          "Microsoft.Extensions.Logging.Abstractions": "10.0.0"
+        }
+      },
       "SecurityCodeScan.VS2019": {
         "type": "Direct",
         "requested": "[5.6.7, )",
         "resolved": "5.6.7",
         "contentHash": "WIE9RJswdSc2j+rLz2gW6U+gMUjMHzY2j7C/CL8/R2olXNM/+twarfMnWqm+rZodDBvaYDApJyxM8mVYf9FGrQ=="
+      },
+      "Microsoft.Extensions.DependencyInjection.Abstractions": {
+        "type": "Transitive",
+        "resolved": "10.0.5",
+        "contentHash": "iVMtq9eRvzyhx8949EGT0OCYJfXi737SbRVzWXE5GrOgGj5AaZ9eUuxA/BSUfmOMALKn/g8KfFaNQw0eiB3lyA=="
       }
     }
   }
diff --git a/src/GmRelay.Web/Components/Layout/NavMenu.razor b/src/GmRelay.Web/Components/Layout/NavMenu.razor
index 11a6f1b..b23560e 100644
--- a/src/GmRelay.Web/Components/Layout/NavMenu.razor
+++ b/src/GmRelay.Web/Components/Layout/NavMenu.razor
@@ -56,7 +56,7 @@
                     </button>
                 </form>
 
-                <div class="nav-version">v2.4.0</div>
+                <div class="nav-version">v2.5.0</div>
             </div>
         </Authorized>
         <NotAuthorized>
diff --git a/src/GmRelay.Web/packages.lock.json b/src/GmRelay.Web/packages.lock.json
index 8c9ff76..59e2dac 100644
--- a/src/GmRelay.Web/packages.lock.json
+++ b/src/GmRelay.Web/packages.lock.json
@@ -243,7 +243,11 @@
         }
       },
       "gmrelay.shared": {
-        "type": "Project"
+        "type": "Project",
+        "dependencies": {
+          "Dapper": "[2.1.72, )",
+          "Npgsql": "[10.0.2, )"
+        }
       }
     }
   }
diff --git a/tests/GmRelay.Bot.Tests/Discord/DiscordPlatformMessengerTests.cs b/tests/GmRelay.Bot.Tests/Discord/DiscordPlatformMessengerTests.cs
index a59eaee..dfbcb0a 100644
--- a/tests/GmRelay.Bot.Tests/Discord/DiscordPlatformMessengerTests.cs
+++ b/tests/GmRelay.Bot.Tests/Discord/DiscordPlatformMessengerTests.cs
@@ -7,9 +7,13 @@ namespace GmRelay.Bot.Tests.Discord;
 public sealed class DiscordPlatformMessengerTests
 {
     [Fact]
-    public void Constructor_ShouldAcceptRestClient()
+    public void Constructor_ShouldAcceptRestClientAndReplyCache()
     {
-        var constructor = typeof(DiscordPlatformMessenger).GetConstructor(new[] { typeof(NetCord.Rest.RestClient) });
+        var constructor = typeof(DiscordPlatformMessenger).GetConstructor(new[]
+        {
+            typeof(NetCord.Rest.RestClient),
+            typeof(DiscordInteractionReplyCache)
+        });
         Assert.NotNull(constructor);
     }
 
@@ -18,4 +22,30 @@ public sealed class DiscordPlatformMessengerTests
     {
         Assert.True(typeof(IPlatformMessenger).IsAssignableFrom(typeof(DiscordPlatformMessenger)));
     }
+
+    [Fact]
+    public async Task AnswerInteractionAsync_ShouldStoreReplyForComponentModule()
+    {
+        var source = await ReadRepositoryFileAsync("src/GmRelay.DiscordBot/Infrastructure/Discord/DiscordPlatformMessenger.cs");
+
+        Assert.Contains("DiscordInteractionReplyCache", source, StringComparison.Ordinal);
+        Assert.Contains("interactionReplies.Store(reply)", source, StringComparison.Ordinal);
+    }
+
+    private static async Task<string> ReadRepositoryFileAsync(string relativePath)
+    {
+        var directory = new DirectoryInfo(AppContext.BaseDirectory);
+        while (directory is not null)
+        {
+            var candidate = Path.Combine(directory.FullName, relativePath);
+            if (File.Exists(candidate))
+            {
+                return await File.ReadAllTextAsync(candidate);
+            }
+
+            directory = directory.Parent;
+        }
+
+        throw new FileNotFoundException($"Could not locate repository file '{relativePath}'.");
+    }
 }
diff --git a/tests/GmRelay.Bot.Tests/Discord/DiscordProjectStructureTests.cs b/tests/GmRelay.Bot.Tests/Discord/DiscordProjectStructureTests.cs
index 2bc0f84..0f6da97 100644
--- a/tests/GmRelay.Bot.Tests/Discord/DiscordProjectStructureTests.cs
+++ b/tests/GmRelay.Bot.Tests/Discord/DiscordProjectStructureTests.cs
@@ -61,7 +61,7 @@ public sealed class DiscordProjectStructureTests
         var prChecks = File.ReadAllText(Path.Combine(repoRoot, ".gitea", "workflows", "pr-checks.yml"));
         var deploy = File.ReadAllText(Path.Combine(repoRoot, ".gitea", "workflows", "deploy.yml"));
 
-        Assert.Contains("gmrelay-discord-bot:2.4.0", compose);
+        Assert.Contains("gmrelay-discord-bot:2.5.0", compose);
         Assert.Contains("Discord__Token=${DISCORD_BOT_TOKEN:?Set DISCORD_BOT_TOKEN in .env}", compose);
         Assert.Contains("src/GmRelay.DiscordBot/Dockerfile", deploy);
         Assert.Contains("DISCORD_BOT_TOKEN", deploy);
@@ -75,13 +75,13 @@ public sealed class DiscordProjectStructureTests
     {
         var repoRoot = GetRepoRoot();
 
-        Assert.Contains("<Version>2.4.0</Version>", File.ReadAllText(Path.Combine(repoRoot, "Directory.Build.props")));
-        Assert.Contains("VERSION: 2.4.0", File.ReadAllText(Path.Combine(repoRoot, ".gitea", "workflows", "deploy.yml")));
-        Assert.Contains("gmrelay-bot:2.4.0", File.ReadAllText(Path.Combine(repoRoot, "compose.yaml")));
-        Assert.Contains("gmrelay-web:2.4.0", File.ReadAllText(Path.Combine(repoRoot, "compose.yaml")));
-        Assert.Contains("gmrelay-discord-bot:2.4.0", File.ReadAllText(Path.Combine(repoRoot, "compose.yaml")));
+        Assert.Contains("<Version>2.5.0</Version>", File.ReadAllText(Path.Combine(repoRoot, "Directory.Build.props")));
+        Assert.Contains("VERSION: 2.5.0", File.ReadAllText(Path.Combine(repoRoot, ".gitea", "workflows", "deploy.yml")));
+        Assert.Contains("gmrelay-bot:2.5.0", File.ReadAllText(Path.Combine(repoRoot, "compose.yaml")));
+        Assert.Contains("gmrelay-web:2.5.0", File.ReadAllText(Path.Combine(repoRoot, "compose.yaml")));
+        Assert.Contains("gmrelay-discord-bot:2.5.0", File.ReadAllText(Path.Combine(repoRoot, "compose.yaml")));
         Assert.Contains(
-            "v2.4.0",
+            "v2.5.0",
             File.ReadAllText(Path.Combine(repoRoot, "src", "GmRelay.Web", "Components", "Layout", "NavMenu.razor")));
     }
 }
diff --git a/tests/GmRelay.Bot.Tests/Discord/DiscordSessionInteractionMapperTests.cs b/tests/GmRelay.Bot.Tests/Discord/DiscordSessionInteractionMapperTests.cs
new file mode 100644
index 0000000..353d277
--- /dev/null
+++ b/tests/GmRelay.Bot.Tests/Discord/DiscordSessionInteractionMapperTests.cs
@@ -0,0 +1,96 @@
+using GmRelay.DiscordBot.Features.Sessions;
+using GmRelay.Shared.Features.Sessions.CreateSession;
+using GmRelay.Shared.Platform;
+
+namespace GmRelay.Bot.Tests.Discord;
+
+public sealed class DiscordSessionInteractionMapperTests
+{
+    [Fact]
+    public void TryParseCustomId_WhenActionAndSessionIdMatch_ReturnsSessionId()
+    {
+        var sessionId = Guid.NewGuid();
+
+        var result = DiscordSessionInteractionMapper.TryParseCustomId(
+            $"join_session:{sessionId}",
+            "join_session",
+            out var parsedSessionId);
+
+        Assert.True(result);
+        Assert.Equal(sessionId, parsedSessionId);
+    }
+
+    [Fact]
+    public void TryParseCustomId_WhenActionDoesNotMatch_ReturnsFalse()
+    {
+        var result = DiscordSessionInteractionMapper.TryParseCustomId(
+            $"leave_session:{Guid.NewGuid()}",
+            "join_session",
+            out _);
+
+        Assert.False(result);
+    }
+
+    [Fact]
+    public void TryParseCustomId_WhenSessionIdIsInvalid_ReturnsFalse()
+    {
+        var result = DiscordSessionInteractionMapper.TryParseCustomId(
+            "join_session:not-a-guid",
+            "join_session",
+            out _);
+
+        Assert.False(result);
+    }
+
+    [Fact]
+    public void CreateJoinCommand_ShouldBuildPlatformNeutralDiscordCommand()
+    {
+        var sessionId = Guid.NewGuid();
+        var input = CreateInput(sessionId, displayName: "Alice GM");
+
+        JoinSessionCommand command = DiscordSessionInteractionMapper.CreateJoinCommand(input);
+
+        Assert.Equal(sessionId, command.SessionId);
+        Assert.Equal("interaction-1", command.InteractionId);
+        Assert.Equal(PlatformKind.Discord, command.User.Platform);
+        Assert.Equal("42", command.User.ExternalUserId);
+        Assert.Equal("Alice GM", command.User.DisplayName);
+        Assert.Equal("alice", command.User.ExternalUsername);
+        Assert.Equal(PlatformKind.Discord, command.Group.Platform);
+        Assert.Equal("guild-1", command.Group.ExternalGroupId);
+        Assert.Equal("channel-1", command.Group.ExternalChannelId);
+        Assert.Equal(PlatformKind.Discord, command.ScheduleMessage.Platform);
+        Assert.Equal("guild-1", command.ScheduleMessage.ExternalGroupId);
+        Assert.Equal("message-1", command.ScheduleMessage.ExternalMessageId);
+    }
+
+    [Fact]
+    public void CreateLeaveCommand_ShouldBuildPlatformNeutralDiscordCommand()
+    {
+        var sessionId = Guid.NewGuid();
+        var input = CreateInput(sessionId, displayName: null);
+
+        LeaveSessionCommand command = DiscordSessionInteractionMapper.CreateLeaveCommand(input);
+
+        Assert.Equal(sessionId, command.SessionId);
+        Assert.Equal("interaction-1", command.InteractionId);
+        Assert.Equal(PlatformKind.Discord, command.User.Platform);
+        Assert.Equal("42", command.User.ExternalUserId);
+        Assert.Equal("alice", command.User.DisplayName);
+        Assert.Equal("alice", command.User.ExternalUsername);
+        Assert.Equal("guild-1", command.Group.ExternalGroupId);
+        Assert.Equal("channel-1", command.Group.ExternalChannelId);
+        Assert.Equal("message-1", command.ScheduleMessage.ExternalMessageId);
+    }
+
+    private static DiscordSessionInteractionInput CreateInput(Guid sessionId, string? displayName)
+        => new(
+            SessionId: sessionId,
+            InteractionId: "interaction-1",
+            GuildId: "guild-1",
+            ChannelId: "channel-1",
+            MessageId: "message-1",
+            UserId: 42,
+            Username: "alice",
+            DisplayName: displayName);
+}
diff --git a/tests/GmRelay.Bot.Tests/Discord/DiscordSessionInteractionModuleSourceTests.cs b/tests/GmRelay.Bot.Tests/Discord/DiscordSessionInteractionModuleSourceTests.cs
new file mode 100644
index 0000000..b98be76
--- /dev/null
+++ b/tests/GmRelay.Bot.Tests/Discord/DiscordSessionInteractionModuleSourceTests.cs
@@ -0,0 +1,40 @@
+namespace GmRelay.Bot.Tests.Discord;
+
+public sealed class DiscordSessionInteractionModuleSourceTests
+{
+    [Fact]
+    public async Task Module_ShouldRouteJoinAndLeaveButtonsToNeutralHandlers()
+    {
+        var source = await ReadRepositoryFileAsync("src/GmRelay.DiscordBot/Features/Sessions/DiscordSessionInteractionModule.cs");
+
+        Assert.Contains("ComponentInteractionModule<ButtonInteractionContext>", source, StringComparison.Ordinal);
+        Assert.Contains("[ComponentInteraction(\"join_session\")]", source, StringComparison.Ordinal);
+        Assert.Contains("[ComponentInteraction(\"leave_session\")]", source, StringComparison.Ordinal);
+        Assert.Contains("JoinSessionHandler", source, StringComparison.Ordinal);
+        Assert.Contains("LeaveSessionHandler", source, StringComparison.Ordinal);
+        Assert.Contains("DiscordSessionInteractionMapper.CreateJoinCommand", source, StringComparison.Ordinal);
+        Assert.Contains("DiscordSessionInteractionMapper.CreateLeaveCommand", source, StringComparison.Ordinal);
+        Assert.Contains("RespondAsync", source, StringComparison.Ordinal);
+        Assert.Contains("InteractionCallback.DeferredMessage(MessageFlags.Ephemeral)", source, StringComparison.Ordinal);
+        Assert.Contains("ModifyResponseAsync", source, StringComparison.Ordinal);
+        Assert.Contains("Не удалось обработать кнопку.", source, StringComparison.Ordinal);
+        Assert.Contains("MessageFlags.Ephemeral", source, StringComparison.Ordinal);
+    }
+
+    private static async Task<string> ReadRepositoryFileAsync(string relativePath)
+    {
+        var directory = new DirectoryInfo(AppContext.BaseDirectory);
+        while (directory is not null)
+        {
+            var candidate = Path.Combine(directory.FullName, relativePath);
+            if (File.Exists(candidate))
+            {
+                return await File.ReadAllTextAsync(candidate);
+            }
+
+            directory = directory.Parent;
+        }
+
+        throw new FileNotFoundException($"Could not locate repository file '{relativePath}'.");
+    }
+}
diff --git a/tests/GmRelay.Bot.Tests/Discord/DiscordStartupTests.cs b/tests/GmRelay.Bot.Tests/Discord/DiscordStartupTests.cs
index 0fda98f..a7eba6d 100644
--- a/tests/GmRelay.Bot.Tests/Discord/DiscordStartupTests.cs
+++ b/tests/GmRelay.Bot.Tests/Discord/DiscordStartupTests.cs
@@ -77,6 +77,8 @@ public sealed class DiscordStartupTests
         var program = ReadProgram();
         Assert.Contains("DiscordListSessionsHandler", program);
         Assert.Contains("DiscordNewSessionHandler", program);
+        Assert.Contains("JoinSessionHandler", program);
+        Assert.Contains("LeaveSessionHandler", program);
         Assert.Contains("DiscordPermissionChecker", program);
         Assert.Contains("DiscordPlatformMessenger", program);
         Assert.Contains("IPlatformMessenger", program);
diff --git a/tests/GmRelay.Bot.Tests/Features/Sessions/CreateSession/PlatformNeutralSessionInteractionCommandTests.cs b/tests/GmRelay.Bot.Tests/Features/Sessions/CreateSession/PlatformNeutralSessionInteractionCommandTests.cs
index b7e2049..29b8b60 100644
--- a/tests/GmRelay.Bot.Tests/Features/Sessions/CreateSession/PlatformNeutralSessionInteractionCommandTests.cs
+++ b/tests/GmRelay.Bot.Tests/Features/Sessions/CreateSession/PlatformNeutralSessionInteractionCommandTests.cs
@@ -1,4 +1,4 @@
-using GmRelay.Bot.Features.Sessions.CreateSession;
+using GmRelay.Shared.Features.Sessions.CreateSession;
 using GmRelay.Shared.Platform;
 
 namespace GmRelay.Bot.Tests.Features.Sessions.CreateSession;
diff --git a/tests/GmRelay.Bot.Tests/Features/Sessions/CreateSession/PlatformNeutralSessionInteractionSqlTests.cs b/tests/GmRelay.Bot.Tests/Features/Sessions/CreateSession/PlatformNeutralSessionInteractionSqlTests.cs
index 71ef4aa..b7c01fe 100644
--- a/tests/GmRelay.Bot.Tests/Features/Sessions/CreateSession/PlatformNeutralSessionInteractionSqlTests.cs
+++ b/tests/GmRelay.Bot.Tests/Features/Sessions/CreateSession/PlatformNeutralSessionInteractionSqlTests.cs
@@ -5,7 +5,7 @@ public sealed class PlatformNeutralSessionInteractionSqlTests
     [Fact]
     public async Task JoinSessionHandler_ShouldPersistPlayersByPlatformIdentity()
     {
-        var handler = await ReadRepositoryFileAsync("src/GmRelay.Bot/Features/Sessions/CreateSession/JoinSessionHandler.cs");
+        var handler = await ReadRepositoryFileAsync("src/GmRelay.Shared/Features/Sessions/CreateSession/JoinSessionHandler.cs");
 
         Assert.Contains("platform, external_user_id", handler, StringComparison.Ordinal);
         Assert.Contains("ON CONFLICT (platform, external_user_id)", handler, StringComparison.Ordinal);
@@ -16,10 +16,20 @@ public sealed class PlatformNeutralSessionInteractionSqlTests
         Assert.DoesNotContain("command.TelegramUsername", handler, StringComparison.Ordinal);
     }
 
+    [Fact]
+    public async Task JoinSessionHandler_ShouldRejectCancelledSessionsBeforeInsert()
+    {
+        var handler = await ReadRepositoryFileAsync("src/GmRelay.Shared/Features/Sessions/CreateSession/JoinSessionHandler.cs");
+
+        Assert.Contains("Status", handler, StringComparison.Ordinal);
+        Assert.Contains("SessionStatus.IsCancelled(batchInfo.Status)", handler, StringComparison.Ordinal);
+        Assert.Contains("Сессия уже отменена.", handler, StringComparison.Ordinal);
+    }
+
     [Fact]
     public async Task LeaveSessionHandler_ShouldFindParticipantsByPlatformIdentity()
     {
-        var handler = await ReadRepositoryFileAsync("src/GmRelay.Bot/Features/Sessions/CreateSession/LeaveSessionHandler.cs");
+        var handler = await ReadRepositoryFileAsync("src/GmRelay.Shared/Features/Sessions/CreateSession/LeaveSessionHandler.cs");
 
         Assert.Contains("p.platform = @Platform", handler, StringComparison.Ordinal);
         Assert.Contains("p.external_user_id = @ExternalUserId", handler, StringComparison.Ordinal);
@@ -31,8 +41,8 @@ public sealed class PlatformNeutralSessionInteractionSqlTests
     [Fact]
     public async Task SessionInteractionHandlers_ShouldUpdateSchedulesThroughCommandMessageReference()
     {
-        var joinHandler = await ReadRepositoryFileAsync("src/GmRelay.Bot/Features/Sessions/CreateSession/JoinSessionHandler.cs");
-        var leaveHandler = await ReadRepositoryFileAsync("src/GmRelay.Bot/Features/Sessions/CreateSession/LeaveSessionHandler.cs");
+        var joinHandler = await ReadRepositoryFileAsync("src/GmRelay.Shared/Features/Sessions/CreateSession/JoinSessionHandler.cs");
+        var leaveHandler = await ReadRepositoryFileAsync("src/GmRelay.Shared/Features/Sessions/CreateSession/LeaveSessionHandler.cs");
 
         Assert.Contains("new PlatformScheduleMessage(", joinHandler, StringComparison.Ordinal);
         Assert.Contains("command.Group", joinHandler, StringComparison.Ordinal);
@@ -42,6 +52,16 @@ public sealed class PlatformNeutralSessionInteractionSqlTests
         Assert.Contains("command.ScheduleMessage", leaveHandler, StringComparison.Ordinal);
     }
 
+    [Fact]
+    public async Task SessionInteractionHandlers_ShouldSerializeScheduleMessageUpdates()
+    {
+        var joinHandler = await ReadRepositoryFileAsync("src/GmRelay.Shared/Features/Sessions/CreateSession/JoinSessionHandler.cs");
+        var leaveHandler = await ReadRepositoryFileAsync("src/GmRelay.Shared/Features/Sessions/CreateSession/LeaveSessionHandler.cs");
+
+        Assert.Contains("scheduleUpdateLock.AcquireAsync(command.ScheduleMessage", joinHandler, StringComparison.Ordinal);
+        Assert.Contains("scheduleUpdateLock.AcquireAsync(command.ScheduleMessage", leaveHandler, StringComparison.Ordinal);
+    }
+
     private static async Task<string> ReadRepositoryFileAsync(string relativePath)
     {
         var directory = new DirectoryInfo(AppContext.BaseDirectory);
diff --git a/tests/GmRelay.Bot.Tests/Infrastructure/Database/PlatformIdentityMigrationTests.cs b/tests/GmRelay.Bot.Tests/Infrastructure/Database/PlatformIdentityMigrationTests.cs
index 7a6f723..9a2009c 100644
--- a/tests/GmRelay.Bot.Tests/Infrastructure/Database/PlatformIdentityMigrationTests.cs
+++ b/tests/GmRelay.Bot.Tests/Infrastructure/Database/PlatformIdentityMigrationTests.cs
@@ -74,7 +74,7 @@ public sealed class PlatformIdentityMigrationTests
     [Fact]
     public async Task JoinSessionHandler_ShouldDualWritePlatformIdentity()
     {
-        var handler = await ReadRepositoryFileAsync("src/GmRelay.Bot/Features/Sessions/CreateSession/JoinSessionHandler.cs");
+        var handler = await ReadRepositoryFileAsync("src/GmRelay.Shared/Features/Sessions/CreateSession/JoinSessionHandler.cs");
 
         Assert.Contains("external_user_id", handler, StringComparison.Ordinal);
         Assert.Contains("external_username", handler, StringComparison.Ordinal);
diff --git a/tests/GmRelay.Bot.Tests/Infrastructure/Telegram/TelegramPlatformMessengerSourceTests.cs b/tests/GmRelay.Bot.Tests/Infrastructure/Telegram/TelegramPlatformMessengerSourceTests.cs
index e3787e0..12dea04 100644
--- a/tests/GmRelay.Bot.Tests/Infrastructure/Telegram/TelegramPlatformMessengerSourceTests.cs
+++ b/tests/GmRelay.Bot.Tests/Infrastructure/Telegram/TelegramPlatformMessengerSourceTests.cs
@@ -12,8 +12,8 @@ public sealed class TelegramPlatformMessengerSourceTests
     }
 
     [Theory]
-    [InlineData("src/GmRelay.Bot/Features/Sessions/CreateSession/JoinSessionHandler.cs")]
-    [InlineData("src/GmRelay.Bot/Features/Sessions/CreateSession/LeaveSessionHandler.cs")]
+    [InlineData("src/GmRelay.Shared/Features/Sessions/CreateSession/JoinSessionHandler.cs")]
+    [InlineData("src/GmRelay.Shared/Features/Sessions/CreateSession/LeaveSessionHandler.cs")]
     [InlineData("src/GmRelay.Bot/Features/Sessions/CreateSession/CancelSessionHandler.cs")]
     [InlineData("src/GmRelay.Bot/Features/Sessions/CreateSession/PromoteWaitlistedPlayerHandler.cs")]
     [InlineData("src/GmRelay.Bot/Features/Sessions/RescheduleSession/InitiateRescheduleHandler.cs")]
diff --git a/tests/GmRelay.Bot.Tests/Platform/ScheduleMessageUpdateLockTests.cs b/tests/GmRelay.Bot.Tests/Platform/ScheduleMessageUpdateLockTests.cs
new file mode 100644
index 0000000..00441c4
--- /dev/null
+++ b/tests/GmRelay.Bot.Tests/Platform/ScheduleMessageUpdateLockTests.cs
@@ -0,0 +1,41 @@
+using GmRelay.Shared.Features.Sessions.CreateSession;
+using GmRelay.Shared.Platform;
+
+namespace GmRelay.Bot.Tests.Platform;
+
+public sealed class ScheduleMessageUpdateLockTests
+{
+    [Fact]
+    public async Task AcquireAsync_ShouldSerializeSameScheduleMessage()
+    {
+        var updateLock = new ScheduleMessageUpdateLock();
+        var message = CreateMessage("message-1");
+
+        var first = await updateLock.AcquireAsync(message, CancellationToken.None);
+        var secondTask = updateLock.AcquireAsync(message, CancellationToken.None).AsTask();
+
+        Assert.False(secondTask.IsCompleted);
+
+        await first.DisposeAsync();
+        var second = await secondTask.WaitAsync(TimeSpan.FromSeconds(1));
+        await second.DisposeAsync();
+    }
+
+    [Fact]
+    public async Task AcquireAsync_ShouldNotBlockDifferentScheduleMessages()
+    {
+        var updateLock = new ScheduleMessageUpdateLock();
+
+        var first = await updateLock.AcquireAsync(CreateMessage("message-1"), CancellationToken.None);
+        var secondTask = updateLock.AcquireAsync(CreateMessage("message-2"), CancellationToken.None).AsTask();
+
+        Assert.True(secondTask.IsCompleted);
+
+        await first.DisposeAsync();
+        var second = await secondTask;
+        await second.DisposeAsync();
+    }
+
+    private static PlatformMessageRef CreateMessage(string messageId) =>
+        new(PlatformKind.Discord, "guild-1", null, messageId);
+}
diff --git a/tests/GmRelay.Bot.Tests/packages.lock.json b/tests/GmRelay.Bot.Tests/packages.lock.json
index c9554c1..2ad87a5 100644
--- a/tests/GmRelay.Bot.Tests/packages.lock.json
+++ b/tests/GmRelay.Bot.Tests/packages.lock.json
@@ -392,8 +392,8 @@
           "Aspire.Npgsql": "[13.2.2, )",
           "Dapper": "[2.1.72, )",
           "Dapper.AOT": "[1.0.48, )",
-          "GmRelay.ServiceDefaults": "[2.3.0, )",
-          "GmRelay.Shared": "[2.3.0, )",
+          "GmRelay.ServiceDefaults": "[2.5.0, )",
+          "GmRelay.Shared": "[2.5.0, )",
           "Npgsql": "[10.0.2, )",
           "Telegram.Bot": "[22.9.5.3, )",
           "dbup-postgresql": "[7.0.1, )"
@@ -404,8 +404,8 @@
         "dependencies": {
           "Aspire.Npgsql": "[13.2.2, )",
           "Dapper": "[2.1.72, )",
-          "GmRelay.ServiceDefaults": "[2.3.0, )",
-          "GmRelay.Shared": "[2.3.0, )",
+          "GmRelay.ServiceDefaults": "[2.5.0, )",
+          "GmRelay.Shared": "[2.5.0, )",
           "NetCord.Hosting": "[1.0.0-alpha.489, )",
           "NetCord.Hosting.Services": "[1.0.0-alpha.489, )",
           "NetCord.Services": "[1.0.0-alpha.489, )",
@@ -425,15 +425,19 @@
         }
       },
       "gmrelay.shared": {
-        "type": "Project"
+        "type": "Project",
+        "dependencies": {
+          "Dapper": "[2.1.72, )",
+          "Npgsql": "[10.0.2, )"
+        }
       },
       "gmrelay.web": {
         "type": "Project",
         "dependencies": {
           "Aspire.Npgsql": "[13.2.2, )",
           "Dapper": "[2.1.72, )",
-          "GmRelay.ServiceDefaults": "[2.3.0, )",
-          "GmRelay.Shared": "[2.3.0, )",
+          "GmRelay.ServiceDefaults": "[2.5.0, )",
+          "GmRelay.Shared": "[2.5.0, )",
           "Npgsql": "[10.0.2, )",
           "Telegram.Bot": "[22.9.6.1, )"
         }