diff --git a/hosts/Volcanic.AgenticCore.Telegram/BotSetupService.cs b/hosts/Volcanic.AgenticCore.Telegram/BotSetupService.cs
index 3ee4014..eece049 100644
--- a/hosts/Volcanic.AgenticCore.Telegram/BotSetupService.cs
+++ b/hosts/Volcanic.AgenticCore.Telegram/BotSetupService.cs
@@ -60,6 +60,9 @@ public sealed class BotSetupService(ITelegramBotClient bot, TelegramOptions opti
                 var menu = GoogleCalendarSetup.MenuFor(ChatCommands.Menu, calendar);
                 await bot.SetMyCommands(menu, cancellationToken: stoppingToken).ConfigureAwait(false);
                 logger.LogInformation("Bot @{Username} ({Id}) is ready", me.Username, me.Id);
+                if (options.Triggers.IsEnabled && !me.CanReadAllGroupMessages)
+                    logger.LogWarning("Privacy mode is on: in groups the bot only sees commands, mentions and replies, so group triggers miss most messages. " +
+                                      "Turn it off with @BotFather (/setprivacy → Disable), then remove and re-add the bot to each group, or make it a group admin.");
                 await SetAdminMenuAsync(menu, stoppingToken).ConfigureAwait(false);
                 return true;
             }
diff --git a/hosts/Volcanic.AgenticCore.Telegram/Chats/ChatCommands.cs b/hosts/Volcanic.AgenticCore.Telegram/Chats/ChatCommands.cs
index 3cf2b44..935f20a 100644
--- a/hosts/Volcanic.AgenticCore.Telegram/Chats/ChatCommands.cs
+++ b/hosts/Volcanic.AgenticCore.Telegram/Chats/ChatCommands.cs
@@ -6,11 +6,12 @@ using Volcanic.AgenticCore.Extensions.Scheduler;
 using Volcanic.AgenticCore.Hosting;
 using Volcanic.AgenticCore.Telegram.Rendering;
 using Volcanic.AgenticCore.Telegram.Scheduling;
+using Volcanic.AgenticCore.Telegram.Triggers;
 
 namespace Volcanic.AgenticCore.Telegram.Chats;
 
 /// <summary>The bot's own slash commands. Anything else starting with <c>/</c> goes to the session (extension commands).</summary>
-public sealed class ChatCommands(TelegramSender sender, ChatTimeZoneService? zones = null, JobScheduler? scheduler = null)
+public sealed class ChatCommands(TelegramSender sender, ChatTimeZoneService? zones = null, JobScheduler? scheduler = null, TriggerServices? triggers = null)
 {
     public static readonly IReadOnlyList<BotCommand> Menu =
     [
@@ -23,6 +24,7 @@ public sealed class ChatCommands(TelegramSender sender, ChatTimeZoneService? zon
         new() { Command = "thinking", Description = "Show or set the thinking level" },
         new() { Command = "timezone", Description = "Show or set this chat's time zone" },
         .. SchedulerSetup.Menu,
+        TriggersSetup.MenuCommand,
         new() { Command = "help", Description = "What this bot does" },
     ];
 
@@ -109,6 +111,10 @@ public sealed class ChatCommands(TelegramSender sender, ChatTimeZoneService? zon
                 await ReplyAsync(chat, await TimeZoneAsync(chat, command.Args, cancellationToken).ConfigureAwait(false), cancellationToken).ConfigureAwait(false);
                 return true;
 
+            case "triggers":
+                await ReplyAsync(chat, triggers is null ? TriggersSetup.DisabledReply : "**Group triggers**\n" + triggers.Describe(chat.ChatId, chat.Session.TimeZone), cancellationToken).ConfigureAwait(false);
+                return true;
+
             case "jobs":
                 await ReplyAsync(chat, Jobs(chat), cancellationToken).ConfigureAwait(false);
                 return true;
@@ -140,7 +146,7 @@ public sealed class ChatCommands(TelegramSender sender, ChatTimeZoneService? zon
         /compact – summarise the conversation to free context
         /thinking [level] – show or set the thinking level
         /timezone [IANA name|reset] – this chat's time zone
-        """ + SchedulerSetup.HelpLines + GoogleCalendarSetup.HelpLines(chat.Session.Commands);
+        """ + SchedulerSetup.HelpLines + TriggersSetup.HelpLines + GoogleCalendarSetup.HelpLines(chat.Session.Commands);
 
     private string Status(ChatContext chat)
     {
diff --git a/hosts/Volcanic.AgenticCore.Telegram/Chats/ChatRegistry.cs b/hosts/Volcanic.AgenticCore.Telegram/Chats/ChatRegistry.cs
index 2f00f49..6e161f9 100644
--- a/hosts/Volcanic.AgenticCore.Telegram/Chats/ChatRegistry.cs
+++ b/hosts/Volcanic.AgenticCore.Telegram/Chats/ChatRegistry.cs
@@ -11,6 +11,7 @@ using Volcanic.AgenticCore.Features.Extensions;
 using Volcanic.AgenticCore.Hosting;
 using Volcanic.AgenticCore.Telegram.Inbound;
 using Volcanic.AgenticCore.Telegram.Rendering;
+using Volcanic.AgenticCore.Telegram.Triggers;
 
 namespace Volcanic.AgenticCore.Telegram.Chats;
 
@@ -78,7 +79,8 @@ public sealed class ChatRegistry(
     ChatSettingsStore? settings = null,
     ChatTimeZoneService? zones = null,
     JobScheduler? scheduler = null,
-    Impersonation? impersonation = null) : IAsyncDisposable
+    Impersonation? impersonation = null,
+    TriggerServices? triggers = null) : IAsyncDisposable
 {
     private readonly ConcurrentDictionary<long, Lazy<Task<ChatContext>>> _chats = new();
     private readonly ILogger _logger = loggerFactory.CreateLogger<ChatRegistry>();
@@ -127,6 +129,7 @@ public sealed class ChatRegistry(
         if (zones is not null) extras.Add(ExtensionRegistration.FromInstance(new ChatSettingsExtension(chatId, zones)));
         if (scheduler is not null)
             extras.Add(ExtensionRegistration.FromInstance(new SchedulerExtension(scheduler, Scheduling.TelegramJobDelivery.TargetOf(chatId))));
+        if (triggers is not null) extras.Add(ExtensionRegistration.FromInstance(new TriggerExtension(chatId, triggers, () => TimeZoneFor(chatId))));
         AgentSession session;
         try
         {
diff --git a/hosts/Volcanic.AgenticCore.Telegram/Chats/UpdateRouter.cs b/hosts/Volcanic.AgenticCore.Telegram/Chats/UpdateRouter.cs
index 99bc3b4..e2d6878 100644
--- a/hosts/Volcanic.AgenticCore.Telegram/Chats/UpdateRouter.cs
+++ b/hosts/Volcanic.AgenticCore.Telegram/Chats/UpdateRouter.cs
@@ -1,6 +1,7 @@
 using Microsoft.Extensions.Logging;
 using Telegram.Bot.Types;
 using Telegram.Bot.Types.Enums;
+using Volcanic.AgenticCore.Telegram.Groups;
 using Volcanic.AgenticCore.Telegram.Inbound;
 using Volcanic.AgenticCore.Telegram.Polling;
 using Volcanic.AgenticCore.Telegram.Rendering;
@@ -12,7 +13,9 @@ namespace Volcanic.AgenticCore.Telegram.Chats;
 /// the chat's pending dialog, bot commands run directly, everything else goes through the chat's <see cref="ChatInbox"/>:
 /// the router takes a lease in update order, composes the message in the background, and the inbox turns the batch into
 /// a prompt that runs in the background. The admin's <c>/impersonate</c> is handled first; while it is on, the admin's
-/// updates are routed as the impersonated user's (see <see cref="Impersonation"/>).
+/// updates are routed as the impersonated user's (see <see cref="Impersonation"/>). Group messages and the bot's own
+/// membership changes go to the <see cref="GroupFeed"/> before any allow-list check (every member's messages are
+/// classified); without one (no OpenRouter key) they are dropped. Nothing is ever sent to a group.
 /// </summary>
 public sealed class UpdateRouter(
     TelegramOptions options,
@@ -21,7 +24,8 @@ public sealed class UpdateRouter(
     TelegramSender sender,
     InboundComposer composer,
     ILogger<UpdateRouter> logger,
-    Impersonation? impersonation = null) : IUpdateRouter
+    Impersonation? impersonation = null,
+    GroupFeed? groups = null) : IUpdateRouter
 {
     /// <summary>The id the bot acts for: the impersonated user's for the admin while impersonating, else <paramref name="id"/>.</summary>
     private long Effective(long id) => impersonation?.EffectiveId(id) ?? id;
@@ -33,9 +37,16 @@ public sealed class UpdateRouter(
             case { CallbackQuery: { } query }:
                 await OnCallbackAsync(query, cancellationToken).ConfigureAwait(false);
                 break;
+            case { Message: { } message } when GroupFeed.IsGroup(message.Chat):
+                if (groups is not null) await groups.OnMessageAsync(message, cancellationToken).ConfigureAwait(false);
+                else logger.LogDebug("Ignored a message in group {ChatId}: group triggers are off", message.Chat.Id);
+                break;
             case { Message: { } message }:
                 await OnMessageAsync(message, cancellationToken).ConfigureAwait(false);
                 break;
+            case { MyChatMember: { } member }:
+                if (groups is not null) await groups.OnMyChatMemberAsync(member, cancellationToken).ConfigureAwait(false);
+                break;
         }
     }
 
diff --git a/hosts/Volcanic.AgenticCore.Telegram/Groups/GroupFeed.cs b/hosts/Volcanic.AgenticCore.Telegram/Groups/GroupFeed.cs
new file mode 100644
index 0000000..1b509d6
--- /dev/null
+++ b/hosts/Volcanic.AgenticCore.Telegram/Groups/GroupFeed.cs
@@ -0,0 +1,108 @@
+using Microsoft.Extensions.Logging;
+using Telegram.Bot;
+using Telegram.Bot.Types;
+using Telegram.Bot.Types.Enums;
+using Volcanic.AgenticCore.Telegram.Triggers;
+
+namespace Volcanic.AgenticCore.Telegram.Groups;
+
+/// <summary>
+/// The router's entry for groups. A message from an unknown group is dropped unless an allowed user posted it (which
+/// vouches for the group); a known group's messages go to <see cref="TriggerEngine"/> in the background, at most
+/// <see cref="TriggerOptions.MaxConcurrency"/> at a time, so polling never waits on Jev. <c>my_chat_member</c>
+/// updates add the group (when an allowed user added the bot) or pause it (when the bot left). Nothing here ever
+/// sends anything to a group.
+/// </summary>
+public sealed class GroupFeed(
+    GroupRegistry groups,
+    TriggerEngine engine,
+    ITelegramBotClient bot,
+    TelegramOptions options,
+    ILogger<GroupFeed> logger)
+{
+    private readonly SemaphoreSlim _gate = new(Math.Max(1, options.Triggers.MaxConcurrency));
+    private readonly Lock _lock = new();
+    private readonly List<Task> _inFlight = [];
+
+    public static bool IsGroup(Chat chat) => chat?.Type is ChatType.Group or ChatType.Supergroup;
+
+    public async Task OnMessageAsync(Message message, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(message);
+        if (message.MigrateToChatId is { } to)
+        {
+            await groups.MigrateAsync(message.Chat.Id, to, cancellationToken).ConfigureAwait(false);
+            await engine.Store.MoveGroupAsync(message.Chat.Id, to, cancellationToken).ConfigureAwait(false);
+            return;
+        }
+        if (message.From?.Id == bot.BotId || message.MigrateFromChatId is not null) return;
+
+        var known = groups.Find(message.Chat.Id);
+        if ((known is null || !known.Active) && options.IsAllowed(message.From?.Id))
+        {
+            await groups.VouchAsync(message.Chat, message.From!.Id, cancellationToken).ConfigureAwait(false);
+            known = groups.Find(message.Chat.Id);
+        }
+        if (known is null || !known.Active)
+        {
+            logger.LogInformation("Group \"{GroupTitle}\" ({GroupId}) msg {MessageId} from {Sender}: skipped, {Reason}",
+                GroupMessage.TitleOf(message.Chat), message.Chat.Id, message.Id, GroupMessage.SenderOf(message), known is null ? "unknown group" : "inactive group");
+            return;
+        }
+        await groups.RefreshAsync(message.Chat, cancellationToken).ConfigureAwait(false);
+
+        var item = GroupMessage.From(message);
+        var task = Task.Run(async () =>
+        {
+            await _gate.WaitAsync(cancellationToken).ConfigureAwait(false);
+            try
+            {
+                await engine.ProcessAsync(item, cancellationToken).ConfigureAwait(false);
+            }
+            catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
+            {
+            }
+            catch (Exception ex)
+            {
+                logger.LogError(ex, "Classifying message {MessageId} of group {GroupId} failed", item.MessageId, item.GroupId);
+            }
+            finally
+            {
+                _gate.Release();
+            }
+        }, CancellationToken.None);
+        lock (_lock)
+        {
+            _inFlight.RemoveAll(t => t.IsCompleted);
+            _inFlight.Add(task);
+        }
+    }
+
+    public async Task OnMyChatMemberAsync(ChatMemberUpdated update, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(update);
+        if (!IsGroup(update.Chat)) return;
+        switch (update.NewChatMember.Status)
+        {
+            case ChatMemberStatus.Member or ChatMemberStatus.Administrator or ChatMemberStatus.Restricted:
+                if (options.IsAllowed(update.From.Id))
+                    await groups.VouchAsync(update.Chat, update.From.Id, cancellationToken).ConfigureAwait(false);
+                else if (groups.Find(update.Chat.Id) is null)
+                    logger.LogWarning("The bot was added to group {GroupId} \"{Title}\" by user {UserId}, who is not allowed; its messages are ignored",
+                        update.Chat.Id, GroupMessage.TitleOf(update.Chat), update.From.Id);
+                break;
+            case ChatMemberStatus.Left or ChatMemberStatus.Kicked:
+                await groups.SetInactiveAsync(update.Chat.Id, cancellationToken).ConfigureAwait(false);
+                break;
+        }
+    }
+
+    /// <summary>Completes when every message handed to the engine so far has been classified (tests).</summary>
+    public async Task IdleAsync()
+    {
+        Task[] pending;
+        lock (_lock) pending = [.. _inFlight];
+        await Task.WhenAll(pending).ConfigureAwait(false);
+        await engine.IdleAsync().ConfigureAwait(false);
+    }
+}
diff --git a/hosts/Volcanic.AgenticCore.Telegram/Groups/GroupMembership.cs b/hosts/Volcanic.AgenticCore.Telegram/Groups/GroupMembership.cs
new file mode 100644
index 0000000..66d160f
--- /dev/null
+++ b/hosts/Volcanic.AgenticCore.Telegram/Groups/GroupMembership.cs
@@ -0,0 +1,33 @@
+using Telegram.Bot;
+using Telegram.Bot.Types;
+using Telegram.Bot.Types.Enums;
+
+namespace Volcanic.AgenticCore.Telegram.Groups;
+
+/// <summary>Whether a user is in a group: only members may put a trigger on it.</summary>
+public interface IGroupMembership
+{
+    Task<bool> IsMemberAsync(long groupId, long userId, CancellationToken cancellationToken);
+}
+
+/// <summary><c>getChatMember</c>; any failure (the bot was removed, the user is unknown) counts as not a member.</summary>
+public sealed class TelegramGroupMembership(ITelegramBotClient bot) : IGroupMembership
+{
+    public async Task<bool> IsMemberAsync(long groupId, long userId, CancellationToken cancellationToken)
+    {
+        try
+        {
+            var member = await bot.GetChatMember(groupId, userId, cancellationToken).ConfigureAwait(false);
+            return member.Status switch
+            {
+                ChatMemberStatus.Creator or ChatMemberStatus.Administrator or ChatMemberStatus.Member => true,
+                ChatMemberStatus.Restricted => member is ChatMemberRestricted { IsMember: true },
+                _ => false,
+            };
+        }
+        catch (Exception ex) when (ex is not OperationCanceledException)
+        {
+            return false;
+        }
+    }
+}
diff --git a/hosts/Volcanic.AgenticCore.Telegram/Polling/PollingService.cs b/hosts/Volcanic.AgenticCore.Telegram/Polling/PollingService.cs
index 3ea1360..7a09921 100644
--- a/hosts/Volcanic.AgenticCore.Telegram/Polling/PollingService.cs
+++ b/hosts/Volcanic.AgenticCore.Telegram/Polling/PollingService.cs
@@ -33,7 +33,7 @@ public sealed class PollingService(
     IHostApplicationLifetime lifetime,
     ILogger<PollingService> logger) : BackgroundService, IUpdateHandler
 {
-    internal static readonly UpdateType[] AllowedUpdates = [UpdateType.Message, UpdateType.CallbackQuery];
+    internal static readonly UpdateType[] AllowedUpdates = [UpdateType.Message, UpdateType.CallbackQuery, UpdateType.MyChatMember];
 
     private int _offset;
 
diff --git a/hosts/Volcanic.AgenticCore.Telegram/Program.cs b/hosts/Volcanic.AgenticCore.Telegram/Program.cs
index 586c0ee..d47bd60 100644
--- a/hosts/Volcanic.AgenticCore.Telegram/Program.cs
+++ b/hosts/Volcanic.AgenticCore.Telegram/Program.cs
@@ -1,4 +1,5 @@
-// Telegram front end for the agent: long polling, one agent session per private chat, Claude Code as the model.
+// Telegram front end for the agent: long polling, one agent session per private chat, Claude Code as the model;
+// groups are watched silently for the owners' topic triggers (Jev through OpenRouter).
 //
 //   TELEGRAM_BOT_TOKEN=123:abc TELEGRAM_ALLOWED_USER_IDS=111111 dotnet run --project hosts/Volcanic.AgenticCore.Telegram
 
@@ -21,6 +22,7 @@ using Volcanic.AgenticCore.Telegram.Polling;
 using Volcanic.AgenticCore.Telegram.Rendering;
 using Volcanic.AgenticCore.Telegram.Scheduling;
 using Volcanic.AgenticCore.Telegram.Speech;
+using Volcanic.AgenticCore.Telegram.Triggers;
 
 var builder = Host.CreateApplicationBuilder(args);
 
@@ -96,6 +98,7 @@ builder.Services.AddSingleton<IUpdateRouter, UpdateRouter>();
 builder.Services.AddSingleton<PollingService>();
 builder.Services.AddHostedService(sp => sp.GetRequiredService<PollingService>());
 if (scheduling.Enabled) SchedulerSetup.Register(builder.Services); // the hosted service starts after PollingService
+if (options.Triggers.IsEnabled) TriggersSetup.Register(builder.Services, options, agentDir); // groups are ignored without a key
 // Watchers get a short-lived GOOGLE_ACCESS_TOKEN for their chat's calendar, never the client secret or refresh token.
 if (scheduling.Enabled && calendar is not null) builder.Services.AddSingleton<IScriptEnvironment, CalendarScriptEnvironment>();
 builder.Services.AddHostedService<BotSetupService>();
@@ -108,6 +111,7 @@ HostProcessHardening.Apply(processEnvironment, logger);
 logger.LogInformation("{ProcessEnvironment}", TelegramProcessEnvironment.Describe(processEnvironment));
 logger.LogInformation("{Mcp}", mcp.DescribePlaywright());
 logger.LogInformation("{Speech}", options.Speech.Describe());
+logger.LogInformation("{Triggers}", options.Triggers.Describe());
 if (ClaudeInstallation.Locate(Environment.GetEnvironmentVariable) is { } claude)
     logger.LogInformation("Using Claude Code at {Path}, model {Model}", claude, options.Model);
 else
diff --git a/hosts/Volcanic.AgenticCore.Telegram/Triggers/TriggerTool.cs b/hosts/Volcanic.AgenticCore.Telegram/Triggers/TriggerTool.cs
new file mode 100644
index 0000000..abfda57
--- /dev/null
+++ b/hosts/Volcanic.AgenticCore.Telegram/Triggers/TriggerTool.cs
@@ -0,0 +1,234 @@
+using System.ComponentModel;
+using System.Globalization;
+using System.Text;
+using Volcanic.AgenticCore.Abstractions.Extensions;
+using Volcanic.AgenticCore.Abstractions.Tools;
+using Volcanic.AgenticCore.Telegram.Groups;
+
+namespace Volcanic.AgenticCore.Telegram.Triggers;
+
+/// <summary>What the trigger tool, the extension and <c>/triggers</c> share; registered only when triggers are on.</summary>
+public sealed class TriggerServices(TriggerEngine engine, GroupRegistry groups, IGroupMembership membership, TriggerOptions options)
+{
+    public TriggerEngine Engine => engine;
+    public TriggerStore Store => engine.Store;
+    public GroupRegistry Groups => groups;
+    public IGroupMembership Membership => membership;
+    public TriggerOptions Options => options;
+
+    /// <summary>The chat's triggers as text (<c>list</c> and <c>/triggers</c>).</summary>
+    public string Describe(long owner, TimeZoneInfo zone)
+    {
+        ArgumentNullException.ThrowIfNull(zone);
+        var now = engine.Now;
+        var triggers = Store.List(owner);
+        var body = triggers.Count == 0
+            ? "No triggers."
+            : string.Join("\n", triggers.Select(t => TriggerPrompts.Line(t, zone, now, t.SnoozedUntil is null ? 0 : engine.Queued(owner, t.Id))));
+        return body + $"\nNow: {TriggerPrompts.Stamp(now, zone)} ({zone.Id})";
+    }
+}
+
+public sealed record TriggerArgs(
+    [property: Description("groups, create, list, update, delete, snooze or unsnooze")] string Action,
+    [property: Description("update, delete, snooze, unsnooze: the trigger id (see list). snooze and unsnooze without id apply to every trigger of this chat")] string? Id = null,
+    [property: Description("create: the group's title or id (see groups)")] string? Group = null,
+    [property: Description("create, update: a short label, e.g. \"deploys\"")] string? Name = null,
+    [property: Description("create, update: the yes/no question asked about ONE group message, e.g. \"Is this message about deployments, releases or production outages?\"")] string? Instructions = null,
+    [property: Description("create, update: what counts as yes, concretely (empty clears)")] string? CriteriaTrue = null,
+    [property: Description("create, update: what counts as no, concretely (empty clears)")] string? CriteriaFalse = null,
+    [property: Description("create, update: the yes-probability (0-1, exclusive) a message needs to match; default 0.7")] double? Threshold = null,
+    [property: Description("update: false pauses the trigger, true resumes it")] bool? Enabled = null,
+    [property: Description("snooze: for how long, e.g. 90m, 2h, 1d, 1h30m")] string? Duration = null,
+    [property: Description("snooze: until this ISO 8601 date-time; without an offset it's the chat's local time")] string? Until = null);
+
+/// <summary>
+/// The model's view of this chat's group triggers. Bound to one owner (the private chat); it never sees another
+/// chat's triggers. Membership is checked against the owner's Telegram user id, which is the private chat's id.
+/// </summary>
+public sealed class TriggerTool(long owner, TriggerServices services, Func<TimeZoneInfo> zone) : Tool<TriggerArgs>
+{
+    public const string ToolName = "trigger";
+
+    public override string Name => ToolName;
+
+    public override string Description =>
+        "Watch Telegram groups the bot is in for topics the user cares about. A trigger is a yes/no question a fast classifier (Jev) asks about every message of one group; " +
+        "when a message scores at or above the threshold you get it as a prompt (with its score) and decide how to tell the user. " +
+        "Actions: groups (watched groups), create, list, update, delete, snooze (collect quietly, then check everything as one batch when the snooze ends), unsnooze.";
+
+    public override string? PromptSnippet => "trigger: watch Telegram groups for topics and get relevant messages as prompts";
+
+    public override IReadOnlyList<string> PromptGuidelines =>
+    [
+        "trigger: write instructions as a yes/no question about ONE message, with concrete criteriaTrue/criteriaFalse (what counts, what doesn't). Restate the trigger in plain words and get the user's confirmation before create.",
+        "trigger: a match arrives as a prompt starting with [Trigger …] and listing each message with its score. Tell the user what matters, briefly, with the link; never post in the group.",
+        "trigger: when the user says a match wasn't relevant: if it scored well above the threshold, tighten the criteria (the question is ambiguous); if it was close to the threshold, raise the threshold. When the user reports a missed message, lower the threshold or broaden the criteria. Always say what you changed.",
+        "trigger: when the user wants quiet (\"not until tonight\", \"only once an hour\"), snooze: messages are collected and checked as one batch when it ends, and you get one prompt if anything is related. For \"once an hour\" snooze again after each batch.",
+        "trigger: the bot only sees group messages if privacy mode is off (@BotFather /setprivacy → Disable) or it is a group admin; an allowed user must add it to the group (or post there once).",
+    ];
+
+    public override ToolExecutionMode ExecutionMode => ToolExecutionMode.Sequential;
+
+    protected override async Task<ToolResult> ExecuteAsync(TriggerArgs args, ToolInvocation invocation, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(args);
+        try
+        {
+            return (args.Action ?? "").Trim().ToLowerInvariant() switch
+            {
+                "groups" => ToolResult.Text(Groups()),
+                "create" => await CreateAsync(args, cancellationToken).ConfigureAwait(false),
+                "list" => ToolResult.Text(services.Describe(owner, zone())),
+                "update" => await UpdateAsync(args, cancellationToken).ConfigureAwait(false),
+                "delete" => await DeleteAsync(args, cancellationToken).ConfigureAwait(false),
+                "snooze" => await SnoozeAsync(args, cancellationToken).ConfigureAwait(false),
+                "unsnooze" => await UnsnoozeAsync(args, cancellationToken).ConfigureAwait(false),
+                _ => throw Error("action must be groups, create, list, update, delete, snooze or unsnooze."),
+            };
+        }
+        catch (TriggerLimitException ex)
+        {
+            throw Error(ex.Message);
+        }
+    }
+
+    private string Groups()
+    {
+        var groups = services.Groups.All().Where(g => g.Active).ToList();
+        if (groups.Count == 0)
+            return "The bot isn't watching any group yet. An allowed user has to add it to a group (or post there once while it's a member), " +
+                   "and privacy mode must be off (@BotFather /setprivacy → Disable) or the bot must be an admin, so it sees every message.";
+        var mine = services.Store.List(owner);
+        var sb = new StringBuilder("Watched groups:");
+        foreach (var g in groups)
+        {
+            sb.Append(CultureInfo.InvariantCulture, $"\n- {g.Title} (id {g.Id.ToString(CultureInfo.InvariantCulture)})");
+            var ids = mine.Where(t => t.GroupId == g.Id).Select(t => t.Id).ToList();
+            if (ids.Count > 0) sb.Append(" · your triggers: ").Append(string.Join(", ", ids));
+        }
+        return sb.ToString();
+    }
+
+    private async Task<ToolResult> CreateAsync(TriggerArgs args, CancellationToken cancellationToken)
+    {
+        var group = ResolveGroup(args.Group);
+        if (string.IsNullOrWhiteSpace(args.Name)) throw Error("create needs name.");
+        if (string.IsNullOrWhiteSpace(args.Instructions)) throw Error("create needs instructions (a yes/no question about one message).");
+        var threshold = Threshold(args.Threshold) ?? services.Options.DefaultThreshold;
+        if (!await services.Membership.IsMemberAsync(group.Id, owner, cancellationToken).ConfigureAwait(false))
+            throw Error($"The user isn't a member of \"{group.Title}\" (or the bot can't check), so no trigger can watch it for them.");
+        var created = await services.Store.AddAsync(owner, new NewTrigger(args.Name.Trim(), group.Id, group.Title, args.Instructions.Trim(),
+            Clean(args.CriteriaTrue), Clean(args.CriteriaFalse), threshold), cancellationToken).ConfigureAwait(false);
+        return ToolResult.Text("Created: " + TriggerPrompts.Line(created, zone(), services.Engine.Now, 0));
+    }
+
+    private async Task<ToolResult> UpdateAsync(TriggerArgs args, CancellationToken cancellationToken)
+    {
+        var id = RequireId(args.Id, "update");
+        var threshold = Threshold(args.Threshold);
+        if (args.Name is not null && args.Name.Trim().Length == 0) throw Error("name can't be empty.");
+        if (args.Instructions is not null && args.Instructions.Trim().Length == 0) throw Error("instructions can't be empty.");
+        var updated = await services.Store.UpdateAsync(owner, id, t => t with
+        {
+            Name = args.Name?.Trim() ?? t.Name,
+            Instructions = args.Instructions?.Trim() ?? t.Instructions,
+            CriteriaTrue = args.CriteriaTrue is null ? t.CriteriaTrue : Clean(args.CriteriaTrue),
+            CriteriaFalse = args.CriteriaFalse is null ? t.CriteriaFalse : Clean(args.CriteriaFalse),
+            Threshold = threshold ?? t.Threshold,
+            Enabled = args.Enabled ?? t.Enabled,
+        }, cancellationToken).ConfigureAwait(false) ?? throw Error($"No trigger {id} in this chat.");
+        return ToolResult.Text("Updated: " + TriggerPrompts.Line(updated, zone(), services.Engine.Now, services.Engine.Queued(owner, updated.Id)));
+    }
+
+    private async Task<ToolResult> DeleteAsync(TriggerArgs args, CancellationToken cancellationToken)
+    {
+        var id = RequireId(args.Id, "delete");
+        var removed = await services.Engine.DeleteAsync(owner, id, cancellationToken).ConfigureAwait(false) ?? throw Error($"No trigger {id} in this chat.");
+        return ToolResult.Text($"Deleted {removed.Id} (\"{removed.Name}\").");
+    }
+
+    private async Task<ToolResult> SnoozeAsync(TriggerArgs args, CancellationToken cancellationToken)
+    {
+        var tz = zone();
+        var now = services.Engine.Now;
+        DateTimeOffset until;
+        if (!string.IsNullOrWhiteSpace(args.Duration) && !string.IsNullOrWhiteSpace(args.Until)) throw Error("snooze takes duration or until, not both.");
+        if (!string.IsNullOrWhiteSpace(args.Duration))
+            until = TriggerPrompts.TryParseDuration(args.Duration, out var duration) ? now + duration : throw Error("duration looks like 90m, 2h, 1d or 1h30m.");
+        else if (!string.IsNullOrWhiteSpace(args.Until))
+            until = TriggerPrompts.TryParseUntil(args.Until, tz, out var at) ? at : throw Error("until must be an ISO 8601 date-time, e.g. 2026-10-05T18:00.");
+        else
+            throw Error("snooze needs duration or until.");
+        if (until <= now) throw Error("That time has already passed.");
+        if (until - now > services.Options.MaxSnooze)
+            throw Error($"A snooze can last at most {services.Options.MaxSnooze.TotalDays.ToString("0.#", CultureInfo.InvariantCulture)} days.");
+
+        var snoozed = await services.Engine.SnoozeAsync(owner, Id(args.Id), until, cancellationToken).ConfigureAwait(false);
+        if (snoozed.Count == 0) throw Error(args.Id is null ? "This chat has no triggers." : $"No trigger {args.Id.Trim()} in this chat.");
+        return ToolResult.Text($"Snoozed {string.Join(", ", snoozed.Select(t => t.Id))} until {TriggerPrompts.Stamp(until, tz)} ({tz.Id}). " +
+                               "Messages are collected meanwhile and checked as one batch when the snooze ends; you get one prompt if anything is related.");
+    }
+
+    private async Task<ToolResult> UnsnoozeAsync(TriggerArgs args, CancellationToken cancellationToken)
+    {
+        var id = Id(args.Id);
+        if (id is not null && services.Store.Find(owner, id) is null) throw Error($"No trigger {id} in this chat.");
+        var results = await services.Engine.UnsnoozeAsync(owner, id, cancellationToken).ConfigureAwait(false);
+        if (results.Count == 0) return ToolResult.Text("Nothing is snoozed.");
+        var lines = results.Select(r => r switch
+        {
+            { Error: { } error } => $"{r.Trigger.Id}: Jev failed ({error}); the {Count(r.Count)} were lost.",
+            { Count: 0 } => $"{r.Trigger.Id}: nothing was queued.",
+            { Matched: true } => $"{r.Trigger.Id}: {Count(r.Count)}, related (score {r.Score!.Value.ToString("0.00", CultureInfo.InvariantCulture)}); they follow as a separate prompt.",
+            { Score: { } score } => $"{r.Trigger.Id}: {Count(r.Count)}, nothing related (best score {score.ToString("0.00", CultureInfo.InvariantCulture)}).",
+            _ => $"{r.Trigger.Id}: {Count(r.Count)} dropped (the trigger is off).",
+        });
+        return ToolResult.Text("Unsnoozed.\n" + string.Join("\n", lines));
+    }
+
+    private KnownGroup ResolveGroup(string? text)
+    {
+        var key = text?.Trim() ?? "";
+        if (key.Length == 0) throw Error("create needs group (see action groups).");
+        var groups = services.Groups.All().Where(g => g.Active).ToList();
+        if (long.TryParse(key, NumberStyles.AllowLeadingSign, CultureInfo.InvariantCulture, out var id))
+            return groups.Find(g => g.Id == id) ?? throw Error($"The bot isn't watching a group with id {key} (see action groups).");
+        var exact = groups.Where(g => string.Equals(g.Title, key, StringComparison.OrdinalIgnoreCase)).ToList();
+        var matches = exact.Count > 0 ? exact : groups.Where(g => g.Title.Contains(key, StringComparison.OrdinalIgnoreCase)).ToList();
+        return matches.Count switch
+        {
+            1 => matches[0],
+            0 => throw Error($"No watched group matches \"{key}\" (see action groups)."),
+            _ => throw Error($"\"{key}\" matches several groups: {string.Join(", ", matches.Select(g => $"{g.Title} ({g.Id.ToString(CultureInfo.InvariantCulture)})"))}. Use the id."),
+        };
+    }
+
+    private static double? Threshold(double? value) =>
+        value is { } v && (v <= 0 || v >= 1 || double.IsNaN(v)) ? throw Error("threshold must be between 0 and 1 (exclusive).") : value;
+
+    private static string RequireId(string? id, string action) => Id(id) ?? throw Error($"{action} needs id (see action list).");
+
+    private static string? Id(string? id) => string.IsNullOrWhiteSpace(id) ? null : id.Trim().ToLowerInvariant();
+
+    private static string? Clean(string? text) => string.IsNullOrWhiteSpace(text) ? null : text.Trim();
+
+    private static string Count(int n) => n.ToString(CultureInfo.InvariantCulture) + (n == 1 ? " message" : " messages");
+
+    private static ToolExecutionException Error(string message) => new(ToolResult.Text(message));
+}
+
+/// <summary>Host extension per private chat: the <c>trigger</c> tool.</summary>
+public sealed class TriggerExtension(long chatId, TriggerServices services, Func<TimeZoneInfo> zone) : IExtension
+{
+    public const string ExtensionName = "telegram-triggers";
+
+    public string Name => ExtensionName;
+
+    public ValueTask ActivateAsync(IExtensionApi api, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(api);
+        api.RegisterTool(new TriggerTool(chatId, services, zone));
+        return ValueTask.CompletedTask;
+    }
+}
diff --git a/hosts/Volcanic.AgenticCore.Telegram/Triggers/TriggersSetup.cs b/hosts/Volcanic.AgenticCore.Telegram/Triggers/TriggersSetup.cs
new file mode 100644
index 0000000..1bc63fe
--- /dev/null
+++ b/hosts/Volcanic.AgenticCore.Telegram/Triggers/TriggersSetup.cs
@@ -0,0 +1,58 @@
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Telegram.Bot.Types;
+using Volcanic.AgenticCore.Telegram.Chats;
+using Volcanic.AgenticCore.Telegram.Groups;
+
+namespace Volcanic.AgenticCore.Telegram.Triggers;
+
+/// <summary>Everything the Telegram host does for group triggers, kept out of the shared host files.</summary>
+public static class TriggersSetup
+{
+    public const string DisabledReply = "Group triggers are off on this bot (no OPENROUTER_API_KEY).";
+
+    public const string HelpLines = "\n/triggers – this chat's group triggers (ask me to create, change or snooze them)";
+
+    public static readonly BotCommand MenuCommand = new() { Command = "triggers", Description = "Group triggers watching for topics" };
+
+    /// <summary>The Jev client, groups, store, engine, delivery, feed and the hosted service. Only when triggers are on.</summary>
+    public static void Register(IServiceCollection services, TelegramOptions options, string agentDir)
+    {
+        ArgumentNullException.ThrowIfNull(services);
+        ArgumentNullException.ThrowIfNull(options);
+        var triggers = options.Triggers;
+        services.TryAddSingleton(TimeProvider.System);
+        services.AddSingleton(triggers);
+        // The engine (a singleton) keeps this typed client for the process lifetime: let the handler recycle its pooled
+        // connections instead, so DNS changes are still picked up.
+        services.AddHttpClient<IJevClient, JevClient>(client => client.Timeout = TimeSpan.FromSeconds(30))
+            .ConfigurePrimaryHttpMessageHandler(() => new SocketsHttpHandler { PooledConnectionLifetime = TimeSpan.FromMinutes(5) })
+            .SetHandlerLifetime(Timeout.InfiniteTimeSpan);
+        services.AddSingleton(sp => new GroupRegistry(GroupRegistry.DefaultPath(agentDir), sp.GetRequiredService<ILogger<GroupRegistry>>(), sp.GetRequiredService<TimeProvider>()));
+        services.AddSingleton(sp => new TriggerStore(options.WorkspaceRoot, triggers.MaxTriggersPerChat, sp.GetRequiredService<ILogger<TriggerStore>>(), sp.GetRequiredService<TimeProvider>()));
+        services.AddSingleton(new SnoozeQueue(triggers.MaxQueuedPerTrigger));
+        // Resolves the registry at call time: ChatRegistry → trigger extension → engine → delivery would be a cycle.
+        services.AddSingleton<ITriggerDelivery>(sp => new TelegramTriggerDelivery(
+            () => sp.GetRequiredService<ChatRegistry>(), sp.GetRequiredService<TimeProvider>(), sp.GetRequiredService<ILogger<TelegramTriggerDelivery>>()));
+        services.AddSingleton<TriggerDispatcher>();
+        services.AddSingleton<TriggerEngine>();
+        services.AddSingleton<IGroupMembership, TelegramGroupMembership>();
+        services.AddSingleton<TriggerServices>();
+        services.AddSingleton<GroupFeed>();
+        services.AddHostedService<TriggersHostedService>();
+    }
+}
+
+/// <summary>Flushes snoozes that ended while the host was down and arms the snooze timer.</summary>
+public sealed class TriggersHostedService(TriggerEngine engine) : IHostedService
+{
+    public Task StartAsync(CancellationToken cancellationToken) => engine.StartAsync(cancellationToken);
+
+    public Task StopAsync(CancellationToken cancellationToken)
+    {
+        engine.Dispose();
+        return Task.CompletedTask;
+    }
+}
diff --git a/tests/Volcanic.AgenticCore.Telegram.Tests/GroupChatTests.cs b/tests/Volcanic.AgenticCore.Telegram.Tests/GroupChatTests.cs
new file mode 100644
index 0000000..cc21843
--- /dev/null
+++ b/tests/Volcanic.AgenticCore.Telegram.Tests/GroupChatTests.cs
@@ -0,0 +1,173 @@
+using Microsoft.Extensions.Time.Testing;
+using Telegram.Bot.Requests;
+using Telegram.Bot.Types.Enums;
+using Volcanic.AgenticCore.Abstractions.Messages;
+using Volcanic.AgenticCore.Telegram.Tests.Support;
+using Volcanic.AgenticCore.Telegram.Triggers;
+using Volcanic.AgenticCore.Testing;
+
+namespace Volcanic.AgenticCore.Telegram.Tests;
+
+/// <summary>Groups end to end: the bot watches silently, triggers are set up in the private chat, matches reach it.</summary>
+public sealed class GroupChatTests
+{
+    private const long Owner = Updates.AllowedUser;
+    private const long Group = Updates.GroupId;
+    private static readonly DateTimeOffset Now = new(2026, 10, 5, 12, 0, 0, TimeSpan.Zero);
+
+    private static ChatHost Host(FakeTimeProvider? time = null) =>
+        new(time: time ?? new FakeTimeProvider(Now), triggers: new TriggerOptions { ApiKey = "k", Debounce = TimeSpan.FromSeconds(10) });
+
+    private static Task<Trigger> AddTriggerAsync(ChatHost host, long owner = Owner) =>
+        host.Triggers!.Store.AddAsync(owner, new NewTrigger("deploys", Group, "Dev Team", "Is this about deploys?", null, null, 0.7), CancellationToken.None);
+
+    private static bool SentToGroup(ChatHost host) =>
+        host.Bot.Requests.Any(r => r is SendMessageRequest { ChatId.Identifier: Group } or SetMessageReactionRequest { ChatId.Identifier: Group }
+                                       or SendChatActionRequest { ChatId.Identifier: Group });
+
+    [Fact]
+    public async Task A_strangers_matching_message_reaches_the_owners_session_and_nothing_goes_to_the_group()
+    {
+        var time = new FakeTimeProvider(Now);
+        await using var host = Host(time);
+        await host.RouteAsync(Updates.BotMembership(ChatMemberStatus.Member)); // an allowed user adds the bot
+        await AddTriggerAsync(host);
+        host.Faux.Enqueue(FauxTurn.Say("Heads up: Alice says prod deploy is failing."));
+
+        await host.RouteAsync(Updates.GroupText("prod deploy is failing again", Updates.Stranger));
+        await host.RouteAsync(Updates.GroupText("anyone for lunch?", Updates.Stranger));
+        await host.Feed!.IdleAsync();
+        time.Advance(TimeSpan.FromSeconds(10));
+        await host.Engine!.IdleAsync();
+        await host.SettleAsync();
+
+        var prompt = Assert.Single(host.Faux.Requests).Messages.Last().Text;
+        Assert.Contains("[Trigger \"deploys\" (t1) matched 1 message in \"Dev Team\"]", prompt, StringComparison.Ordinal);
+        Assert.Contains("Alice, score 0.95: prod deploy is failing again", prompt, StringComparison.Ordinal);
+        Assert.DoesNotContain("lunch", prompt, StringComparison.Ordinal);
+        Assert.Contains(host.Texts, t => t.Contains("Heads up", StringComparison.Ordinal));
+        Assert.False(SentToGroup(host));
+        Assert.Null(host.Chats.Find(Group)); // a group never gets a session
+        Assert.Equal(2, host.TriggerLog.Entries.Count(e => e.Text.StartsWith("Group \"Dev Team\"", StringComparison.Ordinal)));
+    }
+
+    [Fact]
+    public async Task A_group_nobody_allowed_vouched_for_is_ignored_until_an_allowed_user_posts()
+    {
+        await using var host = Host();
+        await AddTriggerAsync(host);
+        await host.RouteAsync(Updates.BotMembership(ChatMemberStatus.Member, byUser: Updates.Stranger));
+
+        await host.RouteAsync(Updates.GroupText("deploy now", Updates.Stranger));
+        await host.Feed!.IdleAsync();
+        Assert.Null(host.Groups!.Find(Group));
+        Assert.Empty(((FakeJev)host.Jev!).Calls);
+
+        await host.RouteAsync(Updates.GroupText("deploy please", Owner));
+        await host.Feed.IdleAsync();
+        Assert.True(host.Groups.Find(Group)!.Active);
+        Assert.Single(((FakeJev)host.Jev).Calls);
+        Assert.False(SentToGroup(host));
+    }
+
+    [Fact]
+    public async Task Removing_the_bot_pauses_the_group_and_migration_moves_its_triggers()
+    {
+        await using var host = Host();
+        await host.RouteAsync(Updates.BotMembership(ChatMemberStatus.Administrator));
+        await AddTriggerAsync(host);
+
+        await host.RouteAsync(Updates.BotMembership(ChatMemberStatus.Kicked));
+        await host.RouteAsync(Updates.GroupText("deploy", Updates.Stranger));
+        await host.Feed!.IdleAsync();
+        Assert.False(host.Groups!.Find(Group)!.Active);
+        Assert.Empty(((FakeJev)host.Jev!).Calls);
+
+        await host.RouteAsync(Updates.BotMembership(ChatMemberStatus.Member, groupId: -5, title: "Old"));
+        await host.Triggers!.Store.AddAsync(Owner, new NewTrigger("old", -5, "Old", "q?", null, null, 0.7), CancellationToken.None);
+        var migrate = Updates.GroupText("", Updates.Stranger, groupId: -5, title: "Old", type: ChatType.Group);
+        migrate.Message!.Text = null;
+        migrate.Message.MigrateToChatId = -1009;
+        await host.RouteAsync(migrate);
+
+        Assert.Equal(-1009, host.Triggers.Store.Find(Owner, "t2")!.GroupId);
+        Assert.NotNull(host.Groups.Find(-1009));
+    }
+
+    [Fact]
+    public async Task Without_triggers_group_messages_are_dropped()
+    {
+        await using var host = new ChatHost();
+        await host.RouteAsync(Updates.GroupText("deploy", Owner));
+        Assert.Null(host.Chats.Find(Group));
+        Assert.Null(host.Chats.Find(Owner));
+        Assert.Empty(host.Bot.Sent);
+    }
+
+    [Fact]
+    public async Task The_agent_creates_lists_and_snoozes_a_trigger_through_the_tool()
+    {
+        await using var host = Host();
+        await host.RouteAsync(Updates.BotMembership(ChatMemberStatus.Member));
+        host.Faux.Enqueue(
+            FauxTurn.Tool("trigger", new { action = "groups" }),
+            FauxTurn.Tool("trigger", new { action = "create", group = "dev", name = "deploys", instructions = "Is this message about deploys?", criteriaTrue = "Deploys, releases, rollbacks", criteriaFalse = "Anything else", threshold = 0.8 }),
+            FauxTurn.Tool("trigger", new { action = "snooze", duration = "2h" }),
+            FauxTurn.Say("Done."));
+        var chat = await host.ChatAsync();
+
+        await chat.Session.PromptAsync("watch Dev Team for deploys, but keep quiet for two hours");
+
+        var results = chat.Session.Messages.OfType<ToolResultMessage>().ToList();
+        Assert.All(results, r => Assert.False(r.IsError, r.Text));
+        Assert.Contains("- Dev Team (id -1001234567890)", results[0].Text, StringComparison.Ordinal);
+        Assert.StartsWith("Created: t1 \"deploys\" · Dev Team · threshold 0.80", results[1].Text, StringComparison.Ordinal);
+        Assert.StartsWith("Snoozed t1 until", results[2].Text, StringComparison.Ordinal);
+        var trigger = host.Triggers!.Store.Find(Owner, "t1")!;
+        Assert.Equal(("Deploys, releases, rollbacks", Now.AddHours(2)), (trigger.CriteriaTrue, trigger.SnoozedUntil));
+
+        await host.SendAsync("/triggers");
+        await Wait.UntilAsync(() => host.Bot.Sent.Any(s => s.Text.Contains("snoozed until", StringComparison.Ordinal)), "the /triggers reply");
+    }
+
+    [Fact]
+    public async Task Only_members_of_a_group_can_put_a_trigger_on_it()
+    {
+        await using var host = Host();
+        await host.RouteAsync(Updates.BotMembership(ChatMemberStatus.Member));
+        host.Bot.NonMembers[Owner] = true;
+        host.Faux.Enqueue(FauxTurn.Tool("trigger", new { action = "create", group = "Dev Team", name = "x", instructions = "q?" }), FauxTurn.Say("Sorry."));
+        var chat = await host.ChatAsync();
+
+        await chat.Session.PromptAsync("watch Dev Team");
+
+        var result = chat.Session.Messages.OfType<ToolResultMessage>().Single();
+        Assert.True(result.IsError);
+        Assert.Contains("isn't a member", result.Text, StringComparison.Ordinal);
+        Assert.Empty(host.Triggers!.Store.List(Owner));
+    }
+
+    [Fact]
+    public async Task Tool_errors_explain_what_is_wrong()
+    {
+        await using var host = Host();
+        await host.RouteAsync(Updates.BotMembership(ChatMemberStatus.Member));
+        await host.RouteAsync(Updates.BotMembership(ChatMemberStatus.Member, groupId: -1009, title: "Dev Ops"));
+        host.Faux.Enqueue(
+            FauxTurn.Tool("trigger", new { action = "create", group = "dev", name = "x", instructions = "q?" }),
+            FauxTurn.Tool("trigger", new { action = "create", group = "Dev Team", name = "x", instructions = "q?", threshold = 1.5 }),
+            FauxTurn.Tool("trigger", new { action = "snooze", duration = "soon" }),
+            FauxTurn.Tool("trigger", new { action = "update", id = "t7", threshold = 0.5 }),
+            FauxTurn.Say("Sorry."));
+        var chat = await host.ChatAsync();
+
+        await chat.Session.PromptAsync("try things");
+
+        var results = chat.Session.Messages.OfType<ToolResultMessage>().ToList();
+        Assert.All(results, r => Assert.True(r.IsError));
+        Assert.Contains("matches several groups", results[0].Text, StringComparison.Ordinal);
+        Assert.Contains("threshold must be between 0 and 1", results[1].Text, StringComparison.Ordinal);
+        Assert.Contains("duration looks like", results[2].Text, StringComparison.Ordinal);
+        Assert.Contains("No trigger t7", results[3].Text, StringComparison.Ordinal);
+    }
+}
diff --git a/tests/Volcanic.AgenticCore.Telegram.Tests/Support/ChatHost.cs b/tests/Volcanic.AgenticCore.Telegram.Tests/Support/ChatHost.cs
index 0a997ed..1a52f80 100644
--- a/tests/Volcanic.AgenticCore.Telegram.Tests/Support/ChatHost.cs
+++ b/tests/Volcanic.AgenticCore.Telegram.Tests/Support/ChatHost.cs
@@ -12,6 +12,8 @@ using Volcanic.AgenticCore.Telegram.Chats;
 using Volcanic.AgenticCore.Telegram.Inbound;
 using Volcanic.AgenticCore.Telegram.Rendering;
 using Volcanic.AgenticCore.Telegram.Scheduling;
+using Volcanic.AgenticCore.Telegram.Groups;
+using Volcanic.AgenticCore.Telegram.Triggers;
 using Volcanic.AgenticCore.Testing;
 
 namespace Volcanic.AgenticCore.Telegram.Tests.Support;
@@ -53,7 +55,7 @@ public sealed class ChatHost : IAsyncDisposable
     public ChatHost(Action<ChatHost, IServiceCollection>? configure = null, Action<AgenticCoreOptions>? core = null, TimeProvider? time = null,
         Volcanic.AgenticCore.Extensions.GoogleCalendar.GoogleCalendarOptions? calendar = null,
         Volcanic.AgenticCore.Telegram.Speech.ISpeechToText? speech = null, string? root = null, SchedulerOptions? scheduler = null,
-        IScriptRunner? runner = null)
+        IScriptRunner? runner = null, TriggerOptions? triggers = null, IJevClient? jev = null)
     {
         _ownsRoot = root is null;
         _root = root ?? Path.Combine(Path.GetTempPath(), "volcanic-telegram", Guid.NewGuid().ToString("N"));
@@ -68,6 +70,7 @@ public sealed class ChatHost : IAsyncDisposable
             TypingInterval = TimeSpan.FromMilliseconds(50),
             InputDebounce = TimeSpan.FromMilliseconds(20),
         };
+        if (triggers is not null) Options.Triggers = triggers;
         var store = new InMemorySessionStore();
         var services = new ServiceCollection();
         if (time is not null) services.AddSingleton(time); // sessions render the prompt date from it
@@ -97,13 +100,36 @@ public sealed class ChatHost : IAsyncDisposable
         }
         Zones = new ChatTimeZoneService(Settings, id => Chats!.Find(id)?.Session, clock, Scheduler);
         Impersonation = new Impersonation(Options);
-        Chats = new ChatRegistry(_services.GetRequiredService<IAgentSessionFactory>(), sender, Options, loggers, time, calendar, Settings, Zones, Scheduler, Impersonation);
+        if (triggers is not null)
+        {
+            Jev = jev ?? new FakeJev();
+            Groups = new GroupRegistry(GroupRegistry.DefaultPath(agentDir), NullLogger<GroupRegistry>.Instance, clock);
+            var triggerStore = new TriggerStore(Options.WorkspaceRoot, triggers.MaxTriggersPerChat, NullLogger<TriggerStore>.Instance, clock);
+            var delivery = new TelegramTriggerDelivery(() => Chats!, clock, NullLogger<TelegramTriggerDelivery>.Instance);
+            _dispatcher = new TriggerDispatcher(delivery, triggers, clock, NullLogger<TriggerDispatcher>.Instance);
+            Engine = new TriggerEngine(triggerStore, new SnoozeQueue(triggers.MaxQueuedPerTrigger), Jev, _dispatcher, delivery, clock, TriggerLog);
+            Triggers = new TriggerServices(Engine, Groups, new TelegramGroupMembership(Bot), triggers);
+            Feed = new GroupFeed(Groups, Engine, Bot, Options, NullLogger<GroupFeed>.Instance);
+        }
+        Chats = new ChatRegistry(_services.GetRequiredService<IAgentSessionFactory>(), sender, Options, loggers, time, calendar, Settings, Zones, Scheduler, Impersonation, Triggers);
         if (Scheduler is not null) Delivery = new TelegramJobDelivery(Chats, Settings, Options, clock, NullLogger<TelegramJobDelivery>.Instance);
         var media = new InboundMedia(sender, Options, time ?? TimeProvider.System, NullLogger<InboundMedia>.Instance, speech);
         Composer = new InboundComposer(sender, media, NullLogger<InboundComposer>.Instance);
-        Router = new UpdateRouter(Options, Chats, new ChatCommands(sender, Zones, Scheduler), sender, Composer, NullLogger<UpdateRouter>.Instance, Impersonation);
+        Router = new UpdateRouter(Options, Chats, new ChatCommands(sender, Zones, Scheduler, Triggers), sender, Composer, NullLogger<UpdateRouter>.Instance, Impersonation, Feed);
     }
 
+    private readonly TriggerDispatcher? _dispatcher;
+
+    /// <summary>Set when the host was built with <c>triggers:</c> options.</summary>
+    public TriggerServices? Triggers { get; }
+    public TriggerEngine? Engine { get; }
+    public GroupRegistry? Groups { get; }
+    public GroupFeed? Feed { get; }
+    public IJevClient? Jev { get; }
+
+    /// <summary>The engine's log lines (one per group message).</summary>
+    public ListLogger<TriggerEngine> TriggerLog { get; } = new();
+
     /// <summary>Off until <see cref="TelegramOptions.AdminUserId"/> is set on <see cref="Options"/>.</summary>
     public Impersonation Impersonation { get; }
 
@@ -140,6 +166,9 @@ public sealed class ChatHost : IAsyncDisposable
     public async ValueTask DisposeAsync()
     {
         if (Scheduler is not null) await Scheduler.StopAsync(CancellationToken.None);
+        if (Feed is not null) await Feed.IdleAsync();
+        Engine?.Dispose();
+        _dispatcher?.Dispose();
         await Chats.DisposeAsync();
         await _services.DisposeAsync();
         if (_ownsRoot)
diff --git a/tests/Volcanic.AgenticCore.Telegram.Tests/Support/FakeBotClient.cs b/tests/Volcanic.AgenticCore.Telegram.Tests/Support/FakeBotClient.cs
index 076d191..9fd814c 100644
--- a/tests/Volcanic.AgenticCore.Telegram.Tests/Support/FakeBotClient.cs
+++ b/tests/Volcanic.AgenticCore.Telegram.Tests/Support/FakeBotClient.cs
@@ -34,6 +34,9 @@ public sealed class FakeBotClient : ITelegramBotClient
     /// <summary>When set, a download of a scripted file writes one byte and then fails with a network error.</summary>
     public bool FailDownloads { get; set; }
 
+    /// <summary>Users <c>getChatMember</c> reports as having left (everyone else is a member).</summary>
+    public ConcurrentDictionary<long, bool> NonMembers { get; } = new();
+
     /// <summary>Called for every non-poll request before it is answered; throw to simulate a failure.</summary>
     public Action<IRequest>? OnSend { get; set; }
 
@@ -127,6 +130,10 @@ public sealed class FakeBotClient : ITelegramBotClient
             case GetFileRequest getFile:
                 result = new TGFile { FileId = getFile.FileId, FileUniqueId = getFile.FileId + "-u", FilePath = $"photos/{getFile.FileId}.jpg", FileSize = 3 };
                 break;
+            case GetChatMemberRequest member:
+                var user = new User { Id = member.UserId, FirstName = "Member" };
+                result = NonMembers.ContainsKey(member.UserId) ? new ChatMemberLeft { User = user } : new ChatMemberMember { User = user };
+                break;
             case SendPhotoRequest photo:
                 result = RecordUpload("sendPhoto", photo.ChatId, photo.Photo, photo.Caption, photo.ParseMode);
                 break;
diff --git a/tests/Volcanic.AgenticCore.Telegram.Tests/Support/Updates.cs b/tests/Volcanic.AgenticCore.Telegram.Tests/Support/Updates.cs
index aa9547d..2ae5334 100644
--- a/tests/Volcanic.AgenticCore.Telegram.Tests/Support/Updates.cs
+++ b/tests/Volcanic.AgenticCore.Telegram.Tests/Support/Updates.cs
@@ -39,6 +39,43 @@ public static class Updates
         },
     };
 
+    public const long GroupId = -1001234567890;
+
+    /// <summary>A text message in a group (a supergroup unless <paramref name="type"/> says otherwise).</summary>
+    public static Update GroupText(string text, long userId = Stranger, long groupId = GroupId, string title = "Dev Team", ChatType type = ChatType.Supergroup,
+        string firstName = "Alice") => new()
+    {
+        Id = Interlocked.Increment(ref _nextUpdateId),
+        Message = new Message
+        {
+            Id = Interlocked.Increment(ref _nextMessageId),
+            From = new User { Id = userId, FirstName = firstName },
+            Chat = new Chat { Id = groupId, Type = type, Title = title },
+            Text = text,
+            Date = DateTime.UtcNow,
+        },
+    };
+
+    /// <summary>The bot's own membership in a group changed (added by <paramref name="byUser"/>, or removed).</summary>
+    public static Update BotMembership(ChatMemberStatus status, long byUser = AllowedUser, long groupId = GroupId, string title = "Dev Team") => new()
+    {
+        Id = Interlocked.Increment(ref _nextUpdateId),
+        MyChatMember = new ChatMemberUpdated
+        {
+            Chat = new Chat { Id = groupId, Type = ChatType.Supergroup, Title = title },
+            From = new User { Id = byUser, FirstName = "Adder" },
+            Date = DateTime.UtcNow,
+            OldChatMember = new ChatMemberLeft { User = new User { Id = BotUserId, IsBot = true, FirstName = "Fake" } },
+            NewChatMember = status switch
+            {
+                ChatMemberStatus.Administrator => new ChatMemberAdministrator { User = new User { Id = BotUserId, IsBot = true, FirstName = "Fake" } },
+                ChatMemberStatus.Kicked => new ChatMemberBanned { User = new User { Id = BotUserId, IsBot = true, FirstName = "Fake" } },
+                ChatMemberStatus.Left => new ChatMemberLeft { User = new User { Id = BotUserId, IsBot = true, FirstName = "Fake" } },
+                _ => new ChatMemberMember { User = new User { Id = BotUserId, IsBot = true, FirstName = "Fake" } },
+            },
+        },
+    };
+
     public static Update WithId(int id) => new() { Id = id, Message = Text("#" + id).Message };
 
     /// <summary>The fake bot's user id (<see cref="FakeBotClient.BotId"/>).</summary>