feat: Add invite codes and message replies functionality

- Introduced a new migration to add InviteCodes table and ReplyToMessageId column in Messages.
- Updated ChatHub to support replying to messages.
- Enhanced ChatService to handle message replies and validate reply targets.
- Modified UserService to implement invite-only registration mode with invite code consumption.
- Added configuration options for registration modes in appsettings.
- Created unit tests for new features including invite code registration and message reply formatting.

src/EchoHub.Client/UI/Chat/ChatLine.cs

@@ -31,6 +31,12 @@ public partial class ChatLine
     public AttachmentKind? AttachmentKind { get; set; }
     public string? SenderUsername { get; set; }
 
+    /// <summary>
+    /// Set on a reply's quote line: activating the line jumps to this message
+    /// if it is in the loaded history.
+    /// </summary>
+    public Guid? JumpToMessageId { get; set; }
+
     /// <summary>
     /// Clickable sub-line targets (e.g. the "[open]" and "[save original]" brackets under an
     /// image). Columns are relative to the unwrapped line, so only the first wrapped line
@@ -176,6 +182,7 @@ public partial class ChatLine
             wrapped.MessageId = MessageId;
             wrapped.SenderUsername = SenderUsername;
             wrapped.IsMention = IsMention;
+            wrapped.JumpToMessageId = JumpToMessageId;
         }
 
         // Span columns only line up with the first wrapped line; later lines fall

src/EchoHub.Client/UI/Chat/ChatMessageManager.cs

@@ -1,6 +1,7 @@
 using System.Text;
 using System.Text.RegularExpressions;
 using EchoHub.Client.UI.Helpers;
+using EchoHub.Core.Constants;
 using EchoHub.Core.DTOs;
 using EchoHub.Core.Models;
 using Terminal.Gui.Drawing;
@@ -312,7 +313,9 @@ public sealed class ChatMessageManager
         if (!string.IsNullOrEmpty(_currentUser))
         {
             var pattern = $@"@{Regex.Escape(_currentUser)}\b";
-            if (messages.Skip(firstUnread).Any(m => Regex.IsMatch(m.Content, pattern, RegexOptions.IgnoreCase)))
+            if (messages.Skip(firstUnread).Any(m =>
+                    Regex.IsMatch(m.Content, pattern, RegexOptions.IgnoreCase)
+                    || (m.ReplyTo is { } reply && reply.SenderUsername.Equals(_currentUser, StringComparison.OrdinalIgnoreCase))))
                 _mentionChannels.Add(channelName);
         }
     }
@@ -391,8 +394,36 @@ public sealed class ChatMessageManager
         var hasContent = !string.IsNullOrWhiteSpace(message.Content);
         var attachments = message.Attachments ?? [];
 
+        // Reply → dim quote line above the message; activating it jumps to the original
+        if (message.ReplyTo is { } replyTo)
+            lines.Add(ReplyQuoteLine(replyTo));
+
+        // /me action → "* nick waves" (CTCP ACTION content)
+        string? actionText = null;
+        var isAction = hasContent && MessageConventions.TryParseAction(message.Content, out actionText);
+        if (isAction)
+        {
+            var actionLines = EmojiHelper.ReplaceEmoji(actionText!).Split('\n');
+            var header = ActionHeaderSegments(time);
+            header.Add(new(senderName, senderColor));
+            header.Add(new(" ", null));
+            header.AddRange(ChatColors.SplitMentions(actionLines[0].TrimEnd('\r')));
+            lines.Add(new ChatLine(header));
+
+            for (int i = 1; i < actionLines.Length; i++)
+            {
+                var segments = RailPrefix();
+                segments.AddRange(ChatColors.SplitMentions(actionLines[i].TrimEnd('\r')));
+                lines.Add(new ChatLine(segments));
+            }
+        }
+
         // Header line: caption text, or a summary when the message is attachments-only
-        if (hasContent)
+        if (isAction)
+        {
+            // already rendered above
+        }
+        else if (hasContent)
         {
             var displayContent = EmojiHelper.ReplaceEmoji(message.Content);
             var contentLines = displayContent.Split('\n');
@@ -474,10 +505,14 @@ public sealed class ChatMessageManager
             line.SenderUsername = message.SenderUsername;
         }
 
-        if (hasContent && !string.IsNullOrEmpty(_currentUser))
+        if (!string.IsNullOrEmpty(_currentUser))
         {
+            // Being replied to counts as a mention, same as an explicit @nick
+            var isReplyToMe = message.ReplyTo is { } reply
+                && reply.SenderUsername.Equals(_currentUser, StringComparison.OrdinalIgnoreCase);
             var pattern = $@"@{Regex.Escape(_currentUser)}\b";
-            if (Regex.IsMatch(message.Content, pattern, RegexOptions.IgnoreCase))
+            if (isReplyToMe
+                || ((hasContent || isAction) && Regex.IsMatch(message.Content, pattern, RegexOptions.IgnoreCase)))
             {
                 foreach (var line in lines)
                     line.IsMention = true;
@@ -558,6 +593,54 @@ public sealed class ChatMessageManager
         new(" │ ", ChatColors.RailAttr),
     ];
 
+    /// <summary>Header variant for /me actions: "*" in the nick column, "* nick text" content.</summary>
+    private static List<ChatSegment> ActionHeaderSegments(string time) =>
+    [
+        new($"{time} ", ChatColors.TimestampAttr),
+        new(PadNick("*"), ChatColors.TimestampAttr),
+        new(" │ ", ChatColors.RailAttr),
+    ];
+
+    /// <summary>
+    /// The dim "┌ nick: snippet" line above a reply. Carries the original message id so
+    /// activating it jumps there. Room-encrypted snippets arrive already decrypted (or as
+    /// the locked placeholder) — this only truncates for display.
+    /// </summary>
+    private static ChatLine ReplyQuoteLine(ReplyRefDto replyTo)
+    {
+        const int maxSnippetCols = 60;
+
+        var snippet = replyTo.Content.Replace('\n', ' ').Replace('\r', ' ');
+        if (MessageConventions.TryParseAction(snippet, out var actionText))
+            snippet = $"* {replyTo.SenderUsername} {actionText}";
+
+        snippet = EmojiHelper.ReplaceEmoji(snippet);
+        if (snippet.GetColumns() > maxSnippetCols)
+        {
+            var sb = new StringBuilder();
+            int used = 0;
+            foreach (var g in GraphemeHelper.GetGraphemes(snippet))
+            {
+                var gCols = Math.Max(g.GetColumns(), 1);
+                if (used + gCols > maxSnippetCols - 1) break;
+                sb.Append(g);
+                used += gCols;
+            }
+            snippet = sb.Append('…').ToString();
+        }
+
+        var segments = RailPrefix();
+        segments.Add(new("┌ ", ChatColors.RailAttr));
+        segments.Add(new($"{replyTo.SenderUsername}: ", NickColorHelper.GetAttribute(replyTo.SenderUsername)));
+        segments.Add(new(snippet, ChatColors.SystemAttr));
+
+        return new ChatLine(segments)
+        {
+            JumpToMessageId = replyTo.MessageId,
+            ContinuationPrefixSegments = RailPrefix(),
+        };
+    }
+
     /// <summary>
     /// Indent segments aligning continuation/attachment/embed lines under the message
     /// text, extending the │ rail. Returns a fresh mutable list each call.

src/EchoHub.Client/UI/Dialogs/ConnectDialog.cs

@@ -11,7 +11,8 @@ namespace EchoHub.Client.UI.Dialogs;
 /// </summary>
 public record ConnectDialogResult(
     string ServerUrl, string Username, string Password,
-    bool IsRegister, bool RememberMe, string? SavedRefreshToken);
+    bool IsRegister, bool RememberMe, string? SavedRefreshToken,
+    string? DisplayName = null, string? InviteCode = null);
 
 /// <summary>
 /// A Terminal.Gui dialog for entering server connection and authentication details.
@@ -29,7 +30,7 @@ public sealed class ConnectDialog
         savedServers ??= [];
 
         var hasSavedServers = savedServers.Count > 0;
-        var dialogHeight = hasSavedServers ? 22 : 18;
+        var dialogHeight = hasSavedServers ? 24 : 20;
 
         var dialog = new Dialog { Title = "Connect to Server", Width = 60, Height = dialogHeight };
 
@@ -153,26 +154,41 @@ public sealed class ConnectDialog
             Width = Dim.Fill(2)
         };
 
+        // Only needed on servers with invite-gated registration; harmless elsewhere
+        var inviteLabel = new Label
+        {
+            Text = "Invite Code:",
+            X = 1,
+            Y = yOffset + 11
+        };
+        var inviteField = new TextField
+        {
+            Text = "",
+            X = 15,
+            Y = yOffset + 11,
+            Width = Dim.Fill(2)
+        };
+
         var loginButton = new Button
         {
             Text = "Login",
             IsDefault = true,
             X = Pos.Center() - 20,
-            Y = yOffset + 11
+            Y = yOffset + 13
         };
 
         var registerButton = new Button
         {
             Text = "Register",
             X = Pos.Center() - 5,
-            Y = yOffset + 11
+            Y = yOffset + 13
         };
 
         var cancelButton = new Button
         {
             Text = "Cancel",
             X = Pos.Center() + 10,
-            Y = yOffset + 11
+            Y = yOffset + 13
         };
 
         // Wire saved server selection to auto-fill fields
@@ -262,7 +278,11 @@ public sealed class ConnectDialog
                 return;
             }
 
-            result = new ConnectDialogResult(url, user, pass, IsRegister: true, rememberMe, SavedRefreshToken: null);
+            var displayName = displayField.Text?.Trim();
+            var inviteCode = inviteField.Text?.Trim();
+            result = new ConnectDialogResult(url, user, pass, IsRegister: true, rememberMe, SavedRefreshToken: null,
+                DisplayName: string.IsNullOrEmpty(displayName) ? null : displayName,
+                InviteCode: string.IsNullOrEmpty(inviteCode) ? null : inviteCode);
             e.Handled = true;
             app.RequestStop();
         };
@@ -276,6 +296,7 @@ public sealed class ConnectDialog
 
         dialog.Add(urlLabel, urlField, userLabel, userField, passLabel, passField,
             tokenHintLabel, rememberMeCheckbox, displayLabel, displayField,
+            inviteLabel, inviteField,
             loginButton, registerButton, cancelButton);
 
         if (hasSavedServers && savedServerList is not null)

src/EchoHub.Client/UI/MainWindow.cs

@@ -64,10 +64,11 @@ public sealed partial class MainWindow : Runnable
     // Available slash commands for Tab autocomplete
     private static readonly string[] SlashCommands =
     [
-        "/status", "/nick", "/color", "/theme", "/send",
+        "/status", "/nick", "/color", "/theme", "/send", "/me", "/banner",
         "/avatar", "/profile", "/servers", "/join", "/passwd", "/leave", "/clear", "/size", "/downloadpath",
         "/topic", "/users", "/kick", "/ban", "/unban",
-        "/mute", "/unmute", "/role", "/nuke", "/test-sound", "/quit", "/help"
+        "/mute", "/unmute", "/role", "/invite", "/export", "/deleteaccount",
+        "/nuke", "/test-sound", "/quit", "/help"
     ];
 
     private readonly List<string> _channelNames = [];
@@ -187,6 +188,17 @@ public sealed partial class MainWindow : Runnable
     /// </summary>
     public event Action<Guid>? OnDeleteMessageRequested;
 
+    /// <summary>
+    /// Fired when the user picks "Reply" on a message. Parameters: message id, sender username,
+    /// a short plain-text snippet for the reply strip.
+    /// </summary>
+    public event Action<Guid, string, string>? OnReplyRequested;
+
+    /// <summary>
+    /// Fired when the user cancels a pending reply (Esc in the input field).
+    /// </summary>
+    public event Action? OnReplyCancelRequested;
+
     /// <summary>
     /// Fired when the user activates a username (in userlist or message). Parameter is the username.
     /// </summary>
@@ -357,6 +369,9 @@ public sealed partial class MainWindow : Runnable
         KeyDown += OnWindowKeyDown;
     }
 
+    private string? _stagedTitleFragment;
+    private string? _replyTitleFragment;
+
     /// <summary>
     /// Updates the attachment staging indicator shown on the input frame's title, including the
     /// current ASCII-art size for images. Passing an empty list restores the default hint.
@@ -366,15 +381,38 @@ public sealed partial class MainWindow : Runnable
         _hasStagedAttachments = fileNames.Count > 0;
         if (fileNames.Count == 0)
         {
-            _inputFrame.Title = DefaultInputTitle;
+            _stagedTitleFragment = null;
         }
         else
         {
             var names = string.Join(", ", fileNames);
             if (names.Length > 45)
                 names = names[..42] + "...";
-            _inputFrame.Title = $"📎 {fileNames.Count}: {names} │ art: {asciiSizeLabel} (/size) │ Enter=send │ /clear";
+            _stagedTitleFragment = $"📎 {fileNames.Count}: {names} │ art: {asciiSizeLabel} (/size) │ Enter=send │ /clear";
         }
+        UpdateInputTitle();
+    }
+
+    /// <summary>
+    /// Shows/clears the "replying to" strip on the input frame's title. Pass null to clear.
+    /// </summary>
+    public void SetReplyingTo(string? label)
+    {
+        _replyTitleFragment = label is null ? null : $"↩ Replying to {label} │ Esc=cancel";
+        UpdateInputTitle();
+    }
+
+    public bool HasPendingReplyIndicator => _replyTitleFragment is not null;
+
+    private void UpdateInputTitle()
+    {
+        _inputFrame.Title = (_replyTitleFragment, _stagedTitleFragment) switch
+        {
+            (null, null) => DefaultInputTitle,
+            ({ } reply, null) => reply,
+            (null, { } staged) => staged,
+            ({ } reply, { } staged) => $"{reply} │ {staged}",
+        };
         _inputFrame.SetNeedsDraw();
     }
 
@@ -519,6 +557,14 @@ public sealed partial class MainWindow : Runnable
         var line = source.GetLine(index.Value);
         if (line is null) return;
 
+        // A reply's quote line jumps to the original message (if it's in the buffer)
+        if (line.JumpToMessageId is { } jumpTarget)
+        {
+            ScrollToMessage(jumpTarget);
+            e.Handled = true;
+            return;
+        }
+
         // Audio/file attachments take priority
         if (line.AttachmentUrl is not null && line.AttachmentFileName is not null)
         {
@@ -681,6 +727,20 @@ public sealed partial class MainWindow : Runnable
             }
         }
 
+        if (sender is not null && line.MessageId is { } replyTargetId)
+        {
+            items.Add(new MenuItem("Reply", "", () =>
+            {
+                // Strip the "HH:mm nick │ " header so the strip shows just the text
+                var snippet = line.ToString();
+                var railIdx = snippet.IndexOf(" │ ", StringComparison.Ordinal);
+                if (railIdx >= 0)
+                    snippet = snippet[(railIdx + 3)..];
+                OnReplyRequested?.Invoke(replyTargetId, sender, snippet.Trim());
+                _inputField.SetFocus();
+            }, Key.Empty));
+        }
+
         if (sender is not null)
         {
             items.Add(new MenuItem($"Mention @{sender}", "", () => MentionUser(sender), Key.Empty));
@@ -722,6 +782,30 @@ public sealed partial class MainWindow : Runnable
         }
     }
 
+    /// <summary>
+    /// Scrolls the message list to a message's first line (used by reply quote lines).
+    /// No-op when the message isn't in the loaded buffer.
+    /// </summary>
+    private void ScrollToMessage(Guid messageId)
+    {
+        if (_messageList.Source is not ChatListSource source)
+            return;
+
+        for (int i = 0; i < source.Count; i++)
+        {
+            var line = source.GetLine(i);
+            // Match the message's own lines, not other replies' quote lines pointing at it
+            if (line?.MessageId == messageId && line.JumpToMessageId is null)
+            {
+                _messageList.SelectedItem = i;
+                _messageList.TopItem = Math.Max(0, i - 3);
+                _messageList.SetFocus();
+                _messageList.SetNeedsDraw();
+                return;
+            }
+        }
+    }
+
     private void ConfirmDeleteMessage(Guid messageId)
     {
         var confirm = MessageBox.Query(_app, "Delete Message", "Delete this message?", "Delete", "Cancel");
@@ -757,6 +841,10 @@ public sealed partial class MainWindow : Runnable
                 TryAutocompleteCommand();
                 break;
 
+            case KeyCode.Esc when HasPendingReplyIndicator:
+                OnReplyCancelRequested?.Invoke();
+                break;
+
             case NewlineKey:
                 _inputField.InsertText("\n");
                 break;