feat: enhance user presence and channel interaction features

- Fix userlist not refreshing after creating a new channel.
- Implement unmute timer with a background job to automatically unmute users.
- Improve userlist display by filtering invisible users and ensuring proper transitions between statuses.
- Add clickable usernames, @mentions, and #channels for easier navigation.
- Embed theme colors from source sites for a more cohesive UI.
- Introduce a stateful userlist that updates incrementally via SignalR events.
- Restrict auto-opening of files to safe types only, enhancing security.
- Refactor user management into a dedicated service to reduce code duplication.
- Add a MuteExpirationService to handle timed mutes.
- Update documentation with Mermaid diagrams for major flows.

docs/changelog/v0.2.8.md

@@ -7,6 +7,14 @@
 - Fix connection failure cleanup — `ConnectionManager.ConnectAsync` now properly disposes `ApiClient` and `EchoHubConnection` on any failure path (previously only cleaned up on saved-token auth failures)
 - Fix IRC gateway sending UTF-8 BOM on first message, breaking CAP negotiation and SASL auth for all clients
 - Handle `AUTHENTICATE *` (SASL abort) instead of crashing on invalid base64
+- Fix userlist not refreshing when creating a new channel — now fetches online users after channel creation
+- Fix unmute timer not working — add `MuteExpirationService` background job that proactively unmutes users when their timed mute expires (previously only checked on message send)
+- Fix missing space between mod/admin role icon and username in the userlist
+- Fix invisible users still visible in the userlist — `GetOnlineUsersAsync` now filters invisible users; server skips `UserJoined` broadcast for invisible users
+- Fix invisible→online transition — user reappears in cached userlist when switching from invisible back to a visible status
+- Fix thread safety — `_channelUsers` presence cache now protected by `Lock` to prevent races between SignalR events and background fetches
+- Fix `@mention` regex matching email addresses and `#channel` regex matching hex colors / issue numbers — both now use lookbehind and letter-requirement guards
+- Fix `ParseThemeColor` accepting non-hex characters — now validates `[0-9a-fA-F]` digits
 
 ## New Features
 
@@ -15,17 +23,31 @@
 - Auto-updater rollback — pre-update backup created automatically before each update; restore via File > Rollback menu or `--rollback` CLI flag
 - Update failure recovery — if an update fails mid-extraction, offers to restore from the backup immediately
 - Defensive Unix permission check — verify execute permission on startup after auto-update (defense-in-depth)
+- Clickable usernames — press Enter on a username in the userlist or message sender to view their profile
+- Clickable @mentions — press Enter on a message containing `@username` to open that user's profile
+- Clickable #channels — press Enter on a message containing `#channel` to join/switch to that channel; `#channel` references are now highlighted in chat
+- Embed theme colors — embed vertical border line now uses the source site's `theme-color` meta tag when available
+- Stateful userlist — user presence is cached per channel and updated incrementally via SignalR events instead of re-fetching the full list on every join/leave/status change
+
+## Security
+
+- Restrict file auto-open — only safe file types (video, PDF, text) are opened with the system default app; all other files are downloaded to temp without executing (prevents script execution via `.bat`, `.exe`, etc.)
 
 ## Refactoring
 
 - Extract `IUserService`/`UserService` — consolidate user registration, authentication, and profile management into a dedicated service, eliminating duplicated logic between `AuthController` and `ChatService`
 - IRC gateway now checks ban status during authentication (previously skipped)
+- EchoHubSpace directory updates — server now only sends user count when it actually changes instead of every 30 seconds
 
 ## Distribution
 
 - Add Chocolatey package — `choco install echohub` for Windows users, auto-published from CI on each release
 - Add Linux/macOS install script — `curl -sSfL .../install.sh | sh` with automatic OS/arch detection
 
+## Documentation
+
+- Add Flows section — Mermaid sequence diagrams documenting all major request/event flows (auth, connection, messaging, channels, moderation, file upload, link embeds, server directory) with inline code references
+
 ## CI
 
 - Add Docker workflow — builds and pushes multi-arch (`amd64`/`arm64`) server image to GHCR on release

src/EchoHub.Client/AppOrchestrator.cs

@@ -28,6 +28,8 @@ public sealed class AppOrchestrator : IDisposable
     private readonly AudioPlaybackService _audioPlayback = new();
     private readonly UpdateChecker _updateService;
     private readonly ConnectionManager _conn = new();
+    private readonly Dictionary<string, List<UserPresenceDto>> _channelUsers = new(StringComparer.OrdinalIgnoreCase);
+    private readonly Lock _channelUsersLock = new();
 
     private ClientConfig _config;
     private readonly UserSession _session = new();
@@ -87,6 +89,8 @@ public sealed class AppOrchestrator : IDisposable
         _mainWindow.OnFileDownloadRequested += HandleFileDownloadRequested;
         _mainWindow.OnCheckForUpdatesRequested += HandleCheckForUpdatesRequested;
         _mainWindow.OnRollbackRequested += HandleRollbackRequested;
+        _mainWindow.OnUserProfileRequested += HandleViewProfile;
+        _mainWindow.OnChannelJoinRequested += HandleChannelJoinFromMessage;
     }
 
     // ── Command Handler Wiring ─────────────────────────────────────────────
@@ -381,17 +385,48 @@ public sealed class AppOrchestrator : IDisposable
             }
         };
 
-        _conn.UserJoined += (channelName, username) =>
+        _conn.UserJoined += (channelName, username, presence) =>
         {
             InvokeUI(() => _messageManager.AddSystemMessage(channelName, $"{username} joined the channel"));
-            if (channelName == _mainWindow.CurrentChannel)
+
+            List<UserPresenceDto>? snapshot = null;
+            lock (_channelUsersLock)
+            {
+                if (presence is not null && _channelUsers.TryGetValue(channelName, out var users))
+                {
+                    if (!users.Any(u => u.Username.Equals(presence.Username, StringComparison.OrdinalIgnoreCase)))
+                        users.Add(presence);
+
+                    if (channelName.Equals(_mainWindow.CurrentChannel, StringComparison.OrdinalIgnoreCase))
+                        snapshot = [.. users];
+                }
+            }
+
+            if (snapshot is not null)
+                InvokeUI(() => _mainWindow.UpdateOnlineUsers(snapshot));
+            else if (channelName.Equals(_mainWindow.CurrentChannel, StringComparison.OrdinalIgnoreCase))
                 FetchAndUpdateOnlineUsers();
         };
 
         _conn.UserLeft += (channelName, username) =>
         {
             InvokeUI(() => _messageManager.AddSystemMessage(channelName, $"{username} left the channel"));
-            if (channelName == _mainWindow.CurrentChannel)
+
+            List<UserPresenceDto>? snapshot = null;
+            lock (_channelUsersLock)
+            {
+                if (_channelUsers.TryGetValue(channelName, out var users))
+                {
+                    users.RemoveAll(u => u.Username.Equals(username, StringComparison.OrdinalIgnoreCase));
+
+                    if (channelName.Equals(_mainWindow.CurrentChannel, StringComparison.OrdinalIgnoreCase))
+                        snapshot = [.. users];
+                }
+            }
+
+            if (snapshot is not null)
+                InvokeUI(() => _mainWindow.UpdateOnlineUsers(snapshot));
+            else if (channelName.Equals(_mainWindow.CurrentChannel, StringComparison.OrdinalIgnoreCase))
                 FetchAndUpdateOnlineUsers();
         };
 
@@ -407,18 +442,75 @@ public sealed class AppOrchestrator : IDisposable
                 foreach (var channelName in _mainWindow.GetChannelNames())
                     _messageManager.AddStatusMessage(channelName, displayName, statusText);
             });
-            FetchAndUpdateOnlineUsers();
+
+            // Update presence in all cached channel lists
+            List<UserPresenceDto>? snapshot = null;
+            lock (_channelUsersLock)
+            {
+                foreach (var (channel, users) in _channelUsers)
+                {
+                    var idx = users.FindIndex(u => u.Username.Equals(presence.Username, StringComparison.OrdinalIgnoreCase));
+                    if (idx >= 0)
+                    {
+                        if (presence.Status == UserStatus.Invisible)
+                            users.RemoveAt(idx);
+                        else
+                            users[idx] = presence;
+                    }
+                    else if (presence.Status != UserStatus.Invisible)
+                    {
+                        // User came back from invisible — re-add them
+                        users.Add(presence);
+                    }
+                }
+
+                var currentChannel = _mainWindow.CurrentChannel;
+                if (!string.IsNullOrEmpty(currentChannel) && _channelUsers.TryGetValue(currentChannel, out var currentUsers))
+                    snapshot = [.. currentUsers];
+            }
+
+            if (snapshot is not null)
+                InvokeUI(() => _mainWindow.UpdateOnlineUsers(snapshot));
         };
 
         _conn.UserKicked += (channelName, username, reason) =>
         {
             var reasonText = reason is not null ? $" ({reason})" : "";
             InvokeUI(() => _messageManager.AddSystemMessage(channelName, $"{username} was kicked{reasonText}"));
+
+            List<UserPresenceDto>? snapshot = null;
+            lock (_channelUsersLock)
+            {
+                if (_channelUsers.TryGetValue(channelName, out var users))
+                {
+                    users.RemoveAll(u => u.Username.Equals(username, StringComparison.OrdinalIgnoreCase));
+                    if (channelName.Equals(_mainWindow.CurrentChannel, StringComparison.OrdinalIgnoreCase))
+                        snapshot = [.. users];
+                }
+            }
+
+            if (snapshot is not null)
+                InvokeUI(() => _mainWindow.UpdateOnlineUsers(snapshot));
         };
 
         _conn.UserBanned += (username, reason) =>
         {
             var reasonText = reason is not null ? $" ({reason})" : "";
+
+            List<UserPresenceDto>? snapshot = null;
+            lock (_channelUsersLock)
+            {
+                // Remove banned user from all cached channel lists
+                foreach (var (channel, users) in _channelUsers)
+                {
+                    users.RemoveAll(u => u.Username.Equals(username, StringComparison.OrdinalIgnoreCase));
+                }
+
+                var currentChannel = _mainWindow.CurrentChannel;
+                if (!string.IsNullOrEmpty(currentChannel) && _channelUsers.TryGetValue(currentChannel, out var currentUsers))
+                    snapshot = [.. currentUsers];
+            }
+
             InvokeUI(() =>
             {
                 if (!username.Equals(_session.Username, StringComparison.OrdinalIgnoreCase))
@@ -426,6 +518,9 @@ public sealed class AppOrchestrator : IDisposable
                     var channel = _mainWindow.CurrentChannel;
                     if (!string.IsNullOrEmpty(channel))
                         _messageManager.AddSystemMessage(channel, $"{username} was banned{reasonText}");
+
+                    if (snapshot is not null)
+                        _mainWindow.UpdateOnlineUsers(snapshot);
                 }
             });
         };
@@ -469,6 +564,7 @@ public sealed class AppOrchestrator : IDisposable
 
         _conn.Reconnected += () =>
         {
+            lock (_channelUsersLock) _channelUsers.Clear();
             RunAsync(
                 async () => await _conn.RejoinChannelsAsync(),
                 "Failed to rejoin channels after reconnect");
@@ -535,6 +631,7 @@ public sealed class AppOrchestrator : IDisposable
     private void HandleDisconnect()
     {
         Log.Information("Disconnecting from server");
+        lock (_channelUsersLock) _channelUsers.Clear();
 
         RunAsync(async () =>
         {
@@ -623,6 +720,19 @@ public sealed class AppOrchestrator : IDisposable
         }, "Failed to join channel");
     }
 
+    private void HandleChannelJoinFromMessage(string channelName)
+    {
+        if (!_conn.IsConnected) return;
+
+        InvokeUI(() =>
+        {
+            _mainWindow.EnsureChannelInList(channelName);
+            _mainWindow.SwitchToChannel(channelName);
+        });
+
+        HandleChannelSelected(channelName);
+    }
+
     private void HandleProfileRequested()
     {
         HandleViewProfile(null);
@@ -826,6 +936,8 @@ public sealed class AppOrchestrator : IDisposable
                 if (history.Count > 0)
                     _messageManager.LoadHistory(channel.Name, history);
             });
+
+            FetchAndUpdateOnlineUsers();
         }, "Failed to create channel");
     }
 
@@ -881,6 +993,16 @@ public sealed class AppOrchestrator : IDisposable
         }, "Failed to play audio");
     }
 
+    /// <summary>
+    /// File extensions considered safe to open with the system default application.
+    /// Everything else is downloaded only — never auto-opened via UseShellExecute.
+    /// </summary>
+    private static readonly HashSet<string> SafeOpenExtensions = new(StringComparer.OrdinalIgnoreCase)
+    {
+        ".mp4", ".webm", ".mkv", ".avi", ".mov",  // video
+        ".pdf", ".txt", ".csv", ".json", ".xml",   // documents
+    };
+
     private void HandleFileDownloadRequested(string attachmentUrl, string fileName)
     {
         if (!_conn.IsAuthenticated) return;
@@ -890,6 +1012,9 @@ public sealed class AppOrchestrator : IDisposable
             InvokeUI(() => _messageManager.AddSystemMessage(_mainWindow.CurrentChannel, $"Downloading {fileName}..."));
             var tempPath = await _conn.Api!.DownloadFileToTempAsync(attachmentUrl, fileName);
 
+            var ext = Path.GetExtension(fileName);
+            if (SafeOpenExtensions.Contains(ext))
+            {
                 try
                 {
                     var psi = new System.Diagnostics.ProcessStartInfo(tempPath) { UseShellExecute = true };
@@ -900,6 +1025,11 @@ public sealed class AppOrchestrator : IDisposable
                     Log.Warning(ex, "Failed to open file with default app: {Path}", tempPath);
                     InvokeUI(() => _messageManager.AddSystemMessage(_mainWindow.CurrentChannel, $"Downloaded to: {tempPath}"));
                 }
+            }
+            else
+            {
+                InvokeUI(() => _messageManager.AddSystemMessage(_mainWindow.CurrentChannel, $"Downloaded to: {tempPath}"));
+            }
         }, "Failed to download file");
     }
 
@@ -946,6 +1076,7 @@ public sealed class AppOrchestrator : IDisposable
             try
             {
                 var users = await _conn.GetOnlineUsersAsync(channel);
+                lock (_channelUsersLock) _channelUsers[channel] = users;
                 InvokeUI(() => _mainWindow.UpdateOnlineUsers(users));
             }
             catch (Exception ex)

src/EchoHub.Client/Services/ConnectionManager.cs

@@ -35,7 +35,7 @@ internal sealed class ConnectionManager : IAsyncDisposable
     // ── Events (forwarded from SignalR) ───────────────────────────────────
 
     public event Action<MessageDto>? MessageReceived;
-    public event Action<string, string>? UserJoined;
+    public event Action<string, string, UserPresenceDto?>? UserJoined;
     public event Action<string, string>? UserLeft;
     public event Action<UserPresenceDto>? UserStatusChanged;
     public event Action<string, string, string?>? UserKicked;
@@ -234,7 +234,7 @@ internal sealed class ConnectionManager : IAsyncDisposable
     private void WireConnectionEvents(EchoHubConnection connection)
     {
         connection.OnMessageReceived += msg => MessageReceived?.Invoke(msg);
-        connection.OnUserJoined += (ch, user) => UserJoined?.Invoke(ch, user);
+        connection.OnUserJoined += (ch, user, presence) => UserJoined?.Invoke(ch, user, presence);
         connection.OnUserLeft += (ch, user) => UserLeft?.Invoke(ch, user);
         connection.OnUserStatusChanged += p => UserStatusChanged?.Invoke(p);
         connection.OnUserKicked += (ch, user, reason) => UserKicked?.Invoke(ch, user, reason);

src/EchoHub.Client/Services/EchoHubConnection.cs

@@ -11,7 +11,7 @@ public sealed class EchoHubConnection : IAsyncDisposable
     private readonly ClientEncryptionService _encryption;
 
     public event Action<MessageDto>? OnMessageReceived;
-    public event Action<string, string>? OnUserJoined;
+    public event Action<string, string, UserPresenceDto?>? OnUserJoined;
     public event Action<string, string>? OnUserLeft;
     public event Action<ChannelDto>? OnChannelUpdated;
     public event Action<UserPresenceDto>? OnUserStatusChanged;
@@ -70,9 +70,9 @@ public sealed class EchoHubConnection : IAsyncDisposable
             OnMessageReceived?.Invoke(decrypted);
         });
 
-        _connection.On<string, string>(nameof(Core.Contracts.IEchoHubClient.UserJoined), (channelName, username) =>
+        _connection.On<string, string, UserPresenceDto?>(nameof(Core.Contracts.IEchoHubClient.UserJoined), (channelName, username, presence) =>
         {
-            OnUserJoined?.Invoke(channelName, username);
+            OnUserJoined?.Invoke(channelName, username, presence);
         });
 
         _connection.On<string, string>(nameof(Core.Contracts.IEchoHubClient.UserLeft), (channelName, username) =>

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

@@ -13,6 +13,7 @@ public static partial class ChatColors
     public static readonly Attribute SystemAttr = new(new Color(0, 180, 180), Color.None);
     public static readonly Attribute MentionHighlightAttr = new(Color.White, new Color(80, 40, 0));
     public static readonly Attribute MentionTextAttr = new(new Color(255, 180, 50), Color.None);
+    public static readonly Attribute ChannelRefAttr = new(new Color(100, 200, 255), Color.None);
     public static readonly Attribute EmbedBorderAttr = new(new Color(91, 155, 213), Color.None);
     public static readonly Attribute EmbedTitleAttr = new(Color.White, Color.None);
     public static readonly Attribute EmbedDescAttr = new(new Color(160, 160, 160), Color.None);
@@ -21,8 +22,8 @@ public static partial class ChatColors
     public static readonly Attribute FileAttr = new(new Color(100, 180, 255), Color.None);
 
     /// <summary>
-    /// Split text around @mentions, giving each @word the MentionTextAttr accent color.
-    /// Non-mention text uses the provided default color.
+    /// Split text around @mentions and #channels, giving each the appropriate accent color.
+    /// Non-special text uses the provided default color.
     /// </summary>
     public static List<ChatSegment> SplitMentions(string text, Attribute? defaultColor = null)
     {
@@ -38,12 +39,40 @@ public static partial class ChatColors
             lastIndex = match.Index + match.Length;
         }
 
-        if (lastIndex < text.Length)
-            segments.Add(new ChatSegment(text[lastIndex..], defaultColor));
+        // Second pass: highlight #channels in non-mention segments
+        var mentionSegments = segments;
+        segments = [];
+        foreach (var seg in mentionSegments)
+        {
+            if (seg.Color != null && seg.Color != defaultColor)
+            {
+                // Already colored (mention) — keep as-is
+                segments.Add(seg);
+                continue;
+            }
+
+            int segLast = 0;
+            foreach (Match match in ChannelRefRegex().Matches(seg.Text))
+            {
+                if (match.Index > segLast)
+                    segments.Add(new ChatSegment(seg.Text[segLast..match.Index], defaultColor));
+
+                segments.Add(new ChatSegment(match.Value, ChannelRefAttr));
+                segLast = match.Index + match.Length;
+            }
+
+            if (segLast < seg.Text.Length)
+                segments.Add(new ChatSegment(seg.Text[segLast..], defaultColor));
+        }
 
         return segments;
     }
 
-    [GeneratedRegex(@"@[\w-]+")]
+    // @mention — not preceded by a word char (avoids emails)
+    [GeneratedRegex(@"(?<!\w)@[\w-]+")]
     private static partial Regex MentionRegex();
+
+    // #channel — not preceded by a word char, must contain at least one letter (avoids hex colors / issue numbers)
+    [GeneratedRegex(@"(?<!\w)#(?=.*[a-zA-Z])[\w-]+")]
+    private static partial Regex ChannelRefRegex();
 }

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

@@ -19,6 +19,7 @@ public partial class ChatLine
     public string? AttachmentUrl { get; set; }
     public string? AttachmentFileName { get; set; }
     public MessageType? Type { get; set; }
+    public string? SenderUsername { get; set; }
     /// <summary>Number of spaces to prepend on continuation lines when this line is word-wrapped.</summary>
     public int ContinuationIndent { get; set; }
 
@@ -118,13 +119,14 @@ public partial class ChatLine
         if (results.Count == 0)
             return [this];
 
-        // Propagate attachment/type metadata to all wrapped lines so they remain clickable
+        // Propagate metadata to all wrapped lines so they remain clickable
         foreach (var wrapped in results)
         {
             wrapped.AttachmentUrl = AttachmentUrl;
             wrapped.AttachmentFileName = AttachmentFileName;
             wrapped.Type = Type;
             wrapped.MessageId = MessageId;
+            wrapped.SenderUsername = SenderUsername;
         }
 
         return results;

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

@@ -272,7 +272,10 @@ public sealed class ChatMessageManager
         }
 
         foreach (var line in lines)
+        {
             line.MessageId = message.Id;
+            line.SenderUsername = message.SenderUsername;
+        }
 
         if (!string.IsNullOrEmpty(_currentUser) && message.Type == MessageType.Text)
         {
@@ -329,18 +332,20 @@ public sealed class ChatMessageManager
         int textWidth = chatWidth - indentCols - borderCols;
         if (textWidth < 20) textWidth = 20;
 
+        var borderAttr = HexColorHelper.ParseHexColor(embed.ThemeColor) ?? ChatColors.EmbedBorderAttr;
+
         void AddTextLine(string text, Attribute? color)
         {
             lines.Add(new ChatLine(
             [
                 new ChatSegment(indent, null),
-                new ChatSegment(border, ChatColors.EmbedBorderAttr),
+                new ChatSegment(border, borderAttr),
                 new ChatSegment(text, color)
             ]));
         }
 
         if (!string.IsNullOrWhiteSpace(embed.SiteName))
-            AddTextLine(embed.SiteName, ChatColors.EmbedBorderAttr);
+            AddTextLine(embed.SiteName, borderAttr);
 
         if (!string.IsNullOrWhiteSpace(embed.Title))
         {

src/EchoHub.Client/UI/ListSources/UserListSource.cs

@@ -12,14 +12,14 @@ namespace EchoHub.Client.UI.ListSources;
 /// </summary>
 public class UserListSource : IListDataSource
 {
-    private readonly List<(string Text, Attribute? NameColor)> _users = [];
+    private readonly List<(string Text, Attribute? NameColor, string Username)> _users = [];
 
     public event NotifyCollectionChangedEventHandler? CollectionChanged;
     public int Count => _users.Count;
     public int MaxItemLength { get; private set; }
     public bool SuspendCollectionChangedEvent { get; set; }
 
-    public void Update(List<(string Text, Attribute? NameColor)> users)
+    public void Update(List<(string Text, Attribute? NameColor, string Username)> users)
     {
         _users.Clear();
         _users.AddRange(users);
@@ -28,15 +28,18 @@ public class UserListSource : IListDataSource
             CollectionChanged?.Invoke(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
     }
 
+    public string? GetUsername(int index) =>
+        index >= 0 && index < _users.Count ? _users[index].Username : null;
+
     public bool IsMarked(int item) => false;
     public void SetMark(int item, bool value) { }
-    public IList ToList() => _users.Select(u => u.Text).ToList();
+    public IList ToList() => _users.Select(u => (object)u.Text).ToList();
 
     public void Render(ListView listView, bool selected, int item, int col, int row, int width, int viewportX = 0)
     {
         listView.Move(Math.Max(col - viewportX, 0), row);
 
-        var (text, nameColor) = _users[item];
+        var (text, nameColor, _) = _users[item];
         var normalAttr = listView.GetAttributeForRole(selected ? VisualRole.Focus : VisualRole.Normal);
 
         // Find where the name starts (after status icon + space + optional role badge)

src/EchoHub.Client/UI/MainWindow.cs

@@ -1,3 +1,4 @@
+using System.Text.RegularExpressions;
 using EchoHub.Client.Services;
 using EchoHub.Client.Themes;
 using EchoHub.Client.UI.Chat;
@@ -19,7 +20,7 @@ namespace EchoHub.Client.UI;
 /// <summary>
 /// Main Terminal.Gui window for the EchoHub chat client.
 /// </summary>
-public sealed class MainWindow : Runnable
+public sealed partial class MainWindow : Runnable
 {
     private readonly IApplication _app;
     private readonly ListView _channelList;
@@ -140,6 +141,16 @@ public sealed class MainWindow : Runnable
     /// </summary>
     public event Action<string, string>? OnFileDownloadRequested;
 
+    /// <summary>
+    /// Fired when the user activates a username (in userlist or message). Parameter is the username.
+    /// </summary>
+    public event Action<string>? OnUserProfileRequested;
+
+    /// <summary>
+    /// Fired when the user activates a #channel reference in a message. Parameter is the channel name.
+    /// </summary>
+    public event Action<string>? OnChannelJoinRequested;
+
     public MainWindow(IApplication app, ChatMessageManager messageManager)
     {
         _app = app;
@@ -250,6 +261,7 @@ public sealed class MainWindow : Runnable
         };
         _usersListSource = new UserListSource();
         _usersList.Source = _usersListSource;
+        _usersList.Accepting += OnUsersListAccepting;
         _usersFrame.Add(_usersList);
         Add(_usersFrame);
 
@@ -410,18 +422,67 @@ public sealed class MainWindow : Runnable
             return;
 
         var line = source.GetLine(index.Value);
-        if (line?.AttachmentUrl is null || line.AttachmentFileName is null)
-            return;
+        if (line is null) return;
 
+        // Audio/file attachments take priority
+        if (line.AttachmentUrl is not null && line.AttachmentFileName is not null)
+        {
             if (line.Type == MessageType.Audio)
             {
                 OnAudioPlayRequested?.Invoke(line.AttachmentUrl, line.AttachmentFileName);
                 e.Handled = true;
+                return;
             }
-        else if (line.Type == MessageType.File)
+
+            if (line.Type == MessageType.File)
             {
                 OnFileDownloadRequested?.Invoke(line.AttachmentUrl, line.AttachmentFileName);
                 e.Handled = true;
+                return;
+            }
+        }
+
+        var lineText = line.ToString();
+
+        // Check for @mention — open mentioned user's profile
+        // Negative lookbehind prevents matching emails (user@domain)
+        var mentionMatch = ClickMentionRegex().Match(lineText);
+        if (mentionMatch.Success)
+        {
+            OnUserProfileRequested?.Invoke(mentionMatch.Groups[1].Value);
+            e.Handled = true;
+            return;
+        }
+
+        // Check for #channel — join/switch to that channel
+        // Require at least one letter to avoid matching hex colors (#ff0000) or issue numbers (#123)
+        var channelMatch = ClickChannelRegex().Match(lineText);
+        if (channelMatch.Success)
+        {
+            OnChannelJoinRequested?.Invoke(channelMatch.Groups[1].Value);
+            e.Handled = true;
+            return;
+        }
+
+        // Default: open sender's profile
+        if (line.SenderUsername is not null)
+        {
+            OnUserProfileRequested?.Invoke(line.SenderUsername);
+            e.Handled = true;
+        }
+    }
+
+    private void OnUsersListAccepting(object? sender, CommandEventArgs e)
+    {
+        var index = _usersList.SelectedItem;
+        if (!index.HasValue || index.Value < 0 || index.Value >= _usersListSource.Count)
+            return;
+
+        var username = _usersListSource.GetUsername(index.Value);
+        if (username is not null)
+        {
+            OnUserProfileRequested?.Invoke(username);
+            e.Handled = true;
         }
     }
 
@@ -869,7 +930,7 @@ public sealed class MainWindow : Runnable
             };
             var text = $"{statusIcon} {roleTag}{name}";
             var nameColor = HexColorHelper.ParseHexColor(u.NicknameColor);
-            return (text, nameColor);
+            return (text, nameColor, u.Username);
         }).ToList();
 
         _usersListSource.Update(displayItems);
@@ -877,4 +938,11 @@ public sealed class MainWindow : Runnable
         _usersFrame.Title = $"Users ({users.Count})";
     }
 
+    // @mention — not preceded by a word char (avoids emails)
+    [GeneratedRegex(@"(?<!\w)@([\w-]+)")]
+    private static partial Regex ClickMentionRegex();
+
+    // #channel — not preceded by a word char, must contain at least one letter (avoids hex colors / issue numbers)
+    [GeneratedRegex(@"(?<!\w)#((?=.*[a-zA-Z])[\w-]+)")]
+    private static partial Regex ClickChannelRegex();
 }

src/EchoHub.Core/Contracts/IChatBroadcaster.cs

@@ -5,7 +5,7 @@ namespace EchoHub.Core.Contracts;
 public interface IChatBroadcaster
 {
     Task SendMessageToChannelAsync(string channelName, MessageDto message);
-    Task SendUserJoinedAsync(string channelName, string username, string? excludeConnectionId = null);
+    Task SendUserJoinedAsync(string channelName, string username, UserPresenceDto? presence, string? excludeConnectionId = null);
     Task SendUserLeftAsync(string channelName, string username);
     Task SendChannelUpdatedAsync(ChannelDto channel, string? channelName = null);
     Task SendUserStatusChangedAsync(List<string> channelNames, UserPresenceDto presence);

src/EchoHub.Core/Contracts/IEchoHubClient.cs

@@ -8,7 +8,7 @@ namespace EchoHub.Core.Contracts;
 public interface IEchoHubClient
 {
     Task ReceiveMessage(MessageDto message);
-    Task UserJoined(string channelName, string username);
+    Task UserJoined(string channelName, string username, UserPresenceDto? presence);
     Task UserLeft(string channelName, string username);
     Task ChannelUpdated(ChannelDto channel);
     Task UserStatusChanged(UserPresenceDto presence);

src/EchoHub.Core/DTOs/ChatDtos.cs

@@ -44,4 +44,5 @@ public record EmbedDto(
     string? Title,
     string? Description,
     string? ImageAscii,
-    string Url);
+    string Url,
+    string? ThemeColor = null);

src/EchoHub.Server.Irc/IrcBroadcaster.cs

@@ -31,7 +31,7 @@ public class IrcBroadcaster : IChatBroadcaster
         }
     }
 
-    public async Task SendUserJoinedAsync(string channelName, string username, string? excludeConnectionId = null)
+    public async Task SendUserJoinedAsync(string channelName, string username, UserPresenceDto? presence, string? excludeConnectionId = null)
     {
         foreach (var conn in _gateway.GetConnectionsInChannel(channelName))
         {

src/EchoHub.Server/Program.cs

@@ -109,6 +109,7 @@ while (true)
         builder.Services.AddSingleton<LinkEmbedService>();
         builder.Services.AddHostedService<ServerDirectoryService>();
         builder.Services.AddHostedService<FileCleanupService>();
+        builder.Services.AddHostedService<MuteExpirationService>();
 
         // ── Encryption ─────────────────────────────────────────────────────
         builder.Services.AddSingleton<IMessageEncryptionService, MessageEncryptionService>();

src/EchoHub.Server/Services/ChatService.cs

@@ -107,7 +107,31 @@ public class ChatService : IChatService
 
         if (isNewJoin)
         {
-            await BroadcastToAllAsync(b => b.SendUserJoinedAsync(channelName, username, connectionId));
+            // Fetch presence data so clients can update their lists incrementally
+            UserPresenceDto? presence = null;
+            try
+            {
+                using var presenceScope = _scopeFactory.CreateScope();
+                var presenceDb = presenceScope.ServiceProvider.GetRequiredService<EchoHubDbContext>();
+                var user = await presenceDb.Users.FindAsync(userId);
+                if (user is not null)
+                {
+                    presence = new UserPresenceDto(
+                        user.Username, user.DisplayName, user.NicknameColor,
+                        user.Status, user.StatusMessage, user.Role);
+                }
+            }
+            catch (Exception ex)
+            {
+                _logger.LogDebug(ex, "Failed to fetch presence for {User} on join", username);
+            }
+
+            // Don't broadcast join for invisible users — they still get history but stay hidden
+            if (presence is null || presence.Status != UserStatus.Invisible)
+            {
+                await BroadcastToAllAsync(b => b.SendUserJoinedAsync(channelName, username, presence, connectionId));
+            }
+
             _logger.LogInformation("{User} joined channel '{Channel}'", username, channelName);
         }
 
@@ -272,7 +296,7 @@ public class ChatService : IChatService
         var db = scope.ServiceProvider.GetRequiredService<EchoHubDbContext>();
 
         return await db.Users
-            .Where(u => onlineUsernames.Contains(u.Username))
+            .Where(u => onlineUsernames.Contains(u.Username) && u.Status != UserStatus.Invisible)
             .Select(u => new UserPresenceDto(
                 u.Username,
                 u.DisplayName,

src/EchoHub.Server/Services/LinkEmbedService.cs

@@ -108,9 +108,47 @@ public partial class LinkEmbedService
         siteName = siteName is not null ? WebUtility.HtmlDecode(siteName) : null;
         description = description is not null ? WebUtility.HtmlDecode(description) : null;
 
-        return new EmbedDto(siteName, title, description, null, url);
+        // Extract theme-color meta tag for embed border color
+        var themeColor = ParseThemeColor(html);
+
+        return new EmbedDto(siteName, title, description, null, url, themeColor);
     }
 
+    private static string? ParseThemeColor(string html)
+    {
+        // ThemeColorRegex: group 3 = color value
+        var match = ThemeColorRegex().Match(html);
+        var color = match.Success ? match.Groups[3].Value.Trim() : null;
+
+        if (color is null)
+        {
+            // ThemeColorReversedRegex: group 2 = color value
+            match = ThemeColorReversedRegex().Match(html);
+            color = match.Success ? match.Groups[2].Value.Trim() : null;
+        }
+
+        if (color is null)
+            return null;
+
+        if (color.Length == 4 && color[0] == '#'
+            && IsHexDigit(color[1]) && IsHexDigit(color[2]) && IsHexDigit(color[3]))
+        {
+            // Expand #RGB to #RRGGBB
+            return $"#{color[1]}{color[1]}{color[2]}{color[2]}{color[3]}{color[3]}";
+        }
+
+        if (color.Length == 7 && color[0] == '#'
+            && color[1..].All(IsHexDigit))
+        {
+            return color;
+        }
+
+        return null;
+    }
+
+    private static bool IsHexDigit(char c) =>
+        c is (>= '0' and <= '9') or (>= 'a' and <= 'f') or (>= 'A' and <= 'F');
+
     private static List<string> ExtractUrls(string content)
     {
         var urls = new List<string>();
@@ -213,4 +251,14 @@ public partial class LinkEmbedService
 
     [GeneratedRegex(@"<title[^>]*>([^<]+)</title>", RegexOptions.IgnoreCase | RegexOptions.Compiled)]
     private static partial Regex TitleTagRegex();
+
+    // <meta name="theme-color" content="#hex">
+    [GeneratedRegex(@"<meta\s+[^>]*?name\s*=\s*([""'])theme-color\1[^>]*?content\s*=\s*([""'])(.*?)\2[^>]*/?>",
+        RegexOptions.IgnoreCase | RegexOptions.Singleline | RegexOptions.Compiled)]
+    private static partial Regex ThemeColorRegex();
+
+    // <meta content="#hex" name="theme-color">
+    [GeneratedRegex(@"<meta\s+[^>]*?content\s*=\s*([""'])(.*?)\1[^>]*?name\s*=\s*([""'])theme-color\3[^>]*/?>",
+        RegexOptions.IgnoreCase | RegexOptions.Singleline | RegexOptions.Compiled)]
+    private static partial Regex ThemeColorReversedRegex();
 }

src/EchoHub.Server/Services/MuteExpirationService.cs

@@ -0,0 +1,63 @@
+using EchoHub.Server.Data;
+using Microsoft.EntityFrameworkCore;
+
+namespace EchoHub.Server.Services;
+
+/// <summary>
+/// Background service that periodically unmutes users whose timed mute has expired.
+/// </summary>
+public sealed class MuteExpirationService : BackgroundService
+{
+    private static readonly TimeSpan CheckInterval = TimeSpan.FromSeconds(15);
+
+    private readonly IServiceScopeFactory _scopeFactory;
+    private readonly ILogger<MuteExpirationService> _logger;
+
+    public MuteExpirationService(IServiceScopeFactory scopeFactory, ILogger<MuteExpirationService> logger)
+    {
+        _scopeFactory = scopeFactory;
+        _logger = logger;
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        await Task.Yield();
+
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            try
+            {
+                await UnmuteExpiredUsersAsync(stoppingToken);
+            }
+            catch (Exception ex) when (ex is not OperationCanceledException)
+            {
+                _logger.LogWarning(ex, "Error checking mute expirations");
+            }
+
+            await Task.Delay(CheckInterval, stoppingToken);
+        }
+    }
+
+    private async Task UnmuteExpiredUsersAsync(CancellationToken ct)
+    {
+        using var scope = _scopeFactory.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<EchoHubDbContext>();
+
+        var now = DateTimeOffset.UtcNow;
+        var expired = await db.Users
+            .Where(u => u.IsMuted && u.MutedUntil.HasValue && u.MutedUntil.Value <= now)
+            .ToListAsync(ct);
+
+        if (expired.Count == 0)
+            return;
+
+        foreach (var user in expired)
+        {
+            user.IsMuted = false;
+            user.MutedUntil = null;
+            _logger.LogInformation("Auto-unmuted user {Username} (timed mute expired)", user.Username);
+        }
+
+        await db.SaveChangesAsync(ct);
+    }
+}

src/EchoHub.Server/Services/PresenceTracker.cs

@@ -14,6 +14,8 @@ public class PresenceTracker
     {
         _connections[connectionId] = (userId, username);
 
+        // Lock is required: ConcurrentDictionary only protects its own slots, not the HashSet values inside.
+        // It also makes the TryGetValue → add sequence atomic to prevent race conditions.
         lock (_lock)
         {
             if (!_userConnections.TryGetValue(username, out var connections))

src/EchoHub.Server/Services/ServerDirectoryService.cs

@@ -170,6 +170,9 @@ public sealed class ServerDirectoryService : BackgroundService
 
             var currentCount = _presenceTracker.GetOnlineUserCount();
 
+            if (currentCount == _lastReportedUserCount)
+                continue;
+
             try
             {
                 await connection.InvokeAsync("UpdateUserCount", currentCount, ct);

src/EchoHub.Server/Services/SignalRBroadcaster.cs

@@ -23,12 +23,12 @@ public class SignalRBroadcaster : IChatBroadcaster
     public Task SendMessageToChannelAsync(string channelName, MessageDto message)
         => HubContext.Clients.Group(channelName).ReceiveMessage(message);
 
-    public Task SendUserJoinedAsync(string channelName, string username, string? excludeConnectionId = null)
+    public Task SendUserJoinedAsync(string channelName, string username, UserPresenceDto? presence, string? excludeConnectionId = null)
     {
         if (excludeConnectionId is not null && !excludeConnectionId.StartsWith("irc-"))
-            return HubContext.Clients.GroupExcept(channelName, [excludeConnectionId]).UserJoined(channelName, username);
+            return HubContext.Clients.GroupExcept(channelName, [excludeConnectionId]).UserJoined(channelName, username, presence);
 
-        return HubContext.Clients.Group(channelName).UserJoined(channelName, username);
+        return HubContext.Clients.Group(channelName).UserJoined(channelName, username, presence);
     }
 
     public Task SendUserLeftAsync(string channelName, string username)

src/EchoHub.Tests/Irc/IrcBroadcasterTests.cs

@@ -132,7 +132,7 @@ public class IrcBroadcasterTests
     {
         var (_, bobStream) = AddConnectionWithCapture("bob", "general");
 
-        await _broadcaster.SendUserJoinedAsync("general", "alice");
+        await _broadcaster.SendUserJoinedAsync("general", "alice", null);
 
         var output = bobStream.GetOutputLines();
         Assert.Contains(output, l => l.Contains("JOIN #general") && l.Contains("alice"));
@@ -144,7 +144,7 @@ public class IrcBroadcasterTests
         var (conn, excludedStream) = AddConnectionWithCapture("alice", "general");
         var (_, bobStream) = AddConnectionWithCapture("bob", "general");
 
-        await _broadcaster.SendUserJoinedAsync("general", "alice", conn.ConnectionId);
+        await _broadcaster.SendUserJoinedAsync("general", "alice", null, conn.ConnectionId);
 
         // Excluded connection should not get the message
         Assert.Empty(excludedStream.GetOutputLines());