feat: add @mention highlighting in chat lines with new SplitMentions method

src/EchoHub.Client/UI/ChatRenderer.cs

@@ -453,11 +453,40 @@ public class UserListSource : IListDataSource
 /// <summary>
 /// Shared color attributes for chat rendering (timestamps, system messages).
 /// </summary>
-public static class ChatColors
+public static partial class ChatColors
 {
     public static readonly Attribute TimestampAttr = new(Color.DarkGray, Color.Black);
     public static readonly Attribute SystemAttr = new(new Color(0, 180, 180), Color.Black);
     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.Black);
+
+    /// <summary>
+    /// Split text around @mentions, giving each @word the MentionTextAttr accent color.
+    /// Non-mention text uses the provided default color.
+    /// </summary>
+    public static List<ChatSegment> SplitMentions(string text, Attribute? defaultColor = null)
+    {
+        var segments = new List<ChatSegment>();
+        int lastIndex = 0;
+
+        foreach (Match match in MentionRegex().Matches(text))
+        {
+            if (match.Index > lastIndex)
+                segments.Add(new ChatSegment(text[lastIndex..match.Index], defaultColor));
+
+            segments.Add(new ChatSegment(match.Value, MentionTextAttr));
+            lastIndex = match.Index + match.Length;
+        }
+
+        if (lastIndex < text.Length)
+            segments.Add(new ChatSegment(text[lastIndex..], defaultColor));
+
+        return segments;
+    }
+
+    // Matches @username (letters, digits, underscores, hyphens — same as channel name chars)
+    [GeneratedRegex(@"@[\w-]+")]
+    private static partial Regex MentionRegex();
 }
 
 /// <summary>

src/EchoHub.Client/UI/MainWindow.cs

@@ -872,12 +872,13 @@ public sealed class MainWindow : Runnable
             default:
                 var contentLines = message.Content.Split('\n');
                 var firstLine = contentLines[0].TrimEnd('\r');
-                lines.Add(BuildChatLine(time, senderName, senderColor, $" {firstLine}"));
+                lines.Add(BuildChatLineWithMentions(time, senderName, senderColor, $" {firstLine}"));
                 // Continuation lines indented to align with first line's content
                 var indent = new string(' ', $"[{time}] {senderName} ".Length);
                 for (int i = 1; i < contentLines.Length; i++)
                 {
-                    lines.Add(new ChatLine($"{indent}{contentLines[i].TrimEnd('\r')}"));
+                    var contText = $"{indent}{contentLines[i].TrimEnd('\r')}";
+                    lines.Add(new ChatLine(ChatColors.SplitMentions(contText)));
                 }
                 break;
         }
@@ -913,4 +914,18 @@ public sealed class MainWindow : Runnable
         };
         return new ChatLine(segments);
     }
+
+    /// <summary>
+    /// Build a chat line with @mention highlighting in the suffix text.
+    /// </summary>
+    private static ChatLine BuildChatLineWithMentions(string time, string senderName, Attribute? senderColor, string suffix)
+    {
+        var segments = new List<ChatSegment>
+        {
+            new($"[{time}] ", ChatColors.TimestampAttr),
+            new(senderName, senderColor),
+        };
+        segments.AddRange(ChatColors.SplitMentions(suffix));
+        return new ChatLine(segments);
+    }
 }