Fix user chat bubble text rendering

Fixes #880

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: shanselman

src/OpenClaw.Tray.WinUI/Chat/OpenClawChatTimeline.cs

@@ -141,6 +141,9 @@ private static readonly System.Runtime.CompilerServices.ConditionalWeakTable<Tex
     private const string MonoFontFamilySource = "Cascadia Code, Cascadia Mono, Consolas";
     private static readonly System.Runtime.CompilerServices.ConditionalWeakTable<
         Microsoft.UI.Dispatching.DispatcherQueue, FontFamily> s_monoFontByDispatcher = new();
+    private const string ChatTextFontFamilySource = "Segoe UI Variable Text, Segoe UI";
+    private static readonly System.Runtime.CompilerServices.ConditionalWeakTable<
+        Microsoft.UI.Dispatching.DispatcherQueue, FontFamily> s_chatTextFontByDispatcher = new();
     private static FontFamily s_monoFontFamily
     {
         get
@@ -158,6 +161,23 @@ private static FontFamily s_monoFontFamily
             return family;
         }
     }
+    private static FontFamily s_chatTextFontFamily
+    {
+        get
+        {
+            var dispatcher = Microsoft.UI.Dispatching.DispatcherQueue.GetForCurrentThread();
+            if (dispatcher is null)
+            {
+                return new FontFamily(ChatTextFontFamilySource);
+            }
+            if (!s_chatTextFontByDispatcher.TryGetValue(dispatcher, out var family))
+            {
+                family = new FontFamily(ChatTextFontFamilySource);
+                s_chatTextFontByDispatcher.Add(dispatcher, family);
+            }
+            return family;
+        }
+    }
 
     // Per-DispatcherQueue selection-highlight brushes for the user
     // bubble. The bubble background is the user's chosen system accent
@@ -1117,6 +1137,14 @@ Element RenderUserEntry(ChatTimelineItem entry, bool startsBurst, bool endsBurst
                             t.FontSize = 14;
                             t.Foreground = userBubbleFg;
                             t.IsTextSelectionEnabled = true;
+                            t.FontFamily = s_chatTextFontFamily;
+                            t.TextTrimming = TextTrimming.None;
+                            t.MaxLines = 0;
+                            t.LineHeight = 0;
+                            t.CharacterSpacing = 0;
+                            t.Width = double.NaN;
+                            t.MinWidth = 0;
+                            t.MaxWidth = double.PositiveInfinity;
                             // The default SelectionHighlightColor is the
                             // system accent — which equals the user bubble's
                             // background — so the highlight band is invisible

tests/OpenClaw.Tray.Tests/ChatUserBubbleTextContractTests.cs

@@ -0,0 +1,26 @@
+using System.Text.RegularExpressions;
+
+namespace OpenClaw.Tray.Tests;
+
+public sealed class ChatUserBubbleTextContractTests
+{
+    [Fact]
+    public void UserPromptText_ResetsStaleTextBlockVisualStateBeforeApplyingInlines()
+    {
+        var timeline = Read("src", "OpenClaw.Tray.WinUI", "Chat", "OpenClawChatTimeline.cs");
+
+        Assert.Contains("private const string ChatTextFontFamilySource", timeline);
+        Assert.Contains("TextBlock(string.Empty)", timeline);
+        Assert.Contains("t.FontFamily = s_chatTextFontFamily;", timeline);
+        Assert.Contains("t.TextTrimming = TextTrimming.None;", timeline);
+        Assert.Contains("t.MaxLines = 0;", timeline);
+        Assert.Contains("t.Width = double.NaN;", timeline);
+        Assert.Contains("t.MaxWidth = double.PositiveInfinity;", timeline);
+        Assert.Matches(
+            new Regex(@"t\.TextTrimming\s*=\s*TextTrimming\.None;[\s\S]*ApplyPlainSelectableInlines\(t,\s*messageText\);"),
+            timeline);
+    }
+
+    private static string Read(params string[] parts)
+        => File.ReadAllText(Path.Combine(new[] { TestRepositoryPaths.GetRepositoryRoot() }.Concat(parts).ToArray()));
+}