[codex] Improve markdown accessibility and selection

MarkdownRenderer/MarkdownRenderer.Gfm/Renderers/TaskListItemRenderer.cs

@@ -2,6 +2,7 @@
 using Markdig.Syntax;
 using Markdig.Syntax.Inlines;
 using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Automation;
 using Microsoft.UI.Xaml.Controls;
 using MarkdownRenderer.Layout;
 using MarkdownRenderer.Layout.Boxes;
@@ -42,23 +43,16 @@ public sealed class TaskListItemRenderer : MarkdownNodeRenderer<ListItemBlock>
 
         var marker = new InlineContainerBox(context, MarkdownElementKeys.ListMarker);
         marker.BlockIndex = context.NextBlockIndex();
-        marker.Add(new InlineEmbedRun(20f, 20f, () => new CheckBox
-        {
-            IsChecked = isChecked,
-            IsEnabled = false,
-            MinWidth = 20,
-            MinHeight = 20,
-            Padding = new Thickness(0),
-            Margin = new Thickness(0),
-            HorizontalContentAlignment = HorizontalAlignment.Left,
-            VerticalContentAlignment = VerticalAlignment.Center,
-        })
+        marker.Add(new InlineEmbedRun(20f, 20f, () => CreateTaskCheckBox(isChecked))
         {
             ElementKey = MarkdownElementKeys.ListMarker,
             SourceSpan = new MarkdownRenderer.SourceSpan(listItem.Span.Start, 0)
         });
 
-        var content = new StackBox();
+        var content = new StackBox
+        {
+            FlowDirection = context.FlowDirection,
+        };
         content.BlockIndex = context.NextBlockIndex();
 
         foreach (var child in listItem)
@@ -69,7 +63,7 @@ public sealed class TaskListItemRenderer : MarkdownNodeRenderer<ListItemBlock>
                 contentBox.BlockIndex = context.NextBlockIndex();
                 // Skip the TaskList inline — it's the marker, not body content.
                 GfmChildBuilder.AddInlines(contentBox, p.Inline, skipFirstIf: i => i is TaskList);
-            content.Add(contentBox);
+                content.Add(contentBox);
             }
             else
             {
@@ -78,6 +72,38 @@ public sealed class TaskListItemRenderer : MarkdownNodeRenderer<ListItemBlock>
             }
         }
 
-        return new ListItemBox(marker, content, markerWidth: 28f);
+        return new ListItemBox(marker, content, markerWidth: 28f)
+        {
+            FlowDirection = context.FlowDirection,
+        };
+    }
+
+    private static CheckBox CreateTaskCheckBox(bool isChecked)
+    {
+        var checkBox = new CheckBox
+        {
+            IsChecked = isChecked,
+            IsEnabled = true,
+            IsTabStop = true,
+            MinWidth = 20,
+            MinHeight = 20,
+            Padding = new Thickness(0),
+            Margin = new Thickness(0),
+            HorizontalContentAlignment = HorizontalAlignment.Left,
+            VerticalContentAlignment = VerticalAlignment.Center,
+        };
+
+        AutomationProperties.SetName(checkBox, isChecked ? "Completed task" : "Incomplete task");
+        AutomationProperties.SetHelpText(checkBox, "Read-only task checkbox");
+
+        void RestoreCheckedState(object sender, RoutedEventArgs e)
+        {
+            if (checkBox.IsChecked != isChecked)
+                checkBox.IsChecked = isChecked;
+        }
+
+        checkBox.Checked += RestoreCheckedState;
+        checkBox.Unchecked += RestoreCheckedState;
+        return checkBox;
     }
 }

MarkdownRenderer/MarkdownRenderer.Sample/App.xaml.cs

@@ -1,3 +1,4 @@
+using System;
 using Microsoft.UI.Xaml;
 
 namespace MarkdownRenderer.Sample;
@@ -13,11 +14,9 @@ public App()
 
     protected override void OnLaunched(LaunchActivatedEventArgs args)
     {
-        // Enable diagnostic logger by default in the sample app so any
-        // reproduction of the selection-shake bug captures per-frame paint
-        // coordinates to text_shaking2.log next to the repo root.
-        // Flip to false to silence.
-        MarkdownRenderer.Diagnostics.ShakeLogger.Enabled = true;
+        if (args.Arguments.Contains("--markdown-renderer-diagnostics", StringComparison.OrdinalIgnoreCase))
+            MarkdownRenderer.Diagnostics.ShakeLogger.Enabled = true;
+
         _window = new MainWindow();
         _window.Activate();
     }