[AI-3828] app: Show the text cursor over chat prose

src/Capacitor.App/Views/MarkdownImage.cs

@@ -51,7 +51,8 @@ public MarkdownImage(string url, string label, ImageSize? size, string? target,
         Children.Add(_picture);
         // A transparent fill makes the whole box hit-testable, not just the glyphs or pixels.
         Background = Brushes.Transparent;
-        if (target is not null) Cursor = new Cursor(StandardCursorType.Hand);
+        // Cursor inherits, so an unset value would take the viewer's I-beam. A bare image is not text.
+        Cursor = new Cursor(target is not null ? StandardCursorType.Hand : StandardCursorType.Arrow);
     }
 
     public string Url { get; }

src/Capacitor.App/Views/MarkdownView.cs

@@ -40,6 +40,9 @@ public sealed class MarkdownView : ContentControl {
     // The extension builds its TextMate highlighters on first use and keeps them, so one
     // instance serves the app; a per-view instance rebuilds them on every render.
     static readonly TextMateExtension Highlighting = new();
+    static readonly Cursor IBeamCursor = new(StandardCursorType.Ibeam);
+    static readonly Cursor HandCursor = new(StandardCursorType.Hand);
+    static readonly Cursor ArrowCursor = new(StandardCursorType.Arrow);
 
     readonly MarkdownViewer _viewer = new();
     readonly DetailsState _details = new();
@@ -72,6 +75,8 @@ public MarkdownView() {
             if (OpenLink is { } open && open.CanExecute(e.Url)) open.Execute(e.Url);
         };
         MarkViewSelection.Attach(this, _viewer, CopySelectionAsync);
+        // Bubble on the host runs after the viewer's own move, which has already chosen Hand or
+        // the arrow. Prose takes the I-beam and a link the hand; a bare image stays on the arrow.
         AddHandler(PointerMovedEvent, OnPointerMoved, RoutingStrategies.Bubble, handledEventsToo: true);
         ContextFlyout = TextContextMenu.ForMarkdown;
         Content = _viewer;
@@ -84,10 +89,15 @@ internal void ExtendSelection(Point pointInView) {
     }
 
     void OnPointerMoved(object? sender, PointerEventArgs e) {
-        var tip = FindHyperlinkAt(_viewer, e.GetPosition(_viewer))?.NavigateUri?.ToString()
-            ?? ImageUnder(e.Source as Visual)?.Target;
+        var link = FindHyperlinkAt(_viewer, e.GetPosition(_viewer));
+        var image = ImageUnder(e.Source as Visual);
+        var tip = link?.NavigateUri?.ToString() ?? image?.Target;
         if (!string.Equals(ToolTip.GetTip(_viewer) as string, tip, StringComparison.Ordinal))
             ToolTip.SetTip(_viewer, tip);
+        // Cursor inherits, so the viewer's value is what a child with none of its own shows.
+        _viewer.Cursor = link is not null || image?.Target is not null ? HandCursor
+            : image is not null ? ArrowCursor
+            : IBeamCursor;
     }
 
     static MarkdownImage? ImageUnder(Visual? visual) {

test/Capacitor.App.Tests.Unit/ChatCursorTests.cs

@@ -0,0 +1,63 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Headless;
+using Avalonia.Threading;
+using Capacitor.App.Views;
+using static Capacitor.App.Tests.Unit.AvaloniaSession;
+using static Capacitor.App.Tests.Unit.MarkdownViewHarness;
+
+namespace Capacitor.App.Tests.Unit;
+
+public class ChatCursorTests {
+    [Test]
+    [NotInParallel("AvaloniaSession")]
+    public async Task Prose_uses_the_text_cursor_and_a_link_uses_the_hand() {
+        await RunOnUiAsync(async () => {
+            var (window, root, _) = Show("See [docs](https://example.com/docs) now.");
+            try {
+                var paragraph = Paragraphs(root).Single();
+                var viewer = Viewer(root);
+                Move(window, paragraph, 0);
+                await Assert.That(viewer.Cursor?.ToString()).IsEqualTo("Ibeam");
+                Move(window, paragraph, StartOf(paragraph, Links(root).Single()));
+                await Assert.That(viewer.Cursor?.ToString()).IsEqualTo("Hand");
+            } finally { window.Close(); }
+        });
+    }
+
+    [Test]
+    [NotInParallel("AvaloniaSession")]
+    public async Task A_bare_image_keeps_the_arrow_and_a_linked_image_keeps_the_hand() {
+        await RunOnUiAsync(async () => {
+            var (window, root, _) = Show(
+                "See ![shot](https://h/x.png) here.\n\n[![badge](https://h/b.png)](https://outer.example)",
+                MarkdownFlavor.GitHub);
+            try {
+                var bare = Images(root).Single(i => i.Target is null);
+                var linked = Images(root).Single(i => i.Target is not null);
+                var viewer = Viewer(root);
+                MoveOver(window, bare);
+                await Assert.That(bare.Cursor?.ToString()).IsEqualTo("Arrow");
+                await Assert.That(viewer.Cursor?.ToString()).IsEqualTo("Arrow");
+                MoveOver(window, linked);
+                await Assert.That(linked.Cursor?.ToString()).IsEqualTo("Hand");
+                await Assert.That(viewer.Cursor?.ToString()).IsEqualTo("Hand");
+                Move(window, Paragraphs(root).Single(p => Reads(p).Contains("See")), 0);
+                await Assert.That(viewer.Cursor?.ToString()).IsEqualTo("Ibeam");
+            } finally { window.Close(); }
+        });
+    }
+
+    static void MoveOver(Window window, Control control) {
+        var point = control.TranslatePoint(new Point(control.Bounds.Width / 2, control.Bounds.Height / 2), window)!.Value;
+        window.MouseMove(point);
+        Dispatcher.UIThread.RunJobs();
+    }
+
+    static void Move(Window window, TextBlock block, int index) {
+        var glyph = block.TextLayout.HitTestTextPosition(index);
+        var point = block.TranslatePoint(new Point(glyph.X + 2, glyph.Y + glyph.Height / 2), window)!.Value;
+        window.MouseMove(point);
+        Dispatcher.UIThread.RunJobs();
+    }
+}