[AI-3823] app: Make emphasized chat links clickable while working

src/Capacitor.App/GitHubHtml/ChatPipeline.cs

@@ -0,0 +1,35 @@
+using Markdig;
+using Markdig.Renderers;
+using Markdig.Syntax;
+using Markdig.Syntax.Inlines;
+using MarkView.Avalonia;
+
+namespace Capacitor.App.GitHubHtml;
+
+/// Chat markdown is MarkView's supported set, with links hoisted out of emphasis. A bare builder
+/// is CommonMark and drops the tables and autolinks chat already renders. MarkView only activates
+/// a hyperlink that is a direct inline of its text block.
+public static class ChatPipeline {
+    public static MarkdownPipeline Instance { get; } =
+        new MarkdownPipelineBuilder().UseSupportedExtensions().Use(new Hoist()).Build();
+
+    sealed class Hoist : IMarkdownExtension {
+        public void Setup(MarkdownPipelineBuilder pipeline) => pipeline.DocumentProcessed += Process;
+
+        public void Setup(MarkdownPipeline pipeline, IMarkdownRenderer renderer) { }
+
+        static void Process(MarkdownDocument document) {
+            foreach (var leaf in document.Descendants<LeafBlock>())
+                if (leaf.Inline is { } root) {
+                    foreach (var auto in root.Descendants<AutolinkInline>().ToArray()) {
+                        var link = new LinkInline(auto.IsEmail ? "mailto:" + auto.Url : auto.Url, "") {
+                            IsAutoLink = true, IsClosed = true,
+                        };
+                        link.AppendChild(new LiteralInline(auto.Url));
+                        auto.ReplaceBy(link, copyChildren: false);
+                    }
+                    LinkHoister.Hoist(root, includeImages: false);
+                }
+        }
+    }
+}

src/Capacitor.App/GitHubHtml/LinkHoister.cs

@@ -5,18 +5,18 @@ namespace Capacitor.App.GitHubHtml;
 /// Lifts links above their emphasis ancestors. MarkView activates only a hyperlink that is a
 /// direct inline of its text block, and the emphasis renders the same from inside the link.
 static class LinkHoister {
-    public static void Hoist(ContainerInline root) {
+    public static void Hoist(ContainerInline root, bool includeImages = true) {
         var links = new List<LinkInline>();
-        Collect(root, links);
+        Collect(root, links, includeImages);
         // Last link first: what follows a link inside its emphasis moves to a trailing copy, and
         // going backwards leaves each inline to be moved once rather than once per earlier link.
         for (var i = links.Count - 1; i >= 0; i--) HoistOne(links[i]);
     }
 
-    static void Collect(ContainerInline container, List<LinkInline> links) {
+    static void Collect(ContainerInline container, List<LinkInline> links, bool includeImages) {
         for (var child = container.FirstChild; child is not null; child = child.NextSibling) {
-            if (child is LinkInline link) links.Add(link);
-            if (child is ContainerInline nested) Collect(nested, links);
+            if (child is LinkInline link && (includeImages || !link.IsImage)) links.Add(link);
+            if (child is ContainerInline nested) Collect(nested, links, includeImages);
         }
     }
 

src/Capacitor.App/Views/ChatTabView.axaml.cs

@@ -33,6 +33,12 @@ public partial class ChatTabView : UserControl {
     bool _edgeScrollQueued;
     Point _dragInScroll;
     MarkdownView? _dragView;
+    /// A press is in flight. Follow-tail must not move the transcript under that pointer, or a
+    /// link click is measured as a drag and dropped.
+    IPointer? _primaryPointer;
+    TopLevel? _pointerRoot;
+    bool _tailDeferred;
+    bool PrimaryDown => _primaryPointer is not null;
     double? _thumbFraction;
     double _smoothRemaining;
     bool _smoothFrameQueued;
@@ -88,6 +94,10 @@ public ChatTabView() {
     /// the same view, and a behaviour disposed on the way out has to come back with it.
     protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e) {
         base.OnAttachedToVisualTree(e);
+        _pointerRoot = TopLevel.GetTopLevel(this);
+        _pointerRoot?.AddHandler(PointerReleasedEvent, OnPrimaryReleased, RoutingStrategies.Tunnel, handledEventsToo: true);
+        _pointerRoot?.AddHandler(PointerCaptureLostEvent, OnPrimaryCaptureLost, RoutingStrategies.Direct | RoutingStrategies.Bubble, handledEventsToo: true);
+        if (_pointerRoot is Window window) window.Deactivated += OnWindowDeactivated;
         _attachments ??= AttachmentDropPaste.Attach(
             ComposerCard, ComposerInput, AttachButton,
             () => (DataContext as ChatTabViewModel)?.Attachments, TimeProvider.System);
@@ -103,6 +113,8 @@ protected override void OnDataContextChanged(EventArgs e) {
         _readerGesture = false;
         _dragSelecting = false;
         _dragView = null;
+        _primaryPointer = null;
+        _tailDeferred = false;
         _followTail = true;
         base.OnDataContextChanged(e);
     }
@@ -114,6 +126,12 @@ protected override void OnDetachedFromVisualTree(VisualTreeAttachmentEventArgs e
         _thumbFraction = null;
         _dragSelecting = false;
         _dragView = null;
+        _primaryPointer = null;
+        _tailDeferred = false;
+        _pointerRoot?.RemoveHandler(PointerReleasedEvent, OnPrimaryReleased);
+        _pointerRoot?.RemoveHandler(PointerCaptureLostEvent, OnPrimaryCaptureLost);
+        if (_pointerRoot is Window window) window.Deactivated -= OnWindowDeactivated;
+        _pointerRoot = null;
         _attachments?.Dispose();
         _attachments = null;
         base.OnDetachedFromVisualTree(e);
@@ -124,6 +142,9 @@ protected override void OnDetachedFromVisualTree(VisualTreeAttachmentEventArgs e
     internal bool CanPreserveReadingPosition => !_followTail && _anchorItem is null && _thumbFraction is null;
 
     void OnReaderGesture(object? sender, RoutedEventArgs e) {
+        if (e is PointerPressedEventArgs pressed && _primaryPointer is null
+            && pressed.GetCurrentPoint(ChatItems).Properties.PointerUpdateKind == PointerUpdateKind.LeftButtonPressed)
+            _primaryPointer = pressed.Pointer;
         _listInputVersion++;
         // A TextBox in the list (Other…, free-text) is editing, not reading: arming follow-tail
         // would ScrollToEnd and recycle its virtualizing row, which drops the caret.
@@ -144,6 +165,31 @@ void OnReaderGesture(object? sender, RoutedEventArgs e) {
         Dispatcher.UIThread.Post(() => _readerGesture = false, DispatcherPriority.Background);
     }
 
+    void OnPrimaryReleased(object? sender, PointerReleasedEventArgs e) {
+        if (ReferenceEquals(e.Pointer, _primaryPointer) && e.InitialPressMouseButton == MouseButton.Left)
+            CompletePrimaryPress();
+    }
+
+    void OnPrimaryCaptureLost(object? sender, PointerCaptureLostEventArgs e) {
+        if (ReferenceEquals(e.Pointer, _primaryPointer)) CompletePrimaryPress();
+    }
+
+    void OnWindowDeactivated(object? sender, EventArgs e) => CompletePrimaryPress();
+
+    void CompletePrimaryPress() {
+        _primaryPointer = null;
+        _dragSelecting = false;
+        if (!_tailDeferred) return;
+        _tailDeferred = false;
+        var context = DataContext;
+        Dispatcher.UIThread.Post(() => {
+            if (PrimaryDown || !_followTail || _dragSelecting || _anchorItem is not null
+                || _thumbFraction is not null || ListTextBoxOwnsFocus()
+                || !ReferenceEquals(context, DataContext) || _pointerRoot is null) return;
+            _scroll?.ScrollToEnd();
+        }, DispatcherPriority.Background);
+    }
+
     void OnChatWheelChanged(object? sender, PointerWheelEventArgs e) {
         if (e.Handled || e.KeyModifiers != KeyModifiers.None || OriginatesFromTextBox(e)) return;
         EnsureChatScroll();
@@ -396,8 +442,13 @@ void OnScrollChanged(object? sender, ScrollChangedEventArgs e) {
         // same layout pass. That still counts as the reader returning to the bottom.
         var reachedEstimatedEnd = e.OffsetDelta.Y > 0 && e.ExtentDelta.Y > 0
             && ChatItems.ItemsPanelRoot is ChatVirtualizingPanel { MeasuredAtEstimatedEnd: true };
-        _followTail = _readerGesture ? atBottom || reachedEstimatedEnd : _followTail || atBottom || reachedEstimatedEnd;
-        if (_followTail && !atBottom) scroll.ScrollToEnd();
+        var extentOnlyWhilePressed = PrimaryDown && _followTail
+            && e.ExtentDelta.Y > 0 && Math.Abs(e.OffsetDelta.Y) <= 0.5;
+        _followTail = extentOnlyWhilePressed || (_readerGesture ? atBottom || reachedEstimatedEnd : _followTail || atBottom || reachedEstimatedEnd);
+        if (_followTail && !atBottom) {
+            if (PrimaryDown) _tailDeferred = true;
+            else scroll.ScrollToEnd();
+        }
     }
 
     void OnSelectionDrag(object? sender, PointerEventArgs e) {

src/Capacitor.App/Views/MarkdownView.cs

@@ -178,7 +178,7 @@ void ApplyFlavor() {
         // After the highlighter, whose code block renderer this one wraps.
         _viewer.Extensions.Add(_codeActions);
         // Only the pipeline change re-renders, so it goes last.
-        _viewer.Pipeline = Flavor == MarkdownFlavor.GitHub ? GitHubPipeline.Instance : null;
+        _viewer.Pipeline = Flavor == MarkdownFlavor.GitHub ? GitHubPipeline.Instance : ChatPipeline.Instance;
     }
 
     /// Re-rendering rebuilds MarkView's selection index, so it always matches what is visible.

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

@@ -0,0 +1,37 @@
+using Avalonia.Controls.Documents;
+using Avalonia.Media;
+using MarkView.Avalonia.Rendering.Inlines;
+using static Capacitor.App.Tests.Unit.AvaloniaSession;
+using static Capacitor.App.Tests.Unit.MarkdownViewHarness;
+
+namespace Capacitor.App.Tests.Unit;
+
+public class ChatLinkHoistTests {
+    [Test]
+    [Arguments("See **[docs](https://example.com/docs)** now.")]
+    [Arguments("See **<https://example.com/docs>** now.")]
+    [Arguments("See **https://example.com/docs** now.")]
+    [NotInParallel("AvaloniaSession")]
+    public async Task A_bold_markdown_link_is_clickable(string markdown) {
+        await RunOnUiAsync(async () => {
+            var (window, root, opened) = Show(markdown);
+            try {
+                var paragraph = Paragraphs(root).Single();
+                var link = paragraph.Inlines!.OfType<MarkdownHyperlink>().Single();
+                await Assert.That(link.NavigateUri?.ToString()).IsEqualTo("https://example.com/docs");
+                Click(window, paragraph, link);
+                await Assert.That(opened).IsEquivalentTo(new[] { "https://example.com/docs" });
+            } finally { window.Close(); }
+        });
+    }
+    [Test]
+    [NotInParallel("AvaloniaSession")]
+    public Task An_emphasized_image_placeholder_keeps_its_style() => RunOnUiAsync(async () => {
+        var (window, root, _) = Show("**![badge](https://example.com/image.png)**");
+        try {
+            var bold = Paragraphs(root).Single().Inlines!.OfType<Bold>().Single();
+            await Assert.That(bold.Inlines.Text).IsEqualTo("![badge](https://example.com/image.png)");
+            await Assert.That(bold.FontWeight).IsEqualTo(FontWeight.Bold);
+        } finally { window.Close(); }
+    });
+}

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

@@ -574,23 +574,66 @@ await RunOnUiAsync(async () => {
     public async Task A_link_in_an_assistant_row_opens_through_the_tabs_command() {
         await RunOnUiAsync(async () => {
             var host = new Host();
-            await host.LoadAsync(Tmp.CreateFile("link.jsonl", [AssistantLinkLine]));
+            var path = Tmp.CreateFile("link.jsonl", Enumerable.Repeat(UserLine, 40).Append(AssistantLinkLine).ToArray());
+            await host.LoadAsync(path);
 
-            await Assert.That(host.Chat.Items).Count().IsEqualTo(1);
+            await Assert.That(host.Chat.Items).Count().IsEqualTo(41);
 
-            var paragraph = host.View.GetVisualDescendants().OfType<TextBlock>().Single(t => t.Classes.Contains("markdown-paragraph"));
+            var paragraph = host.View.GetVisualDescendants().OfType<TextBlock>().Single(t => t.Classes.Contains("markdown-paragraph") && MarkdownViewHarness.Reads(t).Contains("docs", StringComparison.Ordinal));
             var glyph = paragraph.TextLayout.HitTestTextPosition("See ".Length);
             var origin = paragraph.TranslatePoint(new Point(glyph.X + paragraph.Padding.Left + 2, glyph.Y + paragraph.Padding.Top + glyph.Height / 2), host.Window)!.Value;
             host.Window.MouseMove(origin);
             host.Window.MouseDown(origin, MouseButton.Left);
+            await host.AppendAndTickAsync(path, 4);
+            host.Settle();
+            await Assert.That(host.AtBottom()).IsFalse();
             host.Window.MouseUp(origin, MouseButton.Left);
-            Dispatcher.UIThread.RunJobs();
+            host.Settle();
 
+            await Assert.That(host.AtBottom()).IsTrue();
             await Assert.That(host.Opener.Opened).IsEquivalentTo(new[] { "https://example.com/docs" });
             await host.CloseAsync();
         });
     }
 
+    [Test]
+    [Arguments(false, false)]
+    [Arguments(true, false)]
+    [Arguments(false, true)]
+    [NotInParallel("AvaloniaSession")]
+    public Task Follow_tail_resumes_after_a_primary_press(bool releaseOutside, bool loseCapture) => RunOnUiAsync(async () => {
+        var host = new Host();
+        try {
+            var path = Tmp.CreateFile("press-tail.jsonl", Enumerable.Repeat(UserLine, 40).ToArray());
+            await host.LoadAsync(path);
+            var items = host.View.FindControl<ItemsControl>("ChatItems")!;
+            var point = PresentAndLocate(host, items);
+            host.Window.MouseMove(point);
+            host.Window.MouseDown(point, MouseButton.Left);
+            await host.AppendAndTickAsync(path, 4);
+            host.Settle();
+            await Assert.That(host.AtBottom()).IsFalse();
+            host.Window.MouseDown(point, MouseButton.Right, RawInputModifiers.LeftMouseButton);
+            host.Window.MouseUp(point, MouseButton.Right, RawInputModifiers.LeftMouseButton);
+            await host.AppendAndTickAsync(path, 2);
+            host.Settle();
+            await Assert.That(host.AtBottom()).IsFalse();
+            if (loseCapture) {
+                IPointer? pointer = null;
+                host.Window.AddHandler(InputElement.PointerMovedEvent, (_, e) => pointer = e.Pointer, RoutingStrategies.Tunnel);
+                host.Window.MouseMove(point, RawInputModifiers.LeftMouseButton);
+                pointer!.Capture(items);
+                pointer.Capture(null);
+            } else {
+                var release = releaseOutside ? PresentAndLocate(host, host.Composer) : point;
+                host.Window.MouseUp(release, MouseButton.Left);
+            }
+            host.Settle();
+            await Assert.That(host.AtBottom()).IsTrue();
+            if (loseCapture) host.Window.MouseUp(point, MouseButton.Left);
+        } finally { await host.CloseAsync(); }
+    });
+
     /// A labelled row shows its verb phrase beside the detail; once the result lands the same item
     /// renders as a card with the page's name and its actions, and the plain row is gone.
     [Test]