feat(details): attach clipboard image on Ctrl+V in the task description

Extracts the clipboard bitmap read into a shared ClipboardBitmap helper
(also used by the terminal view); the description TextBox now routes an
image paste through AddFilesAsync as a unique paste-*.png attachment.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/ClaudeDo.Ui/Services/ClipboardBitmap.cs

@@ -0,0 +1,26 @@
+using System;
+using System.Threading.Tasks;
+using Avalonia.Controls;
+using Avalonia.Input;
+using Avalonia.Media.Imaging;
+
+namespace ClaudeDo.Ui.Services;
+
+/// <summary>Reads a bitmap off the clipboard; shared by the terminal view and the description editor.</summary>
+public static class ClipboardBitmap
+{
+    /// <summary>The clipboard bitmap (caller disposes), or null if there is none or the read failed.</summary>
+    public static async Task<Bitmap?> TryGetAsync(TopLevel? topLevel)
+    {
+        if (topLevel?.Clipboard is not { } clipboard) return null;
+        try
+        {
+            using var data = await clipboard.TryGetDataAsync();
+            return data is null ? null : await AsyncDataTransferExtensions.TryGetBitmapAsync(data);
+        }
+        catch (Exception)
+        {
+            return null;
+        }
+    }
+}

src/ClaudeDo.Ui/Services/ClipboardImageTempStore.cs

@@ -22,8 +22,11 @@ public static class ClipboardImageTempStore
 
     /// <summary>Test seam for <see cref="NewPngPath(DateTime)"/> — takes the target dir explicitly
     /// instead of the real app data root.</summary>
-    internal static string NewPngPath(string dir, DateTime utcNow) =>
+    internal static string NewPngPath(string dir, DateTime utcNow) => Path.Combine(dir, NewPngFileName(utcNow));
-        Path.Combine(dir, $"paste-{utcNow:yyyyMMdd-HHmmssfff}-{Guid.NewGuid():N}.png");
+
+    /// <summary>A fresh, collision-free <c>paste-….png</c> file name (also used as an attachment name).</summary>
+    public static string NewPngFileName(DateTime utcNow) =>
+        $"paste-{utcNow:yyyyMMdd-HHmmssfff}-{Guid.NewGuid():N}.png";
 
     /// <summary>Test seam for <see cref="DeleteOlderThan(TimeSpan,DateTime)"/> — takes the target dir
     /// explicitly instead of the real app data root.</summary>

src/ClaudeDo.Ui/Views/InteractiveTerminalView.axaml.cs

@@ -67,7 +67,7 @@ public partial class InteractiveTerminalView : UserControl
         Avalonia.Media.Imaging.Bitmap? bitmap = null;
         try
         {
-            bitmap = await TryGetClipboardBitmapAsync(TopLevel.GetTopLevel(view));
+            bitmap = await ClipboardBitmap.TryGetAsync(TopLevel.GetTopLevel(view));
             if (bitmap is null)
             {
                 if (!await vm.PasteAsync()) vm.ReportSendFailed();
@@ -90,20 +90,6 @@ public partial class InteractiveTerminalView : UserControl
         }
     }
 
-    private static async System.Threading.Tasks.Task<Avalonia.Media.Imaging.Bitmap?> TryGetClipboardBitmapAsync(TopLevel? topLevel)
-    {
-        if (topLevel?.Clipboard is not { } clipboard) return null;
-        try
-        {
-            using var data = await clipboard.TryGetDataAsync();
-            return data is null ? null : await Avalonia.Input.AsyncDataTransferExtensions.TryGetBitmapAsync(data);
-        }
-        catch (Exception)
-        {
-            return null;
-        }
-    }
-
     private static bool IsFilesDrop(DragEventArgs e) => e.DataTransfer?.Contains(DataFormat.File) == true;
 
     private void OnDragOver(object? sender, DragEventArgs e)

src/ClaudeDo.Ui/Views/Islands/Detail/DescriptionStepsCard.axaml

@@ -103,7 +103,8 @@
           <!-- Description -->
           <Panel IsVisible="{Binding IsDescriptionSection}">
             <!-- Edit mode: raw TextBox -->
-            <TextBox Text="{Binding EditableDescription, Mode=TwoWay}"
+            <TextBox x:Name="DescriptionBox"
+                     Text="{Binding EditableDescription, Mode=TwoWay}"
                      AcceptsReturn="True"
                      TextWrapping="Wrap"
                      MinHeight="80"

src/ClaudeDo.Ui/Views/Islands/Detail/DescriptionStepsCard.axaml.cs

@@ -3,6 +3,7 @@ using Avalonia.Input;
 using Avalonia.Input.Platform;
 using Avalonia.Interactivity;
 using Avalonia.Platform.Storage;
+using ClaudeDo.Ui.Services;
 using ClaudeDo.Ui.ViewModels.Islands;
 
 namespace ClaudeDo.Ui.Views.Islands.Detail;
@@ -12,6 +13,41 @@ public partial class DescriptionStepsCard : UserControl
     public DescriptionStepsCard()
     {
         InitializeComponent();
+        // Tunnel: the TextBox handles Ctrl+V itself (text only), so an image paste has to be caught first.
+        DescriptionBox.AddHandler(KeyDownEvent, OnDescriptionPreviewKeyDown, RoutingStrategies.Tunnel);
+    }
+
+    private void OnDescriptionPreviewKeyDown(object? sender, KeyEventArgs e)
+    {
+        if (e.Key != Key.V || !e.KeyModifiers.HasFlag(KeyModifiers.Control) || e.KeyModifiers.HasFlag(KeyModifiers.Alt))
+            return;
+
+        // The clipboard read is async, so swallow the key and replay the text paste when there is no image.
+        e.Handled = true;
+        _ = PasteAsync();
+    }
+
+    /// <summary>Attaches a clipboard bitmap as a PNG file; anything else falls back to the normal text paste.</summary>
+    private async System.Threading.Tasks.Task PasteAsync()
+    {
+        try
+        {
+            using var bitmap = await ClipboardBitmap.TryGetAsync(TopLevel.GetTopLevel(this));
+            if (bitmap is null || DataContext is not DetailsIslandViewModel vm)
+            {
+                DescriptionBox.Paste();
+                return;
+            }
+
+            using var png = new System.IO.MemoryStream();
+            bitmap.Save(png);
+            png.Position = 0;
+            await vm.AddFilesAsync(new[] { (ClipboardImageTempStore.NewPngFileName(DateTime.UtcNow), (System.IO.Stream)png) });
+        }
+        catch (Exception)
+        {
+            // Paste is best-effort; a failed clipboard/encode must not surface as an unhandled UI exception.
+        }
     }
 
     private async void OnCopyClick(object? sender, RoutedEventArgs e)

tests/ClaudeDo.Ui.Tests/Services/ClipboardImageTempStoreTests.cs

@@ -27,6 +27,20 @@ public class ClipboardImageTempStoreTests : IDisposable
         Assert.Equal(".png", Path.GetExtension(a));
     }
 
+    [Fact]
+    public void NewPngFileName_IsUniquePasteNameWithoutDirectory()
+    {
+        var now = new DateTime(2026, 9, 16, 10, 30, 0, 123, DateTimeKind.Utc);
+
+        var a = ClipboardImageTempStore.NewPngFileName(now);
+        var b = ClipboardImageTempStore.NewPngFileName(now);
+
+        Assert.NotEqual(a, b);
+        Assert.StartsWith("paste-20260916-103000123-", a);
+        Assert.EndsWith(".png", a);
+        Assert.Equal(a, Path.GetFileName(a));
+    }
+
     [Fact]
     public void DeleteOlderThan_RemovesOnlyFilesPastTheMaxAge()
     {