Fix: Keep snapshot, history, and note lists stable after deletion

src/MandoCode.Desktop.Tests/MandoCode.Desktop.Tests.csproj

@@ -57,6 +57,7 @@
     <Compile Include="..\MandoCode.Desktop\Services\BuiltInBackgrounds.cs" Link="src\BuiltInBackgrounds.cs" />
     <Compile Include="..\MandoCode.Desktop\Services\TranscriptJournal.cs" Link="src\TranscriptJournal.cs" />
     <Compile Include="..\MandoCode.Desktop\Services\ModelNoticeReplay.cs" Link="src\ModelNoticeReplay.cs" />
+    <Compile Include="..\MandoCode.Desktop\Services\StableCollection.cs" Link="src\StableCollection.cs" />
     <Compile Include="..\MandoCode.Desktop\Services\ConversationLog.cs" Link="src\ConversationLog.cs" />
     <!-- History's full-text matching + snippet extraction. Pure (text in, match out); the file reads
          and caching live in ConversationTextCache, which is NOT compiled here because it touches

src/MandoCode.Desktop.Tests/StableCollectionTests.cs

@@ -0,0 +1,51 @@
+using System.Collections.ObjectModel;
+using System.Collections.Specialized;
+using MandoCode.Desktop.Services;
+using Xunit;
+
+namespace MandoCode.Desktop.Tests;
+
+public class StableCollectionTests
+{
+    private sealed record Row(int Id, string Text);
+
+    [Fact]
+    public void DeleteAndRescanKeepSurvivingRowsWithoutResetOrAdd()
+    {
+        var first = new Row(1, "one");
+        var last = new Row(3, "three");
+        var rows = new ObservableCollection<Row> { first, new(2, "two"), last };
+        var events = new List<NotifyCollectionChangedAction>();
+        rows.CollectionChanged += (_, e) => events.Add(e.Action);
+        StableCollection.Update(rows, new[] { new Row(1, "one"), new Row(3, "three") }, r => r.Id);
+        StableCollection.Update(rows, new[] { new Row(1, "one"), new Row(3, "three") }, r => r.Id);
+        Assert.Equal(new[] { NotifyCollectionChangedAction.Remove }, events);
+        Assert.Same(first, rows[0]);
+        Assert.Same(last, rows[1]);
+    }
+
+    [Fact]
+    public void ChangesReplaceOnlyChangedRowsAndMaintainRequestedOrder()
+    {
+        var retained = new Row(1, "one");
+        var rows = new ObservableCollection<Row> { retained, new(2, "two") };
+        var events = new List<NotifyCollectionChangedAction>();
+        rows.CollectionChanged += (_, e) => events.Add(e.Action);
+        StableCollection.Update(rows, new[] { new Row(2, "edited"), retained, new Row(3, "added") }, r => r.Id);
+        Assert.Equal(new[] { 2, 1, 3 }, rows.Select(r => r.Id));
+        Assert.Equal("edited", rows[0].Text);
+        Assert.Same(retained, rows[1]);
+        Assert.DoesNotContain(NotifyCollectionChangedAction.Reset, events);
+    }
+
+    [Fact]
+    public void RemovingLastGroupDoesNotRecreateRemainingGroup()
+    {
+        var remaining = new ObservableCollection<Row> { new(1, "one") };
+        var deleted = new ObservableCollection<Row> { new(2, "two") };
+        var groups = new ObservableCollection<ObservableCollection<Row>> { deleted, remaining };
+        StableCollection.Update(groups, new[] { remaining }, g => g[0].Id, (a, b) => true);
+        Assert.Single(groups);
+        Assert.Same(remaining, groups[0]);
+    }
+}

src/MandoCode.Desktop/MainWindow.History.cs

@@ -234,6 +234,8 @@ private bool Matches(SessionArchiveEntry s, string q) =>
         || (s.Preview?.Contains(q, StringComparison.OrdinalIgnoreCase) ?? false)
         || _historyContentHits.ContainsKey(s.Key);
 
+    private readonly System.Collections.ObjectModel.ObservableCollection<HistoryGroup> _visibleHistoryGroups = new();
+
     private void PopulateHistory()
     {
         var all = _archive.Items;   // newest-first copy
@@ -244,8 +246,10 @@ private void PopulateHistory()
         var filtered = string.IsNullOrEmpty(q) ? all : all.Where(s => Matches(s, q)).ToList();
 
         // Stamp the snippet onto EVERY row, not just the matches, so a snippet from a previous query
-        // can't linger on a row the new query matched by title. Read once by a OneTime x:Bind —
-        // ItemsSource is reassigned below, so the templates always re-bind.
+        // can't linger on a row the new query matched by title. Rebind rows when snippets change;
+        // ordinary deletes keep surviving rows and expanded groups in place.
+        var snippetsChanged = all.Any(entry => entry.MatchSnippet !=
+            (_historyContentHits.TryGetValue(entry.Key, out var hit) ? hit : null));
         foreach (var entry in all)
             entry.MatchSnippet = _historyContentHits.TryGetValue(entry.Key, out var snippet) ? snippet : null;
 
@@ -257,7 +261,14 @@ private void PopulateHistory()
             .Select(g => new HistoryGroup(g.Key, g) { IsExpanded = !_collapsedHistoryGroups.Contains(g.Key) })
             .ToList();
 
-        HistoryList.ItemsSource = groups;
+        foreach (var incoming in groups)
+        {
+            var existing = _visibleHistoryGroups.FirstOrDefault(g => g.Project == incoming.Project);
+            if (existing != null)
+                StableCollection.Update(existing, incoming, row => row.Key, (a, b) => !snippetsChanged && ReferenceEquals(a, b));
+        }
+        StableCollection.Update(_visibleHistoryGroups, groups, g => g.Project, (a, b) => true);
+        if (HistoryList.ItemsSource == null) HistoryList.ItemsSource = _visibleHistoryGroups;
 
         var nothingToShow = groups.Count == 0;
         HistoryEmpty.Text = storeEmpty

src/MandoCode.Desktop/MainWindow.Notes.cs

@@ -193,6 +193,8 @@ private void RestoreLastNoteOnce()
     /// switches between them: an open note means editor, otherwise the grouped list. Safe to call any
     /// time — everything is derived from state.
     /// </summary>
+    private readonly System.Collections.ObjectModel.ObservableCollection<NoteGroup> _visibleNotesGroups = new();
+
     private void PopulateNotes()
     {
         var editing = NoteEditor.Current != null;
@@ -234,7 +236,14 @@ private void PopulateNotes()
             })
             .ToList();
 
-        NotesList.ItemsSource = groups;
+        foreach (var incoming in groups)
+        {
+            var existing = _visibleNotesGroups.FirstOrDefault(g => g.Project == incoming.Project);
+            if (existing != null)
+                StableCollection.Update(existing, incoming, row => row.Note.Path.ToUpperInvariant(), (a, b) => a.Note == b.Note && a.MatchSnippet == b.MatchSnippet);
+        }
+        StableCollection.Update(_visibleNotesGroups, groups, g => g.Project, (a, b) => true);
+        if (NotesList.ItemsSource == null) NotesList.ItemsSource = _visibleNotesGroups;
 
         var nothingToShow = groups.Count == 0;
         NotesEmpty.Text = !_notesScanned

src/MandoCode.Desktop/MainWindow.Snapshots.cs

@@ -178,6 +178,8 @@ private static bool Matches(ContextSnapshot s, string q) =>
         || s.ProjectLabel.Contains(q, StringComparison.OrdinalIgnoreCase)
         || (s.Recap?.Contains(q, StringComparison.OrdinalIgnoreCase) ?? false);
 
+    private readonly System.Collections.ObjectModel.ObservableCollection<SnapshotGroup> _visibleSnapshotsGroups = new();
+
     private void PopulateSnapshots()
     {
         var all = _snapshotStore.Items;   // newest-first copy of the shared store
@@ -202,7 +204,14 @@ private void PopulateSnapshots()
             .Select(g => new SnapshotGroup(g.Key, g) { IsExpanded = !_collapsedSnapshotGroups.Contains(g.Key) })
             .ToList();
 
-        SnapshotsList.ItemsSource = groups;
+        foreach (var incoming in groups)
+        {
+            var existing = _visibleSnapshotsGroups.FirstOrDefault(g => g.Project == incoming.Project);
+            if (existing != null)
+                StableCollection.Update(existing, incoming, row => row.Id, ReferenceEquals);
+        }
+        StableCollection.Update(_visibleSnapshotsGroups, groups, g => g.Project, (a, b) => true);
+        if (SnapshotsList.ItemsSource == null) SnapshotsList.ItemsSource = _visibleSnapshotsGroups;
 
         var nothingToShow = groups.Count == 0;
         SnapshotsEmpty.Text = storeEmpty

src/MandoCode.Desktop/MainWindow.ViewModels.cs

@@ -38,50 +38,27 @@ public sealed record ModelChoice(string Name, bool IsCloud)
     public string Tag => IsCloud ? "cloud · uses tokens" : "local · free";
 }
 
-/// <summary>A project's snapshots, as one group in the (grouped) snapshots panel. Derives from
-/// <see cref="List{T}"/> so a <see cref="Microsoft.UI.Xaml.Data.CollectionViewSource"/> can group
-/// on it directly — the ListView's group-header template binds to <see cref="Project"/> and
-/// <see cref="Count"/>.</summary>
-public sealed class SnapshotGroup : List<Services.ContextSnapshot>
+/// <summary>A stable project group. Row changes notify counts without recreating its Expander.</summary>
+public abstract class PanelGroup<T> : ObservableCollection<T>
 {
-    public SnapshotGroup(string project, IEnumerable<Services.ContextSnapshot> items) : base(items)
-        => Project = project;
-
+    protected PanelGroup(string project, IEnumerable<T> items) : base(items) => Project = project;
     public string Project { get; }
-
-    /// <summary>Whether the group's Expander is open. Set when the groups are rebuilt (from the
-    /// remembered collapsed-set) and read once via a OneTime x:Bind — the Expander's own
-    /// expand/collapse events keep the remembered set current thereafter.</summary>
     public bool IsExpanded { get; set; } = true;
-
-    /// <summary>Label for the group's "delete everything shown here" button. Computed here rather
-    /// than assembled in XAML so the count is exact; a OneTime binding is always current because the
-    /// groups are rebuilt on every panel populate.</summary>
     public string DeleteAllLabel => $"Delete all {Count}";
-
-    /// <summary>The group action only earns its space once there's more than one item — with a single
-    /// card, that card's own Delete button already does the same job. Bound as Visibility rather than
-    /// a bool because x:Bind does no implicit bool-to-Visibility conversion.</summary>
     public Visibility DeleteAllVisibility => Count > 1 ? Visibility.Visible : Visibility.Collapsed;
+    protected override void OnPropertyChanged(PropertyChangedEventArgs e)
+    {
+        base.OnPropertyChanged(e);
+        if (e.PropertyName == nameof(Count))
+        {
+            base.OnPropertyChanged(new(nameof(DeleteAllLabel)));
+            base.OnPropertyChanged(new(nameof(DeleteAllVisibility)));
+        }
+    }
 }
 
-/// <summary>A project's closed conversations, as one collapsible group in the History panel —
-/// the archive twin of <see cref="SnapshotGroup"/>.</summary>
-public sealed class HistoryGroup : List<Services.SessionArchiveEntry>
-{
-    public HistoryGroup(string project, IEnumerable<Services.SessionArchiveEntry> items) : base(items)
-        => Project = project;
-
-    public string Project { get; }
-
-    public bool IsExpanded { get; set; } = true;
-
-    /// <summary>See <see cref="SnapshotGroup.DeleteAllLabel"/>.</summary>
-    public string DeleteAllLabel => $"Delete all {Count}";
-
-    /// <summary>See <see cref="SnapshotGroup.DeleteAllVisibility"/>.</summary>
-    public Visibility DeleteAllVisibility => Count > 1 ? Visibility.Visible : Visibility.Collapsed;
-}
+public sealed class SnapshotGroup(string project, IEnumerable<ContextSnapshot> items) : PanelGroup<ContextSnapshot>(project, items);
+public sealed class HistoryGroup(string project, IEnumerable<SessionArchiveEntry> items) : PanelGroup<SessionArchiveEntry>(project, items);
 
 /// <summary>
 /// One note as the panel shows it: the note itself plus the search snippet that explains why it
@@ -115,14 +92,7 @@ public sealed class NoteRow
 /// Deliberately WITHOUT the "Delete all n" group action those two carry. A snapshot or an archived
 /// conversation is a derived artifact the app made; a note is something the user wrote by hand, and
 /// one button that deletes a folder's worth of writing is a different class of risk.</summary>
-public sealed class NoteGroup : List<NoteRow>
-{
-    public NoteGroup(string project, IEnumerable<NoteRow> items) : base(items) => Project = project;
-
-    public string Project { get; }
-
-    public bool IsExpanded { get; set; } = true;
-}
+public sealed class NoteGroup(string project, IEnumerable<NoteRow> items) : PanelGroup<NoteRow>(project, items);
 
 /// <summary>
 /// One tile in the Appearance page's shipped-background gallery. Selection is baked in at build

src/MandoCode.Desktop/MainWindow.xaml

@@ -269,6 +269,7 @@
                      across search/import (see _collapsedSnapshotGroups). -->
                 <ScrollViewer x:Name="SnapshotsScroller" Grid.Row="2">
                     <ListView x:Name="SnapshotsList" SelectionMode="None" Padding="10,2,10,12">
+                        <ListView.ItemContainerTransitions><TransitionCollection/></ListView.ItemContainerTransitions>
                         <ListView.ItemContainerStyle>
                             <Style TargetType="ListViewItem">
                                 <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
@@ -289,7 +290,7 @@
                                                        VerticalAlignment="Center" TextTrimming="CharacterEllipsis"/>
                                             <Border CornerRadius="7" Padding="6,0" VerticalAlignment="Center"
                                                     Background="{StaticResource MandoPanelBrush}">
-                                                <TextBlock Text="{x:Bind Count}" FontSize="10" Opacity="0.7"/>
+                                                <TextBlock Text="{x:Bind Count, Mode=OneWay}" FontSize="10" Opacity="0.7"/>
                                             </Border>
                                         </StackPanel>
                                     </Expander.Header>
@@ -301,14 +302,14 @@
                                              Hidden for a single-item group — that card's
                                              own Delete already does the same job. -->
                                         <Button Click="SnapshotDeleteGroup_Click" Tag="{x:Bind}"
-                                                Visibility="{x:Bind DeleteAllVisibility}"
+                                                Visibility="{x:Bind DeleteAllVisibility, Mode=OneWay}"
                                                 HorizontalAlignment="Right" Margin="0,0,0,8" Padding="8,3"
                                                 Background="Transparent" BorderThickness="0"
                                                 ToolTipService.ToolTip="Delete every snapshot shown in this project"
                                                 AutomationProperties.Name="Delete every snapshot shown in this project">
                                             <StackPanel Orientation="Horizontal" Spacing="6">
                                                 <FontIcon Glyph="&#xE74D;" FontSize="11" Opacity="0.75"/>
-                                                <TextBlock Text="{x:Bind DeleteAllLabel}" FontSize="11" Opacity="0.75"/>
+                                                <TextBlock Text="{x:Bind DeleteAllLabel, Mode=OneWay}" FontSize="11" Opacity="0.75"/>
                                             </StackPanel>
                                         </Button>
                                         <ItemsControl ItemsSource="{x:Bind}">
@@ -417,6 +418,7 @@
                      is remembered in code (see _collapsedHistoryGroups). -->
                 <ScrollViewer x:Name="HistoryScroller" Grid.Row="2">
                     <ListView x:Name="HistoryList" SelectionMode="None" Padding="10,2,10,12">
+                        <ListView.ItemContainerTransitions><TransitionCollection/></ListView.ItemContainerTransitions>
                         <ListView.ItemContainerStyle>
                             <Style TargetType="ListViewItem">
                                 <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
@@ -437,7 +439,7 @@
                                                        VerticalAlignment="Center" TextTrimming="CharacterEllipsis"/>
                                             <Border CornerRadius="7" Padding="6,0" VerticalAlignment="Center"
                                                     Background="{StaticResource MandoPanelBrush}">
-                                                <TextBlock Text="{x:Bind Count}" FontSize="10" Opacity="0.7"/>
+                                                <TextBlock Text="{x:Bind Count, Mode=OneWay}" FontSize="10" Opacity="0.7"/>
                                             </Border>
                                         </StackPanel>
                                     </Expander.Header>
@@ -449,14 +451,14 @@
                                              Hidden for a single-item group — that card's
                                              own Delete already does the same job. -->
                                         <Button Click="HistoryDeleteGroup_Click" Tag="{x:Bind}"
-                                                Visibility="{x:Bind DeleteAllVisibility}"
+                                                Visibility="{x:Bind DeleteAllVisibility, Mode=OneWay}"
                                                 HorizontalAlignment="Right" Margin="0,0,0,8" Padding="8,3"
                                                 Background="Transparent" BorderThickness="0"
                                                 ToolTipService.ToolTip="Delete every conversation shown in this project"
                                                 AutomationProperties.Name="Delete every conversation shown in this project">
                                             <StackPanel Orientation="Horizontal" Spacing="6">
                                                 <FontIcon Glyph="&#xE74D;" FontSize="11" Opacity="0.75"/>
-                                                <TextBlock Text="{x:Bind DeleteAllLabel}" FontSize="11" Opacity="0.75"/>
+                                                <TextBlock Text="{x:Bind DeleteAllLabel, Mode=OneWay}" FontSize="11" Opacity="0.75"/>
                                             </StackPanel>
                                         </Button>
                                         <ItemsControl ItemsSource="{x:Bind}">
@@ -622,6 +624,7 @@
 
                 <ScrollViewer x:Name="NotesScroller" Grid.Row="2">
                     <ListView x:Name="NotesList" SelectionMode="None" Padding="10,2,10,12">
+                        <ListView.ItemContainerTransitions><TransitionCollection/></ListView.ItemContainerTransitions>
                         <ListView.ItemContainerStyle>
                             <Style TargetType="ListViewItem">
                                 <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
@@ -642,7 +645,7 @@
                                                        VerticalAlignment="Center" TextTrimming="CharacterEllipsis"/>
                                             <Border CornerRadius="7" Padding="6,0" VerticalAlignment="Center"
                                                     Background="{StaticResource MandoPanelBrush}">
-                                                <TextBlock Text="{x:Bind Count}" FontSize="10" Opacity="0.7"/>
+                                                <TextBlock Text="{x:Bind Count, Mode=OneWay}" FontSize="10" Opacity="0.7"/>
                                             </Border>
                                         </StackPanel>
                                     </Expander.Header>