Upgrade to Avalonia 12

src/PlanViewer.App/App.axaml

@@ -43,11 +43,11 @@
             <Setter Property="AllowAutoHide" Value="True"/>
         </Style>
 
-        <!-- DataGrid does not scroll through a ScrollViewer, and the ScrollBar rule above
-             cannot reach its bars either: it assigns AllowAutoHide to them in code, and a
-             local value outranks any style. There is no DataGrid.AllowAutoHide to set, but
-             the value it pushes down is the ATTACHED ScrollViewer property read off itself,
-             so setting that here is what reaches the grids. -->
+        <!-- DataGrid does not scroll through a ScrollViewer, so the ScrollBar rule above
+             cannot reach its bars: PART_HorizontalScrollbar and PART_VerticalScrollbar are
+             bare ScrollBars inside its own template. There is no DataGrid.AllowAutoHide to
+             set, but the template binds each bar's AllowAutoHide to the ATTACHED ScrollViewer
+             property on the grid, so setting that here is what reaches them. -->
         <Style Selector="DataGrid">
             <Setter Property="ScrollViewer.AllowAutoHide" Value="True"/>
         </Style>

src/PlanViewer.App/Controls/PlanViewerControl.axaml

@@ -525,7 +525,7 @@
                             Background="{DynamicResource BackgroundBrush}"
                             BorderBrush="{DynamicResource BorderBrush}" BorderThickness="0,0,0,1">
                         <TextBox x:Name="PropertiesFilterBox"
-                                 Watermark="Filter properties..."
+                                 PlaceholderText="Filter properties..."
                                  FontSize="11" Height="24" MinHeight="0" Padding="6,1"
                                  VerticalContentAlignment="Center"
                                  TextChanged="PropertiesFilter_TextChanged"

src/PlanViewer.App/Controls/QuerySessionControl.Execution.cs

@@ -82,6 +82,8 @@ private async Task CaptureAndShowPlan(bool estimated, string? queryTextOverride
             Height = 4,
             Margin = new Avalonia.Thickness(0, 0, 0, 12)
         };
+        // This overlay lives in tab content the user switches away from mid-capture.
+        Helpers.ProgressBarBehaviors.SetRestartOnReattach(progressBar, true);
 
         /* #448: SelectableTextBlock and wrapping, because this label doubles as the place a query
            failure is reported. A SQL error is the one string in this app a user most needs to copy
@@ -314,6 +316,8 @@ private async void GetActualPlan_Click(object? sender, RoutedEventArgs e)
             Height = 4,
             Margin = new Avalonia.Thickness(0, 0, 0, 12)
         };
+        // This overlay lives in tab content the user switches away from mid-capture.
+        Helpers.ProgressBarBehaviors.SetRestartOnReattach(progressBar, true);
 
         /* #448: see the note on the estimated-plan path — this label reports failures too. */
         var statusLabel = new SelectableTextBlock
@@ -446,7 +450,10 @@ private Task<bool> ShowConfirmationDialog(string title, string message, string c
 
     private Window GetParentWindow()
     {
-        var parent = this.VisualRoot;
+        /* GetTopLevel rather than VisualRoot because Avalonia 12 hosts a Window inside a
+           TopLevelHost, so the visual root is no longer the Window and casting it to one always
+           misses — silently, since VisualRoot still compiles and still returns something. */
+        var parent = TopLevel.GetTopLevel(this);
         return parent as Window ?? throw new InvalidOperationException("No parent window");
     }
 }

src/PlanViewer.App/Controls/QueryStoreGridControl.axaml

@@ -1,6 +1,7 @@
 <UserControl xmlns="https://github.com/avaloniaui"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:local="using:PlanViewer.App.Controls"
+             xmlns:helpers="using:PlanViewer.App.Helpers"
              xmlns:models="using:PlanViewer.Core.Models"
              x:Class="PlanViewer.App.Controls.QueryStoreGridControl"
              Background="{DynamicResource BackgroundBrush}">
@@ -94,7 +95,7 @@
                 <StackPanel x:Name="SearchValuePanel" Spacing="4">
                     <TextBlock Text=" " FontSize="11"/>
                     <TextBox x:Name="SearchValueBox" Width="200" Height="36" FontSize="13"
-                             Watermark="0x1AB2C3, dbo.MyProc"
+                             PlaceholderText="0x1AB2C3, dbo.MyProc"
                              KeyDown="SearchValue_KeyDown"/>
                 </StackPanel>
                 <StackPanel x:Name="ExecutionTypePanel" Spacing="4" IsVisible="False">
@@ -170,12 +171,12 @@
                         <StackPanel Spacing="2">
                             <TextBlock Text="Query text contains" FontSize="11"
                                        Foreground="{DynamicResource ForegroundBrush}"/>
-                            <TextBox x:Name="TextSearchBox" Width="220" Height="32" Watermark="e.g. Votes"/>
+                            <TextBox x:Name="TextSearchBox" Width="220" Height="32" PlaceholderText="e.g. Votes"/>
                         </StackPanel>
                         <StackPanel Spacing="2">
                             <TextBlock Text="Query text excludes" FontSize="11"
                                        Foreground="{DynamicResource ForegroundBrush}"/>
-                            <TextBox x:Name="TextExcludeBox" Width="220" Height="32" Watermark="e.g. #temp"/>
+                            <TextBox x:Name="TextExcludeBox" Width="220" Height="32" PlaceholderText="e.g. #temp"/>
                         </StackPanel>
                         <CheckBox x:Name="EscapeBracketsBox" Content="Treat [ ] _ as literals"
                                   VerticalAlignment="Bottom"
@@ -186,22 +187,22 @@
                         <StackPanel Spacing="2">
                             <TextBlock Text="Include query IDs" FontSize="11"
                                        Foreground="{DynamicResource ForegroundBrush}"/>
-                            <TextBox x:Name="IncludeQueryIdsBox" Width="180" Height="32" Watermark="1, 2, 3"/>
+                            <TextBox x:Name="IncludeQueryIdsBox" Width="180" Height="32" PlaceholderText="1, 2, 3"/>
                         </StackPanel>
                         <StackPanel Spacing="2">
                             <TextBlock Text="Ignore query IDs" FontSize="11"
                                        Foreground="{DynamicResource ForegroundBrush}"/>
-                            <TextBox x:Name="IgnoreQueryIdsBox" Width="180" Height="32" Watermark="4, 5"/>
+                            <TextBox x:Name="IgnoreQueryIdsBox" Width="180" Height="32" PlaceholderText="4, 5"/>
                         </StackPanel>
                         <StackPanel Spacing="2">
                             <TextBlock Text="Include plan IDs" FontSize="11"
                                        Foreground="{DynamicResource ForegroundBrush}"/>
-                            <TextBox x:Name="IncludePlanIdsBox" Width="180" Height="32" Watermark="10, 11"/>
+                            <TextBox x:Name="IncludePlanIdsBox" Width="180" Height="32" PlaceholderText="10, 11"/>
                         </StackPanel>
                         <StackPanel Spacing="2">
                             <TextBlock Text="Ignore plan IDs" FontSize="11"
                                        Foreground="{DynamicResource ForegroundBrush}"/>
-                            <TextBox x:Name="IgnorePlanIdsBox" Width="180" Height="32" Watermark="12"/>
+                            <TextBox x:Name="IgnorePlanIdsBox" Width="180" Height="32" PlaceholderText="12"/>
                         </StackPanel>
                     </StackPanel>
                     <!-- Actions -->
@@ -487,7 +488,8 @@
                 Background="#80000000" CornerRadius="0"
                 HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
             <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center" Spacing="8">
-                <ProgressBar IsIndeterminate="True" Width="200" Height="4"/>
+                <ProgressBar IsIndeterminate="True" Width="200" Height="4"
+                             helpers:ProgressBarBehaviors.RestartOnReattach="True"/>
                 <TextBlock x:Name="GridLoadingText" Text="Fetching plans..."
                            FontSize="12" HorizontalAlignment="Center"
                            Foreground="{DynamicResource ForegroundBrush}"/>

src/PlanViewer.App/Controls/QueryStoreHistoryControl.axaml

@@ -1,6 +1,7 @@
 <UserControl xmlns="https://github.com/avaloniaui"
 			 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
 			 xmlns:scottplot="clr-namespace:ScottPlot.Avalonia;assembly=ScottPlot.Avalonia"
+			 xmlns:helpers="using:PlanViewer.App.Helpers"
 			 x:Class="PlanViewer.App.Controls.QueryStoreHistoryControl"
 			 Background="{DynamicResource BackgroundBrush}">
 
@@ -71,7 +72,8 @@
 						   FontSize="12" Foreground="{DynamicResource ForegroundBrush}"/>
 				<StackPanel Grid.Column="2" Orientation="Horizontal" Spacing="6" VerticalAlignment="Center"
 							x:Name="LoadingPanel" IsVisible="False" Margin="8,0,0,0">
-					<ProgressBar IsIndeterminate="True" Width="80" Height="6" VerticalAlignment="Center"/>
+					<ProgressBar IsIndeterminate="True" Width="80" Height="6" VerticalAlignment="Center"
+							 helpers:ProgressBarBehaviors.RestartOnReattach="True"/>
 					<Button x:Name="CancelButton" Content="Cancel" Click="Cancel_Click"
 							Height="24" Padding="10,0" FontSize="11"
 							Theme="{StaticResource AppButton}"/>

src/PlanViewer.App/Controls/QueryStoreOverviewControl.axaml

@@ -1,6 +1,7 @@
 <UserControl xmlns="https://github.com/avaloniaui"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:controls="using:PlanViewer.App.Controls"
+             xmlns:helpers="using:PlanViewer.App.Helpers"
              x:Class="PlanViewer.App.Controls.QueryStoreOverviewControl">
     <UserControl.Resources>
         <!--
@@ -179,6 +180,7 @@
         <!-- Row 0: Progress bar + refresh-error badge -->
         <Grid Grid.Row="0">
             <ProgressBar x:Name="LoadingBar" IsIndeterminate="False"
+                         helpers:ProgressBarBehaviors.RestartOnReattach="True"
                          Height="3" Margin="0"
                          VerticalAlignment="Top"
                          Foreground="{DynamicResource AccentBrush}"/>

src/PlanViewer.App/Controls/WaitStatsProfileControl.axaml

@@ -1,6 +1,7 @@
 <UserControl xmlns="https://github.com/avaloniaui"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:local="using:PlanViewer.App.Controls"
+             xmlns:helpers="using:PlanViewer.App.Helpers"
              x:Class="PlanViewer.App.Controls.WaitStatsProfileControl">
     <Grid RowDefinitions="Auto,*">
         <!-- Header row: left controls + right-aligned legend button -->
@@ -35,7 +36,8 @@
                     Background="#80000000" CornerRadius="0"
                     HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
                 <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center" Spacing="6">
-                    <ProgressBar IsIndeterminate="True" Width="140" Height="3"/>
+                    <ProgressBar IsIndeterminate="True" Width="140" Height="3"
+                                 helpers:ProgressBarBehaviors.RestartOnReattach="True"/>
                     <TextBlock Text="Loading wait stats..."
                                FontSize="11" HorizontalAlignment="Center"
                                Foreground="{DynamicResource ForegroundBrush}"/>

src/PlanViewer.App/Dialogs/ConnectionDialog.axaml

@@ -15,7 +15,7 @@
                    FontSize="12" Margin="0,0,0,4"/>
         <Grid Grid.Row="1" x:Name="ServerNameGrid" ColumnDefinitions="*,Auto" Margin="0,0,0,12" ColumnSpacing="0">
             <TextBox x:Name="ServerNameBox"
-                     Watermark="e.g. sql2022 or server.database.windows.net"
+                     PlaceholderText="e.g. sql2022 or server.database.windows.net"
                      TextChanged="RequiredField_TextChanged"
                      FontSize="13" Height="32"/>
             <Button Grid.Column="1" Click="DropdownButton_Click"
@@ -57,7 +57,7 @@
         <StackPanel Grid.Row="4" x:Name="LoginPanel" IsVisible="False" Margin="0,0,0,12">
             <TextBlock Text="Login" Foreground="{DynamicResource ForegroundBrush}"
                        FontSize="12" Margin="0,0,0,4"/>
-            <TextBox x:Name="LoginBox" FontSize="13" Height="32" Watermark="sa"
+            <TextBox x:Name="LoginBox" FontSize="13" Height="32" PlaceholderText="sa"
                      TextChanged="RequiredField_TextChanged"/>
         </StackPanel>
 
@@ -66,7 +66,7 @@
             <TextBlock Text="Password" Foreground="{DynamicResource ForegroundBrush}"
                        FontSize="12" Margin="0,0,0,4"/>
             <TextBox x:Name="PasswordBox" FontSize="13" Height="32"
-                     PasswordChar="&#x25CF;" Watermark="Password"
+                     PasswordChar="&#x25CF;" PlaceholderText="Password"
                      TextChanged="RequiredField_TextChanged"/>
         </StackPanel>
 
@@ -94,7 +94,7 @@
                 <TextBlock Text="Initial database (optional)"
                            Foreground="{DynamicResource ForegroundBrush}" FontSize="12"/>
                 <TextBox x:Name="DatabaseInputBox" FontSize="13" Height="32"
-                         Watermark="Leave empty to connect to master"
+                         PlaceholderText="Leave empty to connect to master"
                          ToolTip.Tip="Connects directly to this database instead of master. Useful for Azure SQL Database or Just-In-Time access where the login can't open master. It is pre-selected below once the database list loads."/>
             </StackPanel>
         </StackPanel>

src/PlanViewer.App/Dialogs/SettingsWindow.axaml.cs

@@ -375,7 +375,7 @@ private void EnsureIntegrationsLoaded()
 
 		/* The stored proxy password is deliberately not put into the TextBox. PasswordChar only
 		   masks the glyph — the cleartext still sits in the visual and accessibility trees. The
-		   watermark says it is saved, and an empty box at save time means "keep what is there". */
+		   placeholder says it is saved, and an empty box at save time means "keep what is there". */
 		var proxy = ProxySettings.Load();
 		_hasStoredProxyPassword = !string.IsNullOrEmpty(proxy.Password);
 		_proxyMode = proxy.Mode;
@@ -506,10 +506,10 @@ void OnProxyModeChanged(object? sender, RoutedEventArgs _)
 		return panel;
 	}
 
-	private static TextBox CreateProxyInput(string text, string watermark) => new()
+	private static TextBox CreateProxyInput(string text, string placeholder) => new()
 	{
 		Text = text,
-		Watermark = watermark,
+		PlaceholderText = placeholder,
 		FontSize = 13,
 		Height = 32,
 		Padding = new Thickness(6, 2)
@@ -582,7 +582,7 @@ private void ResetIntegrations(bool clearStoredPassword)
 
 		/* This is the only way to delete a stored proxy password, because an empty password box
 		   always means "keep what is there" — otherwise anyone who edited the proxy address would
-		   have to retype the password. Clearing the flag too stops the watermark claiming a
+		   have to retype the password. Clearing the flag too stops the placeholder claiming a
 		   password is saved after the reset has taken it away. */
 		_clearStoredProxyPassword = _hasStoredProxyPassword;
 		_hasStoredProxyPassword = false;

src/PlanViewer.App/Helpers/DataGridBehaviors.cs

@@ -35,7 +35,7 @@ public static void AttachCopyGuard(DataGrid grid, Func<object, string?> formatRo
         {
             // Mirror the built-in copy's exact gate: platform command modifier
             // (Ctrl; Cmd on macOS), no Shift, no Alt.
-            var commandModifiers = TopLevel.GetTopLevel(grid)?.PlatformSettings?.HotkeyConfiguration.CommandModifiers
+            var commandModifiers = grid.GetPlatformSettings()?.HotkeyConfiguration.CommandModifiers
                 ?? KeyModifiers.Control;
             if (e.Key is not (Key.C or Key.Insert)
                 || !e.KeyModifiers.HasFlag(commandModifiers)

src/PlanViewer.App/Helpers/ProgressBarBehaviors.cs

@@ -0,0 +1,65 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Threading;
+
+namespace PlanViewer.App.Helpers;
+
+/// <summary>
+/// Restarts an indeterminate <see cref="ProgressBar"/>'s animation when it re-enters the
+/// visual tree.
+///
+/// <para>Avalonia 12 completes a style-applied animation when its visual detaches — a handler
+/// its changelog does not document, sitting outside the <c>PlaybackBehavior</c> pause guard —
+/// and re-attaching re-applies the style without resurrecting the finished animation. Switch
+/// tabs while a fetch is running and its loading bar comes back frozen mid-track, indistinguishable
+/// from a hang. Avalonia 11 had no detach handling at all, so the bar just kept animating; this
+/// restores that behavior at the seven bars whose hosts can detach mid-run.</para>
+///
+/// <para>The restart works by deactivating and reactivating the <c>:indeterminate</c> style:
+/// flipping <see cref="ProgressBar.IsIndeterminate"/> off and, one dispatcher hop later, back on
+/// makes the style system spawn a fresh animation instance. The hop is load-bearing — both flips
+/// in the same pass coalesce into no style change at all.</para>
+///
+/// <para>Verified against the live symptom, not assumed: before this, five window captures
+/// spanning a full animation cycle after a tab round-trip were pixel-identical in the bar's
+/// region; with it, the sweep resumes. The headless suite cannot see any of this (animations
+/// need frames), which is why the proof lives in a driven run rather than a test.</para>
+/// </summary>
+public static class ProgressBarBehaviors
+{
+    /// <summary>
+    /// Set true on any indeterminate bar whose host can detach while it runs — tab content,
+    /// overlays inside documents, detachable panels.
+    /// </summary>
+    public static readonly AttachedProperty<bool> RestartOnReattachProperty =
+        AvaloniaProperty.RegisterAttached<ProgressBar, bool>(
+            "RestartOnReattach", typeof(ProgressBarBehaviors));
+
+    public static void SetRestartOnReattach(ProgressBar bar, bool value) =>
+        bar.SetValue(RestartOnReattachProperty, value);
+
+    public static bool GetRestartOnReattach(ProgressBar bar) =>
+        bar.GetValue(RestartOnReattachProperty);
+
+    static ProgressBarBehaviors()
+    {
+        RestartOnReattachProperty.Changed.AddClassHandler<ProgressBar>((bar, e) =>
+        {
+            if (e.NewValue is true)
+                bar.AttachedToVisualTree += Restart;
+            else
+                bar.AttachedToVisualTree -= Restart;
+        });
+    }
+
+    private static void Restart(object? sender, VisualTreeAttachmentEventArgs e)
+    {
+        /* An idle bar (Overview's LoadingBar between loads) has nothing to restart, and
+           flipping it would wrongly start one. */
+        if (sender is not ProgressBar bar || !bar.IsIndeterminate)
+            return;
+
+        bar.IsIndeterminate = false;
+        Dispatcher.UIThread.Post(() => bar.IsIndeterminate = true, DispatcherPriority.Loaded);
+    }
+}

src/PlanViewer.App/MainWindow.PlanViewer.cs

@@ -475,6 +475,8 @@ emailed around. Name the target so "which server was that?" is answered
             Height = 4,
             Margin = new Avalonia.Thickness(0, 0, 0, 12)
         };
+        // This loading tab detaches whenever the user switches top-level tabs mid-capture.
+        Helpers.ProgressBarBehaviors.SetRestartOnReattach(progressBar, true);
 
         var statusText = new TextBlock
         {

src/PlanViewer.App/MainWindow.axaml.cs

@@ -882,13 +882,8 @@ private void About_Click(object? sender, RoutedEventArgs e)
         about.ShowDialog(this);
     }
 
-#pragma warning disable CS0618 // Data/DataFormats.Files deprecated but IDataTransfer API differs
     private static readonly string[] _supportedExtensions = { ".sqlplan", ".xml", ".sql" };
 
-
-#pragma warning restore CS0618
-
-
     /// <summary>
     /// Re-decides whether Compare Plans is offered, for every Compare button in the window (#447).
     ///