diff --git a/.opencode/commands/issue.md b/.opencode/commands/issue.md
index ffdb70a0..a1d47deb 100644
--- a/.opencode/commands/issue.md
+++ b/.opencode/commands/issue.md
@@ -128,8 +128,9 @@ If that value is blank, stop and ask the user for an issue number before doing a
     - For library/test changes (`src/**`, `tests/**`), trigger `build-library.yml`.
     - For sample changes (`samples/**`), trigger `build-samples.yml`.
     - For template changes (`templates/**`), trigger `build-template.yml`.
+    - For docs changes (`docs/**`, `mkdocs.yml`, `mkdocs.shared.yml`, `mkdocs.production.yml`), trigger `build-docs.yml`.
 
-    Do **not** dispatch `build-docs.yml`. Its `deploy` job has no branch guard, so any `workflow_dispatch` — including from a feature branch — publishes straight to the live GitHub Pages site. 
+    `build-docs.yml`'s `deploy` job only runs for a `release` event, or for `workflow_dispatch` when `github.ref` starts with `refs/tags/`. Dispatching it with `--ref issues/$1` (a branch ref, not a tag) only runs its `build`/`validate` jobs — it is safe to dispatch from a feature branch and will never publish to the live GitHub Pages site. Do not pass a tag ref to `--ref` when dispatching `build-docs.yml` for pre-PR validation.
 
     If none of the changed paths match any of the above, state that no CI workflow applies and continue with local test results only.
 
diff --git a/samples/todoapp/TodoApp.Avalonia/Directory.Build.props b/samples/todoapp/TodoApp.Avalonia/Directory.Build.props
index 5732b26f..3c58333f 100644
--- a/samples/todoapp/TodoApp.Avalonia/Directory.Build.props
+++ b/samples/todoapp/TodoApp.Avalonia/Directory.Build.props
@@ -2,8 +2,9 @@
   <PropertyGroup>
     <Nullable>enable</Nullable>
     <!-- Keep in sync across all Avalonia.* PackageReferences in this sample tree. -->
-    <!-- Bumped to resolve NU1903 (GHSA-xrw6-gwf8-vvr9 / CVE-2026-39959) for Tmds.DBus.Protocol,
-         pulled in transitively via Avalonia.FreeDesktop -> Avalonia.Desktop. See #499. -->
-    <AvaloniaVersion>11.3.18</AvaloniaVersion>
+    <!-- Major-version bump from 11.3.18 to the 12.x line (12.1.0, the latest release as of this
+         writing) for general currency ahead of 11.x reaching end-of-support. See
+         https://docs.avaloniaui.net/docs/avalonia12-breaking-changes and #507. -->
+    <AvaloniaVersion>12.1.0</AvaloniaVersion>
   </PropertyGroup>
 </Project>
diff --git a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Android/Application.cs b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Android/Application.cs
new file mode 100644
index 00000000..3b70f4da
--- /dev/null
+++ b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Android/Application.cs
@@ -0,0 +1,23 @@
+using Android.App;
+using Android.Runtime;
+using Avalonia;
+using Avalonia.Android;
+
+namespace TodoApp.Avalonia.Android;
+
+// Avalonia 12 changed Android app initialization so that CreateAppBuilder()/CustomizeAppBuilder()
+// are handled by an AvaloniaAndroidApplication<TApp> subclass instead of AvaloniaMainActivity<TApp>.
+// See https://docs.avaloniaui.net/docs/avalonia12-breaking-changes#android.
+[Application]
+public class Application : AvaloniaAndroidApplication<App>
+{
+    protected Application(nint javaReference, JniHandleOwnership transfer) : base(javaReference, transfer)
+    {
+    }
+
+    protected override AppBuilder CustomizeAppBuilder(AppBuilder builder)
+    {
+        return base.CustomizeAppBuilder(builder)
+            .WithInterFont();
+    }
+}
diff --git a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Android/MainActivity.cs b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Android/MainActivity.cs
index 5ad26437..d2cb4908 100644
--- a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Android/MainActivity.cs
+++ b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Android/MainActivity.cs
@@ -1,6 +1,5 @@
 using Android.App;
 using Android.Content.PM;
-using Avalonia;
 using Avalonia.Android;
 
 namespace TodoApp.Avalonia.Android;
@@ -11,11 +10,6 @@ namespace TodoApp.Avalonia.Android;
     Icon = "@drawable/icon",
     MainLauncher = true,
     ConfigurationChanges = ConfigChanges.Orientation | ConfigChanges.ScreenSize | ConfigChanges.UiMode)]
-public class MainActivity : AvaloniaMainActivity<App>
+public class MainActivity : AvaloniaMainActivity
 {
-    protected override AppBuilder CustomizeAppBuilder(AppBuilder builder)
-    {
-        return base.CustomizeAppBuilder(builder)
-            .WithInterFont();
-    }
 }
\ No newline at end of file
diff --git a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Android/Properties/AndroidManifest.xml b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Android/Properties/AndroidManifest.xml
index 7d86d689..b7a8b08c 100644
--- a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Android/Properties/AndroidManifest.xml
+++ b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Android/Properties/AndroidManifest.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android" android:installLocation="auto">
 	<uses-permission android:name="android.permission.INTERNET" />
-	<application android:label="TodoApp.Avalonia" android:icon="@drawable/Icon" />
+	<application android:name=".Application" android:label="TodoApp.Avalonia" android:icon="@drawable/Icon" />
 </manifest>
diff --git a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Android/TodoApp.Avalonia.Android.csproj b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Android/TodoApp.Avalonia.Android.csproj
index 10129929..41f42f7f 100644
--- a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Android/TodoApp.Avalonia.Android.csproj
+++ b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Android/TodoApp.Avalonia.Android.csproj
@@ -15,9 +15,9 @@
           `dotnet build` (not just `dotnet publish`) by SDK default. This CI pipeline only ever runs
           `dotnet build` (see build-samples-todoapp-avalonia.yml) - it never publishes with
           PublishTrimmed, so no actual IL trimming/linking happens here; the analyzer is purely
-          diagnostic noise on framework APIs (Avalonia's BindingPlugins.DataValidators, EF Core's
-          DbContext(DbContextOptions) ctor) that their own maintainers have marked
-          [RequiresUnreferencedCode]. Setting this also sets EnableTrimAnalyzer=false (see
+          diagnostic noise on framework APIs (e.g. EF Core's DbContext(DbContextOptions) ctor)
+          that their own maintainers have marked [RequiresUnreferencedCode]. Setting this also
+          sets EnableTrimAnalyzer=false (see
           Microsoft.NET.ILLink.targets), which disables the analyzer pass itself, not just its
           warning output. See https://github.com/CommunityToolkit/Datasync/issues/521.
         -->
diff --git a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Desktop/TodoApp.Avalonia.Desktop.csproj b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Desktop/TodoApp.Avalonia.Desktop.csproj
index 719c5fbd..a5ed319a 100644
--- a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Desktop/TodoApp.Avalonia.Desktop.csproj
+++ b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.Desktop/TodoApp.Avalonia.Desktop.csproj
@@ -14,8 +14,6 @@
 
     <ItemGroup>
         <PackageReference Include="Avalonia.Desktop" Version="$(AvaloniaVersion)" />
-        <!--Condition below is needed to remove Avalonia.Diagnostics package from build output in Release configuration.-->
-        <PackageReference Condition="'$(Configuration)' == 'Debug'" Include="Avalonia.Diagnostics" Version="$(AvaloniaVersion)" />
     </ItemGroup>
 
     <ItemGroup>
diff --git a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.iOS/TodoApp.Avalonia.iOS.csproj b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.iOS/TodoApp.Avalonia.iOS.csproj
index 24c2d933..94f5ae7d 100644
--- a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.iOS/TodoApp.Avalonia.iOS.csproj
+++ b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia.iOS/TodoApp.Avalonia.iOS.csproj
@@ -10,9 +10,9 @@
           because iOS app projects are marked trimmable by the SDK by default. This CI pipeline only
           ever runs `dotnet build` (see build-samples-todoapp-avalonia.yml) - it never publishes with
           PublishTrimmed, so no actual IL trimming/linking happens here; the analyzer is purely
-          diagnostic noise on framework APIs (Avalonia's BindingPlugins.DataValidators, EF Core's
-          DbContext(DbContextOptions) ctor) that their own maintainers have marked
-          [RequiresUnreferencedCode]. Setting this also sets EnableTrimAnalyzer=false (see
+          diagnostic noise on framework APIs (e.g. EF Core's DbContext(DbContextOptions) ctor)
+          that their own maintainers have marked [RequiresUnreferencedCode]. Setting this also
+          sets EnableTrimAnalyzer=false (see
           Microsoft.NET.ILLink.targets), which disables the analyzer pass itself, not just its
           warning output. See https://github.com/CommunityToolkit/Datasync/issues/521.
         -->
diff --git a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia/App.axaml.cs b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia/App.axaml.cs
index b3444e8d..c9f33c42 100644
--- a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia/App.axaml.cs
+++ b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia/App.axaml.cs
@@ -2,8 +2,6 @@
 using System.IO;
 using Avalonia;
 using Avalonia.Controls.ApplicationLifetimes;
-using Avalonia.Data.Core;
-using Avalonia.Data.Core.Plugins;
 using Avalonia.Markup.Xaml;
 using Avalonia.Threading;
 using Microsoft.Data.Sqlite;
@@ -52,16 +50,19 @@ public override void Initialize()
     /// <inheritdoc />
     public override void OnFrameworkInitializationCompleted()
     {
-        // Line below is needed to remove Avalonia data validation.
-        // Without this line you will get duplicate validations from both Avalonia and CT
-        BindingPlugins.DataValidators.RemoveAt(0);
-
         if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
         {
             desktop.MainWindow = new MainWindow { DataContext = GetRequiredService<TodoListViewModel>() };
         }
+        else if (ApplicationLifetime is IActivityApplicationLifetime activityLifetime)
+        {
+            // Android now uses IActivityApplicationLifetime instead of ISingleViewApplicationLifetime.
+            // See https://docs.avaloniaui.net/docs/avalonia12-breaking-changes#android.
+            activityLifetime.MainViewFactory = () => new MainView { DataContext = GetRequiredService<TodoListViewModel>() };
+        }
         else if (ApplicationLifetime is ISingleViewApplicationLifetime singleViewPlatform)
         {
+            // ISingleViewApplicationLifetime is still used by iOS, browser, and embedded Linux platforms.
             singleViewPlatform.MainView = new MainView { DataContext = GetRequiredService<TodoListViewModel>() };
         }
         
diff --git a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia/TodoApp.Avalonia.csproj b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia/TodoApp.Avalonia.csproj
index 93253b0e..3610583d 100644
--- a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia/TodoApp.Avalonia.csproj
+++ b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia/TodoApp.Avalonia.csproj
@@ -14,8 +14,6 @@
         <PackageReference Include="Avalonia" Version="$(AvaloniaVersion)" />
         <PackageReference Include="Avalonia.Themes.Fluent" Version="$(AvaloniaVersion)" />
         <PackageReference Include="Avalonia.Fonts.Inter" Version="$(AvaloniaVersion)" />
-        <!--Condition below is needed to remove Avalonia.Diagnostics package from build output in Release configuration.-->
-        <PackageReference Condition="'$(Configuration)' == 'Debug'" Include="Avalonia.Diagnostics" Version="$(AvaloniaVersion)" />
         <PackageReference Include="CommunityToolkit.Datasync.Client" Version="10.1.0" />
         <PackageReference Include="CommunityToolkit.Mvvm" Version="8.4.0" />
         <PackageReference Include="Microsoft.EntityFrameworkCore" Version="10.0.9" />
diff --git a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia/Views/MainView.axaml b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia/Views/MainView.axaml
index 86ffb4ce..65426cd3 100644
--- a/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia/Views/MainView.axaml
+++ b/samples/todoapp/TodoApp.Avalonia/TodoApp.Avalonia/Views/MainView.axaml
@@ -62,7 +62,7 @@
             <!--  This TextBox can be used to add new ToDoItems  -->
             <TextBox Grid.Row="2"
                      Text="{Binding NewItemContent}"
-                     Watermark="Add a new Item">
+                     PlaceholderText="Add a new Item">
                 <TextBox.InnerRightContent>
                     <Button Command="{Binding AddItemCommand}">
                         <PathIcon Data="{DynamicResource AcceptIconData}"