Address AppType code review: robustness, trimming, cache, tests

Applies the actionable findings from the multi-model reviews of BlazorWebView.AppType:

- Failure latch: set _appTypeRendered only after a successful render so a render
  failure no longer permanently latches a blank host page; a reconnect retries.
- Symmetric setter: clearing AppType now restores the synthetic HostPage and resets
  the rendered state instead of leaving the view claiming a page it no longer serves.
- Unique mount ids: each non-HeadOutlet interactive root gets a unique element id
  (app, app-1, ...) so a host document with multiple interactive boundaries no longer
  emits duplicate #app ids that collide on a single querySelector target.
- Remove the dead MapAppType mapper entry + public method (MapHostPage/MapRootComponents
  already drive startup); drops it from the public API surface.
- Trimming: keep a narrowly-scoped IL2072 suppression with an accurate justification.
  AppType is set via XAML reflection so it cannot carry a DynamicallyAccessedMembers
  annotation (that produces IL2111/IL2114); the component type is preserved by the XAML
  compiler and the Razor SDK trimming roots.
- Manifest: correct the misleading 'readers complete synchronously' comment (Windows
  StorageFile is async), narrow the catch to IO/Json/NotImplemented/UnauthorizedAccess
  and log a corrupt manifest, and cache the immutable manifest for the process lifetime.
- Stable LastModified on the in-memory host page IFileInfo.
- MSBuild: warn when static web asset endpoints exist but zero fingerprinted entries are
  extracted (guards against a silent empty manifest), and guard the output directory.
- Add unit tests for the manifest parser and the file provider, including the
  null-host-page fall-through (silent blank page) path.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 2ca68fe1-bef6-46a6-a0fd-17b7654cef34

Author: mattleibow

src/BlazorWebView/src/Maui/BlazorWebView.cs

@@ -5,6 +5,7 @@
 using Microsoft.AspNetCore.Components.Web;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.FileProviders;
+using Microsoft.Extensions.Logging;
 using Microsoft.Maui;
 using Microsoft.Maui.Controls;
 
@@ -59,6 +60,7 @@ public BlazorWebView()
 
 		private Type? _appType;
 		private bool _appTypeRendered;
+		private bool _syntheticHostPageApplied;
 		private string? _renderedHostPageHtml;
 
 		/// <summary>
@@ -80,11 +82,30 @@ public Type? AppType
 			{
 				_appType = value;
 
-				// Provide a synthetic host page so the existing startup and relative-path logic flows
-				// unchanged; the rendered document is overlaid onto the file provider at this path.
-				if (value is not null && string.IsNullOrEmpty(HostPage))
+				if (value is not null)
 				{
-					HostPage = AppTypeHostPage;
+					// Provide a synthetic host page so the existing startup and relative-path logic
+					// flows unchanged; the rendered document is overlaid onto the file provider at this
+					// path. Only applied when the caller has not set an explicit HostPage.
+					if (string.IsNullOrEmpty(HostPage))
+					{
+						HostPage = AppTypeHostPage;
+						_syntheticHostPageApplied = true;
+					}
+				}
+				else
+				{
+					// Clearing AppType: undo the synthetic host page and reset the rendered state so the
+					// view does not keep claiming a host page it no longer serves (which would otherwise
+					// leave a blank web view).
+					if (_syntheticHostPageApplied)
+					{
+						HostPage = null;
+						_syntheticHostPageApplied = false;
+					}
+
+					_appTypeRendered = false;
+					_renderedHostPageHtml = null;
 				}
 			}
 		}
@@ -177,7 +198,8 @@ public virtual IFileProvider CreateFileProvider(string contentRootDir)
 			// and fingerprinted-route serving work. The manifest lives outside the web root and is read
 			// from the app package, so it is never served to the web view. Absent (or on platforms
 			// without app-package access), fingerprinting simply stays off.
-			var manifest = StaticWebAssetsManifest.TryLoad();
+			var logger = Handler?.MauiContext?.Services?.GetService<ILoggerFactory>()?.CreateLogger<BlazorWebView>();
+			var manifest = StaticWebAssetsManifest.TryLoad(logger);
 
 			// Render the host document once. This also collects any interactive components declared with
 			// a render mode and registers them so they attach to the live document, and resolves @Assets
@@ -188,17 +210,22 @@ public virtual IFileProvider CreateFileProvider(string contentRootDir)
 			return new BlazorWebViewFileProvider(platformFileProvider, hostPageRelativePath, _renderedHostPageHtml, manifest);
 		}
 
+		// IL2072: AppType flows into HybridHostPageRenderer.Render's [DynamicallyAccessedMembers(All)]
+		// parameter. AppType cannot itself be annotated: it is a public property set by XAML via
+		// reflection (AppType="{x:Type components:App}"), and a DynamicallyAccessedMembers requirement on
+		// a reflection-set property/parameter is not satisfiable by the trimmer (it produces IL2111/IL2114
+		// instead). The assigned component type is preserved regardless: a {x:Type} reference is rooted by
+		// the XAML compiler, and the interactive components it renders are rooted by the Razor SDK's
+		// trimming roots (@rendermode / routable assembly), so their members survive trimming.
 		[System.Diagnostics.CodeAnalysis.UnconditionalSuppressMessage("Trimming", "IL2072",
-			Justification = "Blazor components referenced by AppType are preserved by the Razor SDK trimming roots, consistent with RootComponent.ComponentType.")]
+			Justification = "AppType is set via XAML reflection so it cannot carry a DynamicallyAccessedMembers annotation; the component type is preserved by the XAML compiler ({x:Type}) and the Razor SDK trimming roots.")]
 		private void EnsureAppTypeRendered(ResourceAssetCollection? assets)
 		{
 			if (_appTypeRendered || AppType is null)
 			{
 				return;
 			}
 
-			_appTypeRendered = true;
-
 			var services = Handler?.MauiContext?.Services
 				?? throw new InvalidOperationException($"Cannot render {nameof(AppType)} because no service provider is available.");
 
@@ -213,6 +240,11 @@ private void EnsureAppTypeRendered(ResourceAssetCollection? assets)
 					ComponentType = registration.ComponentType,
 				});
 			}
+
+			// Only latch success after the render and registration complete. If rendering throws (an
+			// invalid AppType, a failing OnInitializedAsync, a missing service), the flag stays false so
+			// a later handler reconnect retries instead of permanently serving a blank host page.
+			_appTypeRendered = true;
 		}
 
 		/// <summary>

src/BlazorWebView/src/Maui/BlazorWebViewFileProvider.cs

@@ -78,18 +78,20 @@ private static string NormalizePath(string path) =>
 		private sealed class InMemoryFileInfo : IFileInfo
 		{
 			private readonly byte[] _contents;
+			private readonly DateTimeOffset _lastModified;
 
 			public InMemoryFileInfo(string name, byte[] contents)
 			{
 				Name = name;
 				_contents = contents;
+				_lastModified = DateTimeOffset.UtcNow;
 			}
 
 			public bool Exists => true;
 			public long Length => _contents.Length;
 			public string? PhysicalPath => null;
 			public string Name { get; }
-			public DateTimeOffset LastModified => DateTimeOffset.UtcNow;
+			public DateTimeOffset LastModified => _lastModified;
 			public bool IsDirectory => false;
 
 			public Stream CreateReadStream() => new MemoryStream(_contents, writable: false);

src/BlazorWebView/src/Maui/BlazorWebViewHandler.cs

@@ -30,7 +30,6 @@ public partial class BlazorWebViewHandler : IBlazorWebViewHandler
 		public static PropertyMapper<IBlazorWebView, BlazorWebViewHandler> BlazorWebViewMapper = new(ViewMapper)
 		{
 			[nameof(IBlazorWebView.HostPage)] = MapHostPage,
-			[nameof(IBlazorWebView.AppType)] = MapAppType,
 			[nameof(IBlazorWebView.RootComponents)] = MapRootComponents,
 #if WINDOWS
             [nameof(IView.FlowDirection)] = MapFlowDirection,
@@ -74,27 +73,6 @@ public static void MapHostPage(BlazorWebViewHandler handler, IBlazorWebView webV
 #endif
 		}
 
-		/// <summary>
-		/// Maps the <see cref="IBlazorWebView.AppType"/> property to the specified handler.
-		/// </summary>
-		/// <param name="handler">The <see cref="BlazorWebViewHandler"/>.</param>
-		/// <param name="webView">The <see cref="IBlazorWebView"/>.</param>
-		public static void MapAppType(BlazorWebViewHandler handler, IBlazorWebView webView)
-		{
-#if !(NETSTANDARD || !PLATFORM)
-			// Only views that opt into AppType need this mapper. When AppType is null the legacy
-			// HostPage startup path is left completely untouched (MapHostPage already handled it).
-			if (webView.AppType is null)
-			{
-				return;
-			}
-
-			// AppType provides a synthetic HostPage, so ensure the handler picks it up and attempts startup.
-			handler.HostPage = webView.HostPage;
-			handler.StartWebViewCoreIfPossible();
-#endif
-		}
-
 		/// <summary>
 		/// Maps the <see cref="IBlazorWebView.RootComponents"/> property to the specified handler.
 		/// </summary>

src/BlazorWebView/src/Maui/HybridHostPageRenderer.cs

@@ -35,11 +35,11 @@ namespace Microsoft.AspNetCore.Components.WebView.Maui
 	internal sealed class HybridHostPageRenderer : StaticHtmlRenderer
 	{
 		internal const string AppElementId = "app";
-		internal const string AppSelector = "#" + AppElementId;
 		internal const string HeadOutletSelector = "head::after";
 
 		private readonly List<HybridRootComponentRegistration> _registrations = new();
 		private readonly ResourceAssetCollection _assets;
+		private int _mountElementCount;
 
 		private HybridHostPageRenderer(IServiceProvider serviceProvider, ILoggerFactory loggerFactory, ResourceAssetCollection assets)
 			: base(serviceProvider, loggerFactory)
@@ -122,8 +122,13 @@ protected override IComponent ResolveComponentForRenderMode(
 				}
 
 				// Any other interactive root becomes a mount element that the live component attaches to.
-				_registrations.Add(new HybridRootComponentRegistration(AppSelector, componentType));
-				return new HybridMountPlaceholder(AppElementId);
+				// Each root gets a unique element id (app, app-1, app-2, ...) so a host document that
+				// declares more than one interactive boundary does not emit duplicate ids that collide
+				// on a single querySelector('#app') target.
+				var elementId = _mountElementCount == 0 ? AppElementId : $"{AppElementId}-{_mountElementCount}";
+				_mountElementCount++;
+				_registrations.Add(new HybridRootComponentRegistration("#" + elementId, componentType));
+				return new HybridMountPlaceholder(elementId);
 			}
 
 			return base.ResolveComponentForRenderMode(componentType, parentComponentId, componentActivator, renderMode);

src/BlazorWebView/src/Maui/PublicAPI/net-android/PublicAPI.Unshipped.txt

@@ -14,6 +14,5 @@ Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler.CreateFilePro
 Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler.TryDispatchAsync(System.Action<System.IServiceProvider!>! workItem) -> System.Threading.Tasks.Task<bool>!
 Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions
 override Microsoft.AspNetCore.Components.WebView.Maui.BlazorWebViewHandler.ConnectHandler(Android.Webkit.WebView! platformView) -> void
-static Microsoft.AspNetCore.Components.WebView.Maui.BlazorWebViewHandler.MapAppType(Microsoft.AspNetCore.Components.WebView.Maui.BlazorWebViewHandler! handler, Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebView! webView) -> void
 static Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions.UsePlatformHandler(this Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder! builder, System.Func<System.IServiceProvider!, Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler!>! factory) -> Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder!
 static Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions.UsePlatformHandler<THandler>(this Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder! builder) -> Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder!

src/BlazorWebView/src/Maui/PublicAPI/net-ios/PublicAPI.Unshipped.txt

@@ -13,6 +13,5 @@ Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler
 Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler.CreateFileProvider(string! contentRootDir) -> Microsoft.Extensions.FileProviders.IFileProvider!
 Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler.TryDispatchAsync(System.Action<System.IServiceProvider!>! workItem) -> System.Threading.Tasks.Task<bool>!
 Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions
-static Microsoft.AspNetCore.Components.WebView.Maui.BlazorWebViewHandler.MapAppType(Microsoft.AspNetCore.Components.WebView.Maui.BlazorWebViewHandler! handler, Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebView! webView) -> void
 static Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions.UsePlatformHandler(this Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder! builder, System.Func<System.IServiceProvider!, Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler!>! factory) -> Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder!
 static Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions.UsePlatformHandler<THandler>(this Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder! builder) -> Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder!

src/BlazorWebView/src/Maui/PublicAPI/net-maccatalyst/PublicAPI.Unshipped.txt

@@ -13,6 +13,5 @@ Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler
 Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler.CreateFileProvider(string! contentRootDir) -> Microsoft.Extensions.FileProviders.IFileProvider!
 Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler.TryDispatchAsync(System.Action<System.IServiceProvider!>! workItem) -> System.Threading.Tasks.Task<bool>!
 Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions
-static Microsoft.AspNetCore.Components.WebView.Maui.BlazorWebViewHandler.MapAppType(Microsoft.AspNetCore.Components.WebView.Maui.BlazorWebViewHandler! handler, Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebView! webView) -> void
 static Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions.UsePlatformHandler(this Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder! builder, System.Func<System.IServiceProvider!, Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler!>! factory) -> Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder!
 static Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions.UsePlatformHandler<THandler>(this Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder! builder) -> Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder!

src/BlazorWebView/src/Maui/PublicAPI/net-tizen/PublicAPI.Unshipped.txt

@@ -13,6 +13,5 @@ Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler
 Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler.CreateFileProvider(string! contentRootDir) -> Microsoft.Extensions.FileProviders.IFileProvider!
 Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler.TryDispatchAsync(System.Action<System.IServiceProvider!>! workItem) -> System.Threading.Tasks.Task<bool>!
 Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions
-static Microsoft.AspNetCore.Components.WebView.Maui.BlazorWebViewHandler.MapAppType(Microsoft.AspNetCore.Components.WebView.Maui.BlazorWebViewHandler! handler, Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebView! webView) -> void
 static Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions.UsePlatformHandler(this Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder! builder, System.Func<System.IServiceProvider!, Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler!>! factory) -> Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder!
 static Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions.UsePlatformHandler<THandler>(this Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder! builder) -> Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder!

src/BlazorWebView/src/Maui/PublicAPI/net-windows/PublicAPI.Unshipped.txt

@@ -13,6 +13,5 @@ Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler
 Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler.CreateFileProvider(string! contentRootDir) -> Microsoft.Extensions.FileProviders.IFileProvider!
 Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler.TryDispatchAsync(System.Action<System.IServiceProvider!>! workItem) -> System.Threading.Tasks.Task<bool>!
 Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions
-static Microsoft.AspNetCore.Components.WebView.Maui.BlazorWebViewHandler.MapAppType(Microsoft.AspNetCore.Components.WebView.Maui.BlazorWebViewHandler! handler, Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebView! webView) -> void
 static Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions.UsePlatformHandler(this Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder! builder, System.Func<System.IServiceProvider!, Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler!>! factory) -> Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder!
 static Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions.UsePlatformHandler<THandler>(this Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder! builder) -> Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder!

src/BlazorWebView/src/Maui/PublicAPI/net/PublicAPI.Unshipped.txt

@@ -13,6 +13,5 @@ Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler
 Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler.CreateFileProvider(string! contentRootDir) -> Microsoft.Extensions.FileProviders.IFileProvider!
 Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler.TryDispatchAsync(System.Action<System.IServiceProvider!>! workItem) -> System.Threading.Tasks.Task<bool>!
 Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions
-static Microsoft.AspNetCore.Components.WebView.Maui.BlazorWebViewHandler.MapAppType(Microsoft.AspNetCore.Components.WebView.Maui.BlazorWebViewHandler! handler, Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebView! webView) -> void
 static Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions.UsePlatformHandler(this Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder! builder, System.Func<System.IServiceProvider!, Microsoft.AspNetCore.Components.WebView.Maui.IBlazorWebViewHandler!>! factory) -> Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder!
 static Microsoft.AspNetCore.Components.WebView.Maui.MauiBlazorWebViewBuilderExtensions.UsePlatformHandler<THandler>(this Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder! builder) -> Microsoft.AspNetCore.Components.WebView.Maui.IMauiBlazorWebViewBuilder!