[Blazor][Fixes #13056] Renderer use-after-disposal tweaks

* Improves Renderer handling use after disposal.
* Ensures RemoteRenderer skips resuming the render queue after ACK if it was since disposed

src/Components/Components/src/Rendering/Renderer.cs

@@ -28,6 +28,7 @@ namespace Microsoft.AspNetCore.Components.Rendering
         private bool _isBatchInProgress;
         private ulong _lastEventHandlerId;
         private List<Task> _pendingTasks;
+        private bool _disposed;
 
         /// <summary>
         /// Allows the caller to handle exceptions from the SynchronizationContext when one is available.
@@ -403,6 +404,11 @@ namespace Microsoft.AspNetCore.Components.Rendering
         /// </summary>
         protected virtual void ProcessPendingRender()
         {
+            if (_disposed)
+            {
+                throw new ObjectDisposedException(nameof(Renderer), "Cannot process pending renders after the renderer has been disposed.");
+            }
+
             ProcessRenderQueue();
         }
 
@@ -696,6 +702,8 @@ namespace Microsoft.AspNetCore.Components.Rendering
         /// <param name="disposing"><see langword="true"/> if this method is being invoked by <see cref="IDisposable.Dispose"/>, otherwise <see langword="false"/>.</param>
         protected virtual void Dispose(bool disposing)
         {
+            _disposed = true;
+
             // It's important that we handle all exceptions here before reporting any of them.
             // This way we can dispose all components before an error handler kicks in.
             List<Exception> exceptions = null;
@@ -717,6 +725,7 @@ namespace Microsoft.AspNetCore.Components.Rendering
                 }
             }
 
+            _componentStateById.Clear(); // So we know they were all disposed
             _batchBuilder.Dispose();
 
             if (exceptions?.Count > 1)

src/Components/Components/test/RendererTest.cs

@@ -2552,7 +2552,7 @@ namespace Microsoft.AspNetCore.Components.Test
                 .ComponentId;
             var origEventHandlerId = renderer.Batches.Single()
                 .ReferenceFrames
-                .Where(f => f.FrameType == RenderTreeFrameType.Attribute && f.AttributeName == "onclick")
+                .Where(f => f.FrameType == RenderTreeFrameType.Attribute && f.AttributeName == "onmycustomevent")
                 .Single(f => f.AttributeEventHandlerId != 0)
                 .AttributeEventHandlerId;
 
@@ -3490,6 +3490,41 @@ namespace Microsoft.AspNetCore.Components.Test
             Assert.True(component.Disposed);
         }
 
+        [Fact]
+        public void DisposingRenderer_RejectsAttemptsToStartMoreRenderBatches()
+        {
+            // Arrange
+            var renderer = new TestRenderer();
+            renderer.Dispose();
+
+            // Act/Assert
+            var ex = Assert.Throws<ObjectDisposedException>(() => renderer.ProcessPendingRender());
+            Assert.Contains("Cannot process pending renders after the renderer has been disposed.", ex.Message);
+        }
+
+        [Fact]
+        public void WhenRendererIsDisposed_ComponentRenderRequestsAreSkipped()
+        {
+            // The important point of this is that user code in components may continue to call
+            // StateHasChanged (e.g., after an async task completion), and we don't want that to
+            // show up as an error. In general, components should skip rendering after disposal.
+            // This test shows that we don't add any new entries to the render queue after disposal.
+            // There's a different test showing that if the render queue entry was already added
+            // before a component got individually disposed, that render queue entry gets skipped.
+
+            // Arrange
+            var renderer = new TestRenderer();
+            var component = new DisposableComponent();
+            renderer.AssignRootComponentId(component);
+
+            // Act
+            renderer.Dispose();
+            component.TriggerRender();
+
+            // Assert: no exception, no batch produced
+            Assert.Empty(renderer.Batches);
+        }
+
         [Fact]
         public void DisposingRenderer_DisposesNestedComponents()
         {
@@ -3936,7 +3971,7 @@ namespace Microsoft.AspNetCore.Components.Test
                 => _renderHandle.Render(builder =>
                 {
                     builder.OpenElement(0, "my button");
-                    builder.AddAttribute(1, "my click handler", new Action<EventArgs>(eventArgs => OnClick(eventArgs)));
+                    builder.AddAttribute(1, "onmycustomevent", EventCallback.Factory.Create(this, eventArgs => OnClick(eventArgs)));
                     builder.CloseElement();
                 });
         }

src/Components/Server/src/Circuits/RemoteRenderer.cs

@@ -284,7 +284,15 @@ namespace Microsoft.AspNetCore.Components.Web.Rendering
                 // missing.
 
                 // We return the task in here, but the caller doesn't await it.
-                return Dispatcher.InvokeAsync(() => ProcessPendingRender());
+                return Dispatcher.InvokeAsync(() =>
+                {
+                    // Now we're on the sync context, check again whether we got disposed since this
+                    // work item was queued. If so there's nothing to do.
+                    if (!_disposing)
+                    {
+                        ProcessPendingRender();
+                    }
+                });
             }
         }
 

src/Components/Shared/test/TestRenderer.cs

@@ -125,5 +125,8 @@ namespace Microsoft.AspNetCore.Components.Test.Helpers
             OnUpdateDisplayComplete?.Invoke();
             return NextRenderResultTask;
         }
+
+        public new void ProcessPendingRender()
+            => base.ProcessPendingRender();
     }
 }