Enable hot reloading for Blazor inside an iframe (#51006)

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: javiercn <[email protected]>

Author: Copilot

src/BuiltInTools/BrowserRefresh/BrowserRefreshMiddleware.cs

@@ -170,6 +170,8 @@ internal static bool IsBrowserDocumentRequest(HttpContext context)
             if (request.Headers.TryGetValue("Sec-Fetch-Dest", out var values) &&
                 !StringValues.IsNullOrEmpty(values) &&
                 !string.Equals(values[0], "document", StringComparison.OrdinalIgnoreCase) &&
+                !string.Equals(values[0], "frame", StringComparison.OrdinalIgnoreCase) &&
+                !string.Equals(values[0], "iframe", StringComparison.OrdinalIgnoreCase) &&
                 !IsProgressivelyEnhancedNavigation(context.Request))
             {
                 // See https://github.com/dotnet/aspnetcore/issues/37326.

test/Microsoft.AspNetCore.Watch.BrowserRefresh.Tests/BrowserRefreshMiddlewareTest.cs

@@ -183,6 +183,30 @@ public void IsBrowserDocumentRequest_ReturnsTrue_IfRequestFetchMetadataRequestHe
         [Theory]
         [InlineData("frame")]
         [InlineData("iframe")]
+        public void IsBrowserDocumentRequest_ReturnsTrue_IfRequestFetchMetadataRequestHeaderIsFrame(string headerValue)
+        {
+            // Arrange
+            var context = new DefaultHttpContext
+            {
+                Request =
+                {
+                    Method = "Post",
+                    Headers =
+                    {
+                        ["Accept"] = "text/html",
+                        ["Sec-Fetch-Dest"] = headerValue,
+                    },
+                },
+            };
+
+            // Act
+            var result = BrowserRefreshMiddleware.IsBrowserDocumentRequest(context);
+
+            // Assert
+            Assert.True(result);
+        }
+
+        [Theory]
         [InlineData("serviceworker")]
         public void IsBrowserDocumentRequest_ReturnsFalse_IfRequestFetchMetadataRequestHeaderIsNotDocument(string headerValue)
         {