Fix GenerateMarkerKey to handle string keys properly in Blazor SSR

src/Components/Endpoints/src/Rendering/SSRRenderModeBoundary.cs

@@ -212,7 +212,12 @@ private ComponentMarkerKey GenerateMarkerKey(int sequence, object? componentKey)
         var sequenceString = sequence.ToString(CultureInfo.InvariantCulture);
 
         var locationHash = $"{componentTypeNameHash}:{sequenceString}";
-        var formattedComponentKey = (componentKey as IFormattable)?.ToString(null, CultureInfo.InvariantCulture) ?? string.Empty;
+        var formattedComponentKey = componentKey switch
+        {
+            string str => str,
+            IFormattable formattable => formattable.ToString(null, CultureInfo.InvariantCulture),
+            _ => string.Empty
+        };
 
         return new()
         {

src/Components/Endpoints/test/SSRRenderModeBoundaryTest.cs

@@ -96,6 +96,33 @@ public Task SetParametersAsync(ParameterView parameters)
             => throw new NotImplementedException();
     }
 
+    public static IEnumerable<object[]> ComponentKeyTestData()
+    {
+        yield return new object[] { "test-string-key", "test-string-key" };
+        yield return new object[] { 42, "42" };
+        yield return new object[] { Guid.Parse("12345678-1234-1234-1234-123456789012"), "12345678-1234-1234-1234-123456789012" };
+        yield return new object[] { 123.45, "123.45" };
+        yield return new object[] { new DateTime(2023, 12, 25, 10, 30, 0, DateTimeKind.Utc), "12/25/2023 10:30:00" };
+        yield return new object[] { null, string.Empty };
+        yield return new object[] { new object(), string.Empty };
+    }
+
+    [Theory]
+    [MemberData(nameof(ComponentKeyTestData))]
+    public void GetComponentMarkerKey_WorksWithVariousKeyTypes(object componentKey, string expectedFormattedKey)
+    {
+        // Arrange
+        var httpContext = new DefaultHttpContext();
+        var boundary = new SSRRenderModeBoundary(httpContext, typeof(TestComponent), new InteractiveServerRenderMode());
+
+        // Act
+        var markerKey = boundary.GetComponentMarkerKey(1, componentKey);
+
+        // Assert
+        Assert.Equal(expectedFormattedKey, markerKey.FormattedComponentKey);
+        Assert.NotEmpty(markerKey.LocationHash);
+    }
+
     class ServerRenderModeSubclass : InteractiveServerRenderMode { }
     class WebAssemblyRenderModeSubclass : InteractiveWebAssemblyRenderMode { }
     class AutoRenderModeSubclass : InteractiveAutoRenderMode { }