Complete implementation with reference support and test fixes

Co-authored-by: baywet <7905502+baywet@users.noreply.github.com>

Author: Copilot

src/Microsoft.OpenApi/Models/References/OpenApiResponseReference.cs

@@ -8,7 +8,7 @@ namespace Microsoft.OpenApi
     /// <summary>
     /// Response Object Reference.
     /// </summary>
-    public class OpenApiResponseReference : BaseOpenApiReferenceHolder<OpenApiResponse, IOpenApiResponse, OpenApiReferenceWithDescription>, IOpenApiResponse
+    public class OpenApiResponseReference : BaseOpenApiReferenceHolder<OpenApiResponse, IOpenApiResponse, OpenApiReferenceWithDescription>, IOpenApiResponse, IOpenApiSummarizedElement
     {
         /// <summary>
         /// Constructor initializing the reference object.
@@ -32,6 +32,13 @@ private OpenApiResponseReference(OpenApiResponseReference openApiResponseReferen
 
         }
 
+        /// <inheritdoc/>
+        public string? Summary 
+        { 
+            get => (Target as IOpenApiSummarizedElement)?.Summary; 
+            set { if (Target is IOpenApiSummarizedElement summarizedTarget) summarizedTarget.Summary = value; }
+        }
+
         /// <inheritdoc/>
         public string? Description
         {

test/Microsoft.OpenApi.Readers.Tests/ReferenceService/TryLoadReferenceV2Tests.cs

@@ -67,6 +67,7 @@ public async Task LoadResponseReference()
             Assert.Equivalent(
                 new OpenApiResponse
                 {
+                    Summary = null,
                     Description = "Entity not found.",
                     Content = new Dictionary<string, OpenApiMediaType>()
                     {