.Net: Fix OpenAiResponseAgent chat message images removed by SK (#13019)

### Motivation and Context

Closes #12888 

### Description

<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [ ] The code builds clean without any errors or warnings
- [ ] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [ ] All unit tests pass, and I have added new tests where possible
- [ ] I didn't break anyone 😄

Author: markwallace-microsoft

dotnet/samples/GettingStartedWithAgents/OpenAIResponse/Step01_OpenAIResponseAgent.cs

@@ -111,4 +111,33 @@ public async Task UseOpenAIResponseAgentWithThreadedConversationStreamingAsync()
             agentThread = await WriteAgentStreamMessageAsync(responseItems);
         }
     }
+
+    [Fact]
+    public async Task UseOpenAIResponseAgentWithImageContentAsync()
+    {
+        // Define the agent
+        OpenAIResponseAgent agent = new(this.Client)
+        {
+            Name = "ResponseAgent",
+            Instructions = "Provide a detailed description including the weather conditions.",
+        };
+
+        ICollection<ChatMessageContent> messages =
+        [
+            new ChatMessageContent(
+                AuthorRole.User,
+                items: [
+                    new TextContent("What is in this image?"),
+                    new ImageContent(new Uri("https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Gfp-wisconsin-madison-the-nature-boardwalk.jpg/2560px-Gfp-wisconsin-madison-the-nature-boardwalk.jpg"))
+                ]
+            ),
+        ];
+
+        // Invoke the agent and output the response
+        var responseItems = agent.InvokeAsync(messages);
+        await foreach (ChatMessageContent responseItem in responseItems)
+        {
+            WriteAgentChatMessage(responseItem);
+        }
+    }
 }

dotnet/src/Agents/OpenAI/Extensions/ChatContentMessageExtensions.cs

@@ -43,13 +43,14 @@ public static IEnumerable<ThreadInitializationMessage> ToThreadInitializationMes
     /// <returns>A <see cref="ResponseItem"/> instance.</returns>
     public static ResponseItem ToResponseItem(this ChatMessageContent message)
     {
-        string content = message.Content ?? string.Empty;
+        var items = message.Items;
+        IEnumerable<ResponseContentPart> contentParts = items.Select(item => item.ToResponseContentPart());
         return message.Role.Label.ToUpperInvariant() switch
         {
-            "SYSTEM" => ResponseItem.CreateSystemMessageItem(content),
-            "USER" => ResponseItem.CreateUserMessageItem(content),
-            "DEVELOPER" => ResponseItem.CreateDeveloperMessageItem(content),
-            "ASSISTANT" => ResponseItem.CreateAssistantMessageItem(content),
+            "SYSTEM" => ResponseItem.CreateSystemMessageItem(contentParts),
+            "USER" => ResponseItem.CreateUserMessageItem(contentParts),
+            "DEVELOPER" => ResponseItem.CreateDeveloperMessageItem(contentParts),
+            "ASSISTANT" => ResponseItem.CreateAssistantMessageItem(contentParts),
             _ => throw new NotSupportedException($"Unsupported role {message.Role.Label}. Only system, user, developer or assistant roles are allowed."),
         };
     }

dotnet/src/Agents/OpenAI/Extensions/KernelContentExtensions.cs

@@ -0,0 +1,52 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System;
+using OpenAI.Responses;
+
+namespace Microsoft.SemanticKernel.Agents.OpenAI;
+
+/// <summary>
+/// Extensons methods for <see cref="KernelContent"/>.
+/// </summary>
+internal static class KernelContentExtensions
+{
+    internal static ResponseContentPart ToResponseContentPart(this KernelContent content)
+    {
+        return content switch
+        {
+            TextContent textContent => textContent.ToResponseContentPart(),
+            ImageContent imageContent => imageContent.ToResponseContentPart(),
+            BinaryContent binaryContent => binaryContent.ToResponseContentPart(),
+            FileReferenceContent fileReferenceContent => fileReferenceContent.ToResponseContentPart(),
+            _ => throw new NotSupportedException($"Unsupported content type {content.GetType().Name}. Cannot convert to {nameof(ResponseContentPart)}.")
+        };
+    }
+
+    internal static ResponseContentPart ToResponseContentPart(this TextContent content)
+    {
+        return ResponseContentPart.CreateInputTextPart(content.Text);
+    }
+
+    internal static ResponseContentPart ToResponseContentPart(this ImageContent content)
+    {
+        return content.Uri is not null
+            ? ResponseContentPart.CreateInputImagePart(content.Uri)
+            : content.Data is not null
+            ? ResponseContentPart.CreateInputImagePart(new BinaryData(content.Data), content.MimeType)
+            : throw new NotSupportedException("ImageContent cannot be converted to ResponseContentPart. Only ImageContent with a uri or binary data is supported.");
+    }
+
+    internal static ResponseContentPart ToResponseContentPart(this BinaryContent content)
+    {
+        return content.Data is not null
+            ? ResponseContentPart.CreateInputFilePart(new BinaryData(content.Data), content.MimeType, Guid.NewGuid().ToString())
+            : throw new NotSupportedException("AudioContent cannot be converted to ResponseContentPart. Only AudioContent with binary data is supported.");
+    }
+
+    internal static ResponseContentPart ToResponseContentPart(this FileReferenceContent content)
+    {
+        return content.FileId is not null
+            ? ResponseContentPart.CreateInputFilePart(content.FileId)
+            : throw new NotSupportedException("FileReferenceContent cannot be converted to ResponseContentPart. Only FileReferenceContent with a file id is supported.");
+    }
+}

dotnet/src/Agents/UnitTests/OpenAI/Extensions/ChatContentMessageExtensionsTests.cs

@@ -0,0 +1,67 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System;
+using System.Linq;
+using Microsoft.SemanticKernel;
+using Microsoft.SemanticKernel.Agents.OpenAI;
+using Microsoft.SemanticKernel.ChatCompletion;
+using OpenAI.Responses;
+using Xunit;
+
+namespace SemanticKernel.Agents.UnitTests.OpenAI.Extensions;
+
+/// <summary>
+/// Unit tests for ChatContentMessageExtensions
+/// </summary>
+public class ChatContentMessageExtensionsTests
+{
+    [Theory]
+    [InlineData("User")]
+    [InlineData("Assistant")]
+    [InlineData("System")]
+    public void VerifyToResponseItemWithUserChatMessageContent(string roleLabel)
+    {
+        // Arrange
+        var role = new AuthorRole(roleLabel);
+        var content = new ChatMessageContent(
+                role,
+                items: [
+                    new TextContent("What is in this image?"),
+                    new ImageContent(new Uri("https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Gfp-wisconsin-madison-the-nature-boardwalk.jpg/2560px-Gfp-wisconsin-madison-the-nature-boardwalk.jpg")),
+                    new BinaryContent(new ReadOnlyMemory<byte>([0x52, 0x49, 0x46, 0x46, 0x24, 0x08, 0x00, 0x00, 0x57, 0x41, 0x56, 0x45]), "audio/wav"),
+                    new FileReferenceContent("file-abc123")
+                ]
+            );
+
+        // Act
+        var responseItem = content.ToResponseItem();
+
+        // Assert
+        Assert.NotNull(responseItem);
+        Assert.IsType<MessageResponseItem>(responseItem, exactMatch: false);
+        var messageResponseItem = responseItem as MessageResponseItem;
+        Assert.NotNull(messageResponseItem);
+        Assert.Equal(role.Label.ToUpperInvariant(), messageResponseItem.Role.ToString().ToUpperInvariant());
+        Assert.Equal(4, messageResponseItem.Content.Count);
+
+        // Validate TextContent conversion - should create InputText part
+        var textContent = messageResponseItem.Content.FirstOrDefault(p => p.Kind == ResponseContentPartKind.InputText);
+        Assert.NotNull(textContent);
+        //Assert.IsType<>(textContent);
+        Assert.Equal("What is in this image?", textContent.Text);
+
+        // Validate ImageContent conversion - should create InputImage part
+        var imageContent = messageResponseItem.Content.FirstOrDefault(p => p.Kind == ResponseContentPartKind.InputImage);
+        Assert.NotNull(imageContent);
+
+        // Validate BinaryContent conversion - should create InputFile part
+        var binaryContent = messageResponseItem.Content.FirstOrDefault(p => p.Kind == ResponseContentPartKind.InputFile && p.InputFileBytes is not null);
+        Assert.NotNull(binaryContent);
+        Assert.Equal("audio/wav", binaryContent.InputFileBytesMediaType);
+
+        // Validate FileReferenceContent conversion - should create InputImage part
+        var fileContent = messageResponseItem.Content.FirstOrDefault(p => p.Kind == ResponseContentPartKind.InputFile && p.InputFileId is not null);
+        Assert.NotNull(fileContent);
+        Assert.Equal("file-abc123", fileContent.InputFileId);
+    }
+}