.Net: Bug: OpenAIResponseAgent 'Unsupported response item: OpenAI.Responses.ReasoningResponseItem'

[dglover1]

Describe the bug
The preview OpenAIResponseAgent throws a System.NotImplementedException: 'Unsupported response item: OpenAI.Responses.ReasoningResponseItem' for reasoning responses (from o4-mini etc.). It is uncatchable since OpenAIResponseExtensions and the related classes are internal.

To Reproduce
Steps to reproduce the behavior:

1. Set up an OpenAIResponseAgent using an OpenAI reasoning model e.g. o4-mini
2. Invoke the agent (in my case with InvokeStreamingAsync())
3. Wait for the first reasoning response to be received
4. Error is thrown by the ToChatMessageContentItemCollection() extension method in OpenAIResponseExtensions.

Expected behavior
ToChatMessageContentItemCollection() should handle the ReasoningResponseItem and return a ChatMessageContentItemCollection containing ReasoningContent objects. (if this is not supported yet, it could at least accept the ReasoningResponseItem and do nothing/just log it - throwing an error renders the OpenAIResponseAgent unusable with reasoning models...) e.g. the following added at line 95 of OpenAIResponseExtensions.cs:

else if (item is ReasoningResponseItem reasoningResponseItem)
{
    var collection = new ChatMessageContentItemCollection();
    
    foreach (string part in reasoningResponseItem.SummaryTextParts)
    {
        collection.Add(new ReasoningContent(part));
    }
    return collection;
}

Platform

• Language: C#
• Source: NuGet package (Microsoft.SemanticKernel.Agents.OpenAI) version 1.57.0-preview
• AI model: OpenAI:o4-mini
• IDE: VS Code
• OS: Mac