.Net: Bug: .Net Plugin return[Description] being totaly ignored?

[christianarg]

When I define un a plugin [return:Description("Some description")] as documented in the official documentation https://learn.microsoft.com/en-us/semantic-kernel/concepts/plugins/?pivots=programming-language-csharp#1-define-your-plugin the return description seems to be completely ignored.
After testing many times I've observed that the indications in [return:Description("...")] where completely ignored by the model. Since there is a large discussion about how to capture exact request that is made to azure open ai when using chat completion service here #1239 I made some code to inspect the exact request

public class DiagnosticListenerObserver : IObserver<DiagnosticListener>
{
    private readonly IObserver<KeyValuePair<string, object>> _innerObserver;

    public DiagnosticListenerObserver(IObserver<KeyValuePair<string, object>> innerObserver)
    {
        _innerObserver = innerObserver;
    }

    public void OnNext(DiagnosticListener diagnosticListener)
    {
        if (diagnosticListener.Name == "HttpHandlerDiagnosticListener")
        {
            diagnosticListener.Subscribe(_innerObserver);
        }
    }

    public void OnError(Exception error)
    {
        // Handle errors here, if needed
    }

    public void OnCompleted()
    {
        // Handle completion, if needed
    }
}

public class HttpClientLoggingListener : IObserver<KeyValuePair<string, object>>
{
    public void OnNext(KeyValuePair<string, object> value)
    {
        if (value.Key == "System.Net.Http.HttpRequestOut.Start")
        {
            var request = (HttpRequestMessage)value.Value.GetType().GetProperty("Request")?.GetValue(value.Value);

            //Console.WriteLine($"Request: {request?.Method} {request?.RequestUri}");
            if (request.Method == HttpMethod.Post && request.RequestUri.ToString().Contains("openai.azure.com"))
            {
                Console.WriteLine($"POST Request to {request.RequestUri}");

                if (request.Content != null)
                {
                    // Read the body as a string
                    var contentTask = request.Content.ReadAsStringAsync();
                    string requestBody = contentTask.Result;    // CUIDADO! sync-over-async

                    Console.WriteLine("Request Body:");
                    Console.WriteLine(requestBody);
                }
                else
                {
                    Console.WriteLine("Request Body: <No Content>");
                }
            }
        }
    }

    public void OnError(Exception error) { }

    public void OnCompleted() { }
}

Then having 2 simple plugins

public class M365InvoicePlugin
{
    [KernelFunction()]
    [Description("Obtener facturas de Microsoft 365")]
    public string GetM365Invoices()
    {
        return "Facturas de Microsoft 365. Septiembre 2024:80€";
    }
}


public class AzureInvoicePlugin
{
    [KernelFunction]
    
    [Description("Obtener facturas de Azure")]
    [return:Description("Facturas de Azure del último año")] 
    public string GetAzureInvoices()
    {
        return "Facturas de Azure. Octubre 2024:100€";
    }
}

When invoking with chatCompletions (many lines shortened for brevity, I assume you get the idea)

var listener = new HttpClientLoggingListener();
DiagnosticListener.AllListeners.Subscribe(new DiagnosticListenerObserver(listener));

var builder = Kernel.CreateBuilder();
builder.Plugins.AddFromType<M365InvoicePlugin>();
builder.Plugins.AddFromType<AzureInvoicePlugin>()
// configure azure openai etc
var kernel = builder.Build();
var chatCompletionService = kernel.GetRequiredService<IChatCompletionService>();
var chat = new ChatHistory();
chat.AddUserMessage("Hola");
var result = await chatCompletionService.GetChatMessageContentAsync(
     chat,
     executionSettings: openAIPromptExecutionSettings,
     kernel: kernel);

The captured post does NOT show the text in the [return:Description("")] in the tools parameter:

{
    "messages": [
        {
            "role": "user",
            "content": "hola"
        }
    ],
    "model": "CENSORED",
    "temperature": 0.1,
    "top_p": 1,
    "tools": [
        {
            "type": "function",
            "function": {
                "description": "Obtener facturas de Microsoft 365",
                "name": "M365InvoicePlugin-GetM365Invoices",
                "parameters": {
                    "type": "object",
                    "required": [],
                    "properties": {}
                }
            }
        },
        {
            "type": "function",
            "function": {
                "description": "Obtener facturas de Azure",
                "name": "AzureInvoicePlugin-GetAzureInvoices",
                "parameters": {
                    "type": "object",
                    "required": [],
                    "properties": {}
                }
            }
        }
    ],
    "tool_choice": "auto"
}