.NET: [Bug]: Function call and tool result messages are not stored in the session when using ChatReducer

[marcominerva]

Description

Consider the following code:

#!/usr/bin/env dotnet

#:sdk Microsoft.NET.Sdk

#:property OutputType=Exe
#:property TargetFramework=net10.0
#:property ImplicitUsings=enable
#:property Nullable=enable
#:property NoWarn=$(NoWarn);MEAI001
#:property PublishAot=false

#:package Azure.AI.OpenAI@2.1.0
#:package Azure.Identity@1.18.0
#:package Microsoft.Agents.AI.OpenAI@1.0.0-rc3

using System.ComponentModel;
using Azure.AI.OpenAI;
using Azure.Identity;
using Microsoft.Agents.AI;
using Microsoft.Extensions.AI;
using OpenAI.Chat;

var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4.1";

[Description("Get the weather for a given location.")]
static string GetWeather([Description("The location to get the weather for.")] string location)
    => $"The weather in {location} is cloudy with a high of 15°C.";

AIAgent agent = new AzureOpenAIClient(
    new Uri(endpoint),
    new DefaultAzureCredential())
    .GetChatClient(deploymentName).AsIChatClient()
    .AsAIAgent(new ChatClientAgentOptions
    {
        Name = "Assistant",
        //ChatHistoryProvider = new InMemoryChatHistoryProvider(new()
        //{
        //    ChatReducer = new MessageCountingChatReducer(20),
        //    ReducerTriggerEvent = InMemoryChatHistoryProviderOptions.ChatReducerTriggerEvent.AfterMessageAdded,
        //}),
        ChatOptions = new ChatOptions
        {
            Tools = [AIFunctionFactory.Create(GetWeather)]
        }
    });

var session = await agent.CreateSessionAsync();
var response = await agent.RunAsync("What is the weather like in Taggia?", session);
Console.WriteLine(response);

session.TryGetInMemoryChatHistory(out var messages);
Console.WriteLine($"Messages in session: {messages.Count}");

In particular, the setting of ChatHistoryProvider has been commented out. With this configuration, after calling RunAsync, I have 4 messages in the session:

{
   "messages":[
      {
         "role":"user",
         "contents":[
            {
               "$type":"text",
               "text":"What is the weather like in Taggia?"
            }
         ]
      },
      {
         "authorName":"Assistant",
         "createdAt":"2026-03-05T09:14:51+00:00",
         "role":"assistant",
         "contents":[
            {
               "$type":"functionCall",
               "callId":"call_19muVFBQeEth4xsPu3OAckUP",
               "name":"_Main_g_GetWeather_0_0",
               "arguments":{
                  "location":"Taggia"
               },
               "informationalOnly":true
            }
         ],
         "messageId":"chatcmpl-DFz59TbFUrm2bR3ZeRogTiO4W0vpb"
      },
      {
         "authorName":"Assistant",
         "role":"tool",
         "contents":[
            {
               "$type":"functionResult",
               "callId":"call_19muVFBQeEth4xsPu3OAckUP",
               "result":"The weather in Taggia is cloudy with a high of 15°C."
            }
         ]
      },
      {
         "authorName":"Assistant",
         "createdAt":"2026-03-05T09:14:52+00:00",
         "role":"assistant",
         "contents":[
            {
               "$type":"text",
               "text":"The weather in Taggia is currently cloudy with a high temperature of 15°C."
            }
         ],
         "messageId":"chatcmpl-DFz5A3EVZ0egQlwhVFv11oHYgqnXP"
      }
   ]
}

However, if I uncomment the setting of ChatHistoryProvider to use a ChatReducer, when I call RunAsync, I get only 2 messages:

{
   "messages":[
      {
         "role":"user",
         "contents":[
            {
               "$type":"text",
               "text":"What is the weather like in Taggia?"
            }
         ]
      },
      {
         "authorName":"Assistant",
         "createdAt":"2026-03-05T09:16:15+00:00",
         "role":"assistant",
         "contents":[
            {
               "$type":"text",
               "text":"The weather in Taggia is currently cloudy, with a high temperature of 15°C."
            }
         ],
         "messageId":"chatcmpl-DFz6VO7mqr1FNCQLTgJpYROGGolJo"
      }
   ]
}

Function call and Function result messages aren't present in the session. I have also tried to explicitly set StorageInputRequestMessageFilter and StorageInputResponseMessageFilter properties:

ChatHistoryProvider = new InMemoryChatHistoryProvider(new()
{
    ChatReducer = new MessageCountingChatReducer(20),
    ReducerTriggerEvent = InMemoryChatHistoryProviderOptions.ChatReducerTriggerEvent.AfterMessageAdded,
    StorageInputRequestMessageFilter = messages => messages,
    StorageInputResponseMessageFilter = messages => messages,
}),

In this case, I see that messages collection in StorageInputResponseMessageFilter effectively contains all the response messages, included the ones from the tool call. However, they are not persisted in the session.

Package Versions

Microsoft.Agents.AI.OpenAI: 1.0.0-rc3

.NET Version

.NET 10.0.3