.NET: feat: Implement message filtering to exclude non-portable content typ… (#5410)

* feat: Implement message filtering to exclude non-portable content types before forwarding

Co-authored-by: Copilot <copilot@github.com>

* Added unit tests to cover forwarded message filtering within AI Agent executors

Co-authored-by: Copilot <copilot@github.com>

* Update dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/AIAgentHostExecutor.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/AIAgentHostExecutor.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/AIAgentHostExecutor.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* fix: Disable forwarding of incoming messages in AIAgentHostExecutor tests

Co-authored-by: Copilot <copilot@github.com>

---------

Co-authored-by: Copilot <copilot@github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Jacob Alber <jaalber@microsoft.com>

dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/AIAgentHostExecutor.cs

@@ -181,8 +181,16 @@ internal sealed class AIAgentHostExecutor : ChatProtocolExecutor
 
         AgentResponse response = await this.InvokeAgentAsync(filteredMessages, context, emitEvents, cancellationToken).ConfigureAwait(false);
 
-        await context.SendMessageAsync(response.Messages is List<ChatMessage> list ? list : response.Messages.ToList(), cancellationToken)
+        // Filter out server-side artifacts (reasoning tokens, web search calls, etc.)
-                     .ConfigureAwait(false);
+        // that are internal to this agent. Forwarding them to other agents in the workflow
+        // causes invalid request errors when the receiving agent uses the Responses API,
+        // because these item types are not valid as input items.
+        List<ChatMessage> forwardableMessages = FilterForwardableMessages(response.Messages).ToList();
+        if (forwardableMessages.Count > 0)
+        {
+            await context.SendMessageAsync(forwardableMessages, cancellationToken)
+                         .ConfigureAwait(false);
+        }
 
         // If we have no outstanding requests, we can yield a turn token back to the workflow.
         if (!this.HasOutstandingRequests)
@@ -241,4 +249,60 @@ internal sealed class AIAgentHostExecutor : ChatProtocolExecutor
 
         return response;
     }
+
+    /// <summary>
+    /// Content types that represent meaningful conversational content portable across agents.
+    /// Messages containing only content types not in this set (e.g. reasoning tokens, web search
+    /// calls) are filtered out before forwarding, as they are output-only items that cause
+    /// schema validation errors when sent as input to the Responses API.
+    /// </summary>
+    private static readonly HashSet<Type> s_forwardableContentTypes =
+    [
+        typeof(TextContent),
+        typeof(DataContent),
+        typeof(UriContent),
+        typeof(FunctionCallContent),
+        typeof(FunctionResultContent),
+        typeof(ToolApprovalRequestContent),
+        typeof(ToolApprovalResponseContent),
+        typeof(HostedFileContent),
+        typeof(ErrorContent),
+    ];
+
+    /// <summary>
+    /// Filters response messages to only include those with portable conversational content,
+    /// and strips <see cref="ChatMessage.RawRepresentation"/> so that provider-specific output
+    /// items (e.g. <c>mcp_list_tools</c>, <c>reasoning</c>, <c>fabric_dataagent_preview_call</c>)
+    /// are not round-tripped by the M.E.AI library when the messages are sent to another agent.
+    /// </summary>
+    private static List<ChatMessage> FilterForwardableMessages(IList<ChatMessage> messages)
+    {
+        List<ChatMessage> result = [];
+
+        foreach (ChatMessage message in messages)
+        {
+            // Extract only the content items that are portable across agents.
+            List<AIContent> forwardableContents = message.Contents
+                .Where(c => s_forwardableContentTypes.Any(t => t.IsAssignableFrom(c.GetType())))
+                .ToList();
+
+            if (forwardableContents.Count == 0)
+            {
+                continue;
+            }
+
+            // Build a clean message without the provider-specific RawRepresentation,
+            // which would otherwise cause the M.E.AI library to round-trip the original
+            // output-only items (e.g. mcp_list_tools) as input to the next agent.
+            result.Add(new ChatMessage(message.Role, forwardableContents)
+            {
+                AuthorName = message.AuthorName,
+                MessageId = message.MessageId,
+                CreatedAt = message.CreatedAt,
+                AdditionalProperties = message.AdditionalProperties is null ? null : new(message.AdditionalProperties),
+            });
+        }
+
+        return result;
+    }
 }

dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/AIAgentHostExecutorTests.cs

@@ -3,8 +3,12 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Runtime.CompilerServices;
+using System.Text.Json;
+using System.Threading;
 using System.Threading.Tasks;
 using FluentAssertions;
+using Microsoft.Agents.AI.Workflows.Execution;
 using Microsoft.Agents.AI.Workflows.Specialized;
 using Microsoft.Extensions.AI;
 
@@ -217,4 +221,225 @@ public class AIAgentHostExecutorTests : AIAgentHostingExecutorTestsBase
 
         lastResponseEvent.Response.Text.Should().Be("Done");
     }
+
+    #region FilterForwardableMessages tests
+
+    /// <summary>
+    /// An agent that returns response messages containing a mix of content types,
+    /// including non-portable server-side artifacts like TextReasoningContent and
+    /// unrecognized AIContent subclasses (simulating mcp_list_tools, web_search_call, etc.).
+    /// </summary>
+    private sealed class MixedContentAgent(List<ChatMessage> responseMessages, string? id = null, string? name = null) : AIAgent
+    {
+        protected override string? IdCore => id;
+        public override string? Name => name;
+
+        protected override ValueTask<AgentSession> CreateSessionCoreAsync(CancellationToken cancellationToken = default)
+            => new(new MixedContentSession());
+
+        protected override ValueTask<AgentSession> DeserializeSessionCoreAsync(JsonElement serializedState, JsonSerializerOptions? jsonSerializerOptions = null, CancellationToken cancellationToken = default)
+            => new(new MixedContentSession());
+
+        protected override ValueTask<JsonElement> SerializeSessionCoreAsync(AgentSession session, JsonSerializerOptions? jsonSerializerOptions = null, CancellationToken cancellationToken = default)
+            => default;
+
+        protected override Task<AgentResponse> RunCoreAsync(IEnumerable<ChatMessage> messages, AgentSession? session = null, AgentRunOptions? options = null, CancellationToken cancellationToken = default)
+            => Task.FromResult(new AgentResponse(responseMessages.ToList()) { AgentId = this.Id });
+
+        protected override async IAsyncEnumerable<AgentResponseUpdate> RunCoreStreamingAsync(IEnumerable<ChatMessage> messages, AgentSession? session = null, AgentRunOptions? options = null, [EnumeratorCancellation] CancellationToken cancellationToken = default)
+        {
+            foreach (ChatMessage msg in responseMessages)
+            {
+                foreach (AIContent content in msg.Contents)
+                {
+                    yield return new AgentResponseUpdate
+                    {
+                        AgentId = this.Id,
+                        AuthorName = this.Name,
+                        MessageId = msg.MessageId ?? Guid.NewGuid().ToString("N"),
+                        ResponseId = Guid.NewGuid().ToString("N"),
+                        Contents = [content],
+                        Role = msg.Role,
+                    };
+                }
+            }
+        }
+
+        private sealed class MixedContentSession : AgentSession;
+    }
+
+    /// <summary>
+    /// A custom AIContent subclass that simulates an unrecognized provider-specific content type
+    /// (e.g. mcp_list_tools, web_search_call, fabric_dataagent_preview_call).
+    /// </summary>
+    private sealed class UnrecognizedServerContent(string description) : AIContent
+    {
+        public string Description => description;
+    }
+
+    [Fact]
+    public async Task Test_AgentHostExecutor_FiltersNonPortableContentFromForwardedMessagesAsync()
+    {
+        // Arrange: agent returns a mix of text, reasoning, and unrecognized content
+        var responseMessages = new List<ChatMessage>
+        {
+            new(ChatRole.Assistant, [new TextContent("Useful response text")])
+            {
+                AuthorName = TestAgentName,
+                MessageId = Guid.NewGuid().ToString("N"),
+                RawRepresentation = "original_response_item_1",
+            },
+            new(ChatRole.Assistant, [new TextReasoningContent("internal thinking")])
+            {
+                AuthorName = TestAgentName,
+                MessageId = Guid.NewGuid().ToString("N"),
+                RawRepresentation = "original_reasoning_item",
+            },
+            new(ChatRole.Assistant, [new UnrecognizedServerContent("mcp_list_tools payload")])
+            {
+                AuthorName = TestAgentName,
+                MessageId = Guid.NewGuid().ToString("N"),
+                RawRepresentation = "original_mcp_list_tools_item",
+            },
+        };
+
+        TestRunContext testContext = new();
+        MixedContentAgent agent = new(responseMessages, TestAgentId, TestAgentName);
+        AIAgentHostExecutor executor = new(agent, new());
+        testContext.ConfigureExecutor(executor);
+
+        // Act
+        await executor.TakeTurnAsync(new(), testContext.BindWorkflowContext(executor.Id));
+
+        // Assert: only the text message should be forwarded
+        testContext.QueuedMessages.Should().ContainKey(executor.Id);
+        List<MessageEnvelope> sentEnvelopes = testContext.QueuedMessages[executor.Id];
+
+        // Extract forwarded ChatMessage lists (filter out TurnToken)
+        List<ChatMessage> forwardedMessages = sentEnvelopes
+            .Select(e => e.Message)
+            .OfType<List<ChatMessage>>()
+            .SelectMany(list => list)
+            .ToList();
+
+        forwardedMessages.Should().HaveCount(1);
+        forwardedMessages[0].Role.Should().Be(ChatRole.Assistant);
+        forwardedMessages[0].Contents.Should().HaveCount(1);
+        forwardedMessages[0].Contents[0].Should().BeOfType<TextContent>();
+        ((TextContent)forwardedMessages[0].Contents[0]).Text.Should().Be("Useful response text");
+    }
+
+    [Fact]
+    public async Task Test_AgentHostExecutor_StripsRawRepresentationFromForwardedMessagesAsync()
+    {
+        // Arrange: agent returns a text message with RawRepresentation set
+        var responseMessages = new List<ChatMessage>
+        {
+            new(ChatRole.Assistant, [new TextContent("Response")])
+            {
+                AuthorName = TestAgentName,
+                MessageId = Guid.NewGuid().ToString("N"),
+                RawRepresentation = "provider_specific_response_item",
+            },
+        };
+
+        TestRunContext testContext = new();
+        MixedContentAgent agent = new(responseMessages, TestAgentId, TestAgentName);
+        AIAgentHostExecutor executor = new(agent, new());
+        testContext.ConfigureExecutor(executor);
+
+        // Act
+        await executor.TakeTurnAsync(new(), testContext.BindWorkflowContext(executor.Id));
+
+        // Assert: forwarded message should NOT have RawRepresentation
+        List<ChatMessage> forwardedMessages = testContext.QueuedMessages[executor.Id]
+            .Select(e => e.Message)
+            .OfType<List<ChatMessage>>()
+            .SelectMany(list => list)
+            .ToList();
+
+        forwardedMessages.Should().HaveCount(1);
+        forwardedMessages[0].RawRepresentation.Should().BeNull();
+        forwardedMessages[0].AuthorName.Should().Be(TestAgentName);
+    }
+
+    [Fact]
+    public async Task Test_AgentHostExecutor_PreservesForwardableContentInMixedMessagesAsync()
+    {
+        // Arrange: a single message with both text and reasoning content
+        var responseMessages = new List<ChatMessage>
+        {
+            new(ChatRole.Assistant,
+            [
+                new TextContent("Visible text"),
+                new TextReasoningContent("Hidden reasoning"),
+                new FunctionCallContent("call_1", "my_function", new Dictionary<string, object?> { ["arg"] = "val" }),
+            ])
+            {
+                AuthorName = TestAgentName,
+                MessageId = Guid.NewGuid().ToString("N"),
+                RawRepresentation = "original_mixed_item",
+            },
+        };
+
+        TestRunContext testContext = new();
+        MixedContentAgent agent = new(responseMessages, TestAgentId, TestAgentName);
+        AIAgentHostExecutor executor = new(agent, new());
+        testContext.ConfigureExecutor(executor);
+
+        // Act
+        await executor.TakeTurnAsync(new(), testContext.BindWorkflowContext(executor.Id));
+
+        // Assert: message should be forwarded with only the text and function call content
+        List<ChatMessage> forwardedMessages = testContext.QueuedMessages[executor.Id]
+            .Select(e => e.Message)
+            .OfType<List<ChatMessage>>()
+            .SelectMany(list => list)
+            .ToList();
+
+        forwardedMessages.Should().HaveCount(1);
+        ChatMessage forwarded = forwardedMessages[0];
+        forwarded.Contents.Should().HaveCount(2);
+        forwarded.Contents[0].Should().BeOfType<TextContent>();
+        forwarded.Contents[1].Should().BeOfType<FunctionCallContent>();
+        forwarded.RawRepresentation.Should().BeNull();
+    }
+
+    [Fact]
+    public async Task Test_AgentHostExecutor_DropsMessageWithOnlyNonPortableContentAsync()
+    {
+        // Arrange: agent returns only non-portable content
+        var responseMessages = new List<ChatMessage>
+        {
+            new(ChatRole.Assistant, [new TextReasoningContent("reasoning only")])
+            {
+                AuthorName = TestAgentName,
+                MessageId = Guid.NewGuid().ToString("N"),
+            },
+            new(ChatRole.Assistant, [new UnrecognizedServerContent("web_search_call")])
+            {
+                AuthorName = TestAgentName,
+                MessageId = Guid.NewGuid().ToString("N"),
+            },
+        };
+
+        TestRunContext testContext = new();
+        MixedContentAgent agent = new(responseMessages, TestAgentId, TestAgentName);
+        AIAgentHostExecutor executor = new(agent, new() { ForwardIncomingMessages = false });
+        testContext.ConfigureExecutor(executor);
+
+        // Act
+        await executor.TakeTurnAsync(new(), testContext.BindWorkflowContext(executor.Id));
+
+        // Assert: no ChatMessage lists should be forwarded (only TurnToken)
+        List<ChatMessage> forwardedMessages = testContext.QueuedMessages[executor.Id]
+            .Select(e => e.Message)
+            .OfType<List<ChatMessage>>()
+            .SelectMany(list => list)
+            .ToList();
+
+        forwardedMessages.Should().BeEmpty();
+    }
+
+    #endregion
 }