.NET: feat: Refactor Handoff Orchestration and add HITL support (#5174)

* feat: Refactor Handoff Orchestration and add HITL support

* Change HandoffAgentExecutor to use factory-based instantiation
* Extract shared request collection logic in AIAgentUnservicedRequestsCollector
* Refactor HandoffAgentExecutor to use the "ContinueTurn" pattern as in AIAgentHostExecutor

* fix: Remove '$' from exception strings

dotnet/src/Microsoft.Agents.AI.Workflows/HandoffWorkflowBuilder.cs

@@ -8,6 +8,10 @@ using Microsoft.Agents.AI.Workflows.Specialized;
 using Microsoft.Extensions.AI;
 using Microsoft.Shared.Diagnostics;
 
+using ExecutorFactoryFunc = System.Func<Microsoft.Agents.AI.Workflows.ExecutorConfig<Microsoft.Agents.AI.Workflows.ExecutorOptions>,
+                                        string,
+                                        System.Threading.Tasks.ValueTask<Microsoft.Agents.AI.Workflows.Specialized.HandoffAgentExecutor>>;
+
 namespace Microsoft.Agents.AI.Workflows;
 
 internal static class DiagnosticConstants
@@ -233,6 +237,57 @@ public class HandoffWorkflowBuilderCore<TBuilder> where TBuilder : HandoffWorkfl
         return (TBuilder)this;
     }
 
+    private Dictionary<string, ExecutorBinding> CreateExecutorBindings(WorkflowBuilder builder)
+    {
+        HandoffAgentExecutorOptions options = new(this.HandoffInstructions,
+                                                  this._emitAgentResponseEvents,
+                                                  this._emitAgentResponseUpdateEvents,
+                                                  this._toolCallFilteringBehavior);
+
+        // There are two types of ids being used in this method, and it is critical that we are clear about
+        // which one we are using, and where.
+        // AgentId...: comes from AIAgent.Id, is often an unreadable machine identifier (e.g. a Guid), and is used to address
+        //             the handoffs
+        // ExecutorId: uses AIAgent.GetDescriptiveId() to use a friendlier name in telemetry, and is used for ExecutorBinding,
+        //             which are subsequently used in building the workflow
+
+        // The outgoing dictionary maps from AgentId => ExecutorBinding
+        return this._allAgents.ToDictionary(keySelector: a => a.Id, elementSelector: CreateFactoryBinding);
+
+        ExecutorBinding CreateFactoryBinding(AIAgent agent)
+        {
+            if (!this._targets.TryGetValue(agent, out HashSet<HandoffTarget>? handoffs))
+            {
+                handoffs = new();
+            }
+
+            // Use the ExecutorId as the placeholder id for a (possibly) future-bound factory
+            builder.AddSwitch(HandoffAgentExecutor.IdFor(agent), (SwitchBuilder sb) =>
+            {
+                foreach (HandoffTarget handoff in handoffs)
+                {
+                    sb.AddCase<HandoffState>(state => state?.RequestedHandoffTargetAgentId == handoff.Target.Id, // Use AgentId for target matching
+                                             HandoffAgentExecutor.IdFor(handoff.Target)); // Use ExecutorId in for routing at the workflow level
+                }
+
+                sb.WithDefault(HandoffEndExecutor.ExecutorId);
+            });
+
+            ExecutorFactoryFunc factory =
+                (config, sessionId) => new(
+                    new HandoffAgentExecutor(agent,
+                                             handoffs,
+                                             options));
+
+            // Make sure to use ExecutorId when binding the executor, not AgentId
+            ExecutorBinding binding = factory.BindExecutor(HandoffAgentExecutor.IdFor(agent));
+
+            builder.BindExecutor(binding);
+
+            return binding;
+        }
+    }
+
     /// <summary>
     /// Builds a <see cref="Workflow"/> composed of agents that operate via handoffs, with the next
     /// agent to process messages selected by the current agent.
@@ -240,17 +295,12 @@ public class HandoffWorkflowBuilderCore<TBuilder> where TBuilder : HandoffWorkfl
     /// <returns>The workflow built based on the handoffs in the builder.</returns>
     public Workflow Build()
     {
-        HandoffsStartExecutor start = new(this._returnToPrevious);
-        HandoffsEndExecutor end = new(this._returnToPrevious);
+        HandoffStartExecutor start = new(this._returnToPrevious);
+        HandoffEndExecutor end = new(this._returnToPrevious);
         WorkflowBuilder builder = new(start);
 
-        HandoffAgentExecutorOptions options = new(this.HandoffInstructions,
-                                                  this._emitAgentResponseEvents,
-                                                  this._emitAgentResponseUpdateEvents,
-                                                  this._toolCallFilteringBehavior);
-
-        // Create an AgentExecutor for each agent.
-        Dictionary<string, HandoffAgentExecutor> executors = this._allAgents.ToDictionary(a => a.Id, a => new HandoffAgentExecutor(a, options));
+        // Create an factory-based ExecutorBinding for each agent.
+        Dictionary<string, ExecutorBinding> executors = this.CreateExecutorBindings(builder);
 
         // Connect the start executor to the initial agent (or use dynamic routing when ReturnToPrevious is enabled).
         if (this._returnToPrevious)
@@ -263,7 +313,7 @@ public class HandoffWorkflowBuilderCore<TBuilder> where TBuilder : HandoffWorkfl
                     if (agent.Id != initialAgentId)
                     {
                         string agentId = agent.Id;
-                        sb.AddCase<HandoffState>(state => state?.CurrentAgentId == agentId, executors[agentId]);
+                        sb.AddCase<HandoffState>(state => state?.PreviousAgentId == agentId, executors[agentId]);
                     }
                 }
 
@@ -275,13 +325,6 @@ public class HandoffWorkflowBuilderCore<TBuilder> where TBuilder : HandoffWorkfl
             builder.AddEdge(start, executors[this._initialAgent.Id]);
         }
 
-        // Initialize each executor with its handoff targets to the other executors.
-        foreach (var agent in this._allAgents)
-        {
-            executors[agent.Id].Initialize(builder, end, executors,
-                this._targets.TryGetValue(agent, out HashSet<HandoffTarget>? targets) ? targets : []);
-        }
-
         // Build the workflow.
         return builder.WithOutputFrom(end).Build();
     }

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

@@ -19,6 +19,9 @@ internal static class TurnExtensions
 
     public static bool ShouldEmitStreamingEvents(bool? turnTokenSetting, bool? agentSetting)
         => turnTokenSetting ?? agentSetting ?? false;
+
+    public static bool ShouldEmitStreamingEvents(this HandoffState handoffState, bool? agentSetting)
+        => handoffState.TurnToken.ShouldEmitStreamingEvents(agentSetting);
 }
 
 internal sealed class AIAgentHostExecutor : ChatProtocolExecutor
@@ -81,7 +84,11 @@ internal sealed class AIAgentHostExecutor : ChatProtocolExecutor
         // resumes can be processed in one invocation.
         return this.ProcessTurnMessagesAsync(async (pendingMessages, ctx, ct) =>
         {
-            pendingMessages.Add(new ChatMessage(ChatRole.User, [response]));
+            pendingMessages.Add(new ChatMessage(ChatRole.User, [response])
+            {
+                CreatedAt = DateTimeOffset.UtcNow,
+                MessageId = Guid.NewGuid().ToString("N"),
+            });
 
             await this.ContinueTurnAsync(pendingMessages, ctx, this._currentTurnEmitEvents ?? false, ct).ConfigureAwait(false);
 
@@ -104,7 +111,12 @@ internal sealed class AIAgentHostExecutor : ChatProtocolExecutor
         // resumes can be processed in one invocation.
         return this.ProcessTurnMessagesAsync(async (pendingMessages, ctx, ct) =>
         {
-            pendingMessages.Add(new ChatMessage(ChatRole.Tool, [result]));
+            pendingMessages.Add(new ChatMessage(ChatRole.Tool, [result])
+            {
+                AuthorName = this._agent.Name ?? this._agent.Id,
+                CreatedAt = DateTimeOffset.UtcNow,
+                MessageId = Guid.NewGuid().ToString("N"),
+            });
 
             await this.ContinueTurnAsync(pendingMessages, ctx, this._currentTurnEmitEvents ?? false, ct).ConfigureAwait(false);
 
@@ -186,16 +198,13 @@ internal sealed class AIAgentHostExecutor : ChatProtocolExecutor
                                   TurnExtensions.ShouldEmitStreamingEvents(turnTokenSetting: emitEvents, this._options.EmitAgentUpdateEvents),
                                   cancellationToken);
 
-    private async ValueTask<AgentResponse> InvokeAgentAsync(IEnumerable<ChatMessage> messages, IWorkflowContext context, bool emitEvents, CancellationToken cancellationToken = default)
+    private async ValueTask<AgentResponse> InvokeAgentAsync(IEnumerable<ChatMessage> messages, IWorkflowContext context, bool emitUpdateEvents, CancellationToken cancellationToken = default)
     {
-#pragma warning disable MEAI001
-        Dictionary<string, ToolApprovalRequestContent> userInputRequests = new();
-        Dictionary<string, FunctionCallContent> functionCalls = new();
         AgentResponse response;
+        AIAgentUnservicedRequestsCollector collector = new(this._userInputHandler, this._functionCallHandler);
 
-        if (emitEvents)
+        if (emitUpdateEvents)
         {
-#pragma warning disable MEAI001 // Type is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
             // Run the agent in streaming mode only when agent run update events are to be emitted.
             IAsyncEnumerable<AgentResponseUpdate> agentStream = this._agent.RunStreamingAsync(
                 messages,
@@ -206,7 +215,7 @@ internal sealed class AIAgentHostExecutor : ChatProtocolExecutor
             await foreach (AgentResponseUpdate update in agentStream.ConfigureAwait(false))
             {
                 await context.YieldOutputAsync(update, cancellationToken).ConfigureAwait(false);
-                ExtractUnservicedRequests(update.Contents);
+                collector.ProcessAgentResponseUpdate(update);
                 updates.Add(update);
             }
 
@@ -220,7 +229,7 @@ internal sealed class AIAgentHostExecutor : ChatProtocolExecutor
                                                   cancellationToken: cancellationToken)
                                         .ConfigureAwait(false);
 
-            ExtractUnservicedRequests(response.Messages.SelectMany(message => message.Contents));
+            collector.ProcessAgentResponse(response);
         }
 
         if (this._options.EmitAgentResponseEvents)
@@ -228,45 +237,8 @@ internal sealed class AIAgentHostExecutor : ChatProtocolExecutor
             await context.YieldOutputAsync(response, cancellationToken).ConfigureAwait(false);
         }
 
-        if (userInputRequests.Count > 0 || functionCalls.Count > 0)
-        {
-            Task userInputTask = this._userInputHandler?.ProcessRequestContentsAsync(userInputRequests, context, cancellationToken) ?? Task.CompletedTask;
-            Task functionCallTask = this._functionCallHandler?.ProcessRequestContentsAsync(functionCalls, context, cancellationToken) ?? Task.CompletedTask;
-
-            await Task.WhenAll(userInputTask, functionCallTask)
-                      .ConfigureAwait(false);
-        }
+        await collector.SubmitAsync(context, cancellationToken).ConfigureAwait(false);
 
         return response;
-
-        void ExtractUnservicedRequests(IEnumerable<AIContent> contents)
-        {
-            foreach (AIContent content in contents)
-            {
-                if (content is ToolApprovalRequestContent userInputRequest)
-                {
-                    // It is an error to simultaneously have multiple outstanding user input requests with the same ID.
-                    userInputRequests.Add(userInputRequest.RequestId, userInputRequest);
-                }
-                else if (content is ToolApprovalResponseContent userInputResponse)
-                {
-                    // If the set of messages somehow already has a corresponding user input response, remove it.
-                    _ = userInputRequests.Remove(userInputResponse.RequestId);
-                }
-                else if (content is FunctionCallContent functionCall)
-                {
-                    // For function calls, we emit an event to notify the workflow.
-                    //
-                    // possibility 1: this will be handled inline by the agent abstraction
-                    // possibility 2: this will not be handled inline by the agent abstraction
-                    functionCalls.Add(functionCall.CallId, functionCall);
-                }
-                else if (content is FunctionResultContent functionResult)
-                {
-                    _ = functionCalls.Remove(functionResult.CallId);
-                }
-            }
-        }
-#pragma warning restore MEAI001
     }
 }

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

@@ -0,0 +1,78 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Extensions.AI;
+
+namespace Microsoft.Agents.AI.Workflows.Specialized;
+
+internal sealed class AIAgentUnservicedRequestsCollector(AIContentExternalHandler<ToolApprovalRequestContent, ToolApprovalResponseContent>? userInputHandler,
+                                                         AIContentExternalHandler<FunctionCallContent, FunctionResultContent>? functionCallHandler)
+{
+    private readonly Dictionary<string, ToolApprovalRequestContent> _userInputRequests = [];
+    private readonly Dictionary<string, FunctionCallContent> _functionCalls = [];
+
+    public Task SubmitAsync(IWorkflowContext context, CancellationToken cancellationToken)
+    {
+        Task userInputTask = userInputHandler != null && this._userInputRequests.Count > 0
+                           ? userInputHandler.ProcessRequestContentsAsync(this._userInputRequests, context, cancellationToken)
+                           : Task.CompletedTask;
+
+        Task functionCallTask = functionCallHandler != null && this._functionCalls.Count > 0
+                              ? functionCallHandler.ProcessRequestContentsAsync(this._functionCalls, context, cancellationToken)
+                              : Task.CompletedTask;
+
+        return Task.WhenAll(userInputTask, functionCallTask);
+    }
+
+    public void ProcessAgentResponseUpdate(AgentResponseUpdate update, Func<FunctionCallContent, bool>? functionCallFilter = null)
+        => this.ProcessAIContents(update.Contents, functionCallFilter);
+
+    public void ProcessAgentResponse(AgentResponse response)
+        => this.ProcessAIContents(response.Messages.SelectMany(message => message.Contents));
+
+    public void ProcessAIContents(IEnumerable<AIContent> contents, Func<FunctionCallContent, bool>? functionCallFilter = null)
+    {
+        foreach (AIContent content in contents)
+        {
+            if (content is ToolApprovalRequestContent userInputRequest)
+            {
+                if (this._userInputRequests.ContainsKey(userInputRequest.RequestId))
+                {
+                    throw new InvalidOperationException($"ToolApprovalRequestContent with duplicate RequestId: {userInputRequest.RequestId}");
+                }
+
+                // It is an error to simultaneously have multiple outstanding user input requests with the same ID.
+                this._userInputRequests.Add(userInputRequest.RequestId, userInputRequest);
+            }
+            else if (content is ToolApprovalResponseContent userInputResponse)
+            {
+                // If the set of messages somehow already has a corresponding user input response, remove it.
+                _ = this._userInputRequests.Remove(userInputResponse.RequestId);
+            }
+            else if (content is FunctionCallContent functionCall)
+            {
+                // For function calls, we emit an event to notify the workflow.
+                //
+                // possibility 1: this will be handled inline by the agent abstraction
+                // possibility 2: this will not be handled inline by the agent abstraction
+                if (functionCallFilter == null || functionCallFilter(functionCall))
+                {
+                    if (this._functionCalls.ContainsKey(functionCall.CallId))
+                    {
+                        throw new InvalidOperationException($"FunctionCallContent with duplicate CallId: {functionCall.CallId}");
+                    }
+
+                    this._functionCalls.Add(functionCall.CallId, functionCall);
+                }
+            }
+            else if (content is FunctionResultContent functionResult)
+            {
+                _ = this._functionCalls.Remove(functionResult.CallId);
+            }
+        }
+    }
+}

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

@@ -3,7 +3,6 @@
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
-using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Text.Json;
@@ -166,128 +165,331 @@ internal sealed class HandoffMessagesFilter
     }
 }
 
+internal struct AgentInvocationResult(AgentResponse agentResponse, string? handoffTargetId)
+{
+    public AgentResponse Response => agentResponse;
+
+    public string? HandoffTargetId => handoffTargetId;
+
+    [MemberNotNullWhen(true, nameof(HandoffTargetId))]
+    public bool IsHandoffRequested => this.HandoffTargetId != null;
+}
+
+internal record HandoffAgentHostState(HandoffState? CurrentTurnState, List<ChatMessage> FilteredIncomingMessages, List<ChatMessage> TurnMessages)
+{
+    public HandoffState PrepareHandoff(AgentInvocationResult invocationResult, string currentAgentId)
+    {
+        if (this.CurrentTurnState == null)
+        {
+            throw new InvalidOperationException("Cannot create a handoff request: Out of turn.");
+        }
+
+        IEnumerable<ChatMessage> allMessages = [.. this.CurrentTurnState.Messages, .. this.TurnMessages, .. invocationResult.Response.Messages];
+
+        return new(this.CurrentTurnState.TurnToken, invocationResult.HandoffTargetId, allMessages.ToList(), currentAgentId);
+    }
+}
+
 /// <summary>Executor used to represent an agent in a handoffs workflow, responding to <see cref="HandoffState"/> events.</summary>
 [Experimental(DiagnosticConstants.ExperimentalFeatureDiagnostic)]
-internal sealed class HandoffAgentExecutor(
-    AIAgent agent,
-    HandoffAgentExecutorOptions options) : Executor<HandoffState, HandoffState>(agent.GetDescriptiveId(), declareCrossRunShareable: true), IResettableExecutor
+internal sealed class HandoffAgentExecutor :
+    StatefulExecutor<HandoffAgentHostState, HandoffState>
 {
     private static readonly JsonElement s_handoffSchema = AIFunctionFactory.Create(
         ([Description("The reason for the handoff")] string? reasonForHandoff) => { }).JsonSchema;
 
-    private readonly AIAgent _agent = agent;
+    public static string IdFor(AIAgent agent) => agent.GetDescriptiveId();
+
+    private readonly AIAgent _agent;
+    private readonly ChatClientAgentRunOptions? _agentOptions;
+
+    private readonly HandoffAgentExecutorOptions _options;
+
     private readonly HashSet<string> _handoffFunctionNames = [];
     private readonly Dictionary<string, string> _handoffFunctionToAgentId = [];
-    private ChatClientAgentRunOptions? _agentOptions;
 
-    public void Initialize(
-        WorkflowBuilder builder,
-        Executor end,
-        Dictionary<string, HandoffAgentExecutor> executors,
-        HashSet<HandoffTarget> handoffs) =>
-        builder.AddSwitch(this, sb =>
-        {
-            if (handoffs.Count != 0)
-            {
-                Debug.Assert(this._agentOptions is null);
-                this._agentOptions = new()
-                {
-                    ChatOptions = new()
-                    {
-                        AllowMultipleToolCalls = false,
-                        Instructions = options.HandoffInstructions,
-                        Tools = [],
-                    },
-                };
+    private static HandoffAgentHostState InitialStateFactory() => new(null, [], []);
 
-                int index = 0;
-                foreach (HandoffTarget handoff in handoffs)
-                {
-                    index++;
-                    var handoffFunc = AIFunctionFactory.CreateDeclaration($"{HandoffWorkflowBuilder.FunctionPrefix}{index}", handoff.Reason, s_handoffSchema);
-
-                    this._handoffFunctionNames.Add(handoffFunc.Name);
-                    this._handoffFunctionToAgentId[handoffFunc.Name] = handoff.Target.Id;
-
-                    this._agentOptions.ChatOptions.Tools.Add(handoffFunc);
-
-                    sb.AddCase<HandoffState>(state => state?.InvokedHandoff == handoffFunc.Name, executors[handoff.Target.Id]);
-                }
-            }
-
-            sb.WithDefault(end);
-        });
-
-    public override async ValueTask<HandoffState> HandleAsync(HandoffState message, IWorkflowContext context, CancellationToken cancellationToken = default)
+    public HandoffAgentExecutor(AIAgent agent, HashSet<HandoffTarget> handoffs, HandoffAgentExecutorOptions options)
+        : base(IdFor(agent), InitialStateFactory)
     {
-        string? requestedHandoff = null;
-        List<AgentResponseUpdate> updates = [];
-        List<ChatMessage> allMessages = message.Messages;
+        this._agent = agent;
+        this._options = options;
 
-        List<ChatMessage>? roleChanges = allMessages.ChangeAssistantToUserForOtherParticipants(this._agent.Name ?? this._agent.Id);
+        this._agentOptions = CreateAgentHandoffContext(this._options.HandoffInstructions, handoffs, this._handoffFunctionNames, this._handoffFunctionToAgentId);
+    }
 
-        // If a handoff was invoked by a previous agent, filter out the handoff function
-        // call and tool result messages before sending to the underlying agent. These
-        // are internal workflow mechanics that confuse the target model into ignoring the
-        // original user question.
-        HandoffMessagesFilter handoffMessagesFilter = new(options.ToolCallFilteringBehavior);
-        IEnumerable<ChatMessage> messagesForAgent = message.InvokedHandoff is not null
-            ? handoffMessagesFilter.FilterMessages(allMessages)
-            : allMessages;
+    private static ChatClientAgentRunOptions? CreateAgentHandoffContext(string? handoffInstructions, HashSet<HandoffTarget> handoffs, HashSet<string> functionNames, Dictionary<string, string> functionToAgentId)
+    {
+        ChatClientAgentRunOptions? result = null;
 
-        await foreach (var update in this._agent.RunStreamingAsync(messagesForAgent,
-                                                                   options: this._agentOptions,
-                                                                   cancellationToken: cancellationToken)
-                                                .ConfigureAwait(false))
+        if (handoffs.Count != 0)
         {
-            await AddUpdateAsync(update, cancellationToken).ConfigureAwait(false);
-
-            foreach (var fcc in update.Contents.OfType<FunctionCallContent>()
-                                               .Where(fcc => this._handoffFunctionNames.Contains(fcc.Name)))
+            result = new()
             {
-                requestedHandoff = fcc.Name;
-                await AddUpdateAsync(
-                        new AgentResponseUpdate
-                        {
-                            AgentId = this._agent.Id,
-                            AuthorName = this._agent.Name ?? this._agent.Id,
-                            Contents = [new FunctionResultContent(fcc.CallId, "Transferred.")],
-                            CreatedAt = DateTimeOffset.UtcNow,
-                            MessageId = Guid.NewGuid().ToString("N"),
-                            Role = ChatRole.Tool,
-                        },
-                        cancellationToken
-                     )
-                    .ConfigureAwait(false);
+                ChatOptions = new()
+                {
+                    AllowMultipleToolCalls = false,
+                    Instructions = handoffInstructions,
+                    Tools = [],
+                },
+            };
+
+            int index = 0;
+            foreach (HandoffTarget handoff in handoffs)
+            {
+                index++;
+                var handoffFunc = AIFunctionFactory.CreateDeclaration($"{HandoffWorkflowBuilder.FunctionPrefix}{index}", handoff.Reason, s_handoffSchema);
+
+                functionNames.Add(handoffFunc.Name);
+                functionToAgentId[handoffFunc.Name] = handoff.Target.Id;
+
+                result.ChatOptions.Tools.Add(handoffFunc);
             }
         }
 
-        AgentResponse agentResponse = updates.ToAgentResponse();
+        return result;
+    }
 
-        if (options.EmitAgentResponseEvents)
+    private AIContentExternalHandler<ToolApprovalRequestContent, ToolApprovalResponseContent>? _userInputHandler;
+    private AIContentExternalHandler<FunctionCallContent, FunctionResultContent>? _functionCallHandler;
+
+    protected override ProtocolBuilder ConfigureProtocol(ProtocolBuilder protocolBuilder)
+    {
+        return this.ConfigureUserInputHandling(base.ConfigureProtocol(protocolBuilder))
+                   .SendsMessage<HandoffState>();
+    }
+
+    private ProtocolBuilder ConfigureUserInputHandling(ProtocolBuilder protocolBuilder)
+    {
+        this._userInputHandler = new AIContentExternalHandler<ToolApprovalRequestContent, ToolApprovalResponseContent>(
+            ref protocolBuilder,
+            portId: $"{this.Id}_UserInput",
+            intercepted: false,
+            handler: this.HandleUserInputResponseAsync);
+
+        this._functionCallHandler = new AIContentExternalHandler<FunctionCallContent, FunctionResultContent>(
+            ref protocolBuilder,
+            portId: $"{this.Id}_FunctionCall",
+            intercepted: false, // TODO: Use this instead of manual function handling for handoff?
+            handler: this.HandleFunctionResultAsync);
+
+        return protocolBuilder;
+    }
+
+    private ValueTask HandleUserInputResponseAsync(
+        ToolApprovalResponseContent response,
+        IWorkflowContext context,
+        CancellationToken cancellationToken)
+    {
+        if (!this._userInputHandler!.MarkRequestAsHandled(response.RequestId))
         {
-            await context.YieldOutputAsync(agentResponse, cancellationToken).ConfigureAwait(false);
+            throw new InvalidOperationException($"No pending ToolApprovalRequest found with id '{response.RequestId}'.");
         }
 
-        allMessages.AddRange(agentResponse.Messages);
+        // Merge the external response with any already-buffered regular messages so mixed-content
+        // resumes can be processed in one invocation.
+        return this.InvokeWithStateAsync((state, ctx, ct) =>
+        {
+            state.TurnMessages.Add(new ChatMessage(ChatRole.User, [response])
+            {
+                CreatedAt = DateTimeOffset.UtcNow,
+                MessageId = Guid.NewGuid().ToString("N"),
+            });
+
+            return this.ContinueTurnAsync(state, ctx, ct);
+        }, context, skipCache: false, cancellationToken);
+    }
+
+    private ValueTask HandleFunctionResultAsync(
+        FunctionResultContent result,
+        IWorkflowContext context,
+        CancellationToken cancellationToken)
+    {
+        if (!this._functionCallHandler!.MarkRequestAsHandled(result.CallId))
+        {
+            throw new InvalidOperationException($"No pending FunctionCall found with id '{result.CallId}'.");
+        }
+
+        // Merge the external response with any already-buffered regular messages so mixed-content
+        // resumes can be processed in one invocation.
+        return this.InvokeWithStateAsync((state, ctx, ct) =>
+        {
+            state.TurnMessages.Add(
+                new ChatMessage(ChatRole.Tool, [result])
+                {
+                    AuthorName = this._agent.Name ?? this._agent.Id,
+                    CreatedAt = DateTimeOffset.UtcNow,
+                    MessageId = Guid.NewGuid().ToString("N"),
+                });
+
+            return this.ContinueTurnAsync(state, ctx, ct);
+        }, context, skipCache: false, cancellationToken);
+    }
+
+    private async ValueTask<HandoffAgentHostState?> ContinueTurnAsync(HandoffAgentHostState state, IWorkflowContext context, CancellationToken cancellationToken)
+    {
+        List<ChatMessage>? roleChanges = state.FilteredIncomingMessages.ChangeAssistantToUserForOtherParticipants(this._agent.Name ?? this._agent.Id);
+
+        bool emitUpdateEvents = state.CurrentTurnState!.ShouldEmitStreamingEvents(this._options.EmitAgentResponseUpdateEvents);
+        AgentInvocationResult result = await this.InvokeAgentAsync([.. state.FilteredIncomingMessages, .. state.TurnMessages], context, emitUpdateEvents, cancellationToken)
+                                                     .ConfigureAwait(false);
+
+        if (this.HasOutstandingRequests && result.IsHandoffRequested)
+        {
+            throw new InvalidOperationException("Cannot request a handoff while holding pending requests.");
+        }
 
         roleChanges.ResetUserToAssistantForChangedRoles();
 
-        string currentAgentId = requestedHandoff is not null && this._handoffFunctionToAgentId.TryGetValue(requestedHandoff, out string? targetAgentId)
-            ? targetAgentId
-            : this._agent.Id;
-
-        return new(message.TurnToken, requestedHandoff, allMessages, currentAgentId);
-
-        async Task AddUpdateAsync(AgentResponseUpdate update, CancellationToken cancellationToken)
+        // We send on the HandoffState even if handoff is not requested because we might be terminating the processing, but this only
+        // happens if we have no outstanding requests.
+        if (!this.HasOutstandingRequests)
         {
-            updates.Add(update);
-            if (message.TurnToken.ShouldEmitStreamingEvents(options.EmitAgentResponseUpdateEvents))
+            HandoffState outgoingState = state.PrepareHandoff(result, this._agent.Id);
+
+            await context.SendMessageAsync(outgoingState, cancellationToken).ConfigureAwait(false);
+
+            // reset the state for the next handoff (return-to-current is modeled as a new handoff turn, as opposed to "HITL", which
+            // can be a bit confusing.)
+            return null;
+        }
+
+        state.TurnMessages.AddRange(result.Response.Messages);
+        return state;
+    }
+
+    public override ValueTask HandleAsync(HandoffState message, IWorkflowContext context, CancellationToken cancellationToken = default)
+    {
+        return this.InvokeWithStateAsync(InvokeContinueTurnAsync, context, skipCache: false, cancellationToken);
+
+        ValueTask<HandoffAgentHostState?> InvokeContinueTurnAsync(HandoffAgentHostState state, IWorkflowContext context, CancellationToken cancellationToken)
+        {
+            // Check that we are not getting this message while in the middle of a turn
+            if (state.CurrentTurnState != null)
             {
-                await context.YieldOutputAsync(update, cancellationToken).ConfigureAwait(false);
+                throw new InvalidOperationException("Cannot have multiple simultaneous conversations in Handoff Orchestration.");
             }
+
+            // If a handoff was invoked by a previous agent, filter out the handoff function
+            // call and tool result messages before sending to the underlying agent. These
+            // are internal workflow mechanics that confuse the target model into ignoring the
+            // original user question.
+            HandoffMessagesFilter handoffMessagesFilter = new(this._options.ToolCallFilteringBehavior);
+            IEnumerable<ChatMessage> messagesForAgent = message.RequestedHandoffTargetAgentId is not null
+                ? handoffMessagesFilter.FilterMessages(message.Messages)
+                : message.Messages;
+
+            // This works because the runtime guarantees that a given executor instance will process messages serially,
+            // though there is no global cross-executor ordering guarantee (and in turn, no canonical message delivery order)
+            state = new(message, messagesForAgent.ToList(), []);
+
+            return this.ContinueTurnAsync(state, context, cancellationToken);
         }
     }
 
-    public ValueTask ResetAsync() => default;
+    private const string UserInputRequestStateKey = nameof(_userInputHandler);
+    private const string FunctionCallRequestStateKey = nameof(_functionCallHandler);
+
+    protected internal override async ValueTask OnCheckpointingAsync(IWorkflowContext context, CancellationToken cancellationToken = default)
+    {
+        Task userInputRequestsTask = this._userInputHandler?.OnCheckpointingAsync(UserInputRequestStateKey, context, cancellationToken).AsTask() ?? Task.CompletedTask;
+        Task functionCallRequestsTask = this._functionCallHandler?.OnCheckpointingAsync(FunctionCallRequestStateKey, context, cancellationToken).AsTask() ?? Task.CompletedTask;
+
+        Task baseTask = base.OnCheckpointingAsync(context, cancellationToken).AsTask();
+        await Task.WhenAll(userInputRequestsTask, functionCallRequestsTask, baseTask).ConfigureAwait(false);
+    }
+
+    protected internal override async ValueTask OnCheckpointRestoredAsync(IWorkflowContext context, CancellationToken cancellationToken = default)
+    {
+        Task userInputRestoreTask = this._userInputHandler?.OnCheckpointRestoredAsync(UserInputRequestStateKey, context, cancellationToken).AsTask() ?? Task.CompletedTask;
+        Task functionCallRestoreTask = this._functionCallHandler?.OnCheckpointRestoredAsync(FunctionCallRequestStateKey, context, cancellationToken).AsTask() ?? Task.CompletedTask;
+
+        await Task.WhenAll(userInputRestoreTask, functionCallRestoreTask).ConfigureAwait(false);
+        await base.OnCheckpointRestoredAsync(context, cancellationToken).ConfigureAwait(false);
+    }
+    private bool HasOutstandingRequests => (this._userInputHandler?.HasPendingRequests == true)
+                                        || (this._functionCallHandler?.HasPendingRequests == true);
+
+    private async ValueTask<AgentInvocationResult> InvokeAgentAsync(IEnumerable<ChatMessage> messages, IWorkflowContext context, bool emitUpdateEvents, CancellationToken cancellationToken = default)
+    {
+        AgentResponse response;
+
+        AIAgentUnservicedRequestsCollector collector = new(this._userInputHandler, this._functionCallHandler);
+
+        IAsyncEnumerable<AgentResponseUpdate> agentStream = this._agent.RunStreamingAsync(
+                messages,
+                options: this._agentOptions,
+                cancellationToken: cancellationToken);
+
+        string? requestedHandoff = null;
+        List<AgentResponseUpdate> updates = [];
+        List<FunctionCallContent> candidateRequests = [];
+        await foreach (AgentResponseUpdate update in agentStream.ConfigureAwait(false))
+        {
+            await AddUpdateAsync(update, cancellationToken).ConfigureAwait(false);
+
+            collector.ProcessAgentResponseUpdate(update, CollectHandoffRequestsFilter);
+
+            bool CollectHandoffRequestsFilter(FunctionCallContent candidateHandoffRequest)
+            {
+                bool isHandoffRequest = this._handoffFunctionNames.Contains(candidateHandoffRequest.Name);
+                if (isHandoffRequest)
+                {
+                    candidateRequests.Add(candidateHandoffRequest);
+                }
+
+                return !isHandoffRequest;
+            }
+        }
+
+        if (candidateRequests.Count > 1)
+        {
+            string message = $"Duplicate handoff requests in single turn ([{string.Join(", ", candidateRequests.Select(request => request.Name))}]). Using last ({candidateRequests.Last().Name})";
+            await context.AddEventAsync(new WorkflowWarningEvent(message), cancellationToken).ConfigureAwait(false);
+        }
+
+        if (candidateRequests.Count > 0)
+        {
+            FunctionCallContent handoffRequest = candidateRequests[candidateRequests.Count - 1];
+            requestedHandoff = handoffRequest.Name;
+
+            await AddUpdateAsync(
+                    new AgentResponseUpdate
+                    {
+                        AgentId = this._agent.Id,
+                        AuthorName = this._agent.Name ?? this._agent.Id,
+                        Contents = [new FunctionResultContent(handoffRequest.CallId, "Transferred.")],
+                        CreatedAt = DateTimeOffset.UtcNow,
+                        MessageId = Guid.NewGuid().ToString("N"),
+                        Role = ChatRole.Tool,
+                    },
+                    cancellationToken
+                 )
+                .ConfigureAwait(false);
+        }
+
+        response = updates.ToAgentResponse();
+
+        if (this._options.EmitAgentResponseEvents)
+        {
+            await context.YieldOutputAsync(response, cancellationToken).ConfigureAwait(false);
+        }
+
+        await collector.SubmitAsync(context, cancellationToken).ConfigureAwait(false);
+
+        return new(response, LookupHandoffTarget(requestedHandoff));
+
+        ValueTask AddUpdateAsync(AgentResponseUpdate update, CancellationToken cancellationToken)
+        {
+            updates.Add(update);
+
+            return emitUpdateEvents ? context.YieldOutputAsync(update, cancellationToken) : default;
+        }
+
+        string? LookupHandoffTarget(string? requestedHandoff)
+            => requestedHandoff != null
+             ? this._handoffFunctionToAgentId.TryGetValue(requestedHandoff, out string? targetId) ? targetId : null
+             : null;
+    }
 }

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

@@ -8,7 +8,7 @@ using Microsoft.Extensions.AI;
 namespace Microsoft.Agents.AI.Workflows.Specialized;
 
 /// <summary>Executor used at the end of a handoff workflow to raise a final completed event.</summary>
-internal sealed class HandoffsEndExecutor(bool returnToPrevious) : Executor(ExecutorId, declareCrossRunShareable: true), IResettableExecutor
+internal sealed class HandoffEndExecutor(bool returnToPrevious) : Executor(ExecutorId, declareCrossRunShareable: true), IResettableExecutor
 {
     public const string ExecutorId = "HandoffEnd";
 
@@ -21,9 +21,9 @@ internal sealed class HandoffsEndExecutor(bool returnToPrevious) : Executor(Exec
     {
         if (returnToPrevious)
         {
-            await context.QueueStateUpdateAsync<string?>(HandoffConstants.CurrentAgentTrackerKey,
-                                                         handoff.CurrentAgentId,
-                                                         HandoffConstants.CurrentAgentTrackerScope,
+            await context.QueueStateUpdateAsync<string?>(HandoffConstants.PreviousAgentTrackerKey,
+                                                         handoff.PreviousAgentId,
+                                                         HandoffConstants.PreviousAgentTrackerScope,
                                                          cancellationToken)
                          .ConfigureAwait(false);
         }

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

@@ -9,12 +9,12 @@ namespace Microsoft.Agents.AI.Workflows.Specialized;
 
 internal static class HandoffConstants
 {
-    internal const string CurrentAgentTrackerKey = "LastAgentId";
-    internal const string CurrentAgentTrackerScope = "HandoffOrchestration";
+    internal const string PreviousAgentTrackerKey = "LastAgentId";
+    internal const string PreviousAgentTrackerScope = "HandoffOrchestration";
 }
 
 /// <summary>Executor used at the start of a handoffs workflow to accumulate messages and emit them as HandoffState upon receiving a turn token.</summary>
-internal sealed class HandoffsStartExecutor(bool returnToPrevious) : ChatProtocolExecutor(ExecutorId, DefaultOptions, declareCrossRunShareable: true), IResettableExecutor
+internal sealed class HandoffStartExecutor(bool returnToPrevious) : ChatProtocolExecutor(ExecutorId, DefaultOptions, declareCrossRunShareable: true), IResettableExecutor
 {
     internal const string ExecutorId = "HandoffStart";
 
@@ -32,15 +32,15 @@ internal sealed class HandoffsStartExecutor(bool returnToPrevious) : ChatProtoco
         if (returnToPrevious)
         {
             return context.InvokeWithStateAsync(
-                async (string? currentAgentId, IWorkflowContext context, CancellationToken cancellationToken) =>
+                async (string? previousAgentId, IWorkflowContext context, CancellationToken cancellationToken) =>
                 {
-                    HandoffState handoffState = new(new(emitEvents), null, messages, currentAgentId);
+                    HandoffState handoffState = new(new(emitEvents), null, messages, previousAgentId);
                     await context.SendMessageAsync(handoffState, cancellationToken).ConfigureAwait(false);
 
-                    return currentAgentId;
+                    return previousAgentId;
                 },
-                HandoffConstants.CurrentAgentTrackerKey,
-                HandoffConstants.CurrentAgentTrackerScope,
+                HandoffConstants.PreviousAgentTrackerKey,
+                HandoffConstants.PreviousAgentTrackerScope,
                 cancellationToken);
         }
 

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

@@ -7,6 +7,6 @@ namespace Microsoft.Agents.AI.Workflows.Specialized;
 
 internal sealed record class HandoffState(
     TurnToken TurnToken,
-    string? InvokedHandoff,
+    string? RequestedHandoffTargetAgentId,
     List<ChatMessage> Messages,
-    string? CurrentAgentId = null);
+    string? PreviousAgentId = null);

dotnet/src/Microsoft.Agents.AI.Workflows/StatefulExecutor.cs

@@ -113,6 +113,12 @@ public abstract class StatefulExecutor<TState> : Executor
     {
         if (!skipCache && !context.ConcurrentRunsEnabled)
         {
+            if (this._stateCache is null)
+            {
+                this._stateCache = await context.ReadOrInitStateAsync(this.StateKey, this._initialStateFactory, this.Options.ScopeName, cancellationToken)
+                                                .ConfigureAwait(false);
+            }
+
             TState newState = await invocation(this._stateCache ?? this._initialStateFactory(),
                                                context,
                                                cancellationToken).ConfigureAwait(false)
@@ -168,9 +174,12 @@ public abstract class StatefulExecutor<TState, TInput>(string id,
     /// <inheritdoc/>
     protected override ProtocolBuilder ConfigureProtocol(ProtocolBuilder protocolBuilder)
     {
-        protocolBuilder.RouteBuilder.AddHandler<TInput>(this.HandleAsync);
+        Func<TInput, IWorkflowContext, CancellationToken, ValueTask> handlerDelegate = this.HandleAsync;
 
-        return protocolBuilder.SendsMessageTypes(sentMessageTypes ?? [])
+        return protocolBuilder.ConfigureRoutes(routeBuilder => routeBuilder.AddHandler(handlerDelegate))
+                              .AddMethodAttributeTypes(handlerDelegate.Method)
+                              .AddClassAttributeTypes(this.GetType())
+                              .SendsMessageTypes(sentMessageTypes ?? [])
                               .YieldsOutputTypes(outputTypes ?? []);
     }
 
@@ -203,19 +212,12 @@ public abstract class StatefulExecutor<TState, TInput, TOutput>(string id,
     /// <inheritdoc/>
     protected override ProtocolBuilder ConfigureProtocol(ProtocolBuilder protocolBuilder)
     {
-        protocolBuilder.RouteBuilder.AddHandler<TInput, TOutput>(this.HandleAsync);
-
-        if (this.Options.AutoSendMessageHandlerResultObject)
-        {
-            protocolBuilder.SendsMessage<TOutput>();
-        }
-
-        if (this.Options.AutoYieldOutputHandlerResultObject)
-        {
-            protocolBuilder.YieldsOutput<TOutput>();
-        }
-
-        return protocolBuilder.SendsMessageTypes(sentMessageTypes ?? []).YieldsOutputTypes(outputTypes ?? []);
+        Func<TInput, IWorkflowContext, CancellationToken, ValueTask<TOutput>> handlerDelegate = this.HandleAsync;
+        return protocolBuilder.ConfigureRoutes(routeBuilder => routeBuilder.AddHandler(handlerDelegate))
+                              .AddMethodAttributeTypes(handlerDelegate.Method)
+                              .AddClassAttributeTypes(this.GetType())
+                              .SendsMessageTypes(sentMessageTypes ?? [])
+                              .YieldsOutputTypes(outputTypes ?? []);
     }
 
     /// <inheritdoc/>

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

@@ -9,6 +9,7 @@ using System.Text.Json;
 using System.Text.RegularExpressions;
 using System.Threading;
 using System.Threading.Tasks;
+using FluentAssertions;
 using Microsoft.Agents.AI.Workflows.InProc;
 using Microsoft.Extensions.AI;
 
@@ -147,7 +148,7 @@ public class AgentWorkflowBuilderTests
         for (int iter = 0; iter < 3; iter++)
         {
             const string UserInput = "abc";
-            (string updateText, List<ChatMessage>? result, _) = await RunWorkflowAsync(workflow, [new ChatMessage(ChatRole.User, UserInput)]);
+            (string updateText, List<ChatMessage>? result, _, _) = await RunWorkflowAsync(workflow, [new ChatMessage(ChatRole.User, UserInput)]);
 
             Assert.NotNull(result);
             Assert.Equal(numAgents + 1, result.Count);
@@ -225,7 +226,7 @@ public class AgentWorkflowBuilderTests
             barrier.Value = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
             remaining.Value = 2;
 
-            (string updateText, List<ChatMessage>? result, _) = await RunWorkflowAsync(workflow, [new ChatMessage(ChatRole.User, "abc")]);
+            (string updateText, List<ChatMessage>? result, _, _) = await RunWorkflowAsync(workflow, [new ChatMessage(ChatRole.User, "abc")]);
             Assert.NotEmpty(updateText);
             Assert.NotNull(result);
 
@@ -258,7 +259,7 @@ public class AgentWorkflowBuilderTests
             }), description: "nop"))
             .Build();
 
-        (string updateText, List<ChatMessage>? result, _) = await RunWorkflowAsync(workflow, [new ChatMessage(ChatRole.User, "abc")]);
+        (string updateText, List<ChatMessage>? result, _, _) = await RunWorkflowAsync(workflow, [new ChatMessage(ChatRole.User, "abc")]);
 
         Assert.Equal("Hello from agent1", updateText);
         Assert.NotNull(result);
@@ -296,7 +297,7 @@ public class AgentWorkflowBuilderTests
             .WithHandoff(initialAgent, nextAgent)
             .Build();
 
-        (string updateText, List<ChatMessage>? result, _) = await RunWorkflowAsync(workflow, [new ChatMessage(ChatRole.User, "abc")]);
+        (string updateText, List<ChatMessage>? result, _, _) = await RunWorkflowAsync(workflow, [new ChatMessage(ChatRole.User, "abc")]);
 
         Assert.Equal("Hello from agent2", updateText);
         Assert.NotNull(result);
@@ -406,7 +407,7 @@ public class AgentWorkflowBuilderTests
             .WithHandoff(secondAgent, thirdAgent)
             .Build();
 
-        (string updateText, _, _) = await RunWorkflowAsync(workflow, [new ChatMessage(ChatRole.User, "abc")]);
+        (string updateText, _, _, _) = await RunWorkflowAsync(workflow, [new ChatMessage(ChatRole.User, "abc")]);
 
         Assert.Contains("Hello from agent3", updateText);
 
@@ -604,7 +605,7 @@ public class AgentWorkflowBuilderTests
             .WithHandoff(secondAgent, thirdAgent)
             .Build();
 
-        (string updateText, List<ChatMessage>? result, _) = await RunWorkflowAsync(workflow, [new ChatMessage(ChatRole.User, "abc")]);
+        (string updateText, List<ChatMessage>? result, _, _) = await RunWorkflowAsync(workflow, [new ChatMessage(ChatRole.User, "abc")]);
 
         Assert.Equal("Hello from agent3", updateText);
         Assert.NotNull(result);
@@ -634,6 +635,232 @@ public class AgentWorkflowBuilderTests
         Assert.Contains("thirdAgent", result[5].AuthorName);
     }
 
+    [Fact]
+    public async Task Handoffs_TwoTransfers_SecondAgentUserApproval_ResponseServedByThirdAgentAsync()
+    {
+        var initialAgent = new ChatClientAgent(new MockChatClient((messages, options) =>
+        {
+            ChatMessage message = Assert.Single(messages);
+            Assert.Equal("abc", Assert.IsType<TextContent>(Assert.Single(message.Contents)).Text);
+
+            string? transferFuncName = options?.Tools?.FirstOrDefault(t => t.Name.StartsWith("handoff_to_", StringComparison.Ordinal))?.Name;
+            Assert.NotNull(transferFuncName);
+
+            // Only a handoff function call.
+            return new(new ChatMessage(ChatRole.Assistant, [new FunctionCallContent("call1", transferFuncName)]));
+        }), name: "initialAgent");
+
+        bool secondAgentInvoked = false;
+
+        const string SomeOtherFunctionCallId = "call2first";
+
+        AIFunction someOtherFunction = new ApprovalRequiredAIFunction(AIFunctionFactory.Create(SomeOtherFunction));
+
+        var secondAgent = new ChatClientAgent(new MockChatClient((messages, options) =>
+        {
+            if (!secondAgentInvoked)
+            {
+                secondAgentInvoked = true;
+                return new(new ChatMessage(ChatRole.Assistant, [new FunctionCallContent(SomeOtherFunctionCallId, someOtherFunction.Name)]));
+            }
+
+            // Second agent should receive the conversation so far (including previous assistant + tool messages eventually).
+            string? transferFuncName = options?.Tools?.FirstOrDefault(t => t.Name.StartsWith("handoff_to_", StringComparison.Ordinal))?.Name;
+            Assert.NotNull(transferFuncName);
+
+            return new(new ChatMessage(ChatRole.Assistant, [new FunctionCallContent("call2", transferFuncName)]));
+        }), name: "secondAgent", description: "The second agent", tools: [someOtherFunction]);
+
+        var thirdAgent = new ChatClientAgent(new MockChatClient((messages, options) =>
+            new(new ChatMessage(ChatRole.Assistant, "Hello from agent3"))),
+            name: "thirdAgent",
+            description: "The third / final agent");
+
+        var workflow =
+            AgentWorkflowBuilder.CreateHandoffBuilderWith(initialAgent)
+            .WithHandoff(initialAgent, secondAgent)
+            .WithHandoff(secondAgent, thirdAgent)
+            .Build();
+
+        CheckpointManager checkpointManager = CheckpointManager.CreateInMemory();
+        const ExecutionEnvironment Environment = ExecutionEnvironment.InProcess_Lockstep;
+
+        (string updateText, List<ChatMessage>? result, CheckpointInfo? lastCheckpoint, List<RequestInfoEvent> requests) =
+            await RunWorkflowCheckpointedAsync(workflow, [new ChatMessage(ChatRole.User, "abc")], Environment, checkpointManager);
+
+        Assert.Null(result);
+        Assert.NotNull(requests);
+
+        requests.Should().HaveCount(1);
+        ExternalRequest request = requests[0].Request;
+
+        ToolApprovalRequestContent approvalRequest =
+            request.Data.As<ToolApprovalRequestContent>().Should().NotBeNull()
+                                                              .And.Subject.As<ToolApprovalRequestContent>();
+
+        approvalRequest.ToolCall.CallId.Should().Be(SomeOtherFunctionCallId);
+
+        ExternalResponse response = request.CreateResponse(approvalRequest.CreateResponse(false, "Denied"));
+
+        (updateText, result, _, requests) =
+            await RunWorkflowCheckpointedAsync(workflow, response, Environment, checkpointManager, lastCheckpoint);
+
+        Assert.Equal("Hello from agent3", updateText);
+        Assert.NotNull(result);
+
+        // User + (assistant empty + tool) for each of first two agents + final assistant with text.
+        Assert.Equal(10, result.Count);
+
+        Assert.Equal(ChatRole.User, result[0].Role);
+        Assert.Equal("abc", result[0].Text);
+
+        Assert.Equal(ChatRole.Assistant, result[1].Role);
+        Assert.Equal("", result[1].Text);
+        Assert.Contains("initialAgent", result[1].AuthorName);
+
+        Assert.Equal(ChatRole.Tool, result[2].Role);
+        Assert.Contains("initialAgent", result[2].AuthorName);
+
+        // Non-handoff tool invocation (and user denial)
+        Assert.Equal(ChatRole.Assistant, result[3].Role);
+        Assert.Equal("", result[3].Text);
+        Assert.Contains("secondAgent", result[3].AuthorName);
+
+        Assert.Equal(ChatRole.User, result[4].Role);
+        Assert.Equal("", result[4].Text);
+
+        // Rejected tool call
+        Assert.Equal(ChatRole.Assistant, result[5].Role);
+        Assert.Equal("", result[5].Text);
+        Assert.Contains("secondAgent", result[5].AuthorName);
+
+        Assert.Equal(ChatRole.Tool, result[6].Role);
+        Assert.Contains("secondAgent", result[6].AuthorName);
+
+        // Handoff invocation
+        Assert.Equal(ChatRole.Assistant, result[7].Role);
+        Assert.Equal("", result[7].Text);
+        Assert.Contains("secondAgent", result[7].AuthorName);
+
+        Assert.Equal(ChatRole.Tool, result[8].Role);
+        Assert.Contains("secondAgent", result[8].AuthorName);
+
+        Assert.Equal(ChatRole.Assistant, result[9].Role);
+        Assert.Equal("Hello from agent3", result[9].Text);
+        Assert.Contains("thirdAgent", result[9].AuthorName);
+
+        static bool SomeOtherFunction() => true;
+    }
+
+    [Fact]
+    public async Task Handoffs_TwoTransfers_SecondAgentToolCall_ResponseServedByThirdAgentAsync()
+    {
+        var initialAgent = new ChatClientAgent(new MockChatClient((messages, options) =>
+        {
+            ChatMessage message = Assert.Single(messages);
+            Assert.Equal("abc", Assert.IsType<TextContent>(Assert.Single(message.Contents)).Text);
+
+            string? transferFuncName = options?.Tools?.FirstOrDefault(t => t.Name.StartsWith("handoff_to_", StringComparison.Ordinal))?.Name;
+            Assert.NotNull(transferFuncName);
+
+            // Only a handoff function call.
+            return new(new ChatMessage(ChatRole.Assistant, [new FunctionCallContent("call1", transferFuncName)]));
+        }), name: "initialAgent");
+
+        bool secondAgentInvoked = false;
+
+        const string SomeOtherFunctionName = "SomeOtherFunction";
+        const string SomeOtherFunctionCallId = "call2first";
+
+        JsonElement otherFunctionSchema = AIFunctionFactory.Create(() => true).JsonSchema;
+        AIFunctionDeclaration someOtherFunction = AIFunctionFactory.CreateDeclaration(SomeOtherFunctionName, "Another function", otherFunctionSchema);
+
+        var secondAgent = new ChatClientAgent(new MockChatClient((messages, options) =>
+        {
+            if (!secondAgentInvoked)
+            {
+                secondAgentInvoked = true;
+                return new(new ChatMessage(ChatRole.Assistant, [new FunctionCallContent(SomeOtherFunctionCallId, SomeOtherFunctionName)]));
+            }
+
+            // Second agent should receive the conversation so far (including previous assistant + tool messages eventually).
+            string? transferFuncName = options?.Tools?.FirstOrDefault(t => t.Name.StartsWith("handoff_to_", StringComparison.Ordinal))?.Name;
+            Assert.NotNull(transferFuncName);
+
+            return new(new ChatMessage(ChatRole.Assistant, [new FunctionCallContent("call2", transferFuncName)]));
+        }), name: "secondAgent", description: "The second agent", tools: [someOtherFunction]);
+
+        var thirdAgent = new ChatClientAgent(new MockChatClient((messages, options) =>
+            new(new ChatMessage(ChatRole.Assistant, "Hello from agent3"))),
+            name: "thirdAgent",
+            description: "The third / final agent");
+
+        var workflow =
+            AgentWorkflowBuilder.CreateHandoffBuilderWith(initialAgent)
+            .WithHandoff(initialAgent, secondAgent)
+            .WithHandoff(secondAgent, thirdAgent)
+            .Build();
+
+        CheckpointManager checkpointManager = CheckpointManager.CreateInMemory();
+        const ExecutionEnvironment Environment = ExecutionEnvironment.InProcess_Lockstep;
+
+        (string updateText, List<ChatMessage>? result, CheckpointInfo? lastCheckpoint, List<RequestInfoEvent> requests) =
+            await RunWorkflowCheckpointedAsync(workflow, [new ChatMessage(ChatRole.User, "abc")], Environment, checkpointManager);
+
+        Assert.Null(result);
+        Assert.NotNull(requests);
+
+        requests.Should().HaveCount(1);
+        ExternalRequest request = requests[0].Request;
+
+        FunctionCallContent functionCall = request.Data.As<FunctionCallContent>().Should().NotBeNull()
+                                                                                 .And.Subject.As<FunctionCallContent>();
+
+        functionCall.CallId.Should().Be(SomeOtherFunctionCallId);
+        functionCall.Name.Should().Be(SomeOtherFunctionName);
+
+        ExternalResponse response = request.CreateResponse(new FunctionResultContent(functionCall.CallId, true));
+
+        (updateText, result, _, requests) =
+            await RunWorkflowCheckpointedAsync(workflow, response, Environment, checkpointManager, lastCheckpoint);
+
+        Assert.Equal("Hello from agent3", updateText);
+        Assert.NotNull(result);
+
+        // User + (assistant empty + tool) for each of first two agents + final assistant with text.
+        Assert.Equal(8, result.Count);
+
+        Assert.Equal(ChatRole.User, result[0].Role);
+        Assert.Equal("abc", result[0].Text);
+
+        Assert.Equal(ChatRole.Assistant, result[1].Role);
+        Assert.Equal("", result[1].Text);
+        Assert.Contains("initialAgent", result[1].AuthorName);
+
+        Assert.Equal(ChatRole.Tool, result[2].Role);
+        Assert.Contains("initialAgent", result[2].AuthorName);
+
+        // Non-handoff tool invocation
+        Assert.Equal(ChatRole.Assistant, result[3].Role);
+        Assert.Equal("", result[3].Text);
+        Assert.Contains("secondAgent", result[3].AuthorName);
+
+        Assert.Equal(ChatRole.Tool, result[4].Role);
+        Assert.Contains("secondAgent", result[4].AuthorName);
+
+        // Handoff invocation
+        Assert.Equal(ChatRole.Assistant, result[5].Role);
+        Assert.Equal("", result[5].Text);
+        Assert.Contains("secondAgent", result[5].AuthorName);
+
+        Assert.Equal(ChatRole.Tool, result[6].Role);
+        Assert.Contains("secondAgent", result[6].AuthorName);
+
+        Assert.Equal(ChatRole.Assistant, result[7].Role);
+        Assert.Equal("Hello from agent3", result[7].Text);
+        Assert.Contains("thirdAgent", result[7].AuthorName);
+    }
+
     [Theory]
     [InlineData(1)]
     [InlineData(2)]
@@ -651,7 +878,7 @@ public class AgentWorkflowBuilderTests
         for (int iter = 0; iter < 3; iter++)
         {
             const string UserInput = "abc";
-            (string updateText, List<ChatMessage>? result, _) = await RunWorkflowAsync(workflow, [new ChatMessage(ChatRole.User, UserInput)]);
+            (string updateText, List<ChatMessage>? result, _, _) = await RunWorkflowAsync(workflow, [new ChatMessage(ChatRole.User, UserInput)]);
 
             Assert.NotNull(result);
             Assert.Equal(maxIterations + 1, result.Count);
@@ -832,7 +1059,7 @@ public class AgentWorkflowBuilderTests
         Assert.Equal(1, specialistCallCount);  // specialist NOT called
     }
 
-    private sealed record WorkflowRunResult(string UpdateText, List<ChatMessage>? Result, CheckpointInfo? LastCheckpoint);
+    private sealed record WorkflowRunResult(string UpdateText, List<ChatMessage>? Result, CheckpointInfo? LastCheckpoint, List<RequestInfoEvent> PendingRequests);
 
     private static Task<WorkflowRunResult> RunWorkflowCheckpointedAsync(
         Workflow workflow, List<ChatMessage> input, ExecutionEnvironment executionEnvironment, CheckpointManager checkpointManager, CheckpointInfo? fromCheckpoint = null)
@@ -843,6 +1070,15 @@ public class AgentWorkflowBuilderTests
         return RunWorkflowCheckpointedAsync(workflow, input, environment, fromCheckpoint);
     }
 
+    private static Task<WorkflowRunResult> RunWorkflowCheckpointedAsync(
+        Workflow workflow, ExternalResponse response, ExecutionEnvironment executionEnvironment, CheckpointManager checkpointManager, CheckpointInfo? fromCheckpoint = null)
+    {
+        InProcessExecutionEnvironment environment = executionEnvironment.ToWorkflowExecutionEnvironment()
+                                                                        .WithCheckpointing(checkpointManager);
+
+        return RunWorkflowCheckpointedAsync(workflow, response, environment, fromCheckpoint);
+    }
+
     private static async Task<WorkflowRunResult> RunWorkflowCheckpointedAsync(
         Workflow workflow, List<ChatMessage> input, InProcessExecutionEnvironment environment, CheckpointInfo? fromCheckpoint = null)
     {
@@ -853,15 +1089,39 @@ public class AgentWorkflowBuilderTests
         await run.TrySendMessageAsync(input);
         await run.TrySendMessageAsync(new TurnToken(emitEvents: true));
 
+        return await ProcessWorkflowRunAsync(run);
+    }
+
+    private static async Task<WorkflowRunResult> RunWorkflowCheckpointedAsync(
+        Workflow workflow, ExternalResponse response, InProcessExecutionEnvironment environment, CheckpointInfo? fromCheckpoint = null)
+    {
+        await using StreamingRun run =
+            fromCheckpoint != null ? await environment.ResumeStreamingAsync(workflow, fromCheckpoint)
+                                   : await environment.OpenStreamingAsync(workflow);
+
+        await run.SendResponseAsync(response);
+
+        return await ProcessWorkflowRunAsync(run);
+    }
+
+    private static async Task<WorkflowRunResult> ProcessWorkflowRunAsync(StreamingRun run)
+    {
         StringBuilder sb = new();
         WorkflowOutputEvent? output = null;
         CheckpointInfo? lastCheckpoint = null;
-        await foreach (WorkflowEvent evt in run.WatchStreamAsync().ConfigureAwait(false))
+
+        List<RequestInfoEvent> pendingRequests = [];
+
+        await foreach (WorkflowEvent evt in run.WatchStreamAsync(blockOnPendingRequest: false).ConfigureAwait(false))
         {
             switch (evt)
             {
-                case AgentResponseUpdateEvent executorComplete:
-                    sb.Append(executorComplete.Data);
+                case AgentResponseUpdateEvent responseUpdate:
+                    sb.Append(responseUpdate.Data);
+                    break;
+
+                case RequestInfoEvent requestInfo:
+                    pendingRequests.Add(requestInfo);
                     break;
 
                 case WorkflowOutputEvent e:
@@ -878,7 +1138,7 @@ public class AgentWorkflowBuilderTests
             }
         }
 
-        return new(sb.ToString(), output?.As<List<ChatMessage>>(), lastCheckpoint);
+        return new(sb.ToString(), output?.As<List<ChatMessage>>(), lastCheckpoint, pendingRequests);
     }
 
     private static Task<WorkflowRunResult> RunWorkflowAsync(

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

@@ -29,7 +29,7 @@ public class HandoffAgentExecutorTests : AIAgentHostingExecutorTestsBase
                                                   emitAgentResponseUpdateEvents: executorSetting,
                                                   HandoffToolCallFilteringBehavior.None);
 
-        HandoffAgentExecutor executor = new(agent, options);
+        HandoffAgentExecutor executor = new(agent, [], options);
         testContext.ConfigureExecutor(executor);
 
         // Act
@@ -57,7 +57,7 @@ public class HandoffAgentExecutorTests : AIAgentHostingExecutorTestsBase
                                                   emitAgentResponseUpdateEvents: false,
                                                   HandoffToolCallFilteringBehavior.None);
 
-        HandoffAgentExecutor executor = new(agent, options);
+        HandoffAgentExecutor executor = new(agent, [], options);
         testContext.ConfigureExecutor(executor);
 
         // Act