.NET: fix: WorkflowAsAgent Sample (#1787)

* fix: WorkflowAsAgent Sample

* Also makes ChatForwardingExecutor public

* feat: Expand ChatForwardingExecutor handled types

Make ChatForwardingExecutor match the input types of ChatProtocolExecutor.

* fix: Update for the new AgentRunResponseUpdate merge logic

AIAgent always sends out List<ChatMessage> now.

dotnet/samples/GettingStarted/Workflows/Agents/WorkflowAsAnAgent/WorkflowFactory.cs

@@ -16,7 +16,7 @@ internal static class WorkflowFactory
     internal static Workflow BuildWorkflow(IChatClient chatClient)
     {
         // Create executors
-        var startExecutor = new ConcurrentStartExecutor();
+        var startExecutor = new ChatForwardingExecutor("Start");
         var aggregationExecutor = new ConcurrentAggregationExecutor();
         AIAgent frenchAgent = GetLanguageAgent("French", chatClient);
         AIAgent englishAgent = GetLanguageAgent("English", chatClient);
@@ -38,33 +38,11 @@ internal static class WorkflowFactory
     private static ChatClientAgent GetLanguageAgent(string targetLanguage, IChatClient chatClient) =>
         new(chatClient, instructions: $"You're a helpful assistant who always responds in {targetLanguage}.", name: $"{targetLanguage}Agent");
 
-    /// <summary>
-    /// Executor that starts the concurrent processing by sending messages to the agents.
-    /// </summary>
-    private sealed class ConcurrentStartExecutor() : Executor("ConcurrentStartExecutor")
-    {
-        protected override RouteBuilder ConfigureRoutes(RouteBuilder routeBuilder)
-        {
-            return routeBuilder
-                .AddHandler<List<ChatMessage>>(this.RouteMessages)
-                .AddHandler<TurnToken>(this.RouteTurnTokenAsync);
-        }
-
-        private ValueTask RouteMessages(List<ChatMessage> messages, IWorkflowContext context, CancellationToken cancellationToken)
-        {
-            return context.SendMessageAsync(messages, cancellationToken: cancellationToken);
-        }
-
-        private ValueTask RouteTurnTokenAsync(TurnToken token, IWorkflowContext context, CancellationToken cancellationToken)
-        {
-            return context.SendMessageAsync(token, cancellationToken: cancellationToken);
-        }
-    }
-
     /// <summary>
     /// Executor that aggregates the results from the concurrent agents.
     /// </summary>
-    private sealed class ConcurrentAggregationExecutor() : Executor<List<ChatMessage>>("ConcurrentAggregationExecutor")
+    private sealed class ConcurrentAggregationExecutor() :
+        Executor<List<ChatMessage>>("ConcurrentAggregationExecutor"), IResettableExecutor
     {
         private readonly List<ChatMessage> _messages = [];
 
@@ -85,5 +63,12 @@ internal static class WorkflowFactory
                 await context.YieldOutputAsync(formattedMessages, cancellationToken);
             }
         }
+
+        /// <inheritdoc/>
+        public ValueTask ResetAsync()
+        {
+            this._messages.Clear();
+            return default;
+        }
     }
 }

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

@@ -0,0 +1,71 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Extensions.AI;
+
+namespace Microsoft.Agents.AI.Workflows;
+
+/// <summary>
+/// Provides configuration options for <see cref="ChatForwardingExecutor"/>.
+/// </summary>
+public class ChatForwardingExecutorOptions
+{
+    /// <summary>
+    /// Gets or sets the chat role to use when converting string messages to <see cref="ChatMessage"/> instances.
+    /// If set, the executor will accept string messages and convert them to chat messages with this role.
+    /// </summary>
+    public ChatRole? StringMessageChatRole { get; set; }
+}
+
+/// <summary>
+/// A ChatProtocol executor that forwards all messages it receives. Useful for splitting inputs into parallel
+/// processing paths.
+/// </summary>
+/// <remarks>This executor is designed to be cross-run shareable and can be reset to its initial state. It handles
+/// multiple chat-related types, enabling flexible message forwarding scenarios. Thread safety and reusability are
+/// ensured by its design.</remarks>
+/// <param name="id">The unique identifier for the executor instance. Used to distinguish this executor within the system.</param>
+/// <param name="options">Optional configuration settings for the executor. If null, default options are used.</param>
+public sealed class ChatForwardingExecutor(string id, ChatForwardingExecutorOptions? options = null) : Executor(id, declareCrossRunShareable: true), IResettableExecutor
+{
+    private readonly ChatRole? _stringMessageChatRole = options?.StringMessageChatRole;
+
+    /// <inheritdoc/>
+    protected override RouteBuilder ConfigureRoutes(RouteBuilder routeBuilder)
+    {
+        if (this._stringMessageChatRole.HasValue)
+        {
+            routeBuilder = routeBuilder.AddHandler<string>(
+                (message, context) => context.SendMessageAsync(new ChatMessage(ChatRole.User, message)));
+        }
+
+        return routeBuilder.AddHandler<ChatMessage>(ForwardMessageAsync)
+                           .AddHandler<IEnumerable<ChatMessage>>(ForwardMessagesAsync)
+                           .AddHandler<ChatMessage[]>(ForwardMessagesAsync)
+                           .AddHandler<List<ChatMessage>>(ForwardMessagesAsync)
+                           .AddHandler<TurnToken>(ForwardTurnTokenAsync);
+    }
+
+    private static ValueTask ForwardMessageAsync(ChatMessage message, IWorkflowContext context, CancellationToken cancellationToken)
+        => context.SendMessageAsync(message, cancellationToken);
+
+    // Note that this can be used to split a turn into multiple parallel turns taken, which will cause streaming ChatMessages
+    // to overlap.
+    private static ValueTask ForwardTurnTokenAsync(TurnToken message, IWorkflowContext context, CancellationToken cancellationToken)
+        => context.SendMessageAsync(message, cancellationToken);
+
+    // TODO: This is not ideal, but until we have a way of guaranteeing correct routing of interfaces across serialization
+    // boundaries, we need to do type unification. It behaves better when used as a handler in ChatProtocolExecutor because
+    // it is a strictly contravariant use, whereas this forces invariance on the type because it is directly forwarded.
+    private static ValueTask ForwardMessagesAsync(IEnumerable<ChatMessage> messages, IWorkflowContext context, CancellationToken cancellationToken)
+        => context.SendMessageAsync(messages is List<ChatMessage> messageList ? messageList : messages.ToList(), cancellationToken);
+
+    private static ValueTask ForwardMessagesAsync(ChatMessage[] messages, IWorkflowContext context, CancellationToken cancellationToken)
+        => context.SendMessageAsync(messages, cancellationToken);
+
+    /// <inheritdoc/>
+    public ValueTask ResetAsync() => default;
+}

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

@@ -1,20 +0,0 @@
-// Copyright (c) Microsoft. All rights reserved.
-
-using System.Collections.Generic;
-using System.Threading.Tasks;
-using Microsoft.Extensions.AI;
-
-namespace Microsoft.Agents.AI.Workflows.Specialized;
-
-/// <summary>Executor that forwards all messages.</summary>
-internal sealed class ChatForwardingExecutor(string id) : Executor(id, declareCrossRunShareable: true), IResettableExecutor
-{
-    protected override RouteBuilder ConfigureRoutes(RouteBuilder routeBuilder) =>
-        routeBuilder
-                .AddHandler<string>((message, context, cancellationToken) => context.SendMessageAsync(new ChatMessage(ChatRole.User, message), cancellationToken: cancellationToken))
-                .AddHandler<ChatMessage>((message, context, cancellationToken) => context.SendMessageAsync(message, cancellationToken: cancellationToken))
-                .AddHandler<List<ChatMessage>>((messages, context, cancellationToken) => context.SendMessageAsync(messages, cancellationToken: cancellationToken))
-                .AddHandler<TurnToken>((turnToken, context, cancellationToken) => context.SendMessageAsync(turnToken, cancellationToken: cancellationToken));
-
-    public ValueTask ResetAsync() => default;
-}