refactor: Remove instance-shared current agent tracking in handoffs

Because the tracker was instance-shared between the start and end executors, it would be shared between all sessions, resulting in incorrect behaviour.

The corect way to do this is to keep the data in a shared executor scope, which is per-session.

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

@@ -145,7 +145,7 @@ public static partial class AgentWorkflowBuilder
         return builder.Build();
     }
 
-    /// <summary>Creates a new <see cref="HandoffsWorkflowBuilder"/> using <paramref name="initialAgent"/> as the starting agent in the workflow.</summary>
+    /// <summary>Creates a new <see cref="HandoffWorkflowBuilder"/> using <paramref name="initialAgent"/> as the starting agent in the workflow.</summary>
     /// <param name="initialAgent">The agent that will receive inputs provided to the workflow.</param>
     /// <returns>The builder for creating a workflow based on handoffs.</returns>
     /// <remarks>
@@ -154,7 +154,7 @@ public static partial class AgentWorkflowBuilder
     /// The <see cref="AIAgent"/> must be capable of understanding those <see cref="AgentRunOptions"/> provided. If the agent
     /// ignores the tools or is otherwise unable to advertize them to the underlying provider, handoffs will not occur.
     /// </remarks>
-    public static HandoffsWorkflowBuilder CreateHandoffBuilderWith(AIAgent initialAgent)
+    public static HandoffWorkflowBuilder CreateHandoffBuilderWith(AIAgent initialAgent)
     {
         Throw.IfNull(initialAgent);
         return new(initialAgent);

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

@@ -1,9 +0,0 @@
-// Copyright (c) Microsoft. All rights reserved.
-
-namespace Microsoft.Agents.AI.Workflows.Specialized;
-
-/// <summary>Tracks the current agent ID across turns when return-to-previous routing is enabled.</summary>
-internal sealed class HandoffsCurrentAgentTracker
-{
-    public string? CurrentAgentId { get; set; }
-}

dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/HandoffsEndExecutor.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(HandoffsCurrentAgentTracker? tracker = null) : Executor(ExecutorId, declareCrossRunShareable: true), IResettableExecutor
+internal sealed class HandoffsEndExecutor(bool returnToPrevious) : Executor(ExecutorId, declareCrossRunShareable: true), IResettableExecutor
 {
     public const string ExecutorId = "HandoffEnd";
 
@@ -19,9 +19,13 @@ internal sealed class HandoffsEndExecutor(HandoffsCurrentAgentTracker? tracker =
 
     private async ValueTask HandleAsync(HandoffState handoff, IWorkflowContext context, CancellationToken cancellationToken)
     {
-        if (tracker is not null && handoff.CurrentAgentId is not null)
+        if (returnToPrevious)
         {
-            tracker.CurrentAgentId = handoff.CurrentAgentId;
+            await context.QueueStateUpdateAsync<string?>(HandoffConstants.CurrentAgentTrackerKey,
+                                                         handoff.CurrentAgentId,
+                                                         HandoffConstants.CurrentAgentTrackerScope,
+                                                         cancellationToken)
+                         .ConfigureAwait(false);
         }
 
         await context.YieldOutputAsync(handoff.Messages, cancellationToken).ConfigureAwait(false);

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

@@ -7,8 +7,14 @@ using Microsoft.Extensions.AI;
 
 namespace Microsoft.Agents.AI.Workflows.Specialized;
 
+internal static class HandoffConstants
+{
+    internal const string CurrentAgentTrackerKey = "LastAgentId";
+    internal const string CurrentAgentTrackerScope = "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(HandoffsCurrentAgentTracker? tracker = null) : ChatProtocolExecutor(ExecutorId, DefaultOptions, declareCrossRunShareable: true), IResettableExecutor
+internal sealed class HandoffsStartExecutor(bool returnToPrevious) : ChatProtocolExecutor(ExecutorId, DefaultOptions, declareCrossRunShareable: true), IResettableExecutor
 {
     internal const string ExecutorId = "HandoffStart";
 
@@ -22,7 +28,25 @@ internal sealed class HandoffsStartExecutor(HandoffsCurrentAgentTracker? tracker
         base.ConfigureProtocol(protocolBuilder).SendsMessage<HandoffState>();
 
     protected override ValueTask TakeTurnAsync(List<ChatMessage> messages, IWorkflowContext context, bool? emitEvents, CancellationToken cancellationToken = default)
-        => context.SendMessageAsync(new HandoffState(new(emitEvents), null, messages, tracker?.CurrentAgentId), cancellationToken: cancellationToken);
+    {
+        if (returnToPrevious)
+        {
+            return context.InvokeWithStateAsync(
+                async (string? currentAgentId, IWorkflowContext context, CancellationToken cancellationToken) =>
+                {
+                    HandoffState handoffState = new(new(emitEvents), null, messages, currentAgentId);
+                    await context.SendMessageAsync(handoffState, cancellationToken).ConfigureAwait(false);
+
+                    return currentAgentId;
+                },
+                HandoffConstants.CurrentAgentTrackerKey,
+                HandoffConstants.CurrentAgentTrackerScope,
+                cancellationToken);
+        }
+
+        HandoffState handoff = new(new(emitEvents), null, messages);
+        return context.SendMessageAsync(handoff, cancellationToken);
+    }
 
     public new ValueTask ResetAsync() => base.ResetAsync();
 }

dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/Sample/12_HandOff_HostAsAgent.cs

@@ -20,7 +20,7 @@ internal sealed class HandoffTestEchoAgent(string id, string name, string prefix
         {
             IEnumerable<AITool>? handoffs = chatClientOptions.ChatOptions
                                                              .Tools?
-                                                             .Where(tool => tool.Name?.StartsWith(HandoffsWorkflowBuilder.FunctionPrefix,
+                                                             .Where(tool => tool.Name?.StartsWith(HandoffWorkflowBuilder.FunctionPrefix,
                                                                                                   StringComparison.OrdinalIgnoreCase) is true);
 
             if (handoffs != null)
@@ -58,7 +58,7 @@ internal static class Step12EntryPoint
             .Select(i => new HandoffTestEchoAgent($"{EchoAgentIdPrefix}{i}", $"{EchoAgentNamePrefix}{i}", EchoPrefixForAgent(i)))
             .ToArray();
 
-        return new HandoffsWorkflowBuilder(echoAgents[0])
+        return new HandoffWorkflowBuilder(echoAgents[0])
                    .WithHandoff(echoAgents[0], echoAgents[1])
                    .Build();
     }