.NET: Forward Magentic participant replies to manager (#6156)

MagenticOrchestrator.TakeTurnAsync dropped the `messages` parameter
on subsequent turns, so participant replies never reached the manager's
ChatHistory. The manager kept re-dispatching the same speaker every
round until MaxRounds.

Append the incoming messages to taskContext.ChatHistory before running
the coordination round (matches Python's _handle_response).

Adds RecordingReplayAgent + regression test that asserts the worker's
reply reaches round-2's progress-ledger call.

Co-authored-by: Jacob Alber <jaalber@microsoft.com>

dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/Magentic/MagenticOrchestrator.cs

@@ -195,7 +195,12 @@ internal class MagenticOrchestrator(AIAgent managerAgent, List<AIAgent> team, Ta
         }
         else
         {
-            // Subsequent turns: agent returned control, go directly to coordination (progress ledger only, no replan)
+            // Subsequent turns: agent returned control, go directly to coordination (progress ledger only, no replan).
+            // Capture the participant's reply into the manager-visible chat history so the progress ledger can see it.
+            if (messages is { Count: > 0 })
+            {
+                this._taskContext.ChatHistory.AddRange(messages);
+            }
             await this.RunCoordinationRoundAsync(this._taskContext, context, cancellationToken).ConfigureAwait(false);
         }
     }

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

@@ -361,6 +361,64 @@ public class MagenticOrchestrationTests
         runResult.Result![0].Text.Should().Contain("Multi-round task completed!");
     }
 
+    [Fact]
+    public async Task RunCoordinationRound_Forwards_Participant_Reply_To_ManagerAsync()
+    {
+        // Regression: MagenticOrchestrator.TakeTurnAsync used to drop the `messages`
+        // parameter on subsequent turns, so participant replies never reached the
+        // manager's ChatHistory. The manager then re-dispatched the same speaker
+        // every round until MaxRounds. Assert that round-2's progress-ledger call
+        // actually sees the worker's reply in its input.
+
+        const string TaskPrompt = "Echo back this exact magentic-regression-marker";
+
+        List<ChatMessage> factsResponse = CreatePlanResponse("Facts");
+        List<ChatMessage> planResponse = CreatePlanResponse("Plan");
+        List<ChatMessage> round1Ledger = CreateProgressLedgerResponse(
+            isRequestSatisfied: false,
+            isInLoop: false,
+            isProgressBeingMade: true,
+            nextSpeaker: "Worker",
+            instructionOrQuestion: TaskPrompt);
+        List<ChatMessage> round2Ledger = CreateProgressLedgerResponse(
+            isRequestSatisfied: true,
+            isInLoop: false,
+            isProgressBeingMade: true,
+            nextSpeaker: "Worker",
+            instructionOrQuestion: "Done");
+        List<ChatMessage> finalAnswer = CreateFinalAnswerResponse("All good");
+
+        RecordingReplayAgent manager = new(
+            [factsResponse, planResponse, round1Ledger, round2Ledger, finalAnswer],
+            name: "Manager");
+        TestEchoAgent worker = new(name: "Worker");
+
+        Workflow workflow = new MagenticWorkflowBuilder(manager)
+            .AddParticipants(worker)
+            .RequirePlanSignoff(false)
+            .Build();
+
+        WorkflowRunResult runResult = await RunMagenticWorkflowAsync(
+            workflow,
+            [new ChatMessage(ChatRole.User, TaskPrompt)]);
+
+        runResult.Result.Should().NotBeNull();
+        runResult.Result![0].Text.Should().Contain("All good");
+
+        // Calls in order: facts, plan, ledger1, ledger2, finalAnswer.
+        manager.RecordedInputs.Should().HaveCount(5);
+
+        manager.RecordedInputs[3].Should().Contain(
+            m => m.Role == ChatRole.Assistant
+              && m.AuthorName == "Worker"
+              && m.Text.Contains(TaskPrompt),
+            "round-2 progress ledger must see the worker's reply; without it the manager loops to MaxRounds");
+
+        manager.RecordedInputs[4].Should().Contain(
+            m => m.Role == ChatRole.Assistant && m.AuthorName == "Worker",
+            "final-answer synthesis must see what participants actually said");
+    }
+
     [Fact]
     public async Task PlanReview_Revised_Triggers_ReplanAsync()
     {

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

@@ -0,0 +1,32 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using Microsoft.Extensions.AI;
+
+namespace Microsoft.Agents.AI.Workflows.UnitTests;
+
+/// <summary>
+/// A <see cref="TestReplayAgent"/> that records the input messages it receives on each call.
+/// Used by tests that need to assert what context the agent was actually handed.
+/// </summary>
+internal sealed class RecordingReplayAgent(List<List<ChatMessage>> messages, string? id = null, string? name = null)
+    : TestReplayAgent(messages, id, name)
+{
+    public List<List<ChatMessage>> RecordedInputs { get; } = [];
+
+    protected override async IAsyncEnumerable<AgentResponseUpdate> RunCoreStreamingAsync(
+        IEnumerable<ChatMessage> messages,
+        AgentSession? session = null,
+        AgentRunOptions? options = null,
+        [EnumeratorCancellation] CancellationToken cancellationToken = default)
+    {
+        this.RecordedInputs.Add(messages.ToList());
+        await foreach (AgentResponseUpdate update in base.RunCoreStreamingAsync(messages, session, options, cancellationToken))
+        {
+            yield return update;
+        }
+    }
+}