chore: import upstream snapshot with attribution

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

@@ -0,0 +1,26 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Collections.Generic;
+using Microsoft.Extensions.AI;
+
+namespace Microsoft.Agents.AI.Workflows.UnitTests;
+
+public class AIAgentsAbstractionsExtensionsTests
+{
+    [Fact]
+    public void CopyWithAssistantToUserForOtherParticipants_DoesNotMutateOriginalMessages()
+    {
+        ChatMessage original = new(ChatRole.Assistant, "from first agent")
+        {
+            AuthorName = "firstAgent"
+        };
+
+        List<ChatMessage> copied = new[] { original }
+            .CopyWithAssistantToUserForOtherParticipants("secondAgent");
+
+        Assert.Single(copied);
+        Assert.Equal(ChatRole.Assistant, original.Role);
+        Assert.Equal(ChatRole.User, copied[0].Role);
+        Assert.NotSame(original, copied[0]);
+    }
+}