From 96778996009b30e55d5f3d8135640a79fcada5c8 Mon Sep 17 00:00:00 2001
From: Trung Hieu <81826098+htilssu@users.noreply.github.com>
Date: Thu, 16 Oct 2025 16:24:00 +0700
Subject: [PATCH] .NET: Duplicate System Instruction when creating a
 ChatClientAgentOptions instance with the constructor (#1382)

* unit test for using create agent option by constructor

* remove this for prevent duplicate when ChatClientAgentOption and ChatOption has same Instruction

* update unit test for ChatClientAgentOptions
---
 .../ChatClient/ChatClientAgentOptions.cs      |  5 ----
 .../ChatClient/ChatClientAgentOptionsTests.cs | 17 +++++++------
 .../ChatClient/ChatClientAgentTests.cs        | 25 +++++++++++++++++++
 3 files changed, 35 insertions(+), 12 deletions(-)

diff --git a/dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgentOptions.cs b/dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgentOptions.cs
index b51b86c64e..aede5ef3cb 100644
--- a/dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgentOptions.cs
+++ b/dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgentOptions.cs
@@ -44,11 +44,6 @@ public class ChatClientAgentOptions
         {
             (this.ChatOptions ??= new()).Tools = tools;
         }
-
-        if (instructions is not null)
-        {
-            (this.ChatOptions ??= new()).Instructions = instructions;
-        }
     }
 
     /// <summary>
diff --git a/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgentOptionsTests.cs b/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgentOptionsTests.cs
index 71768d83d2..dc983ef202 100644
--- a/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgentOptionsTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgentOptionsTests.cs
@@ -61,9 +61,7 @@ public class ChatClientAgentOptionsTests
         Assert.Null(options.Name);
         Assert.Equal(Instructions, options.Instructions);
         Assert.Null(options.Description);
-        Assert.NotNull(options.ChatOptions);
-        Assert.Equal(Instructions, options.ChatOptions.Instructions);
-        Assert.Null(options.ChatOptions.Tools);
+        Assert.Null(options.ChatOptions);
     }
 
     [Fact]
@@ -107,7 +105,7 @@ public class ChatClientAgentOptionsTests
         Assert.Equal(Instructions, options.Instructions);
         Assert.Null(options.Description);
         Assert.NotNull(options.ChatOptions);
-        Assert.Equal(Instructions, options.ChatOptions.Instructions);
+        Assert.Null(options.ChatOptions.Instructions);
         Assert.Same(tools, options.ChatOptions.Tools);
     }
 
@@ -132,7 +130,7 @@ public class ChatClientAgentOptionsTests
         Assert.Equal(Instructions, options.Instructions);
         Assert.Equal(Description, options.Description);
         Assert.NotNull(options.ChatOptions);
-        Assert.Equal(Instructions, options.ChatOptions.Instructions);
+        Assert.Null(options.ChatOptions.Instructions);
         Assert.Same(tools, options.ChatOptions.Tools);
     }
 
@@ -165,8 +163,13 @@ public class ChatClientAgentOptionsTests
         const string Name = "Test name";
         const string Description = "Test description";
         var tools = new List<AITool> { AIFunctionFactory.Create(() => "test") };
-        static ChatMessageStore ChatMessageStoreFactory(ChatClientAgentOptions.ChatMessageStoreFactoryContext ctx) => new Mock<ChatMessageStore>().Object;
-        static AIContextProvider AIContextProviderFactory(ChatClientAgentOptions.AIContextProviderFactoryContext ctx) => new Mock<AIContextProvider>().Object;
+
+        static ChatMessageStore ChatMessageStoreFactory(
+            ChatClientAgentOptions.ChatMessageStoreFactoryContext ctx) => new Mock<ChatMessageStore>().Object;
+
+        static AIContextProvider AIContextProviderFactory(
+            ChatClientAgentOptions.AIContextProviderFactoryContext ctx) =>
+            new Mock<AIContextProvider>().Object;
 
         var original = new ChatClientAgentOptions(Instructions, Name, Description, tools)
         {
diff --git a/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgentTests.cs b/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgentTests.cs
index 9b9f0736ac..f20f7fe082 100644
--- a/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgentTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgentTests.cs
@@ -1012,6 +1012,31 @@ public partial class ChatClientAgentTests
         Assert.Equal("test instructions", capturedChatOptions.Instructions);
     }
 
+    [Fact]
+    public async Task ChatOptionsMergingUsesAgentOptionsConstructorWhenRequestHasNoneAsync()
+    {
+        Mock<IChatClient> mockService = new();
+        ChatOptions? capturedChatOptions = null;
+        mockService.Setup(
+                s => s.GetResponseAsync(
+                    It.IsAny<IEnumerable<ChatMessage>>(),
+                    It.IsAny<ChatOptions>(),
+                    It.IsAny<CancellationToken>()))
+            .Callback<IEnumerable<ChatMessage>, ChatOptions, CancellationToken>((msgs, opts, ct) =>
+                capturedChatOptions = opts)
+            .ReturnsAsync(new ChatResponse([new(ChatRole.Assistant, "response")]));
+
+        ChatClientAgent agent = new(mockService.Object, options: new("test instructions"));
+        var messages = new List<ChatMessage> { new(ChatRole.User, "test") };
+
+        // Act
+        await agent.RunAsync(messages);
+
+        // Assert
+        Assert.NotNull(capturedChatOptions);
+        Assert.Equal("test instructions", capturedChatOptions.Instructions);
+    }
+
     /// <summary>
     /// Verify that ChatOptions merging works when request has ChatOptions but agent doesn't.
     /// </summary>