.Net: Fix to ensure OpenAIPromptExecutionSettings ChatSystemPrompt is…

… not ignored (#4530)

### Motivation and Context

Resolves issue #4510 

### Description

Add a system message using the chat system prompt if no system message
is included in the chat history

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [ ] The code builds clean without any errors or warnings
- [ ] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [ ] All unit tests pass, and I have added new tests where possible
- [ ] I didn't break anyone 😄

dotnet/src/Connectors/Connectors.OpenAI/AzureSdk/ClientCore.cs

@@ -799,6 +799,11 @@ private static ChatCompletionsOptions CreateChatCompletionsOptions(
             }
         }
 
+        if (!string.IsNullOrWhiteSpace(executionSettings?.ChatSystemPrompt) && !chatHistory.Any(m => m.Role == AuthorRole.System))
+        {
+            options.Messages.Add(GetRequestMessage(new ChatMessageContent(AuthorRole.System, executionSettings!.ChatSystemPrompt)));
+        }
+
         foreach (var message in chatHistory)
         {
             options.Messages.Add(GetRequestMessage(message));

dotnet/src/Connectors/Connectors.UnitTests/OpenAI/ChatCompletion/OpenAIChatCompletionTests.cs

@@ -121,8 +121,8 @@ public async Task ItAddsIdToChatMessageAsync()
         var actualRequestContent = Encoding.UTF8.GetString(this._messageHandlerStub.RequestContent!);
         Assert.NotNull(actualRequestContent);
         var optionsJson = JsonSerializer.Deserialize<JsonElement>(actualRequestContent);
-        Assert.Equal(1, optionsJson.GetProperty("messages").GetArrayLength());
-        Assert.Equal("John Doe", optionsJson.GetProperty("messages")[0].GetProperty("tool_call_id").GetString());
+        Assert.Equal(2, optionsJson.GetProperty("messages").GetArrayLength());
+        Assert.Equal("John Doe", optionsJson.GetProperty("messages")[1].GetProperty("tool_call_id").GetString());
     }
 
     [Fact]
@@ -163,6 +163,30 @@ public async Task ItGetTextContentsShouldHaveModelIdDefinedAsync()
         Assert.Equal("gpt-3.5-turbo", textContent.ModelId);
     }
 
+    [Fact]
+    public async Task ItAddsSystemMessageAsync()
+    {
+        // Arrange
+        var chatCompletion = new OpenAIChatCompletionService(modelId: "gpt-3.5-turbo", apiKey: "NOKEY", httpClient: this._httpClient);
+        this._messageHandlerStub.ResponseToReturn = new HttpResponseMessage(System.Net.HttpStatusCode.OK)
+        { Content = new StringContent(ChatCompletionResponse) };
+        var chatHistory = new ChatHistory();
+        chatHistory.AddMessage(AuthorRole.User, "Hello");
+
+        // Act
+        await chatCompletion.GetChatMessageContentsAsync(chatHistory, this._executionSettings);
+
+        // Assert
+        var actualRequestContent = Encoding.UTF8.GetString(this._messageHandlerStub.RequestContent!);
+        Assert.NotNull(actualRequestContent);
+        var optionsJson = JsonSerializer.Deserialize<JsonElement>(actualRequestContent);
+        Assert.Equal(2, optionsJson.GetProperty("messages").GetArrayLength());
+        Assert.Equal("Assistant is a large language model.", optionsJson.GetProperty("messages")[0].GetProperty("content").GetString());
+        Assert.Equal("system", optionsJson.GetProperty("messages")[0].GetProperty("role").GetString());
+        Assert.Equal("Hello", optionsJson.GetProperty("messages")[1].GetProperty("content").GetString());
+        Assert.Equal("user", optionsJson.GetProperty("messages")[1].GetProperty("role").GetString());
+    }
+
     public void Dispose()
     {
         this._httpClient.Dispose();

dotnet/src/IntegrationTests/Connectors/OpenAI/ChatHistoryTests.cs

@@ -70,6 +70,54 @@ public async Task ItSerializesAndDeserializesChatHistoryAsync()
         Assert.Null(exception);
     }
 
+    [Fact]
+    public async Task ItUsesChatSystemPromptFromSettingsAsync()
+    {
+        // Arrange
+        this._kernelBuilder.Services.AddSingleton<ILoggerFactory>(this._logger);
+        var builder = this._kernelBuilder;
+        this.ConfigureAzureOpenAIChatAsText(builder);
+        builder.Plugins.AddFromType<FakePlugin>();
+        var kernel = builder.Build();
+
+        string systemPrompt = "You are batman. If asked who you are, say 'I am Batman!'";
+
+        OpenAIPromptExecutionSettings settings = new() { ChatSystemPrompt = systemPrompt };
+        ChatHistory history = new();
+
+        // Act
+        history.AddUserMessage("Who are you?");
+        var service = kernel.GetRequiredService<IChatCompletionService>();
+        ChatMessageContent result = await service.GetChatMessageContentAsync(history, settings, kernel);
+
+        // Assert
+        Assert.Contains("Batman", result.ToString(), StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public async Task ItUsesChatSystemPromptFromChatHistoryAsync()
+    {
+        // Arrange
+        this._kernelBuilder.Services.AddSingleton<ILoggerFactory>(this._logger);
+        var builder = this._kernelBuilder;
+        this.ConfigureAzureOpenAIChatAsText(builder);
+        builder.Plugins.AddFromType<FakePlugin>();
+        var kernel = builder.Build();
+
+        string systemPrompt = "You are batman. If asked who you are, say 'I am Batman!'";
+
+        OpenAIPromptExecutionSettings settings = new();
+        ChatHistory history = new(systemPrompt);
+
+        // Act
+        history.AddUserMessage("Who are you?");
+        var service = kernel.GetRequiredService<IChatCompletionService>();
+        ChatMessageContent result = await service.GetChatMessageContentAsync(history, settings, kernel);
+
+        // Assert
+        Assert.Contains("Batman", result.ToString(), StringComparison.OrdinalIgnoreCase);
+    }
+
     private void ConfigureAzureOpenAIChatAsText(IKernelBuilder kernelBuilder)
     {
         var azureOpenAIConfiguration = this._configuration.GetSection("Planners:AzureOpenAI").Get<AzureOpenAIConfiguration>();