.Net: Return result of the function executed before termination for s…

…treaming API (microsoft#6428)

### Motivation, Context and Description
Fixes: microsoft#6404

Today, the SK chat completion streaming API does not return the result
of a function executed before termination, whereas the non-streaming
version does return the result. This PR resolves this issue by returning
the result of a function executed before termination was requested.

### Contribution Checklist

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

- [x] The code builds clean without any errors or warnings
- [x] 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
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

dotnet/src/Connectors/Connectors.MistralAI.UnitTests/Client/MistralClientTests.cs

@@ -397,6 +397,47 @@ public async Task ValidateGetChatMessageContentsWithAutoFunctionInvocationFilter
         Assert.Contains("GetWeather", invokedFunctions);
     }
 
+    [Fact]
+    public async Task ValidateGetStreamingChatMessageContentWithAutoFunctionInvocationFilterTerminateAsync()
+    {
+        // Arrange
+        var client = this.CreateMistralClientStreaming("mistral-tiny", "https://api.mistral.ai/v1/chat/completions", "chat_completions_streaming_function_call_response.txt");
+
+        var kernel = new Kernel();
+        kernel.Plugins.AddFromType<WeatherPlugin>();
+
+        var filter = new FakeAutoFunctionFilter(async (context, next) =>
+        {
+            await next(context);
+            context.Terminate = true;
+        });
+        kernel.AutoFunctionInvocationFilters.Add(filter);
+
+        var executionSettings = new MistralAIPromptExecutionSettings { ToolCallBehavior = MistralAIToolCallBehavior.AutoInvokeKernelFunctions };
+        var chatHistory = new ChatHistory
+        {
+            new ChatMessageContent(AuthorRole.User, "What is the weather like in Paris?")
+        };
+
+        List<StreamingKernelContent> streamingContent = [];
+
+        // Act
+        await foreach (var item in client.GetStreamingChatMessageContentsAsync(chatHistory, default, executionSettings, kernel))
+        {
+            streamingContent.Add(item);
+        }
+
+        // Assert
+        // Results of function invoked before termination should be returned 
+        Assert.Equal(3, streamingContent.Count);
+
+        var lastMessageContent = streamingContent[^1] as StreamingChatMessageContent;
+        Assert.NotNull(lastMessageContent);
+
+        Assert.Equal("12°C\nWind: 11 KMPH\nHumidity: 48%\nMostly cloudy", lastMessageContent.Content);
+        Assert.Equal(AuthorRole.Tool, lastMessageContent.Role);
+    }
+
     [Theory]
     [InlineData("system", "System Content")]
     [InlineData("user", "User Content")]

dotnet/src/Connectors/Connectors.MistralAI/Client/MistralClient.cs

@@ -447,14 +447,17 @@ internal async IAsyncEnumerable<StreamingChatMessageContent> GetStreamingChatMes
 
                 this.AddResponseMessage(chatRequest, chatHistory, toolCall, result: stringResult, errorMessage: null);
 
-                // If filter requested termination, breaking request iteration loop.
+                // If filter requested termination, returning latest function result and breaking request iteration loop.
                 if (invocationContext.Terminate)
                 {
                     if (this._logger.IsEnabled(LogLevel.Debug))
                     {
                         this._logger.LogDebug("Filter requested termination of automatic function invocation.");
                     }
 
+                    var lastChatMessage = chatHistory.Last();
+
+                    yield return new StreamingChatMessageContent(lastChatMessage.Role, lastChatMessage.Content);
                     yield break;
                 }
             }

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

@@ -859,14 +859,17 @@ internal async IAsyncEnumerable<OpenAIStreamingChatMessageContent> GetStreamingC
 
                 AddResponseMessage(chatOptions, chat, streamedRole, toolCall, metadata, stringResult, errorMessage: null, this.Logger);
 
-                // If filter requested termination, breaking request iteration loop.
+                // If filter requested termination, returning latest function result and breaking request iteration loop.
                 if (invocationContext.Terminate)
                 {
                     if (this.Logger.IsEnabled(LogLevel.Debug))
                     {
                         this.Logger.LogDebug("Filter requested termination of automatic function invocation.");
                     }
 
+                    var lastChatMessage = chat.Last();
+
+                    yield return new OpenAIStreamingChatMessageContent(lastChatMessage.Role, lastChatMessage.Content);
                     yield break;
                 }
 

dotnet/src/Connectors/Connectors.UnitTests/OpenAI/FunctionCalling/AutoFunctionInvocationFilterTests.cs

@@ -497,7 +497,7 @@ public async Task PostFilterCanTerminateOperationAsync()
         this._messageHandlerStub.ResponsesToReturn = GetFunctionCallingResponses();
 
         // Act
-        await kernel.InvokePromptAsync("Test prompt", new(new OpenAIPromptExecutionSettings
+        var result = await kernel.InvokePromptAsync("Test prompt", new(new OpenAIPromptExecutionSettings
         {
             ToolCallBehavior = ToolCallBehavior.AutoInvokeKernelFunctions
         }));
@@ -507,6 +507,13 @@ public async Task PostFilterCanTerminateOperationAsync()
         Assert.Equal(0, secondFunctionInvocations);
         Assert.Equal([0], requestSequenceNumbers);
         Assert.Equal([0], functionSequenceNumbers);
+
+        // Results of function invoked before termination should be returned
+        var lastMessageContent = result.GetValue<ChatMessageContent>();
+        Assert.NotNull(lastMessageContent);
+
+        Assert.Equal("function1-value", lastMessageContent.Content);
+        Assert.Equal(AuthorRole.Tool, lastMessageContent.Role);
     }
 
     [Fact]
@@ -538,15 +545,28 @@ public async Task PostFilterCanTerminateOperationOnStreamingAsync()
 
         var executionSettings = new OpenAIPromptExecutionSettings { ToolCallBehavior = ToolCallBehavior.AutoInvokeKernelFunctions };
 
+        List<StreamingKernelContent> streamingContent = [];
+
         // Act
         await foreach (var item in kernel.InvokePromptStreamingAsync("Test prompt", new(executionSettings)))
-        { }
+        {
+            streamingContent.Add(item);
+        }
 
         // Assert
         Assert.Equal(1, firstFunctionInvocations);
         Assert.Equal(0, secondFunctionInvocations);
         Assert.Equal([0], requestSequenceNumbers);
         Assert.Equal([0], functionSequenceNumbers);
+
+        // Results of function invoked before termination should be returned 
+        Assert.Equal(3, streamingContent.Count);
+
+        var lastMessageContent = streamingContent[^1] as StreamingChatMessageContent;
+        Assert.NotNull(lastMessageContent);
+
+        Assert.Equal("function1-value", lastMessageContent.Content);
+        Assert.Equal(AuthorRole.Tool, lastMessageContent.Role);
     }
 
     public void Dispose()