.Net: Fix Gemini function-response message role

dotnet/src/Connectors/Connectors.Google.UnitTests/Core/Gemini/AuthorRoleConverterTests.cs

@@ -120,7 +120,7 @@ public void WriteWhenRoleIsAssistantReturnsModel()
     }
 
     [Fact]
-    public void WriteWhenRoleIsToolReturnsFunction()
+    public void WriteWhenRoleIsToolReturnsUser()
     {
         // Arrange
         var converter = new AuthorRoleConverter();
@@ -131,7 +131,7 @@ public void WriteWhenRoleIsToolReturnsFunction()
         converter.Write(writer, AuthorRole.Tool, JsonSerializerOptions.Default);
 
         // Assert
-        Assert.Equal("\"function\""u8, bufferWriter.GetSpan().Trim((byte)'\0'));
+        Assert.Equal("\"user\""u8, bufferWriter.GetSpan().Trim((byte)'\0'));
     }
 
     [Fact]

dotnet/src/Connectors/Connectors.Google.UnitTests/Core/Gemini/Clients/GeminiChatGenerationFunctionCallingTests.cs

@@ -147,7 +147,7 @@ public async Task ShouldPassFunctionResponseToRequestAsync()
         GeminiRequest request = JsonSerializer.Deserialize<GeminiRequest>(this._messageHandlerStub.RequestContent)!;
         var content = request.Contents.LastOrDefault();
         Assert.NotNull(content);
-        Assert.Equal(AuthorRole.Tool, content.Role);
+        Assert.Equal(AuthorRole.User, content.Role);
         var functionResponse = content.Parts![0].FunctionResponse;
         Assert.NotNull(functionResponse);
         Assert.Equal(toolCallResponse.FullyQualifiedName, functionResponse.FunctionName);
@@ -426,8 +426,9 @@ public async Task ShouldBatchMultipleToolResponsesIntoSingleMessageAsync()
         Assert.NotNull(request);
 
         // Find the content that represents the batched tool responses
-        var toolResponseContent = request.Contents.FirstOrDefault(c => c.Role == AuthorRole.Tool);
+        var toolResponseContent = request.Contents.FirstOrDefault(c => c.Parts!.Any(p => p.FunctionResponse != null));
         Assert.NotNull(toolResponseContent);
+        Assert.Equal(AuthorRole.User, toolResponseContent.Role);
         Assert.NotNull(toolResponseContent.Parts);
 
         // Verify that all function responses are included as separate parts in the single message
@@ -701,6 +702,48 @@ public async Task ThoughtSignatureIsIncludedInSubsequentRequestAsync()
         var secondRequestContent = handlerStub.GetRequestContentAsString(1);
         Assert.NotNull(secondRequestContent);
         Assert.Contains("test-thought-signature-abc123", secondRequestContent);
+
+        using var requestJson = JsonDocument.Parse(secondRequestContent);
+        var contents = requestJson.RootElement.GetProperty("contents");
+        Assert.Equal("model", contents[3].GetProperty("role").GetString());
+        Assert.Equal("test-thought-signature-abc123", contents[3].GetProperty("parts")[0].GetProperty("thoughtSignature").GetString());
+        Assert.Equal("user", contents[4].GetProperty("role").GetString());
+        Assert.Equal(this._timePluginNow.FullyQualifiedName, contents[4].GetProperty("parts")[0].GetProperty("functionResponse").GetProperty("name").GetString());
+    }
+
+    [Fact]
+    public async Task AutoInvokeSerializesSuccessiveToolResponsesWithUserRoleAsync()
+    {
+        using var handlerStub = new MultipleHttpMessageHandlerStub();
+        handlerStub.AddJsonResponse(this._responseContentWithFunction);
+        handlerStub.AddJsonResponse(this._responseContentWithFunction);
+        handlerStub.AddJsonResponse(this._responseContent);
+
+        using var httpClient = new HttpClient(handlerStub, false);
+        var client = this.CreateChatCompletionClient(httpClient: httpClient);
+        var chatHistory = CreateSampleChatHistory();
+        var executionSettings = new GeminiPromptExecutionSettings
+        {
+            ToolCallBehavior = GeminiToolCallBehavior.AutoInvokeKernelFunctions
+        };
+
+        var responses = await client.GenerateChatMessageAsync(chatHistory, executionSettings: executionSettings, kernel: this._kernelWithFunctions);
+
+        Assert.NotEmpty(Assert.Single(responses).Content!);
+        Assert.Equal(2, chatHistory.Count(m => m.Role == AuthorRole.Tool));
+        for (var requestIndex = 1; requestIndex <= 2; requestIndex++)
+        {
+            var requestContent = handlerStub.GetRequestContentAsString(requestIndex);
+            Assert.NotNull(requestContent);
+            using var requestJson = JsonDocument.Parse(requestContent);
+            var contents = requestJson.RootElement.GetProperty("contents").EnumerateArray().ToArray();
+            var toolResponses = contents.Where(c => c.GetProperty("parts").EnumerateArray()
+                .Any(p => p.TryGetProperty("functionResponse", out _))).ToArray();
+
+            Assert.Equal(requestIndex, toolResponses.Length);
+            Assert.All(toolResponses, content => Assert.Equal("user", content.GetProperty("role").GetString()));
+            Assert.All(contents, content => Assert.Contains(content.GetProperty("role").GetString(), new[] { "user", "model" }));
+        }
     }
 
     private static ChatHistory CreateSampleChatHistory()

dotnet/src/Connectors/Connectors.Google.UnitTests/Core/Gemini/Clients/GeminiChatStreamingFunctionCallingTests.cs

@@ -150,7 +150,7 @@ await client.StreamGenerateChatMessageAsync(chatHistory, executionSettings: exec
         GeminiRequest request = JsonSerializer.Deserialize<GeminiRequest>(this._messageHandlerStub.RequestContent)!;
         var content = request.Contents.LastOrDefault();
         Assert.NotNull(content);
-        Assert.Equal(AuthorRole.Tool, content.Role);
+        Assert.Equal(AuthorRole.User, content.Role);
         var functionResponse = content.Parts![0].FunctionResponse;
         Assert.NotNull(functionResponse);
         Assert.Equal(toolCallResponse.FullyQualifiedName, functionResponse.FunctionName);

dotnet/src/Connectors/Connectors.Google.UnitTests/Core/Gemini/GeminiRequestTests.cs

@@ -439,6 +439,13 @@ public void FromChatHistoryCalledToolNotNullAddsFunctionResponse()
             c => string.Equals(c.Parts![0].FunctionResponse!.FunctionName, toolCallResult.FullyQualifiedName, StringComparison.Ordinal));
         var args = request.Contents[0].Parts![0].FunctionResponse!.Response.Arguments;
         Assert.Equal(expectedArgs.ToJsonString(), args.ToJsonString());
+
+        using var requestJson = JsonDocument.Parse(JsonSerializer.Serialize(request));
+        var content = requestJson.RootElement.GetProperty("contents")[0];
+        Assert.Equal("user", content.GetProperty("role").GetString());
+        var functionResponse = content.GetProperty("parts")[0].GetProperty("functionResponse");
+        Assert.Equal(toolCallResult.FullyQualifiedName, functionResponse.GetProperty("name").GetString());
+        AssertDeepEquals(JsonSerializer.SerializeToElement(expectedArgs), functionResponse.GetProperty("response").GetProperty("content"));
     }
 
     [Fact]

dotnet/src/Connectors/Connectors.Google/Core/Gemini/AuthorRoleConverter.cs

@@ -45,7 +45,8 @@ public override void Write(Utf8JsonWriter writer, AuthorRole? value, JsonSeriali
 
         if (value == AuthorRole.Tool)
         {
-            writer.WriteStringValue("function");
+            // Gemini function responses are carried by user messages.
+            writer.WriteStringValue("user");
         }
         else if (value == AuthorRole.Assistant)
         {