Fix HostedCodeInterpreterTool with Responses (#6817)

When no file IDs are present, we're outputting the wrong JSON.

Author: stephentoub

src/Libraries/Microsoft.Extensions.AI.OpenAI/OpenAIResponsesChatClient.cs

@@ -479,7 +479,7 @@ private ResponseCreationOptions ToOpenAIResponseCreationOptions(ChatOptions? opt
                         }
                         else
                         {
-                            json = """{"type":"code_interpreter","container":"auto"}""";
+                            json = """{"type":"code_interpreter","container":{"type":"auto"}}""";
                         }
 
                         result.Tools.Add(ModelReaderWriter.Read<ResponseTool>(BinaryData.FromString(json)));

test/Libraries/Microsoft.Extensions.AI.OpenAI.Tests/OpenAIResponseClientIntegrationTests.cs

@@ -21,6 +21,22 @@ public class OpenAIResponseClientIntegrationTests : ChatClientIntegrationTests
     // Test structure doesn't make sense with Responses.
     public override Task Caching_AfterFunctionInvocation_FunctionOutputUnchangedAsync() => Task.CompletedTask;
 
+    [ConditionalFact]
+    public async Task UseCodeInterpreter_ProducesCodeExecutionResults()
+    {
+        SkipIfNotEnabled();
+
+        var response = await ChatClient.GetResponseAsync("Use the code interpreter to calculate the square root of 42. Return only the nearest integer value and no other text.", new()
+        {
+            Tools = [new HostedCodeInterpreterTool()],
+        });
+        Assert.NotNull(response);
+
+        ChatMessage message = Assert.Single(response.Messages);
+
+        Assert.Equal("6", message.Text);
+    }
+
     [ConditionalFact]
     public async Task UseWebSearch_AnnotationsReflectResults()
     {