Implement test for user field deletion

Add test to verify deletion of user field in response

internal/translator/codex/openai/responses/codex_openai-responses_request_test.go

@@ -263,3 +263,20 @@ func TestConvertSystemRoleToDeveloper_AssistantRole(t *testing.T) {
 		t.Errorf("Expected third role 'assistant', got '%s'", thirdRole.String())
 	}
 }
+
+func TestUserFieldDeletion(t *testing.T) {  
+	inputJSON := []byte(`{  
+		"model": "gpt-5.2",  
+		"user": "test-user",  
+		"input": [{"role": "user", "content": "Hello"}]  
+	}`)  
+	  
+	output := ConvertOpenAIResponsesRequestToCodex("gpt-5.2", inputJSON, false)  
+	outputStr := string(output)  
+	  
+	// Verify user field is deleted  
+	userField := gjson.Get(outputStr, "user")  
+	if userField.Exists() {  
+		t.Error("user field should be deleted")  
+	}  
+}