The async/sync delete_response_api_handler always passed json=data into
httpx.delete, where data is {} from the transformer. httpx serializes that
to a 2-byte body. The Azure Responses DELETE endpoint now rejects any
request body with code: unexpected_body, breaking
test_basic_openai_responses_delete_endpoint on the llm_responses_api_testing
job. Build the kwargs dict and only set json= when data is truthy.
Add unit tests that patch httpx.delete and assert json/data are not in the
captured kwargs for the Azure DELETE path (sync and async).