- Add full OpenAI Responses API support alongside existing Chat Completions API
- Implement auto_chain parameter to automatically track and pass previous_response_id
- Add auto_chain_reasoning for encrypted reasoning in ZDR (Zero Data Retention) scenarios
- Parse built-in tool outputs: web_search, file_search, computer_use, code_interpreter
- Support all Responses API parameters: reasoning, include, tools, truncation, etc.
- Add streaming support for Responses API with proper event handling
- Include 67 tests covering all new functionality