DEFAULT_INSTRUCTIONS = 'You are ChatGPT, a large language model trained by OpenAI.'Generic fallback for the Responses-API instructions field.
The Codex backend rejects any request missing a top-level instructions
value (400 Instructions are required), so this constant keeps zero-config
construction working. Most callers should override it with their own
prompt — see _ChatOpenAICodex.instructions for the resolution rules.