Base GPT wrapper API using x402 payments. Default direct call: model gpt-5-mini, max_output_tokens=2000, fixed price 0.01 USDC for up to 1000 input tokens. For all other settings the price is computed per model as (input_tokens * input_price_per_million + max_output_tokens * output_price_per_million) / 1,000,000, with a minimum of 0.001 USDC and always rounded up to 6 decimals. Optional max_input_tokens lets you cap the input tokens used for pricing; if the message is longer than this cap the server returns an error instead of under-pricing. Optional action=message (or omitting action) performs a direct GPT call with the given message. Optional action=create creates a custom agent with the given message as preprompt for 0.001 USDC (no OpenAI call), stores a base_price_usdc using (max_input_tokens_for_agent or 1000) + preprompt + max_output_tokens, and returns a custom_id. Optional action=list lists up to 100 recent custom agents for the paying wallet for 0.001 USDC without calling Open