Executes a known capability using the requested ordered providers and provider-native options. Returns normalized records plus complete attempt, native-output, cost, and failure evidence. Requires an Idempotency-Key. To observe ChatGPT or Copilot answers, use source=web and capability=ask_chatgpt or ask_copilot with input.query as the prompt. Inspect the named capability for provider options. Existing web.research provider selections remain supported.