GTM API / Cancel webhook delivery

Cancel a webhook delivery (status → cancelled); no further retries. Allowed from pending / retrying / in_progress; terminal rows → 422 cannot_cancel_terminal. Cancelling an in_progress row may still flip back to success if the worker in-flight attempt returns 2xx (re-read the row; result.in_flight_attempt_pending signals this). Pass expected_status for a CAS write (409 on mismatch). Aborts a pending delivery; state-changing. Contract: - MCP tool cancel_webhook_log, registry package mcp.orchestration/webhook_logs, mount orchestration.webhooks. - Operation action, response envelope action. - Flags: dangerous: the MCP layer gates it behind a preview/commit token, and the effect cannot be undone through this API.