Queue a single order for cancellation.

The {orderId} value may be a live order ID or an order creation request ID (numeric). Order creation is asynchronous — placement returns only a request_id and the engine assigns the order_id shortly after — so passing the request ID lets you cancel an order before it becomes active. The value is resolved as an order ID first; the request-ID fallback only applies when no live order matches.

The order must belong to the authenticated user. Cancellation is asynchronous — the order is queued for cancellation and will be processed shortly.

This endpoint is idempotent: canceling an already-queued order returns success.