/**
 * Subscribes to file upload start events. The callback is invoked whenever a
 * file upload begins within the editor, and the subscription is automatically
 * cleaned up when the component unmounts.
 *
 * @param callback - Function called when an upload starts. Receives the
 * `blockId` of the block where the upload was initiated, if available.
 */
export declare function useOnUploadStart(callback: (blockId?: string) => void): void;