/**
 * Constructs a threaded conversation ID by appending `;messageid={messageId}`
 * to the conversation ID. This is the format APX uses to route messages
 * to a specific thread.
 *
 * @param conversationId the conversation to thread into (e.g. `19:abc@thread.skype`)
 * @param messageId the thread root message ID (must be a non-zero numeric string)
 * @returns the threaded conversation ID (e.g. `19:abc@thread.skype;messageid=123`)
 */
export declare function toThreadedConversationId(conversationId: string, messageId: string): string;