/**
 * Client-side detection of user-message persistence from widget POST responses.
 */
/** Set on streaming responses after the user row INSERT (before AI bytes). */
export declare const USER_MESSAGE_ID_HEADER = "X-Vtilt-User-Message-Id";
/** ISO timestamp for the persisted user row (streaming responses). */
export declare const USER_MESSAGE_CREATED_AT_HEADER = "X-Vtilt-User-Message-Created-At";
/**
 * Returns true when the server has acknowledged the client-minted user row.
 * For streaming responses, reads response headers without consuming the body.
 * For JSON responses, clones and parses `{ message }`.
 *
 * vTilt persists the user row before streaming AI bytes. When the user ack
 * header is absent (older builds), `text/plain` + `response.ok` is treated as
 * persisted so retries do not spin forever.
 */
export declare function isUserMessagePersisted(response: Response, expectedMessageId: string): Promise<boolean>;