/**
 * Generates an identifier for in-memory message keys.
 * Uses `crypto.randomUUID()` when available (Chrome 92+, Firefox 96+, Safari 15.4+).
 * Falls back to a v4-shape UUID derived from Math.random for older browsers.
 *
 * NOT CRYPTOGRAPHIC. Only used for React-style list `key` values and internal id tracking.
 */
export declare function generateId(): string;