/**
 * Logical user id from ACP `_meta` on `session/new` and `session/load`.
 *
 * Resolution order (first non-empty wins):
 * - `_meta["hooman/userId"]` (string)
 * - `_meta.hooman.userId` (string)
 * - `_meta.userId` (string)
 *
 * Values are trimmed, capped in length, and stripped of ASCII control characters.
 * Empty after sanitization is treated as absent.
 */
export declare function extractAcpClientUserId(_meta: unknown): string | undefined;