/**
 * Validate that `raw` is one of `allowed`. Returns the value typed as
 * the union, the `fallback` when `raw` is undefined/empty, or an Error
 * carrying a usage message when `raw` is set but invalid. Callers
 * surface `error.message` to the caller and return early.
 */
export declare function validateEnum<T extends string>(raw: unknown, allowed: readonly T[], argName: string, fallback: T): T | Error;
/** Require a non-empty string arg or return a usage-style error string. */
export declare function requireString(raw: unknown, argName: string, usage: string): {
    ok: true;
    value: string;
} | {
    ok: false;
    message: string;
};