/**
 * Recursively flattens a nested plain object into a single-level object
 * keyed by joined paths. Arrays and non-plain objects are kept as-is.
 *
 * @param {Record<string, unknown>} object - Source nested object
 * @param {string} [separator="."] - Separator used to join path segments
 * @returns {Record<string, unknown>} A flat object
 * @example
 * flattenObject({ a: { b: { c: 1 } }, d: 2 }); // { "a.b.c": 1, d: 2 }
 */
export declare const flattenObject: <T extends Record<string, unknown>>(object: T, separator?: string) => Record<string, unknown>;