export function groupBy<T>(items: T[], keyFn: (item: T) => string): Record<string, T[]> {
  const result: Record<string, T[]> = {};
  for (const item of items) {
    const key = keyFn(item);
    if (!result[key]) {
      result[key] = [];
    }
    result[key].push(item);
  }
  return result;
}