```ts
/**
 * Splits an array into consecutive groups of at most `size` elements,
 * preserving order. The final group is shorter when the length does not
 * divide evenly. An empty array yields an empty array. The input array
 * is not mutated.
 *
 * @throws Error if `size` is not a positive integer.
 */
export function chunk<T>(items: readonly T[], size: number): T[][] {
  if (!Number.isInteger(size) || size <= 0) {
    throw new Error('size must be a positive integer');
  }

  const result: T[][] = [];
  
  for (let i = 0; i < items.length; i += size) {
    result.push(items.slice(i, i + size));
  }
  
  return result;
}
```