```typescript
/**
 * 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 must not be mutated.
 * Throws an Error unless size is a positive integer.
 *
 * @param items - The array to chunk.
 * @param size - The maximum size of each chunk.
 * @returns An array of chunks.
 */
export function chunk<T>(items: readonly T[], size: number): T[][] {
  if (size <= 0 || !Number.isInteger(size)) {
    throw new Error('Size must be a positive integer');
  }

  return items.length > 0
    ? Array.from({ length: Math.ceil(items.length / size) }, (_, i) =>
        items.slice(i * size, (i + 1) * size)
      )
    : [];
}
```