```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. Throws an Error
 * unless size is 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;
}
```