```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. 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[][] = [];
  const length = items.length;

  for (let i = 0; i < length; i += size) {
    result.push(items.slice(i, i + size));
  }

  return result;
}
```