```ts
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");
  }

  return items.reduce((acc, item, index) => {
    const lastGroup = acc[acc.length - 1] ?? [];

    if (lastGroup.length === size) {
      acc.push([item]);
    } else {
      acc[acc.length - 1].push(item);
    }

    return acc;
  }, []);
}
```