```ts
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.reduce((acc, item) => {
    const lastGroup = acc[acc.length - 1];
    if (!lastGroup || lastGroup.length === size) {
      acc.push([item]);
    } else {
      lastGroup.push(item);
    }
    return acc;
  }, [] as T[][]);
}
```