```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 currentGroup = acc[acc.length - 1];
    if (currentGroup && currentGroup.length === size) {
      acc.push([item]);
    } else if (currentGroup && currentGroup.length < size) {
      currentGroup.push(item);
    } else if (!currentGroup) {
      acc.push([item]);
    }
    return acc;
  }, [] as T[][]);
}
```