```typescript
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.length > 0 ? acc[acc.length - 1] : [];
    if (lastGroup.length < size) {
      lastGroup.push(item);
      return [...acc];
    } else {
      return [...acc, [item]];
    }
  }, [] as T[][]);
}
```