```ts
function chunk<T>(items: readonly T[], size: number): T[][] {
  if (typeof size !== 'number' || size < 1) {
    throw new Error('Size must be a positive integer');
  }

  const result: T[][] = [];
  for (let i = 0; i < items.length; i += size) {
    // Ensure we don't access out-of-bounds indices
    result.push(items.slice(i, Math.min(i + size, items.length)));
  }
  return result;
}
```