```typescript
/**
 * Splits an array into consecutive groups of at most size elements,
 * preserving order; the final group is shorter when the length does not divide evenly.
 * An empty array yields an empty array. The input array must not be mutated.
 * Throws an Error unless size is a positive integer.
 *
 * @param items - Array to chunk
 * @param size - Maximum size of each chunk
 * @returns Array of chunks
 */
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");
  }
  if (items.length === 0) return [];
  const chunks: T[][] = [];
  for (let i = 0; i < items.length; i += size) {
    chunks.push(items.slice(i, i + size));
  }
  return chunks;
}
```