```ts
/**
 * Split 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.
 */
export function chunk<T>(items: readonly T[], size: number): T[][] {
    if (size <= 0) {
        throw new Error('Size must be a positive integer.');
    }

    const result: T[][] = [];
    for (let i = 0; i < items.length; i += size) {
        result.push(items.slice(i, i + size));
    }
    return result;
}
```