```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((chunks, item, index) => {
        const lastChunk = chunks[chunks.length - 1];
        if (lastChunk !== undefined && lastChunk.length === size) {
            chunks.push([item]);
        } else if (lastChunk !== undefined) {
            lastChunk.push(item);
        } else {
            chunks.push([item]);
        }
        return chunks;
    }, [] as T[][]);
}
```