Fix the low bound that never advances — find the bug

const piles = [3, 6, 7, 11];
const hours = (s) => piles.reduce((t, p) => t + Math.ceil(p / s), 0);
let lo = 1, hi = Math.max(...piles), guard = 0;
while (lo < hi && guard < 40) {
  const mid = (lo + hi) >>> 1;
  if (hours(mid) <= 8) hi = mid; else lo = mid;
  guard++;
}
document.querySelector('#out').textContent = "speed " + lo;