Setting innerHTML="" on a mock element now detaches and removes all children, matching browser behavior. Previously hs-cleanup! (which sets body.innerHTML="") left stale children attached, causing querySelector to find elements from prior tests. Also clears children when textContent is set (browser behavior). 375 → 393/831 HS tests (+18). Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>