A second tab change during the 420 ms slide now measures where the pill and items are drawn (bounding boxes, which include the running animation) before cancelling the running pill slide and item FLIPs, and starts the next slide from there rather than from the previous destination. Resize and document.fonts.ready also cancel any running slide before re-placing the pill, so it sits on the active item immediately instead of being held by the old keyframes. Tests cover both interruptions; timing, label fade and the reduced-motion jump are unchanged. Maestro task d340ae00-3c2a-48cf-9ac6-35e0b8ed5a7c Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>