A separator sits at `calc(end% - 2px)`, so a boundary in the bar's first
pixels (a 1-second lead-in of an hour on a 400px bar) painted it before
the track's start. Clamp it with max(0px, …); it ends where the next
segment starts, so the right end cannot overflow.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>