Selecting a live channel rendered every programme block of its schedule
(about 240 for the Xtream mock) while the stream was starting: about 6,000
of J3's 6,199 renderer.domMutationsToPlaying. The ribbon now renders the
blocks, ticks and day dividers within half a viewport of the visible range;
the track keeps the full schedule's width, so positions, the scrollbar and
scroll-to-now are unchanged.
A resize reported before the scroll-to-now must not re-centre the window
(it once jumped to the schedule's start and back); resizes only widen it.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
