Replace fragile zoomGuard boolean with userInteracting flag so that
programmatic scale updates (rolling window, resize, fit) never lock
p.xRange. Only genuine mouse drag or scroll-wheel events on the uPlot
canvas set userInteracting=true and allow onZoom to freeze the view.
Also move stale-xRange detection out of the needsRedraw gate so that a
plot whose circular buffer has scrolled past a frozen zoom range
automatically returns to rolling-window mode every frame, fixing the
second bug where data disappeared as the buffer wrapped.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>