Class DataLoadingController

One older page. until (UTC seconds) widens a date feed's window to reach it in one request, up to maxBars bars of a fixed interval; a paged feed keeps its ordinary window.

Supply bars from an existing host subscription instead of subscribing twice.

meta.provisional marks a bar whose open is only the first tick a builder saw, see CandleUpdate.provisional. Pushed onto a bar history already holds for that bucket, it keeps that bar's open and widens the extremes instead of replacing them, so a repair that found the true open is not undone by the next tick.