A drag renders drafts, which have no HDR histogram, so an HDR edit's histogram dropped to the
SDR layout until the drag ended. Now, during a drag of an HDR edit, a small full-quality render
(Slot::HdrHistogram, 192 px, its own stage cache) runs beside the drafts and feeds the panel at
its own pace: the drafts don't wait for it. The panel also keeps an HDR edit's last HDR histogram
when a render without HDR bins arrives (a draft, a cached thumbnail or stand-in), so it never
swaps to the SDR layout mid-drag.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
