Switch picks a lerped AbgrCache during the 300ms crossfade window
(ReduceMotion bypass keeps the snap path). Plugin-load init path
switches to SwitchSilent so opening the plugin no longer fades from
the default theme. WindowBg/ChildBg RGBA path stays bound to the
user's per-window opacity override and never fades.
PushGlobal takes the ThemeRegistry as a parameter -- it is an instance
member on Plugin, not static, so the single Plugin.Draw call-site
threads it through alongside the active theme.
JonKazama-Hellion
a35067f80a