BannerGeometry
Layout geometry supplied by the host for a banner request.
Banner controllers are process-cached and have no layout context of their own (see the invariants in admob-cmp/CLAUDE.md). Before this type existed, each controller reached for one anyway — Android through an Activity, iOS through UIScreen.mainScreen.bounds. The iOS path silently produced full-screen width in iPad split view, Slide Over and popovers, sizing every banner wrong with no error.
BannerAdView supplies this automatically from its BoxWithConstraints measurement. Headless callers must supply it themselves.