The field's platform flag was named `onWayland`. With no `wayland` member
beside it the binding happens to work, but the on-prefixed property audit
(which qt-run.sh runs) rejects any `on<Upper>` name, and an instance
cannot assign it: `onWayland: false` is parsed as a handler for a
nonexistent signal and the component fails to load. It is `isWayland`
now, writable so a test can take the Wayland branch under the offscreen
platform, and a change of it also asks Rust to follow the window.
tst_wallpaper_field covers the Qt position on X11 / macOS / Windows, the
compositor rectangle picked by this window's size on Wayland (a
miniplayer-sized window is ignored, a move is followed), the centred
fallback, and an invisible field that reads nothing. It runs in the
runtime gate.
cc