Window.topPadding..rightPadding and the SafeArea attached type are Qt
6.9; on the Linux pin (6.8 LTS) declaring them on the ApplicationWindow
refuses the whole component at Main.qml:173 ("Cannot assign to
non-existent property"), measured on the CI VM 2026-08-25 and on a Pi 4
with Debian 13's Qt 6.8.2. The paddings are now set imperatively from a
Loader active only on macOS, and HeaderBar reads SafeArea.margins.left
through a macOS-only Loader into a plain property, so no binding names
the type on other platforms. Behaviour on macOS is unchanged.
cc