During the install process meson has code to automatically seek root privileges during install with polkit which depending on the user's settings may result in a password prompt or an unexpected install instead of permission denied errors. This was merged in PR: https://github.com/mesonbuild/meson/pull/3567 This is likely not a problem with emerge, but users may use meson manually or in their personal projects and this behavior is arguably a potential security risk or foot gun. It could be unintentionally triggered with something as simple as a missing DESTDIR. Also see the upstream meson issue which does not appear to be getting a fix anytime soon. https://github.com/mesonbuild/meson/issues/7345
This seems to be working as-designed with regard to polkit integration.
