To call the a script with python3 inside the sdk I'm using the following, for example with rwt: ./Tools/Scripts/webkit-flatpak --wpe --release --verbose -c python3 ./Tools/Scripts/run-webkit-tests <rwt args...> The issue is that the path to the script is not being normalized to the /app/webkit bind-mount.
Nevermind, one can just prepend /app/webkit to the script path manually. As this is not so common in practice, better to avoid more corner cases in the flatpak utils. Closing.