I’m not really familiar with cmake or (C++ for that matter), so just at a quick glance: https://github.com/Igalia/cog/blob/f4196b1482a5070bba9203eba2ed7b39df32ebff/CMakeLists.txt#L85
WEB_ENGINE_INCLUDE_DIRS variable is not set in the cog CMakeLists.txt. If that’s set by some variable in my libraries snap, that might explain the /root/stage part because that’s where those libraries and includes end up during the libraries’ snap build process.
Do you happen to have a pointer what I need change in the libraries snap?
The wpe-webkit CMake files don’t set any such variable, either.