The CAP distribution does not include the webengine-ui jar anymore, this may be linked to module webengine-sites and webengine-blogs removal (
This module may be a requirement for some existing addons, like platform-explorer.
However, this bundle does contains classes for managing UI with WebEngine and jQuery : since this is not really the way we want the UI to evolve, there is no real point in re-adding this to the default distribution.
We must keep it in the build and add it explicitly in MP that requires it.
We could also remove it from webengine default build and push it to addons ...