…the kernel will complain that there is no command in the container’s `PATH` called “`ls -lR /etc`”.

You may then try to split it as…

    /container/add … entrypoint="ls" cmd="-lR /etc"

…but that will earn you error message from `/bin/ls` complaining that it refuses to accept “ ” (space) as an option following the `R`!
…but that will earn you a refusal by `/bin/ls` to accept “ ” (space) as an option following the `R`!

If you get cute and try to “cuddle” the options with the arguments as…

    /container/add … entrypoint="ls" cmd="-lR/etc"

…the `/bin/ls` implementation will certainly attempt to treat `/` as an option and die with an error message.(^Yes, for certain. I tested the GNU, BSD, _and_ BusyBox implementations of `ls`, and they all do this.)