It looks like the overlay dir is not being "preserved" between the `overlay-script` of different parts. This could be important if, for example, two distinct parts want to add users to the ROCK (while we don't have official user support). Here's an example in a rock with an ubuntu base: ```yaml p1: plugin: nil overlay-script: | rm ${CRAFT_OVERLAY}/lib32 p2: after: [p1] plugin: nil overlay-script: | mkdir ${CRAFT_OVERLAY}/lib32 ``` So one part removes the base `lib32` symlink, and then the other part creates a `lib32` dir. I tried to do that in #163 but it failed with "lib32 already exists", but only in ubuntu-18.04. So this needs some investigating.