### Check existing issues - [x] I've verified that this request isn't described by any existing issues. ### Request We have an ongoing effort in snapd to make the handling of snap mount namespaces more robust. This includes ways for simplifying the hierarchy of mounts that are required in order to produce the world view that the snap declared in its snap.yaml. A dedicated piece of snapd - snap-update-ns - is ultimately responsible for making this happen and it does it by various combinations of tmpfs/bind mounts/and mock paths that serve as mount points. Specifically, in the context of this request, in situations when a target of a content mount does not exist e.g. `$SNAP/target`, s-u-n will do the following (simplified): - create a tmpfs on the side - bind mount everything from under the original `$SNAP` location - mkdir `target` - bind mount the temporary directory back onto `$SNAP` This nicely illustrates the additional complexity which could be entirely avoided should `$SNAP/target` already exist inside the squashfs blob. Things only get more complicated form here where the snap adds `layout` on top, or the content provider snap is refreshed. Since the ultimate goal is to make things simpler, easier to set up, debug and reason about we, on the snapd side, are considering making the presence of `content` interface `target` location presence mandatory for snaps using base core26 and later. I have a draft PR in snapd https://github.com/canonical/snapd/pull/16828 which adds the code to enforce this. Let's discuss whether snapcraft could make this transition simpler by ensuring that the directories are created at build time. ### The problem it solves Simplifies steps needed to create the mount setup requested by a snap and thus helps snapd with making snap mount namespaces more robust.