I use the umask 007 in my system. When I built a test package with snapcraft and installed it in a Snappy Core system, most of the files and folders of the package where not accessible by the "other" users, and thus I couldn't run the binaries (no permission). I think snappy/snapcraft should make some permissions/umask checks. Maybe snapcraft or "snappy build" should check the permissions of all packaged files and directories (like how the Debian build tools do), and either correct the permissions or warn the user about files that have strange permissions. Snapcraft could also enforce an umask of 002 or 022.