Rudder

There's a few places where we're calling zypper.
Zypper notices that there's an open tty and runs in interactive mode.
The result is when you have unavailable repositories or key issues (i.e. nightly rudder repos) or anything else that could use manual input, zypper will stop with the relevant dialog.

i.e. in cfengine stdlib:
$ grep -R "zypper pat" *
initial-promises/node-server/common/1.0/cfengine_stdlib.cf: package_patch_list_command => "/usr/bin/zypper patches";
initial-promises/node-server/common/1.0/cfengine_stdlib.cf: package_patch_list_command => "/usr/bin/zypper patches"

same goes with most of the other techniques.

There is a --non-interactive flag, which (great) comes with safe defaults; this could be easily used, otherwise one could also try closing the tty.