Doesn't the "default" case added to the switch statement in 96c755a cover this case?

No, default throws an error because in this case package manager is "".

I see - so if this part of the Bravefile is not specified the built cannot continue. That is a problem.

It does mean that if there are pacakges listed under a blank package manager that they will be skipped. But that's definitely a much smaller issue. Might add a check for that case specifically.

E.g.

packages:
  manager:
  system:
  - bash
  - wget
  - gnupg

In this case, if the manager is not specified, the section is skipped. If the user wants to install packages with a system manager before proceeding to the run section, they must specify explicitly apt/apk (other might be included in the fugure)