Establish ownership/copying convention for shared maps #344

Raised by @porridge in #339 (comment):

getCentralResourcesOperator returns a shared static map. Callers that pass it into mergo.Merge (which mutates the destination) must deep-copy first to avoid corrupting the shared data. There's no documented convention for who is responsible for copying.

Should we adopt a style guideline — e.g. "functions returning shared maps must return copies" or "callers must always copy before mutating"?

— Created by AI agent on behalf of @mclasmeier