I’m not familiar with the term "robust unhygienic macros” and an internet
search didn’t reveal any definitions.

Is there a definition of this term, or better yet, a paper?

I’m a little confused because the SRFI claims that explicit-renaming macros
can produce "robust unhygienic macros” yet syntactic-closure macros cannot.
However, explicit-renaming is virtually identical to “reverse” syntactic-
closure macros, which are syntactic-closure macros with the definition and use
environments flipped.

Chris