I strongly believe the answer is not reasonable using phoboes tools; but Im going to leave it as an open question before I get started on something from scratch.

Given well compliant phoboes-style ranges and a ref string or retro!string that starts with '(',')','[',']','{','}', modify that string so that you a) find the matching pair, b) return a list of indexs for where the top level commas are

"(foo([1,2]),bar!"","(((())))foobar" => "(foo([1,2]),bar!"","(((())))",[12]
retro("abc[1,2,3,4,"❤️❤️❤️❤️","","]") => "[1,2,3,4,"❤️❤️❤️❤️","","]", [2,4,6,8,35]