This allows you to translate from the names Stan uses (like theta.1) to those Posterior wants (theta[1]).

This function exists (privately) in cmdstanr, and is currently very simple:

repair_variable_names <- function(names) {
    names <- sub("\\.", "[", names)
    names <- gsub("\\.", ",", names)
    names[grep("\\[", names)] <- paste0(names[grep("\\[", names)], "]")
    names
}

This doesn't work for complex numbers or tuples, but since posterior doesn't seem to support those either I think this is fine