I disagree with citeproc-php here -- which identical consecutive suffixes should be removed should be handled more judiciously than extending this to all characters.

But I'd take a PR that adds the space there (not the \n character though).

Or is this only and best feasible solution for now?

The best solution is to not use CSL styles to generate BibTeX. We know there is a BibTeX CSL style in the repository, but its use should be avoided if possible. The whole CSL ecosystem was built for human-readable output, and CSL styles and CSL processors are limited in their ability to generate correct computer-readable output, which often has requirements CSL can't satisfy.

There are dedicated software libraries for converting bibliographic formats, such as https://citation.js.org/ (open source and can handle CSL JSON and BibTeX).

(that said, it would be better if the CSL specification was explicit about how punctuation collapsing should work, and as @adam3smith mentioned, this automatic collapsing should probably not extend to curved brackets)

Sorry for the delay in following up on this. I understand building bibtex with CSL is stretching things. But we would prefer not to introduce an additional conversion dependency into our platform if possible.

@adam3smith are you still open to a PR to add the space? If so, I've opened one here: #3651

This can be closed now that #3651 has been merged. Thanks everyone! 👍