I guess, “two-dashes” issue was solved in linkifier linkify-it/CHANGELOG.md at master · markdown-it/linkify-it · GitHub, and auto-propagated to markdown-it.
So, fix was landed to discourse after dependencies uprgade. Proof:
test http://cs--preview.khanacademy.org test
I think, this can be marked as solved. No more <...> scopes required for this kind of links.