Regex matching groups escaped as regular characters

[kjduensing]

I was trying to add a negative lookahead regular expression w/in an endpoint path, and noticed that my matching group was being escaped, causing no endpoint match to be found.

What I was going for:
/letters\/(?![^\/]*(letterBeneficiary))[^\/]*\/generate

What I got:
\/letters\/\(?![^\/]*\(letterBeneficiary\)\)[^\/]*\/generate

The negative lookahead expression contains parentheses, and it looks like this commit removed the ability to include regular expressions like this. I know that commit was intended to support endpoints with the literal characters: ( and ), but I wonder if there's some middle ground we can reach to support both a more general use case and the use case enabled by the previous commit.