That seems less than ideal–usually in this sort of thing one would escape the parens if they wanted the literal version, not the semantic version. Was this intentional?
Edit: never mind, just stumbled across Proposal, require that both ( and ) are always escaped in tag values?
I feel like this change made sense in the proposals there, but the effect on saved search strings is bad enough to possibly outweigh the good.
One reason is what I say above: in search strings, those parens are semantic, not literal, but \ universally means “literal”. The other is that they’re the “normal” case in any reasonably complex search, and escaping should generally address the 20% case instead of the 80% case.
I’m also not sure how often a non-power user might run into nested parens in a tag–the @done case aside–but I’m certain that one would run into this in a search.
I do get the implementation issues you’re wrestling with, and understand that this is all a side effect of “everything is an attribute on an object,” but the end-user experience is damaged here for searches in particular. I don’t have an easy answer for that, but don’t look forward to “escape soup” and fussy quoting issues. 