As far as I am aware, uses of StaticRange prior to css-highlight-api were for ranges created by the User Agent and passed to the author.
In css-highlights-api, it's the other way around, which raises (for the first time?) the question of invalidation of static ranges, as they may have become stale by the time the browser needs to use them.

https://drafts.csswg.org/css-highlight-api-1/#range-invalidation defines a way to evaluate that. Is that reasonable? If not, what should we do instead?