I would have hoped for some shared secret approach where the extension can generate one-time use urls for their bundled resources on demand and use those instead of easily predictable urls.

It seems that extensions like ad blockers that are explicitly targeted by such detection methods have ways for work around that (see https://github.com/gorhill/uBlock/blob/master/src/web_access...). I honestly would have expected for that to be the enforced default behavior.