This scope of this tracking task is somewhat specific to Wikimedia's deplyment, however the sub tasks that resolve this use case will benefit all MediaWiki installs.
When upgrading a wiki from one wmf-branch to the next, we currently invalidate almost all static caches for front-end resources.
* Server-side HTTP response cache (Varnish).
* Client-side HTTP response cache (Web browsers, proxies).
* Client-side module storage (e.g. HTML5 Storage, see [ResourceLoader#Client storage](https://www.mediawiki.org/wiki/ResourceLoader/Features#Store)).
Source of invalidation:
* [ ] T98087: Module versions bump (due to increase of timestamps, due to hardcoding of absolute paths that embed the version, and other factors)
* [ ] T99096: `/static-{branch}` urls to mount static files. The branch changes each deployment. Ironically, these are currently cached too long (T99096). We need to find a way to cache them even longer, and bypass it when they change.
* [ ] LocalisationUpdate: Invalidates message cache every time and bumps the timestamp. Invalidates all modules with one or more messages.
* [ ] ..