Important: #110358 - Site configuration caches resolved site data 

See forge#110358

Description 

TYPO3 now caches all data needed to create Site entity objects in the "core" cache: the site configuration enriched with route enhancers provided by site sets, the composed site settings, information about invalid sets, as well as the contents of the optional per-site files csp.yaml, setup.typoscript, constants.typoscript and page.tsconfig. Previously, this data was recomputed and re-read from the file system on every request.

The Site entity objects themselves are still created at runtime once per request: Expressions of configured base variants ( baseVariants ) continue to be evaluated per request and environment as before.

Any change performed via the TYPO3 backend (Site Management modules) or via the SiteWriter API invalidates this cache automatically.

However, changes applied directly to the files csp.yaml, setup.typoscript, constants.typoscript or page.tsconfig within a site configuration folder (for example config/sites/<identifier>/) now require flushing all caches to become active - as was already the case for config.yaml and settings.yaml before.