What is typically needed is an easily reproducible reference CI environment. That is often approximated with a centralized reference CI environment, that is not

What is typically needed is an easily reproducible reference CI environment. That is often approximated with a centralized reference CI environment, that is not necessarily easy to reproduce, in which case it is only instantiated very few times. Left or right of VCS should not be a big question given the VCS is supposed to be decentralized, but for that to happen the whole dev process (or at least a very substantial portion of it) should be day to day decentralized at well, or at least with a (well tested) ability to decentralize when needed, without friction. If we go back to the more general "configuration management" concept (than merely source code version control), it is obvious the ideal situation is when the whole pipelines can be freely reproduced, in which case you can usefully do it before the integration on a reference branch/repo (and redo it after just to be sure because who knows if the whole configuration has been correctly captured: you better detect discrepensies early too - also because in some workflow you won't test exactly the same branch before merging to a reference as what is the result of the merge)