Currently the git-plugin can checkout the current head, or a specific commit, what I'm missing is an option to checkout the head at the time where the build has started.

Reason: if you have a pipeline build that was triggered at a certain time, and the devlopers checked in something before the checkout takes place these changes are picked up even if the build is already running for a while.

For example I have a pipeline that builds different repositories together one after the other. It now can happen that a build starts, checkout the first repository, then checkout the second but picks up changes commited at a later point at time (and fail because changes from the first repository are not taken into account).

The same happens if you replay a certain pipeline build, it always fetches the ltest changes and not the changes that where current at the time of the build (so replay is more a "rebuild with different script" because the build is not really replayed.