Repositories can end up with broken commit graphs

We have seen in our staging systems that repositories can end up in a broken state with regards to their commit-graphs. The issue is that created commit graphs are expected to have overflow information for generation numbers, but the written commit graphs are somehow lacking this information. The result is that Git dies with fatal: commit-graph requires overflow generation data but has none.

The issue only happens with Git v2.36.0 and newer, which has changed the way generation data is written. Multiple folks on the Git mailing list had hit this issue already, but nobody seemed to have been able to reproduce the exact conditions that can lead to it.

We need to investigate how this issue may happen. In the current state this is blocking the rollout to production because it may render repositories inaccessible.