Your engineers run it after we leave. That only works if the last month of the project is designed around it.
We shadow your team for four weeks while they operate the system, answer questions for two months after that, then step back. Documentation is written during the build, not compiled at the end, and every runbook has been executed by someone from your side at least once.
The measure of a good handover is simple: six months later, has the system changed? If nobody has touched it, we did the handover badly.