The broker step sent the nats module with a plain push, and the controller refuses a push that would
replace the bus: that is a planned step, bus upgrade, which snapshots the streams first and checks
them after (ADR 0236). Genesis stopped at step 18.
The step now snapshots every stream with the module's own snapshot program (no backup holder exists
yet to be asked), asks bus upgrade with that snapshot and why, says the one restart, and waits until
the bus runs the module's image, answers, and the controller ends the step done. The bundle's bus runs
the release the module's image is built on (2.11.17, by the same digest, where it ran 2.10.29), so the
step changes no server release and is said reversible.