To reduce the installation duration visible to the user, an adaptive installation could be performed in the background without activating the target slot. The actual installation triggered by the user would only verify the contents again and optionally migrate data again.

This could be enabled by a new option in the InstallBundle D-Bus API. Hooks should be informed as well to potentially avoid unnecessary migrations. Handling of boot slots needs some more thought, as they are currently switched automatically.

Related to #1176 (reply in thread)