If /run/nextroot/ has been set up, use it, even if the inodes are the same. It could be a verity device that is reused, but with different sub-mounts or other differences. Or the same / tmpfs with different /usr/ mounts. If it was explicitly set up we should use it. Use the new helper to check that the mount IDs are also the same, not just the inodes.
System and Service Manager
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