Switching the destination server or the 4K variant while a previous server's
details were still loading let the late response install the old profiles,
root folders and tags, clear the loading state, and overwrite tags the user
had edited; adopting no server left the spinner stuck.
Every destination/variant adoption, including null, now advances a
selection generation; a detail load applies neither its success nor its
failure unless it still belongs to the accepted generation, defaults hydrate
once per generation, and an explicitly emptied tag list stays empty.
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