The bridge no longer has a private canonical store, so the env var
naming one is gone rather than repointed. What is left is the single
users file it now reads and writes directly.
That line is what made `swarm agent create` fail on this hive: the
bridge found no store at its own JSON path, saw users already in
`users.yml`, and refused to overwrite a file it had not written --
correctly, given two things claimed to be canonical for one file.
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