backupLocationEnsureDir and the config write both went through runFileOp /
runFileWrite, which run as the container user. Backup location configs live
under the system tree, which is owned by the manager — so the mkdir was denied,
the write then failed with "No such file or directory", and locationAdd still
printed "Location N added".
The result was a location that existed in name only: every later command that
sourced its config found nothing. It surfaced in the first-run restore path,
where the installer adds the location it is about to read from and then fails
with "Backup location 2 has no config".
Use runInstallOp/runInstallWrite, which run as the manager and can write there.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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