`updater upgrade <app> --detach` parsed "--detach" as the target version
and refused with "no safe path from 31-fpm-alpine to --detach". It failed
safe, but blaming the version for a misplaced flag is a poor way to say
the flag is not supported here. Unknown options now say so.
Found during the first live ladder run.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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