upperdir is in-use as upperdir/workdir of another mount

```
# dmesg
[ 1938.310669] overlayfs: upperdir is in-use as upperdir/workdir of another mount, accessing files from both mounts will result in undefined behavior.
```

The report provides only a dmesg warning about an overlayfs upperdir being reused; no source files, tests, or entry points are named. Start by reproducing the mount setup and inspecting the installer’s overlayfs configuration, then determine the intended mount ownership and add a regression check if the project provides one.

Written by the indexing model from the issue text.