FileChooser: Portal returns unavailable realpath uri

[valoq]

When using the FileChooser portal in the context of a custom sandbox environment (not flatpak or snap), the xdg-dbus-proxy response includes the uri of the real path, instead of a uri pointing to /run/user/$UID/doc/

The bwrap sandbox I use isolates the home directory and has a dbus-proxy socket mounted to /run/user/$UID/bus with the responsible xdg-dbus-proxy running outside the sandbox. The context menu successfully uses the portal and shows the files outside the sandbox but when a file is opened, it results in a file not found error because the response uri points to the real path that is unavailable for the target process.

I know that the portal is supposed to return the uri to the real path if the target file is actually available inside the sandbox but this isn't the case here.

Is there documentation regarding how to start the dbus-proxy in order for the portal to work as intended?