When attaching to a running geodesic container, if that container has an aws-vault credential server running, the new shell will use it to immediately assume the role being served. You can still assume-role to some other role if desired.
Note that this shell will lose its credentials if the shell that started the server exits, because it will shut down the credential server as part of its cleanup. If that happens, you will need to assume-role, even if it is to the same role.