Make sure your GCP project is set and you have the gcloud SDK installed. This is a quick guide based on a Google blogpost
Install sshfs
apt install sshfs
Test if you can connect with a regular SSH session (this allows SSH from any terminal, so you can use your favorite terminal with Cloudshell too!)
gcloud alpha cloud-shell ssh
Mount your cloudshell files to your local system
gcloud alpha cloud-shell get-mount-command ~/my-cloud-shell
cd my-cloud-shell
ls
server.py README-cloudshell.txt
code server.py