Some of the issues:

• a lot of code duplication in the server and the shim
• sshd relies on the distro-specific sshd_config, with only a handful of options critical to dstack set explicitly
• /etc/ssh/ssh_host_* keys are overwritten by the entrypoint (an issue if there is another sshd server in the image)
• .ssh/authorized_keys is updated by the entrypoint script, not the runner, see this comment