cocoon-agent ships a client subcommand for vsock smoke tests without needing to plumb through cocoon CLI / vk-cocoon. Get the VM’s CID from cocoon vm inspect and run:
cocoon-agent client --cid 3 --port 1024 -- echo "hello from guest"
echo "world" | cocoon-agent client --cid 3 --port 1024 -- cat
Exit codes pass through.