Here it is:
# socat - /var/run/qemu-server/3006.qga
{"execute": "guest-exec", "arguments": {"path": "/bin/bash", "arg": ["-c", "apt update"], "capture-output": true}}
{"return": {"pid": 3566564}}
{"execute": "guest-exec-status", "arguments": {"pid": 3566564}}
{"return": {"exitcode": 100...