get_available_updates triggered firmware/check and slept up to 15 s, too
long for a poll, and returned [] when the check had not finished. For netOrk
MVP 5 it now reads the cached GET /api/core/firmware/status:
- [] only when the last check found nothing; it raises when the firewall
never checked (no last_check) or its connection/repository is not "ok".
- refresh_available_updates(): POST firmware/check, then waits up to 60 s
for last_check to change.
- get_host_status(): reboot_required from the status' needs_reboot.