When an agent re-registers with the same token, the DHCP matching case
would overwrite the Host field with the agent's local IP — even if the
user had edited it to a public URL or different IP. Now agent source
re-registrations always preserve the existing host, while non-agent
DHCP updates still work. Adds 5 regression tests covering hostname
preservation, public-IP preservation, agent DHCP, non-agent DHCP, and
PBS parity.
rcourtman
b445f8d8fa