In addition to query4 the leases4_committed hook takes two arguments leases4 and deleted_leases4 of type isc::dhcp::Leases4CollectionPtr.
I'm trying to update client DNS records on a Samba server. Since Kea doesn't support GSS-TSIG for DDNS I'm hoping to use kea_python and Samba Python modules instead of calling a shell script. The leases4_committed hook seems to be the place to do it.