During the 2026-10-09 outage the control node's resolver stayed active while it no longer listened on
its private address, and nothing on the mesh could ask that address a question or show which sockets
were bound. netcheck_dns takes server (and tcp) to ask one resolver alone and say its response code;
netcheck_listening reads the kernel's socket tables, as ss -lunt does, with the owning program where
the tool's account may see it and a sentence where it may not.
jochen
c0fa282548