Sharpened from 'v6 blind spot' into a general bind-posture rule after
follow-up discussion: no implicit wildcard binds (0.0.0.0 / :: — note
::1 is loopback, not a wildcard); connect_udp is a client socket so
the floor fix is family-correct binding, never a loopback default;
bind_tcp keeps its caller-supplied address (the correct posture) with
a wildcard-bind doc warning. Executable rider sharpened on the
remediation task.