We consider the four-vertex model with a special choice of fixed
boundary conditions giving rise to limit shape phenomena. More
generally, the considered boundary conditions relate vertex models to
scalar products of off-shell Bethe states, boxed plane partitions, and
fishnet diagrams in quantum field theory. In the scaling limit, the
model exhibits the emergence of an arctic curve separating a central
disordered region from six frozen `corners' of ferroelectric or
anti-ferroelectric type. We determine the analytic expression of the
interface by means of the Tangent Method. We supplement this
heuristic method with an alternative, rigorous derivation of the
arctic curve. This is based on the exact evaluation of suitable
correlation functions, devised to detect spatial transition from order
to disorder, in terms of the partition function of some discrete
log-gas associated to the orthogonalizing measure of the Hahn
polynomials. As a by-product, we also deduce that the arctic curve's
fluctuations are governed by the Tracy-Widom distribution.