Classification of simple commutative algebras in the Delannoy category

The Delannoy category is an interesting pre-Tannakian category associated to the oligomorphic group $\mathbb{G}$ of automorphisms of the totally ordered set $(\mathbf{R}, <)$.

By construction, it admits some obvious simple commutative algebras, corresponding to certain transitive $\mathbb{G}$-sets.

We show that these account for all of the simple commutative algebras in the Delannoy category.

Previous results of this kind have been limited to interpolation categories; since the Delannoy category cannot be obtained by interpolation, new methods are required.