It's called unification and exists in many languages, Prolog is a well known one. CUE is in the logical language family. It uses Typed Feature Structures which originated in NLP before deep neural networks became capable.

It is specifically not inheritance where overrides are allowed.

Sort of. Inheritance extends (hence the keyword of the same name) while constraints restrict (or constrain).

Inheritance also allows overrides, which is something CUE errors on. CUE has Go like embedding so you can reuse common schema or config.

CUE's constraints are in the "middle" of the spectrum (lattice, partially ordered graph) from abstract types to concrete data.