The arXiv preprint (abs/2606.04080, June 2026) introduces essential unitarity as a boundary-centric invariant in compact closed categories, generalizing first-order unitarity to polarized boundary linkings and unit-free monoidal sums. This framework realizes the coherent quantum switch as a pure-comb dilation while preserving dagger-monoidal structure and currying. Unlike prior supermap literature that focused on operational characterizations, the work identifies essential unitarity as the unique predicate compatible with coherence reindexing, revealing that every morphism in the quantum core satisfies the condition. As a theoretical preprint without experimental validation or concrete circuit implementations, its methodology relies on categorical semantics rather than empirical sampling; limitations include lack of concrete resource bounds for fault-tolerant scaling and absence of noise models. Related work by Chiribella et al. (Phys. Rev. A 88, 2013) on higher-order quantum maps and by Abramsky and Coecke on categorical quantum mechanics (arXiv:quant-ph/0402130) overlooked boundary-centric unitarity preservation, missing the link to reversible control in one-slot purity-preserving operations. This result implies scalable architectures must embed essential unitarity at the interface level to avoid information leakage in nested quantum combs, a pattern absent from current qubit-centric roadmaps.