Algebraic Phase Theory VI: Duality, Reconstruction, and Structural Toolkit Theorems

Abstract: We prove that any functorial finite-depth reconstruction framework based on representation theory satisfies a strict dichotomy: it either collapses into a rigid regime or necessarily admits intrinsic structural boundaries. In the non-rigid case, reconstruction is uniquely determined up to canonical boundary collapse, and no boundary-free reconstruction theory with the same formal properties can exist. We establish that algebraic phases are \emph{information-complete}. Any phase satisfying the axioms of Algebraic Phase Theory (APT) is uniquely determined, up to intrinsic phase equivalence, by its filtered representation category together with its boundary stratification. Reconstruction is exact on rigidity islands and fails globally only through canonical and unavoidable boundary phenomena. We further show that the axioms of APT force a minimal structural toolkit, including canonical finite generation, rigidity--obstruction equivalence, finite-depth boundary detectability, and the existence of universal obstruction objects. These results apply uniformly across all phase models developed in the APT series. Taken together, the results of this paper complete the foundational development of Algebraic Phase Theory and position it as a canonical and inevitable reconstruction framework extending classical duality theories beyond rigid and semisimple regimes.