A Structural Constraint on Persistence in Evolving Systems A Unified Framework for Understanding Identity Under Irreversible Change

This preprint presents a descriptive, cross-domain framework for understanding how systems maintain identity over time under cumulative irreversible change. The paper formalizes a Persistence Constraint: a system remains identifiable as the same system only while cumulative irreversible change remains below a system-specific tolerance. This constraint is shown to underlie empirical observations across software evolution, biological mutation limits, engineered system fatigue, and computational error accumulation. The contribution is intentionally non-operational. It does not propose mechanisms, algorithms, control strategies, or implementation details, nor does it address how such constraints might be monitored or enforced in practice. The purpose of this preprint is to establish the conceptual framing and mathematical structure of persistence under irreversibility as a unifying, domain-agnostic principle. This work is shared as an early research preprint to establish priority of the conceptual framework and invite empirical and theoretical discussion.