Code Structure Evolution: When Software Outlives Its Reasons

Software is not merely a functional artifact; it encodes human knowledge in the form of invariants, architectural constraints, and historically grounded design decisions. As software evolves-through human modification, automated refactoring, or increasingly through generative artificial intelligence (GenAI) code agents-its functionality may be preserved while the epistemic justification embedded in its structure is gradually eroded. This paper develops the concept of Code Structure Evolution (CSE) to analyze this phenomenon. CSE refers to the transformation of structural relations over time and the associated risk of what I call epistemic drift: the degradation of justificatory continuity across structural change, whether or not this degradation is immediately reflected in invariant violation, traceability loss, structural incoherence, or functional failure. The paper defends a general thesis-that epistemic drift is a latent condition of any evolving software artifact-and examines one contemporary case in which this condition becomes acute and empirically visible: legacy-code modification by a GenAI code agent. An illustrative probe suggests that such modifications can preserve functional and structural indicators while leaving substantial justificatory residue unpreserved. I argue that this dissociation reveals a neglected philosophical problem: the nature of software as a repository of justified understanding and the conditions under which that justification can persist across structural change. CSE thus offers a framework for analyzing the epistemic fragility of evolving technical artifacts. GenAI does not create this fragility; it makes it harder to ignore.