Fungibility Mirage Fraud: Illusory Equivalence in Regulated Stablecoin Systems

Stablecoins are widely assumed to be fungible monetary instruments, where each unit is interchangeable with any other unit of the same denomination. This paper demonstrates that such fungibility is frequently illusory in regulated stablecoin systems. We define Fungibility Mirage Fraud as a systemic condition in which stablecoin units appear identical at the protocol layer while differing materially in legal enforceability, collateral quality, redemption eligibility, or jurisdictional validity. These hidden distinctions introduce asymmetric risk, enable selective enforcement, and undermine monetary integrity under stress conditions. We show that account-based compliance mechanisms, post-hoc audits, and disclosure-based regulatory approaches are structurally incapable of detecting or preventing this failure mode. Finally, we propose a validator-level logic enforcement architecture that binds regulatory attributes to token state and enforces fungibility constraints deterministically at execution time, aligning stablecoin operation with MiCA-class regulatory expectations.