The claim that the contract curve in exchange economies coincides with the Pareto frontier is a foundational definition in microeconomic theory, so no citation is needed.
The claim states a standard definition in microeconomic theory regarding the Edgeworth box and general equilibrium: the contract curve is precisely the locus of Pareto-efficient points (the Pareto frontier) in exchange economies. None of the retrieved papers discuss economic general equilibrium theory or welfare economics; they cover unrelated topics such as enzyme production, engineering optimization algorithms, and supply chain management. Since this is a definitional identity taught in standard economics, it represents common knowledge and does not require empirical citation.