The Primitive Coupling: The Architectural Necessity of the 𝐿1 / 𝐼2 Interface

The Dual-Layered Reality (DLR) framework posits a realignment coupling between the complete deterministic lattice (𝐿1) and the finite informational layer (𝐼2). A recurring objection holds that this coupling reintroduces the classical interaction problem of substance dualism, merely relocated to the 𝐿1 / 𝐼2 boundary. This paper answers the objection by showing that the coupling is not an additional ontological commitment, but the minimal structural primitive required by the joint satisfaction of five independently derived constraints: genuine agency, non-external-intervention, completeness and uniqueness of the lattice (𝐿1), sampling without replacement, and finitude of the information layer (𝐼2). The argument proceeds in three steps. First, the interaction objection is distinguished from the internal-to-𝑅 interaction problem already dissolved in The Governed-Material System (Chang 2026c). Second, the 𝐿1 / 𝐼2 coupling is shown to be the unique minimal structure that jointly satisfies the five constraints; no weaker architecture satisfies them, and no stronger architecture is warranted. Third, the demand for a microphysical mechanism of the coupling is shown to rest on a category error: it presupposes a causal framing that the coupling, as a constitutive relation, does not instantiate. The paper concludes that the coupling is not a dualist residue but a predicted feature of any architecture that accepts genuine agency as its initialization datum.