BIT-GALAXY-P17 — ADDENDUM A: The MIS–BIT Duality — S_shock and G_BIT Are Dual Measures of the Same Boundary

This addendum establishes a formal duality between the MIS (Metasystem Interaction System) framework — developed in the early phase of Boundary Information Theory — and the G_BIT stability parameter introduced in P17. We show that the MIS shock index S_shock and the planetary/galactic G_BIT are not independent constructs but inverse measures of the same underlying boundary dynamic. The unifying relation G_BIT × S_shock ≈ 1 defines a reciprocity principle: a system's capacity to resist shock is the structural complement of its boundary information gradient. This result retroactively unifies the MIS and BIT-Galaxy branches of the theory under a single mathematical identity.