F.1: The Dynamical Substrate Law: Substrate-Locality of DI-Bit Currents at Vertex-Aligned Reading C in the 600-Cell

Abstract: F.1 establishes the substrate-locality property for DI-bit currents on the 600-cell at vertex-aligned Reading C. Under a propagation-rate-asymmetry primitive linking flow to a substrate direction n-hat, the net DI-bit current at any host vertex depends only on the content of its twelve first-shell neighbours, derived through three load-bearing identities: a uniform host-to-first-shell projection of -1/(2 phi^2), perpendicularity between first-shell-to-first-shell edges and n-hat, and a perturbation-theory rule confining order-n corrections to graph-distance-n edges. The three core identities are hardened at publication-grade rigor with explicit hypothesis tracking. The paper is the temporal-sector analog of the Capotauro v2.0 spatial-sector locality theorem, sharing the structural constant -1/(2 phi^2), and supports a candidate thermodynamic-arrow mechanism for the OPEN-SD-CHIR-PRIMITIVE umbrella; five open questions including a Layer 4 axiomatic derivation of Mechanism A are explicitly registered.