Accessibility Geometry Reference Stack: Reference A - Accessibility Variable Register

Accessibility Geometry Reference Stack: Reference A - Accessibility Variable Register is a companion reference document to the Accessibility Geometry framework https://doi.org/10.5281/zenodo.20564076 . This register defines the primary state variables used for observer accessibility modeling, including Accessibility (A(t)), Coherence / Substrate-Indexed Coherence (C(t), C_X(t)), Reconstructability (R_o(t)), Integration (I_g(t)), Projection Horizon (T_h(t)), Audit Bandwidth (B_a(t)), Reorganization Capacity (R_g(t)), Scalar Harmony (H_s(t)), Observer Impedance (\eta_o(t)), Recursive Closure / Zeno Density (\Phi(t)), Recovery Margin (RM(t)), and Constraint Preservation (C_{pres}(t)). The central distinction underlying the register is between possible futures and accessible futures. A future state may be logically possible in abstract state-space while remaining inaccessible to a given observer because of stress, impaired reconstruction, contracted projection horizon, reduced audit bandwidth, poor scalar harmony, observer impedance, recursive closure, or insufficient recovery margin. Reference A is not presented as an empirical validation of Accessibility Geometry, a clinical diagnostic tool, a legal standard, or an executable governance architecture. Its purpose is to establish a controlled vocabulary for later papers, toybox investigations, calibration studies, derivative modeling, governance tools, and applied diagnostic frameworks. Version v0.5 incorporates the Government of Canada Harmonized Threat and Risk Assessment methodology as an external governance and calibration anchor. Institutional threat and risk assessment concepts, including asset valuation, vulnerability assessment, safeguard effectiveness, residual-risk calculation, and risk-acceptance records, are treated as applied analogues rather than primary state-variable sources. This document is part of a developing Accessibility Geometry Reference Stack: Reference A defines state variables. Reference B is reserved for derivative behavior, warning trajectories, acceleration signatures, and Human TAWS logic. Reference C is reserved for calibration artifacts, evidence classes, and cross-domain comparison. The register is intended to support future work across human, organizational, institutional, social, and synthetic observer systems, provided substrate boundaries and measurement limits are clearly stated. Keywords Accessibility Geometry; observer modeling; future-state accessibility; possible futures; accessible futures; coherence; substrate-indexed coherence; reconstructability; integration; projection horizon; audit bandwidth; reorganization capacity; scalar harmony; observer impedance; recursive closure; Zeno density; recovery margin; constraint preservation; Human TAWS; threat and risk assessment; residual risk; safeguard effectiveness; systems theory; cybernetics; adaptive governance; institutional risk; trauma recovery; organizational drift; calibration artifacts; decision architecture; state-variable register; Coherence Dynamics Laboratory