CALCIFER-RETROFIT:A Facility-Compatible Systems-Code Framework for Burn-Survival and Safety-Margin Verification in Existing and Near-Term Fusion Devices

This paper introduces CALCIFER-RETROFIT, a facility-compatible systems-code framework for burn-survival and safety-margin verification in existing and near-term fusion devices. The paper does not propose a new reactor geometry, fuel-handling route, isotope-processing pathway, or autonomous nuclear operation protocol. Instead, it translates the theoretical conditions developed in Papers 18–20 into normalized engineering margins that can be evaluated through facility data, proxy declarations, tiered gates, and reproducible dashboards. The central claim is that fusion viability should not be judged by a single metric such as yield, gain, pulse duration, AI-control score, or tritium breeding ratio alone. A burning-plasma system must remain viable across multiple necessary branches, including plasma survival, burning-basis sharpness, extraction preservation, AI prediction and coupling, tritium accounting, waste-burden reduction, and safety/material/safeguards validity. CALCIFER-RETROFIT therefore evaluates each facility only on the branches it can physically support, while marking unavailable or future-only branches as not applicable, underdetermined, or future required. The strongest empirical demonstration is a cross-machine survival-proximity test on Alcator C-Mod, DIII-D, and EAST. The same training-free survival margin, with no weights fitted to disruption data, separates disruptive from stable slices across all three devices and shows that the dynamic collapse-rate term carries much of the discrimination. Additional demonstrations include synthetic verdict logic, an NIF public-value replay, a single real MAST shot, lead-time actionability, and a reduced-order survival-reserve control study. The contribution of the paper is therefore not a claim that present facilities close the full fusion metabolic gate. Its value is to provide a computable, auditable, and falsifiable systems-code pathway for identifying which branch currently limits progress from demonstrated burning-plasma occurrence toward sustained, safely extracting fusion viability. Keywords: fusion systems code, burning plasma, burn survival, survival margin, safety margin, AI plasma control, digital twin, tritium accounting, safety veto, safeguards, disruption prediction, cross-machine generalization, CALCIFER-RETROFIT.