The chain and its test points: a testable model linking sensory throughput, thiol reserve and copper delivery in post-COVID illness, fatigue and sensory hypersensitivity

Version 1.1 (13 September 2026): The vitamin K cycle is added as an eighth test point (gap G8) with two new falsifiable predictions (P9, P10) and fourteen additional references. With it the model closes into a circle: peroxynitrite, the endpoint of the chain as described in version 1.0, acts through S-nitrosylation of thioredoxin-like domains on vitamin K reduction, and through undercarboxylated matrix Gla protein back onto calcium distribution, where the chain begins. A figure of the closed chain has been added to section 1. Version 1.0 remains citable under the same concept DOI.