SDIS-09 — Central Bank Digital Currencies and Sovereign Financial Rails: Technical Architecture for State-Issued Digital Money Central bank digital currencies are the clearest case where governance-plane sovereignty is unambiguous — a central bank is definitionally the sovereign monetary authority — yet technical sovereignty across the data, compute, and operational planes remains an open design question. This paper traces the history of state-issued digital money as a policy and technical concept and specifies a reference architecture for CBDC systems covering the core ledger, offline payment mechanisms, and privacy-preserving transaction design. The paper uses the EU's digital euro program as a detailed case study following its 2026 legislative progress alongside fifteen further case studies, and addresses the interaction between CBDC identity requirements and the sovereign digital identity architecture in SDIS-04. It examines cross-border interoperability, addresses eight common objections, and closes with economic and organizational considerations, an implementation roadmap, a glossary, and a self-assessment checklist. Keywords: CBDC, digital euro, payment rails, offline payments, monetary sovereignty This is Paper 9 of 12 in the Sovereign Digital Infrastructure Series (D-AI), applying the four-plane framework from SDIS-01 to state monetary infrastructure and connecting directly to the identity architecture in SDIS-04 and the zero trust controls in SDIS-08. A companion series guide (SDIS-00) provides a full cross-citation map, publication registry, and licensing terms for all papers. Series: Sovereign Digital Infrastructure Series (SDIS) · Publication: SDIS-09 · Author: Bijan Burnard · Affiliation: D-AI Research · Version: 1.0 · Publication Date: 23 August 2026 · ISBN: 978-969-9597-37-4 · DOI: 10.5281/zenodo.22085550 · License: CC BY 4.0