Dual-Use Energy-System Modelling for Critical-Infrastructure Resilience: Open-Source Stress-Test Orchestration as a Lever for Technical Interoperability

European energy systems are simultaneously a foundation for civilian welfare and a high-value target for hybrid disruption. This paper argues that open-source energy-system modelling stacks exemplified by PyPSA-Eur with the Romania-specific Visualiser dashboard qualify as dual-use technologies whose maturation supports both Industry 5.0 resilience objectives and contemporary security funding agendas. We describe a six-layer web platform that turns multi-shock stress-tests into a deterministic, reproducible workflow accessible to non-coding analysts. A worked Romania winter case study quantifies the country’s exposure under a hybrid disruption: a 30 % demand surge combined with a complete cross-border import cap and partial gas / hydro derating produces approximately 45 GWh of energy not served and a 31 % system-cost increase over a single winter week. We map these capabilities onto the four-layer European Interoperability Framework, identify EU funding instruments Horizon Europe, the European Defence Fund, the Connecting Europe Facility and rescEU whose objectives align with the platform’s outputs, and discuss governance constraints under EU Regulation 2021/821 and the Critical Entities Resilience Directive. The paper concludes that civilian-by-design open modelling platforms are the most defensible substrate for cross-pillar interoperability in critical-infrastructure security.