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Supply chains require real-time risk prediction and mitigation under high uncertainty and network interdependence. This protocol describes a reproducible digital-twin (DT) workflow that links data ingestion, spatiotemporal risk forecasting, risk propagation simulation, and mitigation policy optimization in a single containerized stack. For prediction, we integrate an interpretable sequence-and-graph model that combines a Bi-LSTM with graph convolution to capture temporal dynamics and network dependencies. For mitigation, proximal policy optimization (PPO) learns actionable decision policies from simulated disruptions, enabling cost-aware responses rather than post hoc diagnosis. To support deployment and replication, we provide a hierarchical key-risk-indicator taxonomy that separates endogenous and exogenous risks, together with version-pinned environments, data contracts, and validation checkpoints. Representative results demonstrate both predictive and decision-level gains. On a 300-node automotive network, the approach improves F1 by 19.3% and extends the early-warning horizon by 5.2 h. In a 2021 U.S. port-congestion replay, PPO reduces delays and emergency-response costs by over 20%. The workflow scales to 500-node simulations with millisecond-level latency while maintaining stable long-horizon performance. Dual validation with historical-event replay and online simulation confirms improved accuracy, robust decision quality, and practical scalability. Limitations and adaptation guidelines are discussed to facilitate transfer to new supply-chain settings.