Star Forge is a nonprofit, open-science initiative to prototype a planetary-scale foresight engine. The architecture combines a central orchestration core, a cross-domain knowledge graph, and plug-and-play specialist simulation modules (climate, economic, security, etc.). A Fork Cascade Engine explores branching what-if scenarios and cascading systemic risks, while an emotional-cognitive layer introduces realistic human decision biases. The paper presents the high-level design, validation roadmap, ethical safeguards, and a five-year nonprofit development plan. Star Forge is released under CC-BY-NC 4.0 as defensive prior art to foster collaboration and prevent proprietary enclosure.