Mergers of neutron stars and pairs of supermassive black holes are among the most energetic events in the universe. They can produce gravitational waves, bright flashes of light, and fast jets; neutron-star mergers can also create heavy elements found in planets and living things. Scientists use large computer simulations to understand the hot, magnetized gas around these objects, but many current simulations treat that gas as a perfect electrical conductor. This simplification makes magnetic-field reconnection, a key source of heat, light, and outflows, occur as an uncontrolled byproduct of numerical error rather than through a physically modeled process. This project develops open-source software that lets researchers model magnetic energy release with physically meaningful inputs and reproducible tests. The project advances the national interest by improving computational tools for scientific discovery, strengthening high-performance computing, and training students in computational science. It also broadens participation in science through activities that include research experiences for Deaf and Hard of Hearing students, outreach to rural K-12 students in Idaho, and public visualizations of cosmic collisions through accessible performances and outreach events. This project develops portable cyberinfrastructure for resistive general-relativistic magnetohydrodynamics (GRMHD), the computational framework used to simulate magnetized, electrically resistive fluids in stron