Analytical TGV3D can now run on a file-backed grid (grid.mode: file). The field is evaluated at the given grid's cell centres instead of the solver replacing the grid with its own [0, 2π]² × [0, 0.2π] box, which allows particle-interpolation verification on curvilinear (for example interior-warped) grids. programmatic_c behaves as before; grid_gen is still rejected.