Experimental: one checkout builds both a 32-bit and, with make INDEX_BITS=64, a 64-bit-index executable set (simulator64, postprocessor64), and picurv run picks the set per run (64-bit only when a particle or grid field outgrows 32-bit indices, a restart keeps its source's width, --petsc-index-bits overrides); the solver refuses any grid or particle field too large for its PETSc's index width.