FixedPatchStepper(..., jets=()) passes jets (coarse cell-edge frame, as
fine_objects) to prepare_fine_boundary, which runs the shared assignment
checks before CUDA. Dense fine path: assign_surface with jets and the
boundary's true hits. Blocked path: surface_link_velocity with jets/hits;
unit-amplitude shapes cached. set_jet_amplitude (new/ready only) validates
first, then rewrites the dense SoA column or the blocked jet rows and
re-uploads only the velocity buffer after a stream sync. Scheduling,
kernels and launch ABI unchanged.
tests/validation/multigrid/test_refinement_jets.py: mocked-driver CPU
checks and frozen GPU gates G1-G3 (layout identity, jet vs legacy <=1e-6,
amplitude switch).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
