"""
Low-level kernels and shared numeric helpers for HHD.

Use this file for pieces that should not live inside the public `nHHD` API or the
`PoissonSolver` class, for example:
- finite-difference helper functions
- small backend-dispatch helpers
- reusable CuPy/OpenCL kernel preparation code
- shared CPU math that does not depend on object state
"""

# No standalone helpers from the old monolithic `HHD.py` are required yet.
# Keep this module in place so future extracted CUDA/OpenCL/CPU helpers have a
# stable home without changing the public package layout again.

__all__ = []
