{
  description = "RustLean FIM Space — local dev shell (CUDA + llama-cpp-python) for RTX 2070 Super";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs {
          inherit system;
          config.allowUnfree = true;
        };
        cuda = pkgs.cudaPackages;
        py = pkgs.python312;
      in {
        devShells.default = pkgs.mkShell {
          packages = [
            py
            py.pkgs.pip
            py.pkgs.virtualenv
            pkgs.cmake
            pkgs.ninja
            pkgs.gcc
            pkgs.gnumake
            pkgs.git
            cuda.cudatoolkit
            cuda.cudnn
          ];

          env = {
            CUDA_HOME = "${cuda.cudatoolkit}";
            CMAKE_ARGS = "-DGGML_CUDA=on -DCMAKE_CUDA_ARCHITECTURES=75";
          };

          shellHook = ''
            export PATH="$CUDA_HOME/bin:$PATH"
            export LD_LIBRARY_PATH="${cuda.cudatoolkit}/lib:${cuda.cudnn}/lib:$LD_LIBRARY_PATH"
            export LIBRARY_PATH="${cuda.cudatoolkit}/lib:${cuda.cudnn}/lib:$LIBRARY_PATH"

            if [ ! -d .venv ]; then
              ${py}/bin/python -m venv .venv
              ./.venv/bin/pip install --upgrade pip wheel setuptools
            fi
            source .venv/bin/activate

            pip install -r requirements.txt
            pip install --force-reinstall --no-binary llama-cpp-python llama-cpp-python

            echo ""
            echo "RustLean dev shell ready.  RTX 2070 Super = sm_75 (Turing)."
            echo "Put your token in .env (HF_TOKEN), then run:  python app.py"
          '';
        };
      });
}