{
  description = "Helicase — Helix-style modal editing for JetBrains IDEs, with a Helix-as-library oracle for differential testing.";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
    flake-utils.url = "github:numtide/flake-utils";
    rust-overlay = {
      url = "github:oxalica/rust-overlay";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };

  outputs = { self, nixpkgs, flake-utils, rust-overlay }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs {
          inherit system;
          overlays = [ rust-overlay.overlays.default ];
        };

        # Match Helix's rust-toolchain.toml (1.90.0 stable + rustfmt, rust-src,
        # clippy). The oracle links Helix as a library, so we want exactly the
        # toolchain Helix was developed with.
        rustToolchain = pkgs.rust-bin.stable."1.90.0".default.override {
          extensions = [ "rust-src" "rustfmt" "clippy" "rust-analyzer" ];
        };
      in
      {
        devShells.default = pkgs.mkShell {
          buildInputs = with pkgs; [
            # Rust — pinned to match Helix's expectations
            rustToolchain

            # JVM toolchain for the eventual Kotlin engine + IntelliJ plugin
            jdk21
            gradle
            kotlin

            # Porter: extracts Helix tests into the JSON corpus
            python3

            # VCS — user uses jj over git
            jujutsu
          ];

          shellHook = ''
            echo "helicase dev shell"
            echo "  rust: $(rustc --version)"
            echo "  jdk:  $(java -version 2>&1 | head -n1)"
            echo "  py:   $(python3 --version)"
          '';

          # Tell IntelliJ Platform Plugin Template-style Gradle builds where
          # the JDK lives, so they don't try to download one. `.home` gives the
          # canonical Java home for the platform (different layout on Mac vs Linux).
          JAVA_HOME = pkgs.jdk21.home;
        };
      });
}