{
  description = "Playpen: vertical-tab terminal with web panes and saved layouts, built on libghostty-vt";

  inputs = {
    # Ghostty tracks nixpkgs-unstable to get GTK 4.20 / GNOME 49. We follow
    # suit so that our zig-gobject bindings (shared with Ghostty) match the
    # GObject introspection data of the GTK we link against.
    nixpkgs.url = "https://channels.nixos.org/nixpkgs-unstable/nixexprs.tar.xz";

    flake-compat = {
      url = "github:edolstra/flake-compat";
      flake = false;
    };

    systems = {
      url = "github:nix-systems/default";
      flake = false;
    };

    # Zig 0.16.0 is not in nixpkgs yet; libghostty-vt requires it.
    zig = {
      url = "github:mitchellh/zig-overlay";
      inputs = {
        nixpkgs.follows = "nixpkgs";
        flake-compat.follows = "flake-compat";
        systems.follows = "systems";
      };
    };
  };

  outputs = {
    self,
    nixpkgs,
    zig,
    systems,
    ...
  }: let
    inherit (nixpkgs) lib legacyPackages;

    forAllSystems = f:
      lib.genAttrs (import systems) (system: f legacyPackages.${system} system);
  in {
    devShells = forAllSystems (pkgs: system: {
      default = pkgs.mkShell {
        name = "playpen";

        nativeBuildInputs = [
          zig.packages.${system}."0.16.0"
          pkgs.pkg-config
          pkgs.gdb

          # The review pane's UI is a React app built by Vite, and `zig build`
          # runs that build (see build.zig) so the bundle it embeds can never be
          # older than the source it came from. Nothing else here needs node.
          pkgs.nodejs_22

          # Used by ./shot.sh to run the app inside a throwaway headless
          # compositor and screenshot it, so UI can be checked without
          # touching the developer's real session.
          pkgs.sway
          pkgs.grim
          pkgs.wtype
        ];

        buildInputs = with pkgs; [
          # GTK4 + libadwaita, the same native UI stack Ghostty uses on Linux.
          gtk4
          libadwaita

          # Powers the web panes. The 6.0 ABI is the GTK4 build of WebKitGTK;
          # the 4.x ABIs are GTK3 and would pull in a second, conflicting GTK.
          webkitgtk_6_0

          # TLS for the web panes. GIO has no TLS backend built in — it loads
          # one as a module — so without this every https:// page fails with
          # "TLS support is not available" while http:// still works.
          glib-networking

          # The GPU stack WebKit's web process renders through. It has to be
          # this mesa and not the host's — see the shellHook below.
          mesa
          glib
          gobject-introspection
          pango
          cairo
          harfbuzz
          gdk-pixbuf
          graphene

          # Windowing backends GTK links against.
          wayland
          libxkbcommon
          libx11

          # Font stack used by Pango for glyph rasterization.
          fontconfig
          freetype

          # Icon themes so the app doesn't render missing-image icons.
          adwaita-icon-theme
          hicolor-icon-theme
        ];

        shellHook = ''
          # The runtime data GTK needs to find at startup: its own GSettings
          # schemas and the icon themes our widgets pull symbolic icons from.
          #
          # These are exported under their own names, rather than only folded
          # into XDG_DATA_DIRS, because `mise run install` reads them back out
          # to bake into the installed launcher. The built binary already has
          # an RPATH into the Nix store and runs fine outside this shell, but
          # it still has to be pointed at this data or GTK aborts on a missing
          # schema and falls back to broken-image icons.
          export PLAYPEN_GSETTINGS_SCHEMA_DIR="${pkgs.gtk4}/share/gsettings-schemas/${pkgs.gtk4.name}/glib-2.0/schemas"
          export PLAYPEN_RUNTIME_DATA_DIRS="${pkgs.gtk4}/share/gsettings-schemas/${pkgs.gtk4.name}:${pkgs.adwaita-icon-theme}/share:${pkgs.hicolor-icon-theme}/share"

          # The GIO module holding the TLS backend. Same story as the schemas:
          # it is found by path at runtime, so the installer bakes it in too.
          export PLAYPEN_GIO_MODULE_DIR="${pkgs.glib-networking}/lib/gio/modules"

          export GSETTINGS_SCHEMA_DIR="$PLAYPEN_GSETTINGS_SCHEMA_DIR"
          export XDG_DATA_DIRS="$PLAYPEN_RUNTIME_DATA_DIRS:$XDG_DATA_DIRS"
          export GIO_EXTRA_MODULES="$PLAYPEN_GIO_MODULE_DIR''${GIO_EXTRA_MODULES:+:$GIO_EXTRA_MODULES}"

          # WebKit's web process renders through mesa, and every piece of that
          # path has to come from the *same* mesa. Two things go wrong on a
          # non-NixOS host if we leave it alone, and both kill the web process
          # at startup with "Could not create default EGL display:
          # EGL_BAD_PARAMETER", leaving web panes permanently blank:
          #
          #  - libglvnd falls back to /usr/share/glvnd/egl_vendor.d and loads
          #    the *host's* mesa as the EGL vendor, while WebKit is linked
          #    against Nix's libgbm. A GBM device made by one mesa is rejected
          #    by the other.
          #  - Nix's libgbm looks for its backend in /run/opengl-driver/lib/gbm,
          #    a path that only exists on NixOS.
          #
          # Pointing all three at this mesa keeps the stack self-consistent.
          # It still uses the real GPU through /dev/dri; this is not a
          # software-rendering fallback.
          export PLAYPEN_EGL_VENDOR_DIR="${pkgs.mesa}/share/glvnd/egl_vendor.d"
          export PLAYPEN_DRI_DRIVERS_PATH="${pkgs.mesa}/lib/dri"
          export PLAYPEN_GBM_BACKENDS_PATH="${pkgs.mesa}/lib/gbm"

          export __EGL_VENDOR_LIBRARY_DIRS="$PLAYPEN_EGL_VENDOR_DIR"
          export LIBGL_DRIVERS_PATH="$PLAYPEN_DRI_DRIVERS_PATH"
          export GBM_BACKENDS_PATH="$PLAYPEN_GBM_BACKENDS_PATH"
        '';
      };
    });

    formatter = forAllSystems (pkgs: _: pkgs.alejandra);
  };
}