Nix flake: pin the toolchain Edge uses

flake.nix

@@ -0,0 +1,52 @@
+{
+  description = "OpenStrap analytics Dart and Flutter development environment";
+
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  # Same Flutter/Dart release as ../edge and its CI.
+  inputs.nixpkgs-flutter.url =
+    "github:NixOS/nixpkgs/27dfede99da61fd1ead9d4a2fa92bc9c242e83d2";
+
+  outputs = { nixpkgs, nixpkgs-flutter, ... }:
+    let
+      systems = [ "x86_64-linux" "aarch64-linux" ];
+      forAllSystems = nixpkgs.lib.genAttrs systems;
+    in {
+      devShells = forAllSystems (system:
+        let
+          pkgs = import nixpkgs { inherit system; };
+          flutterPkgs = import nixpkgs-flutter {
+            inherit system;
+            config.allowUnfree = true;
+          };
+          flutter = flutterPkgs.flutterPackages.v3_41;
+          tools = with pkgs; [
+            flutter git ripgrep jq python3 gnumake unzip which
+            clang cmake ninja pkg-config
+          ];
+          fhs = pkgs.buildFHSEnv {
+            name = "analytics-fhs";
+            targetPkgs = p: tools ++ (with p; [
+              bashInteractive zlib libcxx ncurses5 gtk3 fontconfig libGL
+            ]);
+            profile = ''
+              export IN_ANALYTICS_FHS=1
+            '';
+            runScript = pkgs.writeShellScript "analytics-fhs-run" ''
+              if [[ $# -eq 0 ]]; then exec bash; else exec "$@"; fi
+            '';
+          };
+        in {
+          default = pkgs.mkShell {
+            packages = tools ++ [ fhs ];
+            shellHook = ''
+              # Let the packaged Flutter wrapper select its complete SDK,
+              # including prebuilt engine/test artifacts.
+              unset FLUTTER_ROOT
+              if [[ -z "''${IN_ANALYTICS_FHS:-}" && $- == *i* ]]; then
+                exec analytics-fhs
+              fi
+            '';
+          };
+        });
+    };
+}