try to use generate script

the script fails with:
Couldn't resolve the package 'ffigen' in 'package:ffigen/ffigen.dart'.
Couldn't resolve the package 'path' in 'package:path/path.dart'.

flake.nix

@@ -29,6 +29,22 @@
           ...
         }:
 
+        let
+          src = ./.;
+
+          # from https://discourse.nixos.org/t/is-there-a-way-to-read-a-yaml-file-and-get-back-a-set/18385/5
+          importYAML =
+            file:
+            lib.importJSON (
+              pkgs.runCommand "converted-yaml.json" { } ''${pkgs.yj}/bin/yj < "${file}" > "$out"''
+            );
+
+          package = importYAML "${src}/pubspec.yaml";
+
+          usedFlutter = (pkgs.flutter.override { extraPkgConfigPackages = [ pkgs.libsecret ]; });
+
+          buildInputs = [ pkgs.sqlite ];
+        in
         {
           _module.args.pkgs = import nixpkgs {
             inherit system;
@@ -45,20 +61,35 @@
               olm
               git
               clang
-              (flutter.override { extraPkgConfigPackages = [ pkgs.libsecret ]; })
+              usedFlutter
 
               (pkgs.writeShellScriptBin "rustup" (builtins.readFile ./nix/fake-rustup.sh))
             ];
 
             env = {
-              LD_LIBRARY_PATH = "${
+              LD_LIBRARY_PATH = "${lib.makeLibraryPath buildInputs}:./build/native_assets/linux";
-                pkgs.lib.makeLibraryPath ([
-                  pkgs.sqlite
-                ])
-              }:./build/native_assets/linux";
               CPATH = lib.makeSearchPath "include" [ pkgs.glibc.dev ];
             };
           };
+
+          packages.default = usedFlutter.buildFlutterApplication {
+            inherit src buildInputs;
+            pname = package.name;
+            version = package.version;
+
+            pubspecLock = importYAML "${src}/pubspec.lock";
+            gitHashes = {
+              flutter_chat_ui = "sha256-4fuag7lRH5cMBFD3fUzj2K541JwXLoz8HF/4OMr3uhk=";
+              flutter_link_previewer = "sha256-4fuag7lRH5cMBFD3fUzj2K541JwXLoz8HF/4OMr3uhk=";
+              flyer_chat_text_message = "sha256-4fuag7lRH5cMBFD3fUzj2K541JwXLoz8HF/4OMr3uhk=";
+              window_size = "sha256-XelNtp7tpZ91QCEcvewVphNUtgQX7xrp5QP0oFo6DgM=";
+            };
+
+            patchPhase = /* sh */ ''
+              patchShebangs ./scripts/generate.sh
+              ./scripts/generate.sh # note: this doesn't quit the build on fail
+            '';
+          };
         };
     };
 }