After setting up my aforementioned pnpm build, I am now wondering why the devshell and build derivations behave differently. My outputs look like this:

      devShells.default = pkgs.mkShellNoCC {
        inherit pnpmDeps cargoDeps;
        inputsFrom = [ self.packages.${system}.default ];
      };

      packages.default = pkgs.stdenvNoCC.mkDerivation (finalAttrs: {
        inherit pnpmDeps cargoDeps pname version;
        src = gitignoreSource ./.;
        strict = true;
        doCheck = false;
        nativeBuildInputs = with pkgs; [
          wasm-bindgen-cli
          nodejs
          nodejs.pkgs.pnpm.configHook
          pkgs.rustPlatform.cargoSetupHook
          wrappedWasmPack
          (rust-bin.stable.latest.default.override {targets = ["wasm32-unknown-unknown"];})
        ];

        buildPhase = ''
          pnpm build
        '';
        installPhase = ''
          mv dist/ $out
        '';
      });

The packaging derivation works exactly how I want it. But the devshell does not. Specifically, while in the packaging derivation all the dependencies are installed and then all I need to do is run "pnpm build" in the build phase as shown. But in the dev shell when I execute "pnpm build" pnpm complains that I need to install the dependencies still.

Is there something I am missing? Is mkshell different from mkderivation in a way that prevents this? Obviously it is impure, but I'd like to confine the dependencies in the store as much as I can.

grist-core> no configure script, doing nothing
grist-core> Executing yarnConfigHook
yarn config v1.22.22
success Set "yarn-offline-mirror" to "/nix/store/iswv7iddmhm8py46spivs75x2n53mjcf-offline".
Done in 0.02s.
yarn install v1.22.22
[1/4] Resolving packages...
[2/4] Fetching packages...
error Can't make a request in offline mode ("https://registry.yarnpkg.com/https___registry.npmjs.org_jquery___jquery_3.5.0.tgz")
info Visit https://yarnpkg.com/en/docs/cli/install for documentation about this command.
error Can't make a request in offline mode ("https://registry.yarnpkg.com/node_gyp___node_gyp_8.4.1.tgz")

grist-core> no configure script, doing nothing
grist-core> Executing yarnConfigHook
yarn config v1.22.22
success Set "yarn-offline-mirror" to "/nix/store/iswv7iddmhm8py46spivs75x2n53mjcf-offline".
Done in 0.02s.
yarn install v1.22.22
[1/4] Resolving packages...
[2/4] Fetching packages...
error Can't make a request in offline mode ("https://registry.yarnpkg.com/https___registry.npmjs.org_jquery___jquery_3.5.0.tgz")
info Visit https://yarnpkg.com/en/docs/cli/install for documentation about this command.
error Can't make a request in offline mode ("https://registry.yarnpkg.com/node_gyp___node_gyp_8.4.1.tgz")