use fenix to build package, have runner script; nix run works now!

flake.nix

@@ -1,32 +1,53 @@
 {
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
-    rust-overlay = {
+    fenix = {
       inputs.nixpkgs.follows = "nixpkgs";
-      url = "github:oxalica/rust-overlay";
+      url = "github:nix-community/fenix";
+    };
+    naersk = {
+      inputs.nixpkgs.follows = "nixpkgs";
+      url = "github:nix-community/naersk";
     };
   };
   outputs = {
+    fenix,
+    naersk,
     nixpkgs,
-    rust-overlay,
     ...
   }: let
-    pkgs = import nixpkgs {
-      system = "x86_64-linux";
-      overlays = [(import rust-overlay)];
+    pkgs = nixpkgs.legacyPackages.x86_64-linux;
+    toolchain = fenix.packages.x86_64-linux.fromToolchainFile {
+      file = ./rust-toolchain.toml;
+      sha256 = "sha256-zC8E38iDVJ1oPIzCqTk/Ujo9+9kx9dXq7wAwPMpkpg0=";
     };
-    rust-bin = pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;
   in {
     devShells.x86_64-linux.default = pkgs.mkShell {
       buildInputs = [
         pkgs.espflash
         pkgs.esp-generate
         pkgs.rust-analyzer
-        rust-bin
+        toolchain
       ];
       shellHook = ''
-        export RUSTUP_TOOLCHAIN=${rust-bin}
+        export RUSTUP_TOOLCHAIN=${toolchain}
       '';
     };
+    packages.x86_64-linux.default =
+      (naersk.lib.x86_64-linux.override {
+        cargo = toolchain;
+        rustc = toolchain;
+      }).buildPackage {
+        src = ./.;
+        # UPDATE .cargo/config.toml to reflect changes here in the runner
+        postInstall = ''
+          mv $out/bin/esp32c6-play $out/bin/.esp32c6-play
+          cat<<EOF>$out/bin/esp32c6-play
+          #!/usr/bin/bash
+          ${pkgs.lib.getExe pkgs.espflash} flash --monitor --chip esp32c6 $(echo $out)/bin/.esp32c6-play
+          EOF
+          chmod +x $out/bin/esp32c6-play
+        '';
+      };
   };
 }