chore: add Nix flake with buildable app output

flake.nix

@@ -0,0 +1,109 @@
+{
+  description = "CodexMonitor Tauri app for orchestrating Codex agents";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+        packageJson = builtins.fromJSON (builtins.readFile ./package.json);
+
+        linuxPackages = pkgs.lib.optionals pkgs.stdenv.isLinux [
+          pkgs.gtk3
+          pkgs.libxkbcommon
+          pkgs.librsvg
+          pkgs.libsoup_3
+          pkgs.webkitgtk_4_1
+        ];
+
+        frontend = pkgs.buildNpmPackage {
+          pname = "codex-monitor-frontend";
+          version = packageJson.version;
+          src = ./.;
+          nodejs = pkgs.nodejs_20;
+          npmDepsHash = "sha256-TT9Po/VVzuObcqAkv4HoRSo41IMvouorlPnPTabxcTA=";
+          npmBuildScript = "build";
+          installPhase = ''
+            mkdir -p $out
+            cp -R dist $out/
+          '';
+        };
+
+        tauriConfig = builtins.toJSON {
+          build = {
+            frontendDist = "dist";
+            devUrl = null;
+          };
+        };
+
+        appPackage = pkgs.rustPlatform.buildRustPackage {
+          pname = "codex-monitor";
+          version = packageJson.version;
+          src = ./src-tauri;
+
+          cargoLock = {
+            lockFile = ./src-tauri/Cargo.lock;
+            outputHashes = {
+              "fix-path-env-0.0.0" = "sha256-UygkxJZoiJlsgp8PLf1zaSVsJZx1GGdQyTXqaFv3oGk=";
+            };
+          };
+
+          nativeBuildInputs = [
+            pkgs.cargo-tauri
+            pkgs.cmake
+            pkgs.pkg-config
+          ];
+
+          buildInputs = [
+            pkgs.openssl
+          ] ++ linuxPackages;
+
+          TAURI_CONFIG = tauriConfig;
+
+          preBuild = ''
+            mkdir -p dist
+            cp -R ${frontend}/dist/. dist
+          '';
+
+          cargoBuildFlags = [
+            "--features"
+            "custom-protocol"
+          ];
+
+          installPhase = ''
+            mkdir -p $out/bin
+            target_dir="target/${pkgs.stdenv.hostPlatform.rust.rustcTarget}"
+            cp "$target_dir/release/codex-monitor" $out/bin/
+          '';
+        };
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          packages = [
+            pkgs.cargo
+            pkgs.clang
+            pkgs.cmake
+            pkgs.git
+            pkgs.nodejs_20
+            pkgs.openssl
+            pkgs.pkg-config
+            pkgs.rust-analyzer
+            pkgs.rustc
+            pkgs.rustfmt
+            pkgs.rustPlatform.rustLibSrc
+          ] ++ linuxPackages;
+
+          shellHook = ''
+            export RUST_SRC_PATH=${pkgs.rustPlatform.rustLibSrc}
+          '';
+        };
+
+        formatter = pkgs.alejandra;
+
+        packages.default = appPackage;
+      });
+}

src-tauri/Cargo.toml

@@ -8,6 +8,9 @@ default-run = "codex-monitor"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
+[features]
+custom-protocol = ["tauri/custom-protocol"]
+
 [lib]
 # The `_lib` suffix may seem redundant but it is necessary
 # to make the lib name unique and wouldn't conflict with the bin name.