add Nix flake for building the project (#309)

* feat: add Nix flake for building with crane

Adds flake.nix and flake.lock to build the project reproducibly with Nix.
Uses flake-parts + crane (idiomatic 2026 approach), with dependency caching
via buildDepsOnly, and separate checks for clippy, fmt, and tests.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Use correct branch name

* pr review

* Update Nix installation command in README

Removed outdated instructions for Nix and updated the command.

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: njbrake <njbrake@gmail.com>
Co-authored-by: Nathan Brake <33383515+njbrake@users.noreply.github.com>

Author: 3 people

README.md

@@ -53,6 +53,9 @@ curl -fsSL \
 # Homebrew
 brew install aoe
 
+# Nix
+nix run github:njbrake/agent-of-empires
+
 # Build from source
 git clone https://github.com/njbrake/agent-of-empires
 cd agent-of-empires && cargo build --release

flake.lock

@@ -0,0 +1,84 @@
+{
+  description = "Terminal session manager for AI coding agents";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    crane.url = "github:ipetkov/crane";
+  };
+
+  outputs = inputs @ { flake-parts, ... }:
+    flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
+
+      perSystem = { config, self', inputs', pkgs, system, ... }:
+        let
+          craneLib = inputs.crane.mkLib pkgs;
+
+          # git2 uses vendored-openssl (needs perl to build OpenSSL)
+          # and libgit2-sys vendors libgit2 (needs cmake to build it)
+          nativeBuildInputs = with pkgs; [
+            pkg-config
+            perl
+            cmake
+          ];
+
+          buildInputs = with pkgs; [
+            zlib # required by vendored libgit2
+          ] ++ lib.optionals stdenv.hostPlatform.isDarwin [
+            libiconv
+            darwin.apple_sdk.frameworks.Security
+            darwin.apple_sdk.frameworks.SystemConfiguration
+          ];
+
+          commonArgs = {
+            src = craneLib.cleanCargoSource ./.;
+            strictDeps = true;
+            inherit nativeBuildInputs buildInputs;
+          };
+
+          # Build only workspace dependencies first (for caching)
+          cargoArtifacts = craneLib.buildDepsOnly commonArgs;
+
+          aoe = craneLib.buildPackage (commonArgs // {
+            inherit cargoArtifacts;
+            cargoExtraArgs = "--package agent-of-empires";
+            # Tests are run in the separate aoe-test check below
+            doCheck = false;
+            meta.mainProgram = "aoe";
+          });
+        in
+        {
+          packages.default = aoe;
+
+          checks = {
+            # Build the package as a check too
+            inherit aoe;
+
+            aoe-clippy = craneLib.cargoClippy (commonArgs // {
+              inherit cargoArtifacts;
+              cargoClippyExtraArgs = "--package agent-of-empires --all-targets -- --deny warnings";
+            });
+
+            aoe-fmt = craneLib.cargoFmt {
+              inherit (commonArgs) src;
+            };
+
+            aoe-test = craneLib.cargoTest (commonArgs // {
+              inherit cargoArtifacts;
+              cargoTestExtraArgs = "--package agent-of-empires";
+              # Some git:: unit tests invoke the git binary directly
+              nativeBuildInputs = commonArgs.nativeBuildInputs ++ [ pkgs.git ];
+            });
+          };
+
+          devShells.default = craneLib.devShell {
+            checks = self'.checks;
+            packages = with pkgs; [
+              rust-analyzer
+              tmux
+            ];
+          };
+        };
+    };
+}