Add pinned development shell and cross-platform PR CI

.github/workflows/ci.yaml

@@ -0,0 +1,34 @@
+name: CI
+
+on:
+  pull_request:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
+jobs:
+  test:
+    name: build and test (${{ matrix.system }})
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 30
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - system: x86_64-linux
+            os: ubuntu-24.04
+          - system: aarch64-linux
+            os: ubuntu-24.04-arm
+          - system: aarch64-darwin
+            os: macos-26
+    steps:
+      - uses: actions/checkout@v6.0.2
+      - uses: cachix/install-nix-action@v31.10.1
+      - name: Build
+        run: nix build --no-write-lock-file --print-build-logs
+      - name: Test built package
+        run: nix develop --no-write-lock-file -c python3 test.py ./result/bin/fall

README.md

@@ -282,15 +282,21 @@ ignored: remove old suffix text or replace it with a registered remote and optio
 
 ## Tests
 
+The development shell provides Nushell, Python, and Git pinned by `flake.lock`.
+
 ```sh
-nu codec-test.nu
-nix shell --inputs-from . nixpkgs#python3 -c python3 cli-test.py
+nix develop -c nu codec-test.nu
+nix develop -c python3 test.py
 nix build
-nix shell --inputs-from . nixpkgs#python3 -c python3 cli-test.py ./result/bin/fall
+nix develop -c python3 test.py ./result/bin/fall
 ```
 
 The CLI suite uses temporary configurations and repositories, including a
 worktree, and checks exit codes, diagnostics, boundaries, and state preservation.
+Without an argument, `test.py` runs `fall.nu` with Nushell from PATH; with an
+executable path, it tests that executable instead. Pull request CI builds the
+package and tests `result/bin/fall` once on each supported system
+(`x86_64-linux`, `aarch64-linux`, and `aarch64-darwin`).
 
 ## After Uninstall
 

flake.nix

@@ -13,6 +13,16 @@
         );
     in
     {
+      devShells = forAllSys (pkgs: {
+        default = pkgs.mkShell {
+          packages = [
+            pkgs.nushell
+            pkgs.python3
+            pkgs.gitMinimal
+          ];
+        };
+      });
+
       packages = forAllSys (pkgs: {
         default = pkgs.stdenvNoCC.mkDerivation {
           pname = "fall";

cli-test.py → test.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-"""Isolated integration spec: python3 cli-test.py [installed-fall]."""
+"""Isolated integration spec: python3 test.py [installed-fall]."""
 import os
 import json
 from pathlib import Path