Function runHelper

test/setup-windows-fallback.test.ts:69–100

(
    isWindows: '0' | '1',
    srcKind: 'file' | 'dir',
  )

  // Source the helper into a temp shell with IS_WINDOWS set and exercise
  // each cell of the file/dir × Windows/Unix matrix.
  function runHelper(
    isWindows: '0' | '1',
    srcKind: 'file' | 'dir',
  ): { ok: boolean; targetIsSymlink: boolean; targetExists: boolean; stderr: string } {
    const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-helper-'));
    try {
      const src = path.join(tmp, 'source');
      const dst = path.join(tmp, 'dest');
      if (srcKind === 'file') {
        fs.writeFileSync(src, 'hello\n');
      } else {
        fs.mkdirSync(src);
        fs.writeFileSync(path.join(src, 'inner.txt'), 'hello\n');
      }
      const helper = extractHelper();
      // IS_WINDOWS must exist as a shell-readable var before sourcing.
      const script = `IS_WINDOWS=${isWindows}\n${helper}\n_link_or_copy "${src}" "${dst}"\n`;
      const result = spawnSync('bash', ['-c', script], {
        encoding: 'utf-8',
        timeout: 5000,
      });
      const lst = fs.lstatSync(dst, { throwIfNoEntry: false });
      return {
        ok: result.status === 0,
        targetIsSymlink: lst?.isSymbolicLink() ?? false,
        targetExists: lst !== undefined,
        stderr: result.stderr,
      };
    } finally {
      fs.rmSync(tmp, { recursive: true, force: true });
    }
  }

  test('IS_WINDOWS=0 + file → symlink (existing Unix behavior)', () => {
    const r = runHelper('0', 'file');