resolveUserPath method
Resolves userPath against userRoot (null → the default
<userRoot>/.fah/memory; ~/x → <userRoot>/x).
Implementation
String resolveUserPath(String userRoot) {
final path = userPath;
if (path == null || path.isEmpty) return '$userRoot/.fah/memory';
if (path.startsWith('~/')) return '$userRoot/${path.substring(2)}';
if (path.startsWith('/')) return path;
final stripped = path.startsWith('./') ? path.substring(2) : path;
return '$userRoot/$stripped';
}