jobLogDirOverride function
The shellJobLogDirEnvVar value from env, trimmed; null when unset or
blank. Pure — the executable owns the Platform.environment read.
Implementation
String? jobLogDirOverride(Map<String, String> env) {
final value = env[shellJobLogDirEnvVar]?.trim();
return (value == null || value.isEmpty) ? null : value;
}