Worked on reliability hardening in the thaJeztah/docker repository, focusing on user namespace validation within shell scripts. Addressed a bug where subuid and subgid validation errors were previously suppressed when output was redirected under set -eu, which could obscure critical failures in CI pipelines. Introduced an error_subid mechanism to capture and verify exit statuses, ensuring that validation errors are now surfaced and observable. This change improved the reliability and troubleshooting of user namespace validation processes. The work was implemented using Shell and Shell Scripting, emphasizing robust error handling and enhanced security for automated workflows without introducing new user-facing features.