clone: Operation not permitted when creating user namespace in rootless Podman
Goal: achieve a repeatable development environment that relies on rootless containers (e.g., Podman, bubblewrap) and works identically on any Linux host, regardless of distribution‑specific user namespace settings. Constraints: on Debian/Ubuntu the kernel.unprivileged_userns_clone sysctl may be set to 0, while Ubuntu 23.10+ enforces AppArmor restrictions on