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-r/--run mounts an image, runs a command under bwrap in the foreground (default /bin/sh, overridable via -- <command> [args...]), then unmounts and cleans up when it exits. -c/--cleanup deletes a layer and its ancestor chain from local storage (containers-storage delete-layer, walking parents via `layer --json`), since -u only ever unmounted. bwrap needs to see the merged mount from inside the private namespace containers-storage mount creates when running rootless; run_bwrap() locates the live fuse-overlayfs process and runs bwrap via nsenter into its namespaces. When running as root no such namespace exists (containers-storage doesn't need to reexec for privilege), so nsenter fails with EINVAL; detect geteuid() == 0 and skip it automatically there. -n/--no-nsenter forces it off manually for any other case. process.cpp gains run_process_foreground() (inherited stdio, for the interactive bwrap run) and the relocated find_in_path(), now shared with bwrap.cpp's nsenter lookup. Also: meson test only ran -m, leaking a layer on every run; it now runs tests/run_test.py, which drives mount -> umount -> cleanup and fails if any step does. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>