Rivumi local OS sandboxes: fail-closed execution on macOS, bubblewrap, and Landlock
Rivumi can wrap configured local commands and verification in macOS sandbox-exec, Linux bubblewrap, or Landlock/seccomp. A required unavailable backend stops with exit 126 instead of running bare, but external CLIs, MCP/LSP processes, and the entire Rivumi process are outside this boundary.