LGTM

Could you add a regression test in test/test_sshfs.py? Roughly: run sshfs with -f -o sshfs_debug -o ssh_command='/nonexistent/wrap\\ per arg\\ with\\ space' against a dummy user@host:/ target, capture stderr, and assert the executing … line contains <…/wrap per> and <arg with space> as single tokens with no surviving backslashes. The bogus ssh_command makes exec fail fast, so it doesn't need passwordless localhost. Doubling the backslashes matters — fuse_opt_parse eats one layer before tokenize_on_space sees the value.