Consult a PATH-resolved binary's own --help (mtime-cached, LC_ALL=C,
2s timeout with kill) when a segment's first non-flag token is not a
listed subcommand, and splice the unique close match (ratio >= 0.8,
same first character). Ambiguity, sudo heads, flat-fallback artifact
heads, valid subcommands and nested levels all decline to the rest of
the chain; only <binary> --help is ever run.
Alexander