Function is_cmd_builder_method 

pub fn is_cmd_builder_method(method: &str) -> bool

Whether a subprocess-builder method only MODIFIES the command (.arg, .env, .current_dir) rather than NAMING the program (Command::new, duct::cmd). A WHOLE-CRATE-Exec crate (portable_pty, duct, async_process) classifies every method as Exec, so the head-refinement must skip these: an arg or env-var-name literal that happened to match a head (.env("psql", …), .arg("curl")) would FABRICATE that effect — the §1 under-report rule. The method is the call path’s last segment.