Function timed_json_command 

fn timed_json_command<T>(
    claude_path: &Path,
    cwd_raw: &str,
    args: &[&str],
) -> Result<T, String>
where
    T: for<'de> Deserialize<'de>,

parse_json_command with a per-call duration line, so the “why is the pane slow” question is answerable per spawn.