Function run_via_pty 

async fn run_via_pty(
    args: &Args,
    command: &str,
    mps: Option<&WpsClient>,
    buffered: Arc<Mutex<Vec<u8>>>,
    bash: &Path,
    pair: PtyPair,
) -> Result<i32>

PTY-backed run path. Holds master alive across child.wait() and answers DSR queries from bash at startup.