Method persist

crates/ffi/src/kernel.rs:2840–2845

Print a persistent line that is NOT preceded by a `start`, e.g. the not-found / ungrounded branches where we don't call `check_const`.

(&mut self, line: &str)

      },
      (Err((_kind, msg)), false) => {
        format!("REJECTED ({elapsed:.1?}): {msg}")
      },
      (Err((_kind, msg)), true) => {
        format!("FAIL ({elapsed:.1?}, depth={peak}): {msg}")
      },
    };

    if self.is_slow(slow_threshold) && self.is_expected() {
      format!("{suffix} [slow]")