If a latecomer joins the congregation during Ruku' and bows with the Imam before the Imam raises his head, what is the status of that rak'ah?

Fajr Sunnahs, Joining Congregation, and the Latecomer

• They have missed the rak'ah.
• They have successfully caught that rak'ah.
• They must repeat the entire prayer.
• The rak'ah is counted as voluntary.