What is the ruling if the latecomer performs the opening Takbir while bending down into Ruku', such that they complete the Takbir while in Ruku'?

Fajr Sunnahs, Joining Congregation, and the Latecomer

• The prayer is fully valid.
• The entry is invalid, and their prayer has not commenced.
• They must perform two extra units.
• They must make Salaam immediately.