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'?

Catching Obligatory Prayers Part 2: Sunnah Alignment

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