What is the ruling on doubting the intention of the opening takbir (takbirat al-ihram), and does it necessitate قطع الصلاة وإعادتها (breaking the prayer and repeating it)?

The optimal cure for obsessive doubts (waswasah) is to disregard them and pay them no mind. If you pronounce the Takbir for the opening of prayer (Takbirat al-Ihram), proceed with your prayer and make it a single Takbir, and do not repeat it no matter how much Satan whispers to you.