Is the thought or self-talk of disbelief, God forbid, considered an intention to disbelieve, and do these thoughts necessitate ghusl (ritual bathing) to embrace Islam?

Resolved intent to disbelieve is considered disbelief, because it contradicts faith. What is meant by it is a firm intention to disbelieve. As for mere thoughts, they are from the whispers of the self that are forgiven and do not affect the soundness of faith. It is stated in the Fiqh Encyclopedia that whoever has a thought of disbelief without a firm intention does not disbelieve, because it is a form of waswasa (whispering of Satan/self).