What is the reason for the revelation of the Two Protectors (Al-Mu'awwidhatayn), and what is the meaning of "في جفّ طلعة تحت راعوفة" (fi jaffi ṭalʿatin taḥta rāʿūfatin)?

Some exegetes mentioned that the Two Last Surahs of the Qur’an (Al-Mu’awwidhatayn) were revealed in connection with the incident of the Prophet’s (peace be upon him) being bewitched, even though the original story in the Sahihayn (Bukhari and Muslim) did not mention their revelation. Al-Tha’labi narrated a lengthy story about the Jews bewitching the Prophet and the revelation of Al-Mu’awwidhatayn, but Ibn Kathir, Al-Suyuti, and Ibn Hajar pointed out the weakness or strangeness of its chain of narration. They mentioned that it has supporting evidence, but without mentioning the revelation of the two surahs. As for “Al-Ra’ufah” in the story, it is a stone placed at the top of a well for the water-drawer to stand on, or a hard rock found at the bottom of the well that cannot be removed.