What is the meaning of the phrase "may Allah forgive you"? And does it include past and future sins? And what does "Allah accepts a servant's repentance as long as he has not gurgled" mean, and does that include the forgiveness of all sins?

The statement "May Allah forgive you" depends on the intention of the supplicant. If they intend the forgiveness of past and future sins, it includes both. If they intend only past sins, it does not include future ones. It is not possible to assert with certainty that the supplication will be answered, as the forgiveness of sins is from the unseen. Repentance before the death rattle (ghargara) is accepted, and repentance erases the sins that preceded it. One who has reached the death rattle is not imagined to commit a sin.