In a Hacks doubleheader on Thursday, the show’s comedienne hero Deborah Vance is forced to look both backward and forward — to confront pain from her past, ground herself in the present with her daughter D.J. for the first time (perhaps ever), and, in the second episode’s closing moments, look not toward her own future but that of her only child. That these two episodes, certainly among the stronger half-hours in the show’s swan song season, are paired together is a clever play. And that the second is an Amazing Race crossover makes the feat even more impressive: what could have been a hokey series of gags dunking on reality TV instead becomes a smart device to reunite two characters, advance Deb’s growth as a mother, and give D.J. (the always-welcome Kaitlin Olson) a series-end arc that feels both satisfying and hopeful. The gang, well, most of them, are together at the top of episode four (titled “Episode 5.4,” for reasons that will come to light later), as they walk through Deborah’s past, in literal …