I doubt Braga ever read the story. For all I know, Braga may have thought he invented the time-loop story. While the cause of the main character's experiencing the same day again and again and the story's resolution are totally different from "Cause and Effect," of course, "Tunnel" is the earliest "Groundhog Day" time-loop (or apparent time-loop) story I'm aware of.I'm curious, what makes you think that it was specifically that story which led Braga to write "Cause and Effect"?
There are earlier time loop stories, according to Wikipedia. In 1941, there was an American short story called Doubled and Redoubled where the protagonist repeats a "perfect" day after being cursed by a witch (Groundhog Day's original script used a curse as the cause). That precedes Pohl's story by 13 years.

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