Beneath the blazing summer sun on a former slave plantation, Lamont Gross and fellow prisoners stooped in long rows, picking vegetables by hand under the watchful eyes of armed guards on horseback. He said breaks were short and infrequent, with nothing to protect workers from the heat. “I saw guys collapse,” Gross said of his days on the so-called farm line at Louisiana’s state penitentiary, where men work for pennies an hour or nothing at all and face punishment if they refuse. “There were dudes that got heat stroke. There were dudes with underlying conditions, older or had some sort…