Gregory Santos’ return to the Giants is not a major Mariners regret story, at least not yet. It’s more of a reminder of how quickly a sensible bullpen gamble can disappear when injuries take over. Seattle acquired Santos in 2024 hoping his power sinker and late-inning upside would give the bullpen another nasty look. Two injury-filled seasons later, the Mariners never really got enough of him to know what they had. The Giants are giving Santos another shot after selecting his contract from Triple-A Sacramento. For Mariners fans, that news lands like a tired sigh from a fanbase that remembers exactly what Seattle thought it was getting and exactly how little of it ever actually got. The Mariners traded for him in February 2024 because his 2023 breakout with the White Sox looked like the blueprint for a nasty high-leverage weapon.…