A long-running legal dispute over the fate of a small island in San Francisco Bay ended Wednesday when Point Buckler Island was sold at auction to the John Muir Land Trust, a nonprofit conservation organization. The land trust used a court-awarded credit worth about $3.8 million to purchase the 29-acre private island on a 50-acre parcel that is part of Solano County and is situated in a tidal marsh separating Suisun Bay and Grizzly Bay. It’s a critical habitat and corridor for delta smelt, Chinook salmon and other species. It was the subject of a prolonged legal back-and-forth between its former owner, John Sweeney, and county, state and federal regulators that began in 2016 when the San Francisco Bay Regional Water Quality Control Board ordered Sweeney to remove unpermitted infrastructure he built on the island, including about a mile of levies that he had restored.