SAN FRANCISCO — On the day when Ryan Walker returned from a month back in the minors, Giants manager Tony Vitello — for the first time — named a closer. For now, it will be Caleb Kilian as the staff tries to find a bit more consistency late in games. Walker is hoping to be part of that mix, and soon, but he’ll return as a “fireman,” said Vitello, who pointed out that the right-hander can be an effective weapon if he enters to help get a starting pitcher out of a jam. What’s next for Walker after that will be dependent on how much he actually figured out over the past month.Walker was optioned on May 10 after giving up runs in four consecutive appearances. It was his first time back in the minor leagues since he got called up in 2023, but he didn’t go back to Triple-A right away. Walker instead was sent to Scottsdale, where he worked on mechanical changes in the organization’s “pitch lab,” and then threw a few bullpen sessions under the eye of Matt Yourkin, a well-regarded coordinator. “I was eager the whole time to get back, but I also know that I can’t just go down there and expect...