Astros general manager Jeff Luhnow said Wednesday that shortstop prospect Jonathan Villar is “close” to making his major league breakthrough.

The 21-year-old is expected to be an everyday starter by the 2014 All-Star break, linking up with such young names as Jonathan Singleton and George Springer to provide the rebuilding Astros the first layer of their multiyear construction project.

“If we fast forward … they’re here, and they’re here to stay, and they’re making contributions. They’re not just up, getting a cup of coffee,” Luhnow said.

The real stuff can’t come soon enough. Because baseball’s worst team for two years running continues to go through shortstops like it has no desire to field a consistent major league middle infield.

The Astros signed eight-year veteran Ronny Cedeno to a one-year contract Sunday. Cedeno, 30, instantly became the lead candidate to be named the team’s opening-night and everyday shortstop, despite his .647 career OPS, .247 batting average and yearly output of 4.6 home runs. And despite the fact the light-hitting vet was released Tuesday by the shortstop-needy Cardinals, who are seeking a replacement for injured starter …