Gov. Ned Lamont returned oversight of the state’s massive school construction financing program Friday to the Department of Administrative Services, ending a controversial two-year experiment that had placed the venture within his budget office. “Given the departure of the former director of the office of school construction we felt it made the most sense” to bring the team back to Department of Administrative Services, said Josh Geballe, Lamont’s chief operating officer. The reversal came one day after deputy budget director Kosta Diamantis of Farmington — who directed the school construction unit — abruptly retired in the face of an investigation for unspecified misconduct. The program, which sends hundreds of millions of dollars annually to municipalities to help build new and renovate existing schools, had long been located within DAS. And with Diamantis’ departure, Geballe said, the department is best positioned to manage the program.