Kobbie Mainoo is believed to have committed his long-term future to Manchester United. It signifies not only the final step in his remarkable redemption, but also extends the club’s long history of success with homegrown stars. Mainoo didn’t start a single Premier League game this season until after the club parted with Ruben Amorim on Jan. 4. Since Michael Carrick was appointed interim manager, the 21-year-old has started 12 of 13 league matches— only missing one because of a minor injury . A new contract for Mainoo has been worked on in recent months, something he was understandably hesitant on before, with the midfielder even asking for a loan back in January. Now, after Carrick teased in March an agreement was “getting closer,” The Athletic reported a new deal until 2031 was being signed at the club’s Carrington base on Wednesday. Mainoo’s existing contract, due to expire in 2027 but with an option to extend it by 12 months, was signed back in February of 2023, before his senior breakthrough.…