Celtics co-owner Wyc Grousbeck still exchanges text messages with Ainge about once a week. President of basketball operations Brad Stevens, who was hired by Ainge as the Celtics’ coach in 2013 before replacing him as lead executive last spring, said he and Ainge remain in frequent contact. Assistant general manager Austin Ainge speaks to his father every day. “I was telling him what I think they should be doing against the Mavericks, and he was telling me what he saw against the Nets,” Austin Ainge said. “We even talk about playoff series neither of our teams are involved in. But he’s been rooting very hard for us and is very invested. He obviously cares for us in the front office. He worked with us for so many years. He’s super-invested in the players. He spent hours and hours with these guys, and of course he’s pulling for them.”