Residents hoping that the often-promised, never-delivered revamp of the Jamaica Plain Branch Library have a reason for cautious optimism. An architect has been appointed for the long-delayed project of bringing one of the Boston Public Library's most actively-used branches up to date for handicap accessibility and a host of other improvements. The building was last renovated in 1962, according to Gretchen Grozier, president of the JP Historical Society and member of Friends of the Jamaica Plain Branch Library. Residents can find out much more about the project at a public meeting set set for 6 p.m. on Wednesday, April 9 at Curtis Hall, right across from the library itself. The meeting will be on the second floor.