More than a year after an Islandwide contract with the cable television giant Comcast expired, a proposed new contract that includes service to Chappaquiddick has come before the six-town negotiating committee.A final proposal from Comcast was sent to the Vineyard cable advisory committee on Sept. 6. After months of keeping its cards close to the vest on the subject of service to Chappaquiddick, Comcast is now proposing a $1.58 million project to bring cable service to the small island that is part of the town of Edgartown. Under the proposal, subscribers and the cable company would share the cost of installing conduit.