A drug container closure for mounting on an open-topped drug container to form a ready-to-use drug reconstitution assemblage for use with a needleless syringe. The drug container closure includes a drug container stopper for sealing the drug container and a fluid transfer member with an integral needleless syringe connector and a puncturing cannula. The fluid transfer member is manually disposed along a diametric inverted L-shaped track pair from an initial non-puncturing position to a puncturing position. The inverted L-shaped track pair includes one-way snap members to prevent a user returning the fluid transfer member to an earlier position and indicating progress of the user activation.