Finally wandered down to Moore Park at lunch and finally saw a Citadis 305 up close.
Despite the specification that a Citadis should be able to rescue an Urbos, the 305s appear to have standard Alstom miniature knuckle couplers, not Sharfenburgs. (Which the CAFs inherited from the requirement to couple to a Variotram)
A 'do not step' notice is covering the actual coupling.