It was something of a surprise when Philadelphia mayor John Street, who has never taken a leading role in the city’s arts community, stepped into the middle of the acrimonious Philadelphia Orchestra contract negotiations last week. But apparently, Street means to stay involved in the delicate contract talks: after brokering a new extension of the existing agreement, the mayor and his Commerce Director have taken a direct role in the process, and hope to use their combined clout to avoid a work stoppage. The intervention means that both musicians and management will likely have to stop posturing and actually make a good-faith attempt to settle their differences.