In a mountain valley north of Kabul, the last remnants of Afghanistan’s shattered security forces have vowed to resist the Taliban in a remote region that has defied conquerors before. But any attempt to reenact that history could end in tragedy or farce. Under the leadership of the guerrilla fighter Ahmad Shah Massoud, fighters in the Panjshir Valley held off the Soviets in the 1980s and the Taliban a decade later. But Massoud was assassinated in 2001. His 32-year-old son and officials from the ousted Afghan government have gathered in Panjshir and vow to resist the Taliban, but appear to pose little threat to the country’s new rulers.