London — The walls of the medical room are charred black and the door appears to have melted half away in the flames. Ten days after an apparent petrol bomb was hurled through the synagogue window in the middle of the night, the smell of smoke still catches in the back of the throat. When Rabbi Yehuda Black returned the morning after the attack on what he calls his “gem” of a synagogue — with its wall of stained-glass windows and a ceiling carved with Stars of David — he said he was overwhelmed with emotion. “It’s only the medical room....