sfgate.com — Until she was stabbed by a homeless man just outside her front door, Rosa Rucker was having a nearly perfect San Francisco experience. Strolling over to a 7-Eleven in her Outer Sunset neighborhood to buy a candy bar in the wee hours of the morning of Nov. 21, the 26-year-old German exchange student noticed Robert Hancock, a 23-year-old drifter. . .