San Francisco real estate has never been very accessible. But the record sales happening right now in the city’s high-end market are testing the upper limits of what even this famously unaffordable city thought was possible. Consider a six-bedroom, 5,700-square-foot home in Cow Hollow, one of San Francisco’s most coveted neighborhoods. It was listed two weeks ago at $7.95 million, so, not cheap. It just sold for $15 million. The sellers, who bought the property for $7.8 million in the summer of 2020 as the pandemic was pushing residents out of cities, nearly doubled their money in under five years. San Francisco real estate agent Rohin Dhar flagged the sale on X, where it drew the kind of reactions you’d expect from people who thought they’d seen everything this market had to offer. Then there’s a 4,100-square-foot home in Presidio Heights, one of the city’s most exclusive enclaves, that was listed in late April for $4.4 million and sold a week later for $8.2 million, nearly double the asking price.…