A $3.3 billion construction loan for 350 Park Avenue is the latest sign that New York’s office market can still command enormous capital — provided the building, location and tenant lineup are nearly impossible to replicate. The financing is striking not just for its size but for what it says about lenders’ willingness to back a new office product. But 350 Park is hardly a bet on the average Manhattan office building. That makes the project less a verdict on the broader office market than a confirmation of its increasingly stark two-tier structure. The financing offers an optimistic signal with a significant asterisk: New York can finance office construction at scale, but the bar for doing so has never been higher.