April Fools’ Day will have a special meaning for the Federal Reserve this year: it will be the first day the central bank allows a ravaged U.S. mortgage market to stand on its own two feet. Even if things are a bit wobbly at first, the Fed is unlikely to step in again after its debt purchase program — devised at the height of the financial meltdown — expires. That would take a renewed crisis, like a sudden and destabilizing spike in mortgage rates.