LONDON — When the World Trade Organization’s biennial summit wrapped up without a deal on institutional reforms in March, top officials took an unprecedented gamble. They agreed to extend the talks in the hope that a few more weeks would give Brazil and the United States time to settle their differences over extending the body’s e-commerce moratorium — and unlock its long-awaited reform agenda. But the extra time has failed to break the deadlock.  A WTO official, granted anonymity to discuss