The China reform trade is backfiring in the stock market. After soaring the most in two years on Nov. 18 as the Communist Party unveiled its biggest policy changes since the 1990s, the Hang Seng China Enterprises Index has since posted the world’s worst drop. An index of stocks JPMorgan Chase & Co. says benefit most from reform sank 10 percent this year through yesterday. A plan to link bourses in Hong Kong and Shanghai, which fueled a two-month rally when the idea was first floated in 2007, lifted shares for just one day when it was reintroduced in April.