Stocks posted modest gains Friday, driven by some optimism among traders that Washington’s bickering politicians can reach an agreement on the budget and the federal borrowing limit soon. The stock market rose for just the third time in 12 days. While remote, the possibility of the US failing to pay its bills remains a deep concern to investors. Under normal circumstances, traders would have had the government’s monthly jobs report on the first Friday of the month. But the shutdown forced the Labor Department to delay the release of September data. And few traders are talking about upcoming quarterly earnings reports either.