Hamas had accused Israel of failing to keep its side of the bargain and Israel was threatening to resume its lethal onslaught on the Gaza Strip. Negotiators aboard set to work, seeking to save the cease-fire deal between Israel and Gaza’s Hamas rulers before it fell apart and scuttled weeks of high-stakes diplomatic wrangling. The first public visit by Qatari officials to Israel marked an extraordinary moment for the two countries, which have no official diplomatic relations.