OpenAI's recent funding deal and stunning valuation helped lift U.S. stocks to another record closing high. OpenAI's latest investment round valued the privately held AI company at about $500 billion, and two tech heavyweights, Samsung Electronics and SK Hynix, signed on as memory-chip partners for its "Stargate†infrastructure project. Semiconductor stocks rose, and investors looked past the potential fallout from a government shutdown that is expected to stretch into next week. ...