Which Safari version first introduced fetch duplex support, and can we detect it programmatically before concurrent uploads?
Goal Determine how to programmatically detect whether Safari’s Fetch API will support request streaming (duplex: 'half') when issuing multiple concurrent uploads, rather than relying on ad‑hoc try/catch behavior. Constraints and Uncertainty Safari currently throws or falls back when a ReadableStream body is used with duplex: 'half' . No documented navigator