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 property or feature flag exposes this capability, and the only detection method is a try/catch around the fetch call. The support is version‑sensitive, and edge cases may cause false positives or negatives.

Questions

• Which Safari version first introduced any support for duplex: 'half' in the Fetch API?
• Is there a navigator property or feature flag that can be queried before making a request to determine if request streaming will succeed?
• Can a try/catch around fetch(url, {method:'POST', body:..., duplex:'half'}) reliably indicate support, or are there known edge cases that cause false positives or negatives?