Webfetch on MacOs fails when connected via iPhone hotspot

Using CoPilot App v1.1.2 on MacOs 26.5.2 for some research (eg simplified to: 'Please summarise the last entry in the GitHub changelog') results in a webfetch of the URL, and if that fails, curl is used to fetch the same URL.
- If I connect via typical Wifi networks (home, work, cafe etc) that do not support IPv6, then the webfetch works and curl is never called.
- If I connect via iPhone hotspot (iOS 26.5.2) then the webfetch fails, but curl succeeds. Error message is that DNS resolves to a blocked address, and opening up the full error shows that DNS resolved to an IPv6 address.

I think what is happening is that the network is dual stacked (IPv4 and IPv6 addresses both returned by DNS) and the scenario above gives a synthetic IPv6 address. Webfetch should (and does) block use of the synthetic address, but fails to revert to the valid IPv4 address, which it should do.

I am fairly sure I saw this behaviour in the previous app version, but don't have a record of the version number.

Start by reproducing the webfetch failure in Copilot App v1.1.2 on macOS while connected through an iPhone hotspot, then compare it with a typical Wi-Fi network and the curl fallback. Trace the webfetch handling after DNS returns a blocked synthetic IPv6 address; done means it retries or falls back to the valid IPv4 address instead of failing.

索引モデルが issue の本文から書いたものです。