When allowPrivateProxy is true, the explicit proxy hostname is operator-
configured and trusted. The SSRF guard was checking the proxy hostname
against the target-scoped hostnameAllowlist (e.g. ["api.telegram.org"]),
which rejected localhost and other local proxy hostnames. This broke
Telegram media downloads (and any channel using a local proxy) after
the url-fetch security hardening in 2026.4.x.
Clear the hostnameAllowlist for the proxy hostname check while keeping
private-network IP validation in place via allowPrivateNetwork.
Fixes#61906
Co-authored-by: Devin Robison <drobison00@users.noreply.github.com>
bffb83acf8