WebFetch fails when internet access is available only through a system proxy

Start by locating the WebFetch implementation and comparing its proxy handling with the GitHub Copilot CLI behavior described in the issue. Reproduce the failure with a system-configured proxy; done means WebFetch can retrieve external URLs through that proxy without the host-resolution error.

Short summary

In environments where outbound internet connectivity is provided via a system-configured proxy, the WebFetch tool fails to access external URLs and returns a host resolution error.

Affected version or release

v1.1.22

Installation context

No response

What happened?

When the GitHub Copilot agent attempts to retrieve content from a URL using the WebFetch tool, the request fails with the following error:

WebFetchBlockedUrlError: No such host is known. (os error 11001)

This occurs even when internet connectivity is available and functional through a properly configured system proxy.

Steps to reproduce

1. Configure internet access through a system proxy.
2. Start a GitHub Copilot agent session.
3. Ask the agent to research a topic that requires fetching information from an external URL.
4. Observe that the agent invokes the WebFetch tool and the request fails with: WebFetchBlockedUrlError: No such host is known. (os error 11001)

Expected behavior

When a system proxy is configured, WebFetch should honor the operating system's proxy settings and route outbound requests through the proxy.

The behavior should be consistent with GitHub Copilot CLI, where web access works successfully in the same environment using the configured proxy.

Additional context

WebFetchBlockedUrlError: No such host is known. (os error 11001)

GitHub Copilot CLI can successfully perform web access in the same environment through the configured proxy.

The issue appears specific to the WebFetch implementation not honoring system proxy settings, all other features in Copilot app works.