GitHub Copilot hangs indefinitely on corporate networks with SSL inspection #18785

Description

GitHub Copilot models hang indefinitely with no error on corporate networks that use SSL inspection proxies (Zscaler, Netskope, Fortinet, etc). VS Code and Zed work fine on the same network.

Steps to reproduce

1. Be on a corporate network with SSL inspection (e.g., Zscaler)
2. Login to GitHub Copilot via opencode auth
3. Send any message using a Copilot model (e.g., gpt-4.1)
4. The request hangs forever - no response, no error

Expected behavior

The model should respond, same as VS Code and Zed on the same network.

Root cause

The Copilot plugin sends the raw GitHub OAuth token directly to api.githubcopilot.com. VS Code and Zed perform a token exchange first via api.github.com/copilot_internal/v2/token which returns:

• A short-lived Copilot session JWT
• The correct user-specific API endpoint (e.g., api.individual.githubcopilot.com)

Without this token exchange, the Copilot API does not respond on certain networks.

Environment

• OpenCode 1.3.0
• Windows with Zscaler SSL inspection
• GitHub Copilot subscription active
• VS Code Copilot works on the same machine/network