Copilot Coding Agent: "GitHub host is required" Error on Self-Hosted ARC Runners

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Bug

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Copilot Coding Agent

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Category: Bug Report
Product: GitHub Copilot Coding Agent
Feature: Self-Hosted Runner Support

Summary

GitHub Copilot coding agent fails with Error: GitHub host is required when using self-hosted GitHub Actions runners managed by Actions Runner Controller (ARC). This prevents the agent from completing any tasks.

Environment

• Runner Type: Self-hosted via Actions Runner Controller (ARC)
• Runner OS: Ubuntu x64 Linux
• Runner Name Pattern: host-yoga-repo-flake-*
• Repository Firewall: Disabled (as required for self-hosted runners)
• Feature Announcement: https://github.blog/changelog/2025-10-28-copilot-coding-agent-now-supports-self-hosted-runners/

Issue Details

Error Message

CodeQL asset ID: 304101132
Error ensuring CodeQL: Error: GitHub host is required

Stack Trace

Error: GitHub host is required
    at demandGitHubHost (/home/runner/_work/_temp/******-action-main/src/settings/demand.ts:45:15)
    at async (/home/runner/_work/_temp/******-action-main/src/tools/codeql/download-codeql.ts:45:18)

Reproduction Steps

1. Deploy ARC with scale sets following the docs
2. Create .github/workflows/copilot-setup-steps.yml targeting self-hosted runner
3. Disable repository firewall in Copilot settings (as required)
4. Assign GitHub issue to @copilot
5. Observe: Copilot creates PR but fails during "Processing Request" phase

What's Working

• Self-hosted ARC runners correctly pick up Copilot jobs
• Firewall validation passes
• Basic workflow execution succeeds
• Runner identification: host-yoga-repo-flake-7sgfm-runner-86l6b

What's Broken

• CodeQL tool initialization fails when calling demandGitHubHost()
• This appears to be missing GitHub host configuration in the self-hosted environment
• Prevents any Copilot tasks from completing

Example Workflow Run

Failed run with full logs: https://github.com/i-am-logger/flake/actions/runs/19201998990

Impact

This makes the newly announced self-hosted runner support for Copilot coding agent unusable for repositories that require private package access or internal tooling.

Request

Please investigate why CodeQL requires a GitHub host configuration that isn't properly set in self-hosted ARC environments, and provide:

1. Documentation on any required environment variables or configuration
2. A fix to properly detect/configure GitHub host in self-hosted contexts
3. Guidance on workarounds if available

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