Add GitHub Copilot provider support

[notlikejuice]

Summary

• handle login via GitHub device flow
• save Copilot token in auth.json
• create GithubCopilotClient for Copilot API requests
• initialize Copilot client in agent loop
• expose githubcopilot provider configuration

Testing

• pnpm --filter @openai/codex run format
• pnpm --filter @openai/codex run lint
• pnpm --filter @openai/codex run test (fails: Process with PID XXXX failed to terminate within 500ms)

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https://chatgpt.com/codex/tasks/task_e_684f272bac248326a07facb43efee33f

[Copilot]

Pull Request Overview

This PR adds support for GitHub Copilot as a provider by implementing device flow login, token persistence, a dedicated Copilot client, and integrating it into the CLI and agent loop.

• Introduced GithubCopilotClient for handling Copilot API authentication and requests
• Added device-flow login in get-api-key and updated CLI to persist GITHUBCOPILOT_API_KEY
• Registered the new provider in providers.ts and initialized the client in agent-loop.ts

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
codex-cli/src/utils/providers.ts	Updated provider list with GitHub Copilot entry
codex-cli/src/utils/openai-client.ts	Added GithubCopilotClient class and token-management logic
codex-cli/src/utils/get-api-key.tsx	Implemented getGithubCopilotApiKey for device-flow login
codex-cli/src/utils/agent/agent-loop.ts	Initialized GithubCopilotClient in the agent loop
codex-cli/src/cli.tsx	Integrated Copilot login flow, auth file persistence, and env handling

Comments suppressed due to low confidence (3)

codex-cli/src/utils/providers.ts:56

• [nitpick] Use the official branding 'GitHubCopilot' (capital 'H' in 'Hub') for the provider name to match GitHub’s naming.

name: "GithubCopilot",

codex-cli/src/utils/providers.ts:58

• [nitpick] Consider using 'GITHUB_COPILOT_API_KEY' with an underscore for readability and to stay consistent with other environment variable names.

envKey: "GITHUBCOPILOT_API_KEY",

codex-cli/src/utils/providers.ts:57

• Verify that 'https://api.githubcopilot.com' is the correct API endpoint; the official Copilot API may use a different host or path.

baseURL: "https://api.githubcopilot.com",

[Copilot]

[nitpick] The 'editor-version' header is hardcoded to a VSCode plugin version; consider reflecting the CLI’s version or making this header configurable.

[Copilot]

This block triggers the Copilot login flow unconditionally when no key is present, even without the '--login' flag; consider guarding it under 'cli.flags.login' to avoid unexpected prompts.

Suggested change

	if (provider.toLowerCase() === "githubcopilot" && !apiKey) {
	if (provider.toLowerCase() === "githubcopilot" && !apiKey && cli.flags.login) {

[Copilot]

[nitpick] The GitHub Copilot client initialization mirrors logic in 'createOpenAIClient'; consider refactoring to reuse the factory for consistency and to reduce duplication.