anthropic, openai-codex, and github-copilot flow modules gain OAuthAuth
exports (login/refresh/toAuth) wired to the prompt()/notify() login
callbacks, making the lazyOAuth attachments on the provider factories
functional. Copilot's modifyModels baseUrl rewriting becomes toAuth()
returning ModelAuth.baseUrl derived from the token proxy endpoint.
Callback-server flows race a manual_code prompt and abort it through
AuthPrompt.signal once the flow settles; OAuthAuth has no
usesCallbackServer flag. The old OAuthProviderInterface exports stay
unchanged until the coding-agent migration.
Mario Zechner