Add Google Gemini CLI and Antigravity OAuth providers

- Add google-gemini-cli provider: free Gemini 2.0/2.5 via Cloud Code Assist
- Add google-antigravity provider: free Gemini 3, Claude, GPT-OSS via sandbox
- Move OAuth infrastructure from coding-agent to ai package
- Fix thinking signature handling for cross-model handoff
- Fix OpenAI message ID length limit (max 64 chars)
- Add GitHub Copilot overflow pattern detection
- Add OAuth provider tests for context overflow and streaming

packages/ai/src/utils/oauth/index.ts

@@ -0,0 +1,210 @@
+/**
+ * OAuth credential management for AI providers.
+ *
+ * This module handles login, token refresh, and credential storage
+ * for OAuth-based providers:
+ * - Anthropic (Claude Pro/Max)
+ * - GitHub Copilot
+ * - Google Cloud Code Assist (Gemini CLI)
+ * - Antigravity (Gemini 3, Claude, GPT-OSS via Google Cloud)
+ */
+
+// Anthropic
+export { loginAnthropic, refreshAnthropicToken } from "./anthropic.js";
+// GitHub Copilot
+export {
+	enableAllGitHubCopilotModels,
+	enableGitHubCopilotModel,
+	getBaseUrlFromToken,
+	getGitHubCopilotBaseUrl,
+	loginGitHubCopilot,
+	normalizeDomain,
+	refreshGitHubCopilotToken,
+} from "./github-copilot.js";
+// Google Antigravity
+export {
+	type AntigravityCredentials,
+	loginAntigravity,
+	refreshAntigravityToken,
+} from "./google-antigravity.js";
+// Google Gemini CLI
+export {
+	type GoogleCloudCredentials,
+	loginGeminiCli,
+	refreshGoogleCloudToken,
+} from "./google-gemini-cli.js";
+// Storage
+export {
+	getOAuthPath,
+	hasOAuthCredentials,
+	listOAuthProviders,
+	loadOAuthCredentials,
+	loadOAuthStorage,
+	type OAuthCredentials,
+	type OAuthProvider,
+	type OAuthStorage,
+	removeOAuthCredentials,
+	saveOAuthCredentials,
+} from "./storage.js";
+
+// ============================================================================
+// High-level API
+// ============================================================================
+
+import { refreshAnthropicToken } from "./anthropic.js";
+import { refreshGitHubCopilotToken } from "./github-copilot.js";
+import { refreshAntigravityToken } from "./google-antigravity.js";
+import { refreshGoogleCloudToken } from "./google-gemini-cli.js";
+import type { OAuthCredentials, OAuthProvider } from "./storage.js";
+import { loadOAuthCredentials, removeOAuthCredentials, saveOAuthCredentials } from "./storage.js";
+
+/**
+ * Refresh token for any OAuth provider.
+ * Saves the new credentials and returns the new access token.
+ */
+export async function refreshToken(provider: OAuthProvider): Promise<string> {
+	const credentials = loadOAuthCredentials(provider);
+	if (!credentials) {
+		throw new Error(`No OAuth credentials found for ${provider}`);
+	}
+
+	let newCredentials: OAuthCredentials;
+
+	switch (provider) {
+		case "anthropic":
+			newCredentials = await refreshAnthropicToken(credentials.refresh);
+			break;
+		case "github-copilot":
+			newCredentials = await refreshGitHubCopilotToken(credentials.refresh, credentials.enterpriseUrl);
+			break;
+		case "google-gemini-cli":
+			if (!credentials.projectId) {
+				throw new Error("Google Cloud credentials missing projectId");
+			}
+			newCredentials = await refreshGoogleCloudToken(credentials.refresh, credentials.projectId);
+			break;
+		case "google-antigravity":
+			if (!credentials.projectId) {
+				throw new Error("Antigravity credentials missing projectId");
+			}
+			newCredentials = await refreshAntigravityToken(credentials.refresh, credentials.projectId);
+			break;
+		default:
+			throw new Error(`Unknown OAuth provider: ${provider}`);
+	}
+
+	saveOAuthCredentials(provider, newCredentials);
+	return newCredentials.access;
+}
+
+/**
+ * Get API key for a provider from OAuth credentials.
+ * Automatically refreshes expired tokens.
+ *
+ * For google-gemini-cli and antigravity, returns JSON-encoded { token, projectId }
+ *
+ * @returns API key string, or null if no credentials
+ */
+export async function getOAuthApiKey(provider: OAuthProvider): Promise<string | null> {
+	const credentials = loadOAuthCredentials(provider);
+	if (!credentials) {
+		return null;
+	}
+
+	// Providers that need projectId in the API key
+	const needsProjectId = provider === "google-gemini-cli" || provider === "google-antigravity";
+
+	// Check if expired
+	if (Date.now() >= credentials.expires) {
+		try {
+			const newToken = await refreshToken(provider);
+
+			// For providers that need projectId, return JSON
+			if (needsProjectId) {
+				const refreshedCreds = loadOAuthCredentials(provider);
+				if (refreshedCreds?.projectId) {
+					return JSON.stringify({ token: newToken, projectId: refreshedCreds.projectId });
+				}
+			}
+
+			return newToken;
+		} catch (error) {
+			console.error(`Failed to refresh OAuth token for ${provider}:`, error);
+			removeOAuthCredentials(provider);
+			return null;
+		}
+	}
+
+	// For providers that need projectId, return JSON
+	if (needsProjectId) {
+		if (!credentials.projectId) {
+			return null;
+		}
+		return JSON.stringify({ token: credentials.access, projectId: credentials.projectId });
+	}
+
+	return credentials.access;
+}
+
+/**
+ * Map model provider to OAuth provider.
+ * Returns undefined if the provider doesn't use OAuth.
+ */
+export function getOAuthProviderForModelProvider(modelProvider: string): OAuthProvider | undefined {
+	const mapping: Record<string, OAuthProvider> = {
+		anthropic: "anthropic",
+		"github-copilot": "github-copilot",
+		"google-gemini-cli": "google-gemini-cli",
+		"google-antigravity": "google-antigravity",
+	};
+	return mapping[modelProvider];
+}
+
+// ============================================================================
+// Login/Logout types for convenience
+// ============================================================================
+
+export type OAuthPrompt = {
+	message: string;
+	placeholder?: string;
+	allowEmpty?: boolean;
+};
+
+export type OAuthAuthInfo = {
+	url: string;
+	instructions?: string;
+};
+
+export interface OAuthProviderInfo {
+	id: OAuthProvider;
+	name: string;
+	available: boolean;
+}
+
+/**
+ * Get list of OAuth providers
+ */
+export function getOAuthProviders(): OAuthProviderInfo[] {
+	return [
+		{
+			id: "anthropic",
+			name: "Anthropic (Claude Pro/Max)",
+			available: true,
+		},
+		{
+			id: "github-copilot",
+			name: "GitHub Copilot",
+			available: true,
+		},
+		{
+			id: "google-gemini-cli",
+			name: "Google Cloud Code Assist (Gemini CLI)",
+			available: true,
+		},
+		{
+			id: "google-antigravity",
+			name: "Antigravity (Gemini 3, Claude, GPT-OSS)",
+			available: true,
+		},
+	];
+}