Revert "Remove Anthropic OAuth support"

This reverts commit f5e6bcac1b.

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

@@ -9,6 +9,8 @@
  * - Antigravity (Gemini 3, Claude, GPT-OSS via Google Cloud)
  */
 
+// Anthropic
+export { loginAnthropic, refreshAnthropicToken } from "./anthropic.js";
 // GitHub Copilot
 export {
 	getGitHubCopilotBaseUrl,
@@ -38,6 +40,7 @@ export * from "./types.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";
@@ -59,6 +62,9 @@ export async function refreshOAuthToken(
 	let newCredentials: OAuthCredentials;
 
 	switch (provider) {
+		case "anthropic":
+			newCredentials = await refreshAnthropicToken(credentials.refresh);
+			break;
 		case "github-copilot":
 			newCredentials = await refreshGitHubCopilotToken(credentials.refresh, credentials.enterpriseUrl);
 			break;
@@ -122,6 +128,11 @@ export async function getOAuthApiKey(
  */
 export function getOAuthProviders(): OAuthProviderInfo[] {
 	return [
+		{
+			id: "anthropic",
+			name: "Anthropic (Claude Pro/Max)",
+			available: true,
+		},
 		{
 			id: "openai-codex",
 			name: "ChatGPT Plus/Pro (Codex Subscription)",