test(auth): add regression test and packages/ai changelog for loopback ip redirect

packages/ai/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Changed
+
+- Switched Google OAuth callback hostname from `localhost` to `127.0.0.1` to prevent IPv6 loopback fallback delays and proxy routing interception.
+
 ## [16.0.6] - 2026-06-18
 
 ### Added

packages/ai/test/google-oauth-hostname.test.ts

@@ -0,0 +1,22 @@
+import { describe, expect, it } from "bun:test";
+import { GoogleOAuthFlow } from "../src/registry/oauth/google-oauth-shared";
+import type { OAuthController } from "../src/registry/oauth/types";
+
+describe("GoogleOAuthFlow callback hostname", () => {
+	it("uses 127.0.0.1 as the callback hostname to avoid IPv6 and proxy delays", () => {
+		const ctrl: OAuthController = {
+			onAuth: () => {},
+		};
+		const flow = new GoogleOAuthFlow(ctrl, {
+			clientId: "test-client",
+			clientSecret: "test-secret",
+			authUrl: "https://example.com/auth",
+			tokenUrl: "https://example.com/token",
+			scopes: ["scope1"],
+			callbackPort: 51121,
+			callbackPath: "/callback",
+		});
+
+		expect(flow.callbackHostname).toBe("127.0.0.1");
+	});
+});