feat(ai): refactor device code login for copilot

packages/ai/test/oauth-device-code.test.ts

@@ -0,0 +1,55 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { pollOAuthDeviceCodeFlow } from "../src/utils/oauth/device-code.ts";
+
+describe("OAuth device-code polling", () => {
+	afterEach(() => {
+		vi.useRealTimers();
+	});
+
+	it("waits before the first poll and returns the completed value", async () => {
+		vi.useFakeTimers();
+		vi.setSystemTime(new Date("2026-03-09T00:00:00Z"));
+
+		const pollTimes: number[] = [];
+		const poll = vi.fn(async () => {
+			pollTimes.push(Date.now());
+			return pollTimes.length === 1
+				? { status: "pending" as const }
+				: { status: "complete" as const, accessToken: "token" };
+		});
+
+		const resultPromise = pollOAuthDeviceCodeFlow({
+			intervalSeconds: 2,
+			expiresInSeconds: 30,
+			poll,
+		});
+
+		await vi.advanceTimersByTimeAsync(1999);
+		expect(pollTimes).toEqual([]);
+
+		await vi.advanceTimersByTimeAsync(1);
+		expect(pollTimes).toEqual([new Date("2026-03-09T00:00:02Z").getTime()]);
+
+		await vi.advanceTimersByTimeAsync(2000);
+		await expect(resultPromise).resolves.toBe("token");
+		expect(pollTimes).toEqual([
+			new Date("2026-03-09T00:00:02Z").getTime(),
+			new Date("2026-03-09T00:00:04Z").getTime(),
+		]);
+	});
+
+	it("cancels an in-flight wait", async () => {
+		vi.useFakeTimers();
+		const controller = new AbortController();
+
+		const resultPromise = pollOAuthDeviceCodeFlow({
+			intervalSeconds: 5,
+			expiresInSeconds: 30,
+			poll: async () => ({ status: "pending" }),
+			signal: controller.signal,
+		});
+
+		controller.abort();
+		await expect(resultPromise).rejects.toThrow("Login cancelled");
+	});
+});