fix(ai): honor server-provided slow_down interval in device-code polling

GitHub's device flow documents slow_down as a rate limit: a poll that
arrives inside the throttle window is answered with slow_down instead of
the token, and the response's interval field reports the new required
minimum ("adds 5 seconds to the last interval"). A client that only
tracks its own +5s increment can stay behind the server's ratcheting
requirement when its timers fire early - common with WSL/VM clock drift
(microsoft/WSL#10006) - so every subsequent poll keeps hitting the rate
limit and login appears to hang forever even after the browser reports
the device as authorized.

Adopt the server-provided interval when a slow_down poll result carries
one, falling back to the RFC 8628 section 3.5 +5s increment otherwise.
GitHub Copilot passes the interval field through.

This restores part of the #1994 mitigations that were lost in the #4788
device-code refactor.

refs #6187

packages/ai/CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Fixed
 
 - Fixed GitHub Copilot device-code login polling to wait before the first token poll, avoiding incorrect device-code failures for some users after browser authorization ([#6187](https://github.com/earendil-works/pi/issues/6187)).
+- Fixed OAuth device-code polling to honor the server-provided `slow_down` interval instead of only applying the RFC 8628 5-second increment, so GitHub Copilot login recovers instead of appearing to hang when polls arrive early (e.g. WSL/VM clock drift) ([#6187](https://github.com/earendil-works/pi/issues/6187)).
 - Fixed OpenAI Codex user-agent construction to synchronously load Node OS metadata, avoiding a startup race that could report `pi (browser)` in Node/Bun.
 - Fixed Fireworks GLM 5.2 Fast to use the OpenAI-compatible endpoint and `thinkingLevelMap`, aligning it with GLM 5.2 ([#6195](https://github.com/earendil-works/pi/issues/6195)).
 - Fixed Amazon Bedrock prompt-cache points for Claude Fable 5 and Claude Sonnet 5 ([#6235](https://github.com/earendil-works/pi/issues/6235)).

packages/ai/src/utils/oauth/device-code.ts

@@ -10,7 +10,7 @@ const SLOW_DOWN_INTERVAL_INCREMENT_MS = 5000;
 
 type OAuthDeviceCodeIncompletePollResult =
 	| { status: "pending" }
-	| { status: "slow_down" }
+	| { status: "slow_down"; intervalSeconds?: number }
 	| { status: "failed"; message: string };
 
 export type OAuthDeviceCodePollResult<T> = OAuthDeviceCodeIncompletePollResult | { status: "complete"; value: T };
@@ -75,8 +75,15 @@ export async function pollOAuthDeviceCodeFlow<T>(options: OAuthDeviceCodePollOpt
 		}
 		if (result.status === "slow_down") {
 			slowDownResponses += 1;
-			// RFC 8628 section 3.5: apply this increase to this and all subsequent requests.
-			intervalMs = Math.max(MINIMUM_INTERVAL_MS, intervalMs + SLOW_DOWN_INTERVAL_INCREMENT_MS);
+			// Use the server-provided interval when given (GitHub reports the new required minimum
+			// in `interval`); trusting only a client-tracked value risks polling early forever under
+			// WSL/VM clock drift. Otherwise apply RFC 8628 section 3.5: increase by 5 seconds.
+			intervalMs =
+				typeof result.intervalSeconds === "number" &&
+				Number.isFinite(result.intervalSeconds) &&
+				result.intervalSeconds > 0
+					? Math.max(MINIMUM_INTERVAL_MS, Math.floor(result.intervalSeconds * 1000))
+					: Math.max(MINIMUM_INTERVAL_MS, intervalMs + SLOW_DOWN_INTERVAL_INCREMENT_MS);
 		}
 
 		const remainingMs = deadline - Date.now();

packages/ai/src/utils/oauth/github-copilot.ts

@@ -41,6 +41,7 @@ type DeviceTokenSuccessResponse = {
 type DeviceTokenErrorResponse = {
 	error: string;
 	error_description?: string;
+	interval?: number;
 };
 
 export function normalizeDomain(input: string): string | null {
@@ -229,13 +230,13 @@ async function pollForGitHubAccessToken(
 			}
 
 			if (raw && typeof raw === "object" && typeof (raw as DeviceTokenErrorResponse).error === "string") {
-				const { error, error_description: description } = raw as DeviceTokenErrorResponse;
+				const { error, error_description: description, interval } = raw as DeviceTokenErrorResponse;
 				if (error === "authorization_pending") {
 					return { status: "pending" };
 				}
 
 				if (error === "slow_down") {
-					return { status: "slow_down" };
+					return { status: "slow_down", intervalSeconds: typeof interval === "number" ? interval : undefined };
 				}
 
 				const descriptionSuffix = description ? `: ${description}` : "";

packages/ai/test/github-copilot-oauth.test.ts

@@ -247,7 +247,7 @@ describe("GitHub Copilot OAuth device flow", () => {
 		const accessTokenPollTimes: number[] = [];
 		const accessTokenResponses = [
 			jsonResponse({ error: "authorization_pending", error_description: "pending" }),
-			jsonResponse({ error: "slow_down", error_description: "slow down" }),
+			jsonResponse({ error: "slow_down", error_description: "slow down", interval: 7 }),
 			jsonResponse({ access_token: "ghu_refresh_token" }),
 		];
 
@@ -329,7 +329,8 @@ describe("GitHub Copilot OAuth device flow", () => {
 		await vi.advanceTimersByTimeAsync(1);
 		expect(accessTokenPollTimes).toHaveLength(2);
 
-		await vi.advanceTimersByTimeAsync(9999);
+		// slow_down carried a server-provided interval of 7 seconds.
+		await vi.advanceTimersByTimeAsync(6999);
 		expect(accessTokenPollTimes).toHaveLength(2);
 
 		await vi.advanceTimersByTimeAsync(1);
@@ -338,7 +339,7 @@ describe("GitHub Copilot OAuth device flow", () => {
 		expect(accessTokenPollTimes).toEqual([
 			startTime.getTime() + 5000,
 			startTime.getTime() + 10000,
-			startTime.getTime() + 20000,
+			startTime.getTime() + 17000,
 		]);
 	});
 

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

@@ -61,6 +61,67 @@ describe("OAuth device-code polling", () => {
 		expect(pollTimes).toEqual([new Date("2026-03-09T00:00:02Z").getTime()]);
 	});
 
+	it("increases the interval by 5 seconds after slow_down without a server interval", async () => {
+		vi.useFakeTimers();
+		vi.setSystemTime(new Date("2026-03-09T00:00:00Z"));
+		const startTime = Date.now();
+
+		const pollTimes: number[] = [];
+		const results = [{ status: "slow_down" as const }, { status: "complete" as const, value: "token" }];
+		const resultPromise = pollOAuthDeviceCodeFlow({
+			intervalSeconds: 2,
+			expiresInSeconds: 900,
+			poll: async () => {
+				pollTimes.push(Date.now());
+				const result = results.shift();
+				if (!result) throw new Error("Unexpected extra poll");
+				return result;
+			},
+		});
+
+		await vi.advanceTimersByTimeAsync(0);
+		expect(pollTimes).toEqual([startTime]);
+
+		await vi.advanceTimersByTimeAsync(6999);
+		expect(pollTimes).toEqual([startTime]);
+
+		await vi.advanceTimersByTimeAsync(1);
+		await expect(resultPromise).resolves.toBe("token");
+		expect(pollTimes).toEqual([startTime, startTime + 7000]);
+	});
+
+	it("honors a server-provided slow_down interval", async () => {
+		vi.useFakeTimers();
+		vi.setSystemTime(new Date("2026-03-09T00:00:00Z"));
+		const startTime = Date.now();
+
+		const pollTimes: number[] = [];
+		const results = [
+			{ status: "slow_down" as const, intervalSeconds: 30 },
+			{ status: "complete" as const, value: "token" },
+		];
+		const resultPromise = pollOAuthDeviceCodeFlow({
+			intervalSeconds: 2,
+			expiresInSeconds: 900,
+			poll: async () => {
+				pollTimes.push(Date.now());
+				const result = results.shift();
+				if (!result) throw new Error("Unexpected extra poll");
+				return result;
+			},
+		});
+
+		await vi.advanceTimersByTimeAsync(0);
+		expect(pollTimes).toEqual([startTime]);
+
+		await vi.advanceTimersByTimeAsync(29999);
+		expect(pollTimes).toEqual([startTime]);
+
+		await vi.advanceTimersByTimeAsync(1);
+		await expect(resultPromise).resolves.toBe("token");
+		expect(pollTimes).toEqual([startTime, startTime + 30000]);
+	});
+
 	it("cancels an in-flight wait", async () => {
 		vi.useFakeTimers();
 		const controller = new AbortController();