fix(imports): poll device codes one request at a time

The Trakt/Simkl sign-in dialog polled with setInterval and no in-flight
guard, so while the first "authorized" poll was still fetching the
library, the next tick re-sent the redeemed device code. Trakt answers
409, which was mapped to "expired", producing a false "Device code
expired" error.

- public-api: map Trakt 409 (already redeemed) to pending
- web: add a single-flight device-code poller that drops late responses
  after stop() and aborts the in-flight request
- web: use it in the imports dialog and ignore device-code responses
  that arrive after the dialog was closed

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/public-api/src/importers/trakt.test.ts

@@ -214,3 +214,15 @@ describe("fitToBudget", () => {
     expect(result.warnings).toEqual([]);
   });
 });
+
+describe("trakt.pollForToken", () => {
+  test("treats 409 (code already redeemed) as pending", async () => {
+    stubTrakt((path) => (path === "/oauth/device/token" ? { status: 409 } : undefined));
+    expect(await trakt.pollForToken("id", "secret", "code")).toEqual({ status: "pending" });
+  });
+
+  test("treats 410 as expired", async () => {
+    stubTrakt((path) => (path === "/oauth/device/token" ? { status: 410 } : undefined));
+    expect(await trakt.pollForToken("id", "secret", "code")).toEqual({ status: "expired" });
+  });
+});

apps/public-api/src/importers/trakt.ts

@@ -254,6 +254,9 @@ export const trakt: ImportProvider = {
     if (res.status === 410) return { status: "expired" };
     if (res.status === 418) return { status: "denied" };
     if (res.status === 429) return { status: "pending" };
+    // 409: this code was already redeemed (an earlier poll got the token and is still fetching
+    // the library). Keep the client waiting for that response instead of reporting expiry.
+    if (res.status === 409) return { status: "pending" };
     // 5xx: likely transient — keep polling
     if (res.status >= 500) return { status: "pending" };
     // Unknown 4xx: likely permanent — treat as expired

apps/web/src/components/settings/imports-section.tsx

@@ -21,6 +21,7 @@ import {
 import { Label } from "@/components/ui/label";
 import { Progress } from "@/components/ui/progress";
 import { Spinner } from "@/components/ui/spinner";
+import { startDevicePoll } from "@/lib/device-code-poll";
 import { getErrorMessage } from "@/lib/error-messages";
 import { client, orpc } from "@/lib/orpc/client";
 import { invalidateTrackingQueries } from "@/lib/orpc/invalidate";
@@ -210,7 +211,8 @@ function ImportSourceCard({ config }: { config: SourceConfig }) {
   // OAuth state
   const [deviceCode, setDeviceCode] = useState<DeviceCodeInfo | null>(null);
   const [oauthError, setOauthError] = useState<string | null>(null);
-  const pollTimerRef = useRef<ReturnType<typeof setInterval> | null>(null);
+  const pollRef = useRef<{ stop: () => void } | null>(null);
+  const flowIdRef = useRef(0);
   const importAbortRef = useRef<AbortController | null>(null);
 
   const parseMutation = useMutation(
@@ -344,14 +346,13 @@ function ImportSourceCard({ config }: { config: SourceConfig }) {
 
   // Clean up poll timer on unmount or dialog close
   const stopPolling = useCallback(() => {
-    if (pollTimerRef.current) {
-      clearInterval(pollTimerRef.current);
-      pollTimerRef.current = null;
-    }
+    pollRef.current?.stop();
+    pollRef.current = null;
   }, []);
 
   function handleClose() {
     stopPolling();
+    flowIdRef.current += 1;
     importAbortRef.current?.abort();
     importAbortRef.current = null;
     setDialogOpen(false);
@@ -370,6 +371,7 @@ function ImportSourceCard({ config }: { config: SourceConfig }) {
   // ─── OAuth: Start device code flow ────────────────────────
 
   async function startDeviceCodeFlow() {
+    const flowId = ++flowIdRef.current;
     setOauthError(null);
     setStep("device-code");
     const sourceLabel = config.label;
@@ -382,12 +384,14 @@ function ImportSourceCard({ config }: { config: SourceConfig }) {
         throw new Error("device-code request failed");
       }
       const data = (await res.json()) as DeviceCodeInfo;
+      if (flowIdRef.current !== flowId) return;
       setDeviceCode(data);
       setDialogOpen(true);
 
       // Start polling
       startPolling(data);
     } catch {
+      if (flowIdRef.current !== flowId) return;
       setOauthError(t`Failed to start ${sourceLabel} connection`);
       setStep("choose");
       setDialogOpen(true);
@@ -396,58 +400,61 @@ function ImportSourceCard({ config }: { config: SourceConfig }) {
 
   function startPolling(code: DeviceCodeInfo) {
     stopPolling();
-    const interval = (code.interval || 5) * 1000;
-    const expiresAt = Date.now() + code.expires_in * 1000;
 
-    pollTimerRef.current = setInterval(async () => {
-      if (Date.now() > expiresAt) {
-        stopPolling();
-        setOauthError(t`Device code expired. Please try again.`);
-        setStep("choose");
-        return;
-      }
-
-      try {
+    pollRef.current = startDevicePoll({
+      intervalMs: (code.interval || 5) * 1000,
+      expiresAt: Date.now() + code.expires_in * 1000,
+      poll: async (signal) => {
         const res = await fetch(`${publicApiUrl}/v1/import/${config.source}/poll`, {
           method: "POST",
           headers: { "Content-Type": "application/json" },
           body: JSON.stringify({ device_code: code.device_code }),
+          signal,
         });
-        if (!res.ok) return;
+        if (!res.ok) return null;
 
-        const data = (await res.json()) as {
+        return (await res.json()) as {
           status: string;
           data?: Record<string, unknown>;
           error?: string;
         };
+      },
+      onResponse: (data) => {
+        if (!data) return false;
 
         if (data.status === "authorized" && data.data) {
-          stopPolling();
           setStep("fetching");
           parsePayloadMutation.mutate({
             source: config.source as "trakt" | "simkl",
             rawPayload: data.data,
           });
-        } else if (data.status === "denied") {
-          stopPolling();
+          return true;
+        }
+        if (data.status === "denied") {
           setOauthError(t`Authorization was denied. Please try again.`);
           setStep("choose");
-        } else if (data.status === "expired") {
-          stopPolling();
+          return true;
+        }
+        if (data.status === "expired") {
           setOauthError(t`Device code expired. Please try again.`);
           setStep("choose");
-        } else if (data.status === "fetch_error") {
-          stopPolling();
+          return true;
+        }
+        if (data.status === "fetch_error") {
           setOauthError(
             t`Authorization succeeded but failed to fetch your library. Please try again.`,
           );
           setStep("choose");
+          return true;
         }
         // "pending" → keep polling
-      } catch {
-        // Network error, keep polling
-      }
-    }, interval);
+        return false;
+      },
+      onExpired: () => {
+        setOauthError(t`Device code expired. Please try again.`);
+        setStep("choose");
+      },
+    });
   }
 
   // Clean up on unmount

apps/web/src/lib/device-code-poll.test.ts

@@ -0,0 +1,126 @@
+import { afterEach, beforeEach, describe, expect, test, vi } from "vitest";
+
+import { startDevicePoll } from "./device-code-poll";
+
+const INTERVAL = 1000;
+
+function deferred<T>() {
+  let resolve!: (value: T) => void;
+  const promise = new Promise<T>((r) => {
+    resolve = r;
+  });
+  return { promise, resolve };
+}
+
+describe("startDevicePoll", () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  test("only has one request in flight at a time", async () => {
+    const pending = deferred<string>();
+    const poll = vi.fn<(signal: AbortSignal) => Promise<string>>(() => pending.promise);
+    const poller = startDevicePoll({
+      poll,
+      onResponse: () => false,
+      onExpired: vi.fn<() => void>(),
+      intervalMs: INTERVAL,
+      expiresAt: Date.now() + 60 * INTERVAL,
+    });
+
+    await vi.advanceTimersByTimeAsync(INTERVAL * 3);
+    expect(poll).toHaveBeenCalledTimes(1);
+    poller.stop();
+  });
+
+  test("polls again after a response that is not final", async () => {
+    const first = deferred<string>();
+    const poll = vi.fn<(signal: AbortSignal) => Promise<string>>();
+    poll.mockReturnValueOnce(first.promise);
+    poll.mockResolvedValue("pending");
+    const onResponse = vi.fn<(response: string) => boolean>(() => false);
+    const poller = startDevicePoll({
+      poll,
+      onResponse,
+      onExpired: vi.fn<() => void>(),
+      intervalMs: INTERVAL,
+      expiresAt: Date.now() + 60 * INTERVAL,
+    });
+
+    await vi.advanceTimersByTimeAsync(INTERVAL);
+    expect(poll).toHaveBeenCalledTimes(1);
+
+    first.resolve("pending");
+    await vi.advanceTimersByTimeAsync(INTERVAL);
+    expect(onResponse).toHaveBeenCalledTimes(2);
+    expect(poll).toHaveBeenCalledTimes(2);
+    poller.stop();
+  });
+
+  test("drops late responses after stop()", async () => {
+    const pending = deferred<string>();
+    let received: AbortSignal | undefined;
+    const poll = vi.fn<(signal: AbortSignal) => Promise<string>>((signal) => {
+      received = signal;
+      return pending.promise;
+    });
+    const onResponse = vi.fn<(response: string) => boolean>(() => false);
+    const poller = startDevicePoll({
+      poll,
+      onResponse,
+      onExpired: vi.fn<() => void>(),
+      intervalMs: INTERVAL,
+      expiresAt: Date.now() + 60 * INTERVAL,
+    });
+
+    await vi.advanceTimersByTimeAsync(INTERVAL);
+    expect(poll).toHaveBeenCalledTimes(1);
+
+    poller.stop();
+    pending.resolve("late");
+    await vi.advanceTimersByTimeAsync(INTERVAL * 3);
+
+    expect(onResponse).not.toHaveBeenCalled();
+    expect(received?.aborted).toBe(true);
+    expect(poll).toHaveBeenCalledTimes(1);
+  });
+
+  test("calls onExpired once when the code expires before the first poll", async () => {
+    const poll = vi.fn<(signal: AbortSignal) => Promise<string>>(async () => "pending");
+    const onExpired = vi.fn<() => void>();
+    startDevicePoll({
+      poll,
+      onResponse: () => false,
+      onExpired,
+      intervalMs: INTERVAL,
+      expiresAt: Date.now() + INTERVAL / 2,
+    });
+
+    await vi.advanceTimersByTimeAsync(INTERVAL * 3);
+    expect(onExpired).toHaveBeenCalledTimes(1);
+    expect(poll).not.toHaveBeenCalled();
+  });
+
+  test("keeps polling after a request error", async () => {
+    const poll = vi.fn<(signal: AbortSignal) => Promise<string>>();
+    poll.mockRejectedValueOnce(new Error("network"));
+    poll.mockResolvedValue("ok");
+    const onResponse = vi.fn<(response: string) => boolean>(() => true);
+    startDevicePoll({
+      poll,
+      onResponse,
+      onExpired: vi.fn<() => void>(),
+      intervalMs: INTERVAL,
+      expiresAt: Date.now() + 60 * INTERVAL,
+    });
+
+    await vi.advanceTimersByTimeAsync(INTERVAL * 2);
+    expect(poll).toHaveBeenCalledTimes(2);
+    expect(onResponse).toHaveBeenCalledTimes(1);
+    expect(onResponse).toHaveBeenCalledWith("ok");
+  });
+});

apps/web/src/lib/device-code-poll.ts

@@ -0,0 +1,49 @@
+export interface DevicePollOptions<T> {
+  /** One poll request. Receives an AbortSignal that fires when the poller stops. */
+  poll: (signal: AbortSignal) => Promise<T>;
+  /** Called with each response; return true to stop polling. Never called after stop(). */
+  onResponse: (response: T) => boolean;
+  /** Called once when expiresAt passes without onResponse returning true. */
+  onExpired: () => void;
+  intervalMs: number;
+  expiresAt: number;
+}
+
+/**
+ * Polls one request at a time: the next request is scheduled only after the previous one
+ * settles, and nothing is delivered after stop(). Request errors are ignored (keep polling).
+ */
+export function startDevicePoll<T>(options: DevicePollOptions<T>): { stop: () => void } {
+  const controller = new AbortController();
+  let timer: ReturnType<typeof setTimeout> | null = null;
+  let stopped = false;
+
+  const stop = () => {
+    stopped = true;
+    if (timer) clearTimeout(timer);
+    controller.abort();
+  };
+
+  const tick = async () => {
+    if (stopped) return;
+    if (Date.now() > options.expiresAt) {
+      stop();
+      options.onExpired();
+      return;
+    }
+    try {
+      const response = await options.poll(controller.signal);
+      if (stopped) return;
+      if (options.onResponse(response)) {
+        stop();
+        return;
+      }
+    } catch {
+      if (stopped) return;
+    }
+    timer = setTimeout(tick, options.intervalMs);
+  };
+
+  timer = setTimeout(tick, options.intervalMs);
+  return { stop };
+}