fix: useSmartPolling's backoff only updates currentIntervalRef — the running setInterval never slows down, yet isBackingOff flips isLive to false

src/hooks/useSmartPolling.test.tsx

@@ -78,6 +78,50 @@ describe("useSmartPolling", () => {
     expect(result.current.isBackingOff).toBe(true);
   });
 
+  it("actually slows the timer on backoff (capped at maxBackoff) and resets on refetch", async () => {
+    const fetchFn = jest.fn(async () => ({ n: 1 }));
+    const { result } = renderHook(() =>
+      useSmartPolling({
+        fetchFn,
+        interval: 1000,
+        unchangedThreshold: 2,
+        backoffMultiplier: 2,
+        maxBackoff: 4000,
+      }),
+    );
+    const advance = async (ms: number) => {
+      await act(async () => {
+        await jest.advanceTimersByTimeAsync(ms);
+      });
+    };
+
+    await advance(0);
+    expect(fetchFn).toHaveBeenCalledTimes(1);
+    await advance(1000); // call 2 (unchanged 1)
+    await advance(1000); // call 3 (unchanged 2) → interval 2000
+    expect(fetchFn).toHaveBeenCalledTimes(3);
+    expect(result.current.isBackingOff).toBe(true);
+
+    await advance(1000);
+    expect(fetchFn).toHaveBeenCalledTimes(3); // no call at the old 1s cadence
+    await advance(1000); // call 4 → interval 4000 (max)
+    expect(fetchFn).toHaveBeenCalledTimes(4);
+
+    await advance(3000);
+    expect(fetchFn).toHaveBeenCalledTimes(4);
+    await advance(1000); // call 5, still capped at 4000
+    expect(fetchFn).toHaveBeenCalledTimes(5);
+
+    // refetch resets to the base interval
+    await act(async () => {
+      await result.current.refetch();
+    });
+    expect(fetchFn).toHaveBeenCalledTimes(6);
+    expect(result.current.isBackingOff).toBe(false);
+    await advance(1000);
+    expect(fetchFn).toHaveBeenCalledTimes(7);
+  });
+
   it("does not poll when enabled is false", async () => {
     const ref = { count: 0 };
     const fetchFn = createFetchFn([{ n: 1 }], ref);

src/hooks/useSmartPolling.ts

@@ -73,6 +73,19 @@ export function useSmartPolling<T>({
   const previousDataRef = useRef<T | null>(null);
   const isBackgroundedRef = useRef(false);
 
+  const fetchDataRef = useRef<() => Promise<void>>(async () => {});
+
+  // Restart the running timer so a changed currentIntervalRef takes effect.
+  // No-op when polling isn't active (no timer running).
+  const rescheduleInterval = useCallback(() => {
+    if (!intervalRef.current) return;
+    clearInterval(intervalRef.current);
+    intervalRef.current = setInterval(
+      () => fetchDataRef.current(),
+      currentIntervalRef.current
+    );
+  }, []);
+
   const fetchData = useCallback(async () => {
     if (!isMountedRef.current) return;
 
@@ -90,7 +103,10 @@ export function useSmartPolling<T>({
         setData(result);
         previousDataRef.current = result;
         unchangedCountRef.current = 0;
-        currentIntervalRef.current = interval;
+        if (currentIntervalRef.current !== interval) {
+          currentIntervalRef.current = interval;
+          rescheduleInterval();
+        }
         dispatch({ type: 'STOP_BACKOFF' });
         onDataChange?.(result);
       } else {
@@ -103,6 +119,7 @@ export function useSmartPolling<T>({
           );
           if (newInterval > currentIntervalRef.current) {
             currentIntervalRef.current = newInterval;
+            rescheduleInterval();
             dispatch({ type: 'START_BACKOFF' });
           }
         }
@@ -118,14 +135,19 @@ export function useSmartPolling<T>({
         setIsLoading(false);
       }
     }
-  }, [fetchFn, compareFn, interval, backoffMultiplier, maxBackoff, unchangedThreshold, onDataChange]);
+  }, [fetchFn, compareFn, interval, backoffMultiplier, maxBackoff, unchangedThreshold, onDataChange, rescheduleInterval]);
+
+  fetchDataRef.current = fetchData;
 
   const refetch = useCallback(async () => {
-    currentIntervalRef.current = interval;
+    if (currentIntervalRef.current !== interval) {
+      currentIntervalRef.current = interval;
+      rescheduleInterval();
+    }
     dispatch({ type: 'STOP_BACKOFF' });
     unchangedCountRef.current = 0;
     await fetchData();
-  }, [fetchData, interval]);
+  }, [fetchData, interval, rescheduleInterval]);
 
   // Handle visibility change
   useEffect(() => {