Add AbortSignal support to dashboard/blocklist APIs and hooks

frontend/src/hooks/useBlocklistStatus.ts

@@ -2,7 +2,7 @@
  * React hook for polling blocklist schedule error state.
  */
 
-import { useEffect, useState } from "react";
+import { useEffect, useRef, useState } from "react";
 import { fetchSchedule } from "../api/blocklist";
 
 const BLOCKLIST_POLL_INTERVAL_MS = 60_000;
@@ -17,16 +17,20 @@ export interface UseBlocklistStatusReturn {
  */
 export function useBlocklistStatus(): UseBlocklistStatusReturn {
   const [hasErrors, setHasErrors] = useState(false);
+  const abortRef = useRef<AbortController | null>(null);
 
   useEffect(() => {
-    let cancelled = false;
-
     const poll = (): void => {
-      fetchSchedule()
+      abortRef.current?.abort();
+      const controller = new AbortController();
+      abortRef.current = controller;
+
+      fetchSchedule(controller.signal)
         .then((info) => {
-          if (!cancelled) {
-            setHasErrors(info.last_run_errors === true);
+          if (controller.signal.aborted) {
+            return;
           }
+          setHasErrors(info.last_run_errors === true);
         })
         .catch(() => {
           // Silently swallow network errors — do not change indicator state.
@@ -36,7 +40,7 @@ export function useBlocklistStatus(): UseBlocklistStatusReturn {
     poll();
     const id = window.setInterval(poll, BLOCKLIST_POLL_INTERVAL_MS);
     return (): void => {
-      cancelled = true;
+      abortRef.current?.abort();
       window.clearInterval(id);
     };
   }, []);