fix(web): prevent duplicate searches and background fetching on navigation

- Search page no longer triggers cascading search when validating subjects
- Scraper page stops all refresh timers and API calls when navigating away
- Wrap initial data references in untrack() to silence Svelte warnings

web/src/routes/(app)/admin/scraper/+page.svelte

@@ -71,12 +71,14 @@ function scheduleTick() {
 const MIN_INTERVAL = 5_000;
 const MAX_INTERVAL = 60_000;
 let refreshTimer: ReturnType<typeof setTimeout> | undefined;
+let destroyed = false;
 
 const MIN_SPIN_MS = 700;
 let spinnerVisible = $state(false);
 let spinHoldTimer: ReturnType<typeof setTimeout> | undefined;
 
 async function fetchAll() {
+  if (destroyed) return;
   refreshError = false;
   spinnerVisible = true;
   clearTimeout(spinHoldTimer);
@@ -88,16 +90,19 @@ async function fetchAll() {
       client.getScraperTimeseries(selectedPeriod),
       client.getScraperSubjects(),
     ]);
+    if (destroyed) return;
     stats = statsRes;
     timeseries = timeseriesRes;
     subjects = subjectsRes.subjects;
     error = null;
     refreshInterval = MIN_INTERVAL;
   } catch (e) {
+    if (destroyed) return;
     error = e instanceof Error ? e.message : "Failed to load scraper data";
     refreshError = true;
     refreshInterval = Math.min(refreshInterval * 2, MAX_INTERVAL);
   } finally {
+    if (destroyed) return;
     const elapsed = performance.now() - startedAt;
     const remaining = MIN_SPIN_MS - elapsed;
     if (remaining > 0) {
@@ -112,6 +117,7 @@ async function fetchAll() {
 }
 
 function scheduleRefresh() {
+  if (destroyed) return;
   clearTimeout(refreshTimer);
   refreshTimer = setTimeout(fetchAll, refreshInterval);
 }
@@ -302,20 +308,27 @@ const detailGridCols = "grid-cols-[7fr_5fr_3fr_4fr_4fr_3fr_4fr_minmax(6rem,1fr)]
 // --- Lifecycle ---
 
 onMount(() => {
+  destroyed = false;
+  mounted = true;
   fetchAll();
   scheduleTick();
 });
 
 onDestroy(() => {
+  destroyed = true;
+  mounted = false;
   clearTimeout(tickTimer);
   clearTimeout(refreshTimer);
   clearTimeout(spinHoldTimer);
 });
 
-// Refetch when period changes
+// Refetch when period changes (skip initial run since onMount handles it)
+let mounted = false;
 $effect(() => {
   void selectedPeriod;
-  fetchAll();
+  if (mounted && !destroyed) {
+    fetchAll();
+  }
 });
 </script>
 

web/src/routes/+page.svelte

@@ -21,12 +21,12 @@ let { data } = $props();
 const initialParams = untrack(() => new URLSearchParams(data.url.search));
 
 // The default term is the first one returned by the backend (most current)
-const defaultTermSlug = data.terms[0]?.slug ?? "";
+const defaultTermSlug = untrack(() => data.terms[0]?.slug ?? "");
 
 // Default to the first term when no URL param is present
 const urlTerm = initialParams.get("term");
 let selectedTerm = $state(
-  urlTerm && data.terms.some((t) => t.slug === urlTerm) ? urlTerm : defaultTermSlug
+  untrack(() => (urlTerm && data.terms.some((t) => t.slug === urlTerm) ? urlTerm : defaultTermSlug))
 );
 let selectedSubjects: string[] = $state(untrack(() => initialParams.getAll("subject")));
 let query = $state(initialParams.get("q") ?? "");
@@ -67,6 +67,9 @@ let searchMeta: SearchMeta | null = $state(null);
 let loading = $state(false);
 let error = $state<string | null>(null);
 
+// Track if we're validating subjects to prevent cascading search
+let validatingSubjects = false;
+
 // Fetch subjects when term changes
 $effect(() => {
   const term = selectedTerm;
@@ -76,7 +79,12 @@ $effect(() => {
     .then((s) => {
       subjects = s;
       const validCodes = new Set(s.map((sub) => sub.code));
-      selectedSubjects = selectedSubjects.filter((code) => validCodes.has(code));
+      const filtered = selectedSubjects.filter((code) => validCodes.has(code));
+      if (filtered.length !== selectedSubjects.length) {
+        validatingSubjects = true;
+        selectedSubjects = filtered;
+        validatingSubjects = false;
+      }
     })
     .catch((e) => {
       console.error("Failed to fetch subjects:", e);
@@ -111,7 +119,9 @@ $effect(() => {
 
 $effect(() => {
   selectedSubjects;
-  scheduleSearch("subjects");
+  if (!validatingSubjects) {
+    scheduleSearch("subjects");
+  }
   return () => clearTimeout(searchTimeout);
 });
 
@@ -160,6 +170,7 @@ async function performSearch(
   if (!term) return;
   loading = true;
   error = null;
+  searchMeta = null;
 
   const sortBy = sort.length > 0 ? SORT_COLUMN_MAP[sort[0].id] : undefined;
   const sortDir: SortDirection | undefined =