perf(ui): a next-page fetch joins the one in flight instead of sending the cursor again

react-query's fetchNextPage cancels a next page still loading and sends it again by default.
Our requests ignore the abort signal, so the server ran both: the feed's read-ahead effect
re-runs on scroll frames before isFetchingNextPage reaches it, and on prod every feed page
went out 2-3 times (a 0.8 s title sort queued to 2.3 s). Every call now passes NEXT_PAGE
({cancelRefetch: false}), lint-enforced, with a contract test.

frontend/src/components/AdminLogs.tsx

@@ -13,6 +13,7 @@ import { api, type LogFacet, type LogQuery, type ServerLogRow } from "../lib/api
 import { copyText } from "../lib/clipboard";
 import { formatDateTimeSec } from "../lib/format";
 import { nextNavId, notifyNav, rememberNavPosition } from "../lib/history";
+import { NEXT_PAGE } from "../lib/nextPage";
 import { LEVEL_GROUPS, type LevelGroup } from "../lib/log";
 import {
   DEFAULT_LOGS_STATE,
@@ -156,7 +157,7 @@ export default function AdminLogs() {
           ? "countsFailed"
           : null;
   const retryFailed = () => {
-    if (logs.isFetchNextPageError) void logs.fetchNextPage();
+    if (logs.isFetchNextPageError) void logs.fetchNextPage(NEXT_PAGE);
     else if (logs.isError) void logs.refetch();
     if (facets.isError) void facets.refetch();
   };
@@ -190,7 +191,7 @@ export default function AdminLogs() {
 
   const loadOlder = () => {
     setLive(false);
-    void logs.fetchNextPage();
+    void logs.fetchNextPage(NEXT_PAGE);
   };
 
   const copy = async () => {

frontend/src/components/Feed.tsx

@@ -7,6 +7,7 @@ import {
   useQueryClient,
 } from "@tanstack/react-query";
 import { qk } from "../lib/queryKeys";
+import { NEXT_PAGE } from "../lib/nextPage";
 import {
   ArrowLeft,
   Columns2,
@@ -556,7 +557,7 @@ export default function Feed({
               <div className="text-center pt-4">
                 <Button
                   variant="outline"
-                  onClick={() => ytQuery.fetchNextPage()}
+                  onClick={() => void ytQuery.fetchNextPage(NEXT_PAGE)}
                   loading={ytQuery.isFetchingNextPage}
                 >
                   {ytQuery.isFetchingNextPage

frontend/src/components/PlexBrowse.tsx

@@ -9,6 +9,7 @@ import {
 } from "@tanstack/react-query";
 import { User, X } from "lucide-react";
 import { qk } from "../lib/queryKeys";
+import { NEXT_PAGE } from "../lib/nextPage";
 import { healPlexField } from "../lib/plexSearch";
 import { healPlexSort, plexSortOptions, PLEX_SORT_FALLBACK } from "../lib/plexSort";
 import type { SortState } from "../lib/columnSort";
@@ -321,7 +322,8 @@ export default function PlexBrowse() {
     if (!sentinelEl) return;
     const io = new IntersectionObserver(
       (entries) => {
-        if (entries[0]?.isIntersecting && hasNextPage && !isFetchingNextPage) fetchNextPage();
+        if (entries[0]?.isIntersecting && hasNextPage && !isFetchingNextPage)
+          void fetchNextPage(NEXT_PAGE);
       },
       { rootMargin: "600px" },
     );

frontend/src/components/VirtualFeed.tsx

@@ -1,5 +1,6 @@
 import type { Video, VideoStatus } from "../lib/api";
 import { FEED_VIEW_SPEC, type FeedView } from "../lib/feedView";
+import type { NEXT_PAGE } from "../lib/nextPage";
 import VideoCard from "./VideoCard";
 import { VideoMenu } from "./VideoMenu";
 import { useContextMenu } from "./ui/useContextMenu";
@@ -29,7 +30,7 @@ export interface VirtualFeedProps {
   onOpen: (v: Video, startAt?: number | null) => void;
   hasNextPage: boolean;
   isFetchingNextPage: boolean;
-  fetchNextPage: () => void;
+  fetchNextPage: (options: typeof NEXT_PAGE) => unknown;
 }
 
 // The feed's videos on the shared VirtualGrid engine — this wrapper only maps a FeedView to the

frontend/src/components/ui/VirtualGrid.tsx

@@ -10,6 +10,7 @@ import {
 import { useVirtualizer } from "@tanstack/react-virtual";
 import { useListNav } from "../../lib/listNav";
 import { scrollParent } from "../../lib/listPaging";
+import { NEXT_PAGE } from "../../lib/nextPage";
 import { GRID_GAP, columnsFor, itemWidthFor } from "./gridColumns";
 import { shouldPrefetchNext } from "./readAhead";
 
@@ -66,7 +67,8 @@ export interface VirtualGridProps<T> {
   /** Infinite scroll — omit all three for a finite client-side list. */
   hasNextPage?: boolean;
   isFetchingNextPage?: boolean;
-  fetchNextPage?: () => void;
+  /** Called with `NEXT_PAGE`, so a read-ahead that fires again joins the page already loading. */
+  fetchNextPage?: (options: typeof NEXT_PAGE) => unknown;
 }
 
 export default function VirtualGrid<T>({
@@ -167,7 +169,7 @@ export default function VirtualGrid<T>({
     const last = virtualRows[virtualRows.length - 1];
     if (!last) return;
     if (shouldPrefetchNext(last.index, rows.length, virtualRows.length)) {
-      fetchNextPage();
+      fetchNextPage(NEXT_PAGE);
     }
   }, [virtualRows, rows.length, hasNextPage, isFetchingNextPage, fetchNextPage]);