fix(genre-tree): fail clearly when a full-list page returns no body

CHANGELOG.md

@@ -11,6 +11,10 @@ easy to spot when bumping.
 
 ## [Unreleased]
 
+### Fixed
+
+- **genre-tree**: `useListFullGenrePlaylists` rejects with a clear `page N returned no body` error when a page comes back empty (e.g. a `handleError` callback swallowed the failure) instead of crashing with a `TypeError`.
+
 ## [8.4.1] - 2026-10-02
 
 ### Changed

packages/app-kit/src/genre-tree/useGenrePlaylist.test.ts

@@ -185,6 +185,52 @@ describe("useGenrePlaylist", () => {
       expect(result.overallTotal).toBe(250);
     });
 
+    it("returns empty results with a single request when totalPages is 0", async () => {
+      fetchMock.mockResolvedValueOnce({
+        overallTotal: 0,
+        next: null,
+        previous: null,
+        results: [],
+        page: 1,
+        pageSize: 100,
+        totalPages: 0,
+      });
+      renderHook(() => useListFullGenrePlaylists("reference", getBackendBaseUrl));
+      const { queryFn } = useQueryWithParseMock.mock.calls[0][0];
+
+      const result = await queryFn();
+
+      expect(fetchMock).toHaveBeenCalledTimes(1);
+      expect(result.results).toEqual([]);
+    });
+
+    it("rejects with the page number when a later page returns no body", async () => {
+      fetchMock
+        .mockResolvedValueOnce({
+          overallTotal: 150,
+          next: "https://backend.example.com/genre-playlists/?page=2",
+          previous: null,
+          results: Array.from({ length: 100 }, (_, i) => ({ uuid: `gp${i}` })),
+          page: 1,
+          pageSize: 100,
+          totalPages: 2,
+        })
+        .mockResolvedValueOnce(null);
+      renderHook(() => useListFullGenrePlaylists("reference", getBackendBaseUrl));
+      const { queryFn } = useQueryWithParseMock.mock.calls[0][0];
+
+      await expect(queryFn()).rejects.toThrow("page 2 returned no body");
+    });
+
+    it("rejects when the first page returns no body", async () => {
+      fetchMock.mockResolvedValueOnce(null);
+      renderHook(() => useListFullGenrePlaylists("reference", getBackendBaseUrl));
+      const { queryFn } = useQueryWithParseMock.mock.calls[0][0];
+
+      await expect(queryFn()).rejects.toThrow("page 1 returned no body");
+      expect(fetchMock).toHaveBeenCalledTimes(1);
+    });
+
     it("invalidateFullGenrePlaylists invalidates the scoped full query key", () => {
       const { result } = renderHook(() => useListFullGenrePlaylists("reference", getBackendBaseUrl));
 

packages/app-kit/src/genre-tree/useGenrePlaylist.ts

@@ -32,10 +32,16 @@ type RawPaginatedResponse = {
  */
 // ponytail: unbounded Promise.all; browsers cap per-host connections, add a limiter if pages reach the hundreds.
 const fetchAllPages = async (fetchPage: (page: number) => Promise<unknown>): Promise<RawPaginatedResponse> => {
-  const first = (await fetchPage(1)) as RawPaginatedResponse;
-  const rest = (await Promise.all(
-    Array.from({ length: Math.max(first.totalPages - 1, 0) }, (_, i) => fetchPage(i + 2)),
-  )) as RawPaginatedResponse[];
+  // fetch-wrapper resolves null (instead of throwing) when a handleError callback swallowed the failure.
+  const fetchRequiredPage = async (page: number) => {
+    const response = await fetchPage(page);
+    if (response == null) throw new Error(`Paginated list page ${page} returned no body`);
+    return response as RawPaginatedResponse;
+  };
+  const first = await fetchRequiredPage(1);
+  const rest = await Promise.all(
+    Array.from({ length: Math.max(first.totalPages - 1, 0) }, (_, i) => fetchRequiredPage(i + 2)),
+  );
   const results = [first, ...rest].flatMap((response) => response.results);
   const last = rest[rest.length - 1] ?? first;