v4: playlists have categories of their own — a set apart from the dumps', which admins manage on /manage under "Playlist categories", next to "Dump categories". Each category now has a kind, dump or playlist, its slug and name unique within its kind only; migration 0025 rebuilds categories with the column, every existing one becoming a dump category with its dumps, and adds playlist_categories. A playlist's owner files it under any of them in the create and edit forms, and it shows them as chips on its card and its page, each leading to /playlists/<slug>.

/playlists is the new page of every public playlist, newest first (GET /api/playlists), and /playlists/<slug> a playlist category's, with a menu of the categories, linked from the user menu as "All playlists"; `playlists` is reserved as a dump category's slug, and one that had it is renamed. A profile's Playlists tab narrows to a playlist category with the same menu as its Dumps tab (?category=), and so do the Dumps and Playlists tabs of /search, each with its own kind (category and playlistCategory for GET /api/search), another tab dropping it.

The category service takes the kind throughout, so a dump can't be filed under a playlist category nor the other way round, and categoryJoin is the one filter join the dump, follow and playlist services share. useCategories(kind) gives one kind's set from the one fetch, CategoryChips replaces the chips the dump card and page each drew, useCategoryFilter keeps a list to its category as the socket brings more, and useCategorySelection holds a form's picked categories.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/pages/Playlists.tsx

@@ -0,0 +1,135 @@
+/**
+ * Renders every public playlist, `/playlists`, and those of one playlist
+ * category, `/playlists/:categorySlug`, newest first.
+ *
+ * @module
+ */
+
+import { useCallback } from "react";
+import { useNavigate, useParams } from "react-router";
+import { t } from "@lingui/core/macro";
+import { Trans } from "@lingui/react/macro";
+import { API_URL } from "../config/api.ts";
+import type { Playlist } from "../../shared/playlist.ts";
+import { playlistsPath } from "../../shared/paths.ts";
+import { canLoadMore, pageUrl, readPage } from "../utils/feed/pagedList.ts";
+import {
+  deserializePlaylist,
+  hydratePlaylist,
+} from "../utils/shared/deserialize.ts";
+import { useAuth } from "../hooks/auth/useAuth.ts";
+import { useCategories } from "../hooks/category/useCategories.ts";
+import { useCategoryFilter } from "../hooks/category/useCategoryFilter.ts";
+import { useDocumentTitle } from "../hooks/shared/useDocumentTitle.ts";
+import { useFeedCache } from "../hooks/feed/useFeedCache.ts";
+import { usePagedList } from "../hooks/feed/usePagedList.ts";
+import { useInfiniteScroll } from "../hooks/feed/useInfiniteScroll.ts";
+import {
+  useScrollRestore,
+  useScrollSave,
+} from "../hooks/feed/useScrollSave.ts";
+import { usePlaylistListSync } from "../hooks/playlist/usePlaylistListSync.ts";
+import { PageShell } from "../components/layout/PageShell.tsx";
+import { PageHeader } from "../components/layout/PageHeader.tsx";
+import { CategorySwitcher } from "../components/category/CategorySwitcher.tsx";
+import { PlaylistCardList } from "../components/playlist/PlaylistCardList.tsx";
+import { FeedFooter } from "../components/feed/FeedFooter.tsx";
+import { ListState } from "../components/shared/ListState.tsx";
+import { NotFound } from "./NotFound.tsx";
+
+/**
+ * Renders the list for the route's category, or every public playlist
+ * without one. Each category's list is another, which the page mounts
+ * afresh. A slug that names no playlist category, once the categories have
+ * loaded, is a page not found.
+ */
+export function Playlists(): React.JSX.Element {
+  const { categorySlug } = useParams();
+  const { categories, isLoaded } = useCategories("playlist");
+  const category = categorySlug
+    ? categories.find((c) => c.slug === categorySlug)
+    : undefined;
+  useDocumentTitle(category ? category.name : t`Playlists`);
+
+  if (categorySlug && isLoaded && !category) return <NotFound />;
+  return (
+    <PlaylistsList
+      key={categorySlug ?? ""}
+      categorySlug={categorySlug}
+      categoryId={category?.id}
+    />
+  );
+}
+
+/**
+ * Renders the public playlists, from `GET /api/playlists`, a page at a time
+ * as the list scrolls; with `categorySlug`, only those in that playlist
+ * category, which the menu in the title row switches. The socket keeps them
+ * live, and going back restores the list and the scroll.
+ */
+function PlaylistsList(
+  { categorySlug, categoryId }: { categorySlug?: string; categoryId?: string },
+) {
+  const navigate = useNavigate();
+  const { user, authFetch } = useAuth();
+  const { cached, saveState } = useFeedCache<Playlist>(
+    `feed:playlists:${categorySlug ?? "all"}`,
+    hydratePlaylist,
+  );
+  const url = `${API_URL}/api/playlists${
+    categorySlug ? `?category=${encodeURIComponent(categorySlug)}` : ""
+  }`;
+  const { state, setItems: setAllItems, loadMore } = usePagedList<Playlist>(
+    `${url}:${user?.id ?? "guest"}`,
+    useCallback(
+      (page: number, signal?: AbortSignal) =>
+        authFetch(pageUrl(url, page), { signal })
+          .then((res) => readPage(res, deserializePlaylist)),
+      [authFetch, url],
+    ),
+    cached,
+  );
+  const loaded = state.status === "loaded" ? state.data : null;
+  usePlaylistListSync(useCategoryFilter(setAllItems, categoryId));
+
+  const sentinelRef = useInfiniteScroll(loadMore, canLoadMore(loaded));
+  useScrollSave(
+    !!loaded,
+    useCallback((y) => {
+      if (loaded) saveState(loaded, y);
+    }, [loaded, saveState]),
+  );
+  useScrollRestore(cached?.scrollY, !!loaded);
+
+  return (
+    <PageShell narrow>
+      <PageHeader icon="📋" title={<Trans>Playlists</Trans>}>
+        <CategorySwitcher
+          kind="playlist"
+          categorySlug={categorySlug}
+          onSelect={(slug) => navigate(playlistsPath(slug))}
+        />
+      </PageHeader>
+      <ListState
+        state={state}
+        isEmpty={({ data }) => data.items.length === 0}
+        empty={
+          <p className="empty-state">
+            <Trans>No playlists yet.</Trans>
+          </p>
+        }
+      >
+        {({ data }) => (
+          <>
+            <PlaylistCardList playlists={data.items} />
+            <FeedFooter
+              hasMore={data.hasMore}
+              loadingMore={data.loadingMore}
+              sentinelRef={sentinelRef}
+            />
+          </>
+        )}
+      </ListState>
+    </PageShell>
+  );
+}