feat(flutter): playlist detail nav hydration — header renders before fetch

Same pattern as album + artist detail. PlaylistDetailScreen accepts
optional Playlist seed via go_router extra. While
playlistDetailProvider is still resolving, render the header
(description if any + track count) plus a "loading tracks…" inline
spinner instead of an opaque full-screen CircularProgressIndicator.
The body fills in when tracks arrive via drift watch re-emit.

Routing reads s.extra as Playlist. PlaylistCard +
PlaylistsListScreen pass the playlist via extra. Surfaces with no
seed available (deep links etc.) fall back to the original full-
screen spinner.

Track row rendering already uses ListView.builder so visible row
count was never the bottleneck — the wait was for the detail fetch
itself. Header-on-tap is the win that makes the screen feel snappy.

flutter_client/lib/playlists/playlist_detail_screen.dart

@@ -12,13 +12,26 @@ import '../theme/theme_extension.dart';
 import 'playlists_provider.dart';
 
 class PlaylistDetailScreen extends ConsumerWidget {
-  const PlaylistDetailScreen({required this.id, super.key});
+  const PlaylistDetailScreen({required this.id, this.seed, super.key});
   final String id;
 
+  /// Optional Playlist passed via go_router extra so the header
+  /// (title, cover, track count, play/download CTAs) can render
+  /// before the full detail fetch resolves. Same pattern as album
+  /// + artist nav hydration.
+  final Playlist? seed;
+
   @override
   Widget build(BuildContext context, WidgetRef ref) {
     final fs = Theme.of(context).extension<FabledSwordTheme>()!;
     final detail = ref.watch(playlistDetailProvider(id));
+
+    // Resolve the best playlist info available for the AppBar title.
+    final livePlaylist = detail.value?.playlist;
+    final headerName = (livePlaylist != null && livePlaylist.name.isNotEmpty)
+        ? livePlaylist.name
+        : (seed?.name ?? '');
+
     return Scaffold(
       backgroundColor: fs.obsidian,
       appBar: AppBar(
@@ -28,17 +41,21 @@ class PlaylistDetailScreen extends ConsumerWidget {
           icon: Icon(Icons.arrow_back, color: fs.parchment),
           onPressed: () => context.pop(),
         ),
-        title: detail.maybeWhen(
-          data: (d) => Text(
-            d.playlist.name,
-            style: TextStyle(color: fs.parchment),
-            overflow: TextOverflow.ellipsis,
-          ),
-          orElse: () => const SizedBox.shrink(),
-        ),
+        title: headerName.isEmpty
+            ? const SizedBox.shrink()
+            : Text(
+                headerName,
+                style: TextStyle(color: fs.parchment),
+                overflow: TextOverflow.ellipsis,
+              ),
       ),
       body: detail.when(
-        loading: () => const Center(child: CircularProgressIndicator()),
+        // Loading from a seed: render the header immediately + a
+        // small inline "loading tracks" hint, instead of an opaque
+        // full-screen spinner. The body fills in when tracks arrive.
+        loading: () => seed == null
+            ? const Center(child: CircularProgressIndicator())
+            : _SeedBody(playlist: seed!),
         error: (e, _) =>
             Center(child: Text('$e', style: TextStyle(color: fs.error))),
         data: (d) => _Body(detail: d),
@@ -47,6 +64,43 @@ class PlaylistDetailScreen extends ConsumerWidget {
   }
 }
 
+/// Loading-state body: renders just the header from the seed
+/// playlist + a "loading tracks…" placeholder. CTA buttons are
+/// hidden until the real track list arrives (they need playable
+/// refs to do anything useful).
+class _SeedBody extends StatelessWidget {
+  const _SeedBody({required this.playlist});
+  final Playlist playlist;
+
+  @override
+  Widget build(BuildContext context) {
+    final fs = Theme.of(context).extension<FabledSwordTheme>()!;
+    return ListView(children: [
+      Padding(
+        padding: const EdgeInsets.fromLTRB(16, 8, 16, 16),
+        child: Column(crossAxisAlignment: CrossAxisAlignment.start, children: [
+          if (playlist.description.isNotEmpty)
+            Padding(
+              padding: const EdgeInsets.only(bottom: 12),
+              child: Text(
+                playlist.description,
+                style: TextStyle(color: fs.ash, fontSize: 13),
+              ),
+            ),
+          Text(
+            '${playlist.trackCount} ${playlist.trackCount == 1 ? "track" : "tracks"}',
+            style: TextStyle(color: fs.ash, fontSize: 12),
+          ),
+        ]),
+      ),
+      const Padding(
+        padding: EdgeInsets.symmetric(vertical: 24),
+        child: Center(child: CircularProgressIndicator()),
+      ),
+    ]);
+  }
+}
+
 class _Body extends ConsumerWidget {
   const _Body({required this.detail});
   final PlaylistDetail detail;

flutter_client/lib/playlists/playlists_list_screen.dart

@@ -51,7 +51,7 @@ class PlaylistsListScreen extends ConsumerWidget {
                 final p = items[i];
                 return _PlaylistTile(
                   playlist: p,
-                  onTap: () => ctx.push('/playlists/${p.id}'),
+                  onTap: () => ctx.push('/playlists/${p.id}', extra: p),
                 );
               },
             ),

flutter_client/lib/playlists/widgets/playlist_card.dart

@@ -21,7 +21,8 @@ class PlaylistCard extends StatelessWidget {
       child: Material(
         color: Colors.transparent,
         child: InkWell(
-          onTap: () => context.push('/playlists/${playlist.id}'),
+          onTap: () =>
+              context.push('/playlists/${playlist.id}', extra: playlist),
           child: Padding(
             padding: const EdgeInsets.symmetric(horizontal: 8),
             child: Column(crossAxisAlignment: CrossAxisAlignment.start, children: [

flutter_client/lib/shared/routing.dart

@@ -9,6 +9,7 @@ import '../library/album_detail_screen.dart';
 import '../library/artist_detail_screen.dart';
 import '../models/album.dart';
 import '../models/artist.dart';
+import '../models/playlist.dart';
 import '../discover/discover_screen.dart';
 import '../library/home_screen.dart';
 import '../library/library_screen.dart';
@@ -120,7 +121,10 @@ GoRouter buildRouter(Ref ref) {
           GoRoute(path: '/playlists', builder: (_, __) => const PlaylistsListScreen()),
           GoRoute(
             path: '/playlists/:id',
-            builder: (_, s) => PlaylistDetailScreen(id: s.pathParameters['id']!),
+            builder: (_, s) => PlaylistDetailScreen(
+              id: s.pathParameters['id']!,
+              seed: s.extra is Playlist ? s.extra as Playlist : null,
+            ),
           ),
           GoRoute(path: '/requests',         builder: (_, __) => const RequestsScreen()),
           GoRoute(path: '/admin',            builder: (_, __) => const AdminLandingScreen()),