fix: detect YTM artist channel expansion in getYtmVideoUrls; revert PWA MediaSession changes

- ytdlp.js: watch for [youtube:tab] in yt-dlp output during flat-playlist step;
  return [] when channel expansion is detected so cascade falls through to ytsearch
- Revert player.js / main.js / state.js PWA _changingTrack changes (not effective)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/lib/ytdlp.js

@@ -106,8 +106,17 @@ async function downloadTrack({ jobId, artist, albumArtist, title, album, year, t
   // Fetch YTM search result URLs as a flat list (no channel expansion) and return only
   // actual video URLs (watch?v=…). This prevents yt-dlp from following an artist channel
   // result and treating its uploads as the search result set.
+  //
+  // yt-dlp expands "url_transparent" artist channel entries even under --flat-playlist,
+  // printing the channel's video URLs instead of the channel URL. We detect this by
+  // watching for [youtube:tab] in output (which only fires during channel/tab extraction)
+  // and return [] so the caller falls through to the ytsearch fallback.
   const getYtmVideoUrls = (maxItems) => new Promise(resolve => {
     const urls = [];
+    let channelExpanded = false;
+    const checkExpansion = (text) => {
+      if (text.includes('[youtube:tab]') || text.includes('/browse/UC')) channelExpanded = true;
+    };
     const proc = spawn(CONFIG.ytdlpBin, [
       ytmUrl,
       '--flat-playlist',
@@ -116,15 +125,18 @@ async function downloadTrack({ jobId, artist, albumArtist, title, album, year, t
       '--no-warnings',
     ], { env: { ...process.env, PYTHONUNBUFFERED: '1' } });
     proc.stdout.on('data', d => {
-      d.toString().split('\n').forEach(line => {
+      const text = d.toString();
+      checkExpansion(text);
+      if (!channelExpanded) {
+        text.split('\n').forEach(line => {
           const u = line.trim();
-        // Only accept video URLs — skip /browse/ (artist channel) and /playlist? entries
           if (u.includes('watch?v=')) urls.push(u);
         });
+      }
     });
-    proc.stderr.on('data', () => {});
+    proc.stderr.on('data', d => checkExpansion(d.toString()));
     proc.on('error', () => resolve([]));
-    proc.on('close', () => resolve(urls));
+    proc.on('close', () => resolve(channelExpanded ? [] : urls));
   });
 
   // Search YTM for video URLs (pre-filtered), then pass them all at once to yt-dlp.

src/main.js

@@ -118,8 +118,7 @@ window.addEventListener('load', () => {
   S.audio.addEventListener('pause', () => {
     setPlayIcon(false);
     document.getElementById('player-art').classList.remove('spinning');
-    // Skip during track transitions — src change fires pause but we're about to play() immediately
+    if(navigator.mediaSession) navigator.mediaSession.playbackState = 'paused';
-    if(!S._changingTrack && navigator.mediaSession) navigator.mediaSession.playbackState = 'paused';
   });
   S.previewAudio.addEventListener('timeupdate', updatePreviewProgress);
   S.previewAudio.addEventListener('ended', stopPreview);

src/player.js

@@ -17,14 +17,8 @@ export function playQueue(songs, startIdx) {
 export function playCurrent() {
   if(S.qIdx < 0 || S.qIdx >= S.queue.length) return;
   const s = S.queue[S.qIdx];
-  // Pre-update MediaSession before src change so the OS never sees a "paused" flash
-  // (setting src fires pause synchronously; _changingTrack suppresses that in the pause handler)
-  updateMediaSession(s);
-  if(navigator.mediaSession) navigator.mediaSession.playbackState = 'playing';
-  S._changingTrack = true;
   S.audio.src = streamUrl(s.id);
-  S._changingTrack = false;
+  S.audio.play();
-  S.audio.play().catch(() => {});
   updatePlayerUI(s);
   onNpSongChange(s.id);
   renderQueue();

src/state.js

@@ -12,7 +12,6 @@ export const S = {
   previewAudio: null,
   previewCurrent: null,
   _scrubbing: false,
-  _changingTrack: false,
   _msPosLast: 0,
   queueOpen: false,