fix(mobile): restore playback state + MediaSession stability

- _restoreLastPlayed: set audio.src + call updateMediaSession so play
  button works immediately and notification shows artwork on app open
- visibilitychange: re-register all MediaSession handlers after screen
  unlock, fold/flip, or background return (fixes vanishing notification)
- Stall watchdog (3s interval): detects frozen audio in background and
  calls play() to recover; also catches missed 'ended' events so
  auto-advance works reliably when screen is off
- stalled/error listeners: attempt audio reload on network hiccup

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

src/main.js

@@ -8,7 +8,7 @@ import {
   initProgressScrub, updateProgress, updatePreviewProgress, stopPreview,
   toggleRadioMode, starCurrent, downloadCurrent, renderQueue, playPreview,
   toggleStar, dlSongLocal, _applyRadioBtn, _restoreLastPlayed, setPlayIcon,
-  npToggleStar,
+  npToggleStar, updateMediaSession,
 } from './player.js';
 import {
   navigate, _navGoBack, _navLoad, loadHomeData, onLocalSearch, onMobileSearch,
@@ -106,8 +106,46 @@ window.addEventListener('load', () => {
   });
   S.previewAudio.addEventListener('timeupdate', updatePreviewProgress);
   S.previewAudio.addEventListener('ended', stopPreview);
+
+  // Recovery: try to resume if audio stalls (network hiccup, background throttle)
+  S.audio.addEventListener('stalled', () => { if(!S.audio.paused) S.audio.load(); });
+  S.audio.addEventListener('waiting', () => { /* let browser handle buffering */ });
+  S.audio.addEventListener('error', () => {
+    if(!S.audio.paused && S.queue[S.qIdx]) {
+      const t = setTimeout(() => { S.audio.load(); S.audio.play().catch(()=>{}); }, 2000);
+      S.audio.addEventListener('play', () => clearTimeout(t), { once: true });
+    }
+  });
+
   S.audio.volume = 0.8;
 
+  // Re-register MediaSession handlers when returning from background/screen-off/flip
+  document.addEventListener('visibilitychange', () => {
+    if(document.visibilityState !== 'visible') return;
+    const s = S.queue[S.qIdx];
+    if(!s) return;
+    updateMediaSession(s);
+    if(navigator.mediaSession)
+      navigator.mediaSession.playbackState = S.audio.paused ? 'paused' : 'playing';
+  });
+
+  // Watchdog: detect when audio silently stalled in background (ended event not fired, or frozen)
+  let _wdLast = 0, _wdStalledAt = 0;
+  setInterval(() => {
+    if(!S.audio.src || S.audio.paused) { _wdStalledAt = 0; _wdLast = 0; return; }
+    const dur = S.audio.duration;
+    const cur = S.audio.currentTime;
+    // ended but event didn't fire (background throttling)
+    if(dur > 0 && cur >= dur - 0.5) { onEnded(); _wdStalledAt = 0; _wdLast = 0; return; }
+    if(cur !== _wdLast) { _wdStalledAt = 0; _wdLast = cur; return; }
+    if(!_wdStalledAt) { _wdStalledAt = Date.now(); return; }
+    // frozen for >8s → try to resume
+    if(Date.now() - _wdStalledAt > 8000) {
+      _wdStalledAt = 0;
+      S.audio.play().catch(() => {});
+    }
+  }, 3000);
+
   injectPWA();
   initProgressScrub();
 

src/player.js

@@ -353,5 +353,9 @@ export function _restoreLastPlayed() {
     art.innerHTML = cv ? `<img src="${cv}" style="width:100%;height:100%;object-fit:cover">` : '<div class="no-art">♪</div>';
     updateStarBtn();
     document.title = `${s.title} — NovaSonic`;
+    // set src so the play button works immediately without needing to re-select the song
+    S.audio.src = streamUrl(s.id);
+    S.audio.load();
+    updateMediaSession(s);
   } catch {}
 }