fix: player bar freezes on manual song start in bridge mode

- playQueue: update UI immediately before NSBridge.setQueue so the bar
  reflects the new song without waiting for onTrackChanged
- onTrackChanged: remove index guard that blocked UI refresh when
  S.qIdx was already set; always call updatePlayerUI/onNpSongChange
- nextSong/prevSong: optimistic UI update before calling native next/prev
- _computeNextIdx: extracted helper for shuffle/repeat/linear logic
- _lastPositionMs: new variable for prev() 3s threshold in bridge mode
- updatePlayerUI/_syncNpDirect: guard img.src assignment to prevent
  redundant reloads and flicker on double update

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

src/player.js

@@ -12,6 +12,7 @@ const HAS_BRIDGE = typeof window.NSBridge !== 'undefined';
 // Track native playback state; driven by window.NSPlayer callbacks below.
 let _nativePos      = 0;   // ms
 let _nativePlaying  = false;
+let _lastPositionMs = 0;   // ms — set by onPositionUpdate, used for prev() decision
 let _lastDurationMs = 0;   // ms — set by onPositionUpdate, used for seek calculations
 
 // Unified duration / position / seek helpers — use native state when available,
@@ -109,14 +110,16 @@ window.NSPlayer = {
   // Native moved to a different track (auto-advance, seek, or queue replace).
   onTrackChanged(payloadJson) {
     try {
-      const payload = JSON.parse(payloadJson);
-      if (typeof payload.index === 'number' && payload.index !== S.qIdx) {
-        S.qIdx = payload.index;
+      const p = JSON.parse(payloadJson);
+      if (typeof p.index !== 'number') return;
+      if (p.index < 0 || p.index >= S.queue.length) return;
+      const indexChanged = (p.index !== S.qIdx);
+      S.qIdx = p.index;
       const s = S.queue[S.qIdx];
       if (!s) return;
       updatePlayerUI(s, true);
       onNpSongChange(s.id);
-        renderQueue();
+      if (indexChanged) renderQueue();
       // Radio mode: top up the queue when running low; push new songs to native.
       if (S.radioMode && S.queue.length - S.qIdx < 5) {
         const prevLen = S.queue.length;
@@ -126,13 +129,13 @@ window.NSPlayer = {
           );
         });
       }
-      }
     } catch (e) {}
   },
 
   // ~250 ms position tick while playing.
   onPositionUpdate(posMs, durMs) {
     _nativePos      = posMs;
+    _lastPositionMs = posMs;
     _lastDurationMs = durMs;
     if (S._scrubbing) return;
     const dur = durMs / 1000;
@@ -238,8 +241,12 @@ export function playQueue(songs, startIdx) {
   _clearPreload();
 
   if (HAS_BRIDGE) {
-    window.NSBridge.setQueue(JSON.stringify(buildTrackList()), startIdx, true);
+    const s = S.queue[S.qIdx];
+    if (s) { updatePlayerUI(s, true); onNpSongChange(s.id); }
     renderQueue();
+    try {
+      window.NSBridge.setQueue(JSON.stringify(buildTrackList()), startIdx, true);
+    } catch (e) { console.warn('NSBridge.setQueue failed', e); }
     if (S.radioMode) fillRadioQueue();
     return;
   }
@@ -335,7 +342,7 @@ export function updatePlayerUI(s, _skipMediaSession = false) {
   const art = document.getElementById('player-art');
   const cv = coverUrl(s.coverArt, 256);
   const existingImg = art.querySelector('img');
-  if (cv && existingImg) existingImg.src = cv;
+  if (cv && existingImg) { if (existingImg.src !== cv) existingImg.src = cv; }
   else 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`;
@@ -384,8 +391,8 @@ export function _syncNpDirect(s) {
   const cover = document.getElementById('np-cover');
   if (cover) {
     const existingImg = cover.querySelector('img');
-    if (cv && existingImg) existingImg.src = cv;
-    else if (cover) cover.innerHTML = cv ? `<img src="${cv}" style="width:100%;height:100%;object-fit:cover">` : '<div class="no-art">♪</div>';
+    if (cv && existingImg) { if (existingImg.src !== cv) existingImg.src = cv; }
+    else cover.innerHTML = cv ? `<img src="${cv}" style="width:100%;height:100%;object-fit:cover">` : '<div class="no-art">♪</div>';
   }
   _crossfadeNpBg(cv);
   const t = document.getElementById('np-title'); if(t) t.textContent = s.title || '—';
@@ -424,16 +431,47 @@ export function setPlayIcon(playing) {
   }
 }
 
+function _computeNextIdx() {
+  if (S.repeat === 'one') return S.qIdx;
+  if (S.shuffle && S.queue.length > 1) {
+    let n = S.qIdx;
+    while (n === S.qIdx) n = Math.floor(Math.random() * S.queue.length);
+    return n;
+  }
+  if (S.qIdx + 1 < S.queue.length) return S.qIdx + 1;
+  if (S.repeat === 'all') return 0;
+  return -1;
+}
+
 export function prevSong() {
   _clearPreload();
-  if (HAS_BRIDGE) { _nsBridge('prev'); return; }
+  if (HAS_BRIDGE) {
+    if (_lastPositionMs > 3000) { _nsBridge('prev'); return; }
+    if (S.qIdx > 0) {
+      S.qIdx--;
+      const s = S.queue[S.qIdx];
+      if (s) { updatePlayerUI(s, true); onNpSongChange(s.id); renderQueue(); }
+    }
+    _nsBridge('prev');
+    return;
+  }
   if(S.audio.currentTime > 3) { S.audio.currentTime = 0; return; }
   if(S.qIdx > 0) { S.qIdx--; playCurrent(); }
 }
 
 export function nextSong() {
   _clearPreload();
-  if (HAS_BRIDGE) { _nsBridge('next'); return; }
+  if (HAS_BRIDGE) {
+    const ni = _computeNextIdx();
+    if (ni >= 0 && ni < S.queue.length) {
+      S.qIdx = ni;
+      const s = S.queue[S.qIdx];
+      if (s) { updatePlayerUI(s, true); onNpSongChange(s.id); renderQueue(); }
+    }
+    _nsBridge('next');
+    if (S.radioMode && S.queue.length - S.qIdx < 5) fillRadioQueue();
+    return;
+  }
   if(S.shuffle) S.qIdx = Math.floor(Math.random() * S.queue.length);
   else if(S.qIdx < S.queue.length - 1) S.qIdx++;
   else if(S.repeat) S.qIdx = 0;