fix(03-03): verify playback state and add loop diagnostics

Race condition fix:
- After SessionStartPlay, verify actual playback state
- Add 100ms delay to let native client update
- Check isSessionTrackPlaying() before setting state
- Prevents "double click" issue where component thinks it's playing but isn't

Loop diagnostics:
- Add [LOOP] logging to track loop changes
- Add [POLLING] logging when track reaches end
- Log whether loop is enabled and native client behavior
- Help diagnose why loop not repeating

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

jam-ui/src/components/client/JKSessionBackingTrackPlayer.js

@@ -181,8 +181,10 @@ const JKSessionBackingTrackPlayer = ({
 
           // Check if track reached the end
           if (validPosition >= validDuration && validDuration > 0) {
+            console.log('[POLLING] Track reached end, isLooping:', isLooping);
             // If loop is enabled, don't interfere - let native client handle loop
             if (!isLooping) {
+              console.log('[POLLING] Not looping, stopping and resetting');
               // Stop playback and reset to beginning for clean state
               await jamClient.SessionStopPlay();
               setIsPlaying(false);
@@ -193,6 +195,7 @@ const JKSessionBackingTrackPlayer = ({
               return;
             }
             // If looping, just continue polling - native client will loop
+            console.log('[POLLING] Looping enabled, letting native client handle loop');
           }
 
           // Only update state if values actually changed (lazy updates)
@@ -307,8 +310,14 @@ const JKSessionBackingTrackPlayer = ({
         // Play (1 = normal playback mode)
         console.log('[PLAY] Calling SessionStartPlay');
         await jamClient.SessionStartPlay(1);
-        setIsPlaying(true);
-        console.log('[PLAY] Playback started successfully');
+
+        // Verify playback actually started (small delay to let native client update)
+        await new Promise(resolve => setTimeout(resolve, 100));
+        const actuallyPlaying = await jamClient.isSessionTrackPlaying();
+        console.log('[PLAY] After SessionStartPlay, actuallyPlaying:', actuallyPlaying);
+
+        setIsPlaying(actuallyPlaying);
+        console.log('[PLAY] Playback started, state set to:', actuallyPlaying);
       }
     } catch (error) {
       handleError('playback', 'Failed to start playback', error);
@@ -408,6 +417,7 @@ const JKSessionBackingTrackPlayer = ({
   const handleLoopChange = useCallback(async (e) => {
     const shouldLoop = e.target.checked;
     const previousLoop = isLooping;
+    console.log('[LOOP] Loop change requested:', shouldLoop);
     setIsLooping(shouldLoop);
 
     try {
@@ -420,14 +430,18 @@ const JKSessionBackingTrackPlayer = ({
       // Set loop state using SessionSetBackingTrackFileLoop
       // This requires the file path and loop boolean
       const trackPath = getBackingTrackPath(backingTrack);
+      console.log('[LOOP] Track path:', trackPath);
       if (!trackPath) {
         handleError('playback', 'No backing track available for loop change', null);
         setIsLooping(previousLoop); // Revert checkbox
         return;
       }
 
+      console.log('[LOOP] Calling SessionSetBackingTrackFileLoop with path:', trackPath, 'shouldLoop:', shouldLoop);
       await jamClient.SessionSetBackingTrackFileLoop(trackPath, shouldLoop);
+      console.log('[LOOP] Loop set successfully');
     } catch (error) {
+      console.error('[LOOP] Failed to set loop:', error);
       handleError('playback', 'Failed to toggle loop', error);
       setIsLooping(previousLoop); // Revert checkbox on error
     }