feat(03-02): handle file and network edge cases

Implemented defensive handling for edge cases and failure scenarios:

Cleanup on unmount:
- Added useEffect to stop playback on component unmount
- Prevents stale state when player closes while playing
- Catches errors gracefully

File format validation:
- Validates duration in fetchDuration (rejects 0 or NaN)
- Warns about suspicious durations (<1s or >10h)
- May indicate parsing errors

Network handling:
- Already implemented: consecutivePollingErrorsRef tracks failures
- Shows error after 3 consecutive polling failures
- Stops polling and allows retry

jamClient guards:
- Already implemented: null checks in all handlers
- Early return with error message if unavailable

Invalid state recovery:
- Polling detects mismatched isPlaying state
- Force syncs UI to jamClient state
- Logs warnings for debugging

Graceful degradation:
- Error states show but player stays open
- Provides Dismiss and Retry options
- No crashes or frozen UI

All edge cases handled with defensive coding and proper cleanup.

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

@@ -111,6 +111,13 @@ const JKSessionBackingTrackPlayer = ({
             return;
           }
 
+          // Warn about suspicious durations (file format validation)
+          const tenHoursMs = 10 * 60 * 60 * 1000; // 10 hours
+          const oneSecondMs = 1000;
+          if (validDuration > tenHoursMs || validDuration < oneSecondMs) {
+            console.warn('[BTP] Suspicious duration detected:', validDuration, 'ms. May indicate parsing error.');
+          }
+
           setDurationMs(validDuration);
           setDuration(formatTime(validDuration));
           clearError(); // Clear any previous errors
@@ -191,6 +198,18 @@ const JKSessionBackingTrackPlayer = ({
     };
   }, [isPlaying, jamClient, backingTrack]);
 
+  // Cleanup on unmount: stop playback to prevent stale state
+  useEffect(() => {
+    return () => {
+      // Stop playback when component unmounts
+      if (jamClient && isPlaying) {
+        jamClient.SessionStopPlay().catch((err) => {
+          console.error('[BTP] Error stopping playback on unmount:', err);
+        });
+      }
+    };
+  }, [jamClient, isPlaying]);
+
   const handlePlay = async () => {
     if (isOperating) return; // Prevent rapid clicks
     setIsOperating(true);