feat(20-01): integrate removeVuState with mixer lifecycle

- Destructure removeVuState from useVuContext alongside updateVU3
- Add previousMixerIdsRef to track mixer IDs between renders
- Add cleanup useEffect that detects removed mixers
- Call removeVuState when mixer is removed from allMixers
- Only run cleanup when mixers are ready (isReadyRedux is true)

This prevents unbounded growth of vuStates object as tracks join/leave.

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

jam-ui/src/hooks/useMixerHelper.js

@@ -66,6 +66,7 @@ const useMixerHelper = () => {
   const dispatch = useDispatch();
   const allMixersRef = useRef({});
   const previousMyTracksRef = useRef([]);
+  const previousMixerIdsRef = useRef(null);
 
   // Redux selectors - replace all useState calls
   const chatMixer = useSelector(selectChatMixer);
@@ -108,7 +109,7 @@ const useMixerHelper = () => {
   const currentSession = useSelector(selectActiveSession);
   const inSession = useSelector(selectInSession);
   const { jamClient, isConnected, server } = useJamServerContext();
-  const { updateVU3 } = useVuContext();
+  const { updateVU3, removeVuState } = useVuContext();
   const { getParticipant } = useSessionHelper();
   const { trackVolumeObject, setTrackVolumeObject } = useGlobalContext();
   const faderHelpers = useFaderHelpers();
@@ -316,6 +317,33 @@ const useMixerHelper = () => {
     }
   }, [isReadyRedux]);
 
+  // Cleanup VU state when mixers are removed
+  useEffect(() => {
+    // Skip if not ready or no previous mixers to compare
+    if (!isReadyRedux) return;
+
+    // Get current mixer IDs from allMixers
+    const currentMixerIds = new Set(Object.keys(allMixers));
+
+    // Track previous mixer IDs using a ref
+    if (!previousMixerIdsRef.current) {
+      previousMixerIdsRef.current = currentMixerIds;
+      return;
+    }
+
+    // Find removed mixers (in previous but not in current)
+    for (const mixerId of previousMixerIdsRef.current) {
+      if (!currentMixerIds.has(mixerId)) {
+        // Mixer was removed - clean up its VU state
+        removeVuState(mixerId);
+        console.debug('[useMixerHelper] Cleaned up VU state for removed mixer:', mixerId);
+      }
+    }
+
+    // Update previous for next comparison
+    previousMixerIdsRef.current = currentMixerIds;
+  }, [allMixers, isReadyRedux, removeVuState]);
+
    const getMixerByTrackId = useCallback((trackId, mode) => {
     const mixerPair = mixersByTrackId[trackId];