refactor(28-02): rewrite SessionTrackVU with direct DOM updates

- Remove useVuContext - directly import vuStore
- Remove VuMeter component usage - render lights directly
- Add RAF loop polling vuStore.getLevelSnapshot at ~60fps
- Store light element refs for direct className assignment
- Wrap with React.memo to prevent parent re-renders
- Zero React re-renders for VU visual updates

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

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

@@ -1,44 +1,102 @@
-import React, { useEffect, useRef } from 'react';
-import { useVuContext } from '../../context/VuContext';
+import React, { useEffect, useRef, memo } from 'react';
+import { vuStore } from '../../stores/vuStore';
 
-function SessionTrackVU({ lightCount, orientation, lightWidth, lightHeight, side, ptr, mixers }) {
-  const { VuMeter, updateVuState } = useVuContext();
-  const ptrRef = useRef(ptr || `STV${Date.now()}`);
+const SessionTrackVU = memo(function SessionTrackVU({
+  lightCount = 16,
+  orientation = 'vertical',
+  lightWidth = 15,
+  lightHeight = 10,
+  mixers
+}) {
+  const containerRef = useRef(null);
+  const lightsRef = useRef([]);
   const mixerIdRef = useRef(null);
+  const rafIdRef = useRef(null);
 
+  // Update mixerId when mixers prop changes
   useEffect(() => {
     const mixer = mixers?.vuMixer;
+    mixerIdRef.current = mixer ? `${mixer.mode ? 'M' : 'P'}${mixer.id}` : null;
 
-    if (!mixer) {
-      mixerIdRef.current = null;
+    return () => {
+      // Cleanup VU state on unmount
+      if (mixerIdRef.current) {
+        vuStore.removeLevel(mixerIdRef.current);
+      }
+    };
+  }, [mixers]);
+
+  // Animation loop for direct DOM updates - separate from React lifecycle
+  useEffect(() => {
+    const updateVisuals = () => {
+      const mixerId = mixerIdRef.current;
+
+      if (!mixerId) {
+        rafIdRef.current = requestAnimationFrame(updateVisuals);
         return;
       }
 
-    // Create a unique ID for this VU meter
-    const mixerId = `${mixer.mode ? 'M' : 'P'}${mixer.id}`;
-    mixerIdRef.current = mixerId;
+      const data = vuStore.getLevelSnapshot(mixerId);
+      const level = data?.level ?? 0;
+      const clipping = data?.clipping ?? false;
+      const activeLights = Math.round(level * lightCount);
 
-    //console.debug("SessionTrackVU: VU registered for mixer", mixerId);
+      // Direct DOM manipulation - no React involvement
+      for (let i = 0; i < lightCount; i++) {
+        const light = lightsRef.current[i];
+        if (!light) continue;
+
+        const positionFromBottom = lightCount - 1 - i;
+        const isActive = positionFromBottom < activeLights;
+
+        // Use className assignment for efficient class manipulation
+        // (faster than classList.add/remove for multiple classes)
+        if (isActive) {
+          if (clipping || positionFromBottom >= Math.floor(lightCount * 0.75)) {
+            light.className = 'vu-light vu-bg-danger';
+          } else if (positionFromBottom >= Math.floor(lightCount * 0.5)) {
+            light.className = 'vu-light vu-bg-warning';
+          } else {
+            light.className = 'vu-light vu-bg-success';
+          }
+        } else {
+          light.className = 'vu-light vu-bg-secondary';
+        }
+      }
+
+      rafIdRef.current = requestAnimationFrame(updateVisuals);
+    };
+
+    rafIdRef.current = requestAnimationFrame(updateVisuals);
 
     return () => {
-      // Cleanup: reset VU state when component unmounts or mixer changes
-      if (mixerIdRef.current) {
-        updateVuState(mixerIdRef.current, 0, false);
-        mixerIdRef.current = null;
+      if (rafIdRef.current) {
+        cancelAnimationFrame(rafIdRef.current);
       }
     };
-  }, [mixers, updateVuState]);
+  }, [lightCount]);
 
-  // Use the React component for rendering
+  // Render ONCE - never re-renders for VU updates
   return (
-    <VuMeter
-      mixerId={mixerIdRef.current}
-      orientation={orientation}
-      lightCount={lightCount}
-      lightWidth={lightWidth}
-      lightHeight={lightHeight}
+    <div ref={containerRef} className="vu">
+      <div className="d-flex flex-column" style={{ height: `${lightCount * (lightHeight + 1)}px` }}>
+        {Array.from({ length: lightCount }).map((_, i) => (
+          <div
+            key={i}
+            ref={el => lightsRef.current[i] = el}
+            className="vu-light vu-bg-secondary"
+            style={{
+              height: `${lightHeight}px`,
+              width: '25px',
+              marginTop: '1px',
+              borderRadius: '2px',
+              border: '1px solid #eee'
+            }}
           />
+        ))}
+      </div>
+    </div>
   );
-}
+});
 
 export default SessionTrackVU;