final cpu fix

Shared/Audio/AudioPlayer.swift

@@ -139,20 +139,26 @@ class AudioPlayer: NSObject, ObservableObject {
         analysisTask = nil
         AudioPreFetcher.shared.cancelAll()
         removeTimeObserver()
-        alog("Background: timers + time observer + analysis + prefetch suspended")
+        // SmartCrossfadeManager has its own 10Hz time observer that writes
+        // @Published currentTime/duration — same SwiftUI churn as AudioPlayer's
+        if isUsingCrossfade {
+            SmartCrossfadeManager.shared.suspendForBackground()
+        }
+        alog("Background: all timers + observers suspended")
     }
 
     private func resumeVisTimers() {
         guard isPlaying else { return }
-        // Reinstall the time observer before restarting vis timers so currentTime
-        // is accurate when the offline vis timer first reads position.
         reinstallTimeObserver()
+        if isUsingCrossfade {
+            SmartCrossfadeManager.shared.resumeFromBackground()
+        }
         if isUsingOfflineVis {
             startOfflineVisSync()
-        } else {
+        } else if !isUsingCrossfade {
             startLevelSimulation()
         }
-        alog("Foreground: timers + time observer resumed (offlineVis=\(isUsingOfflineVis))")
+        alog("Foreground: timers + observers resumed (crossfade=\(isUsingCrossfade) offlineVis=\(isUsingOfflineVis))")
     }
 
     private func removeTimeObserver() {

iOS/Data/AudioPreFetcher.swift

@@ -1,4 +1,5 @@
 import Foundation
+import UIKit
 
 /// Pre-fetches the next few tracks in the queue so playback is instant.
 /// Uses OfflineManager's download system but marks pre-fetched files as temporary

iOS/Views/Companion/SmartCrossfadeManager.swift

@@ -363,6 +363,20 @@ class SmartCrossfadeManager: ObservableObject {
             timeObserver = nil
         }
     }
+
+    /// Called when app enters background — removes the 10Hz time observer that
+    /// drives @Published currentTime/duration updates and burns main-thread CPU.
+    func suspendForBackground() {
+        removeTimeObserver()
+        displayLink?.invalidate()
+        displayLink = nil
+    }
+
+    /// Called when app returns to foreground — reinstalls the time observer.
+    func resumeFromBackground() {
+        guard timeObserver == nil else { return }
+        installTimeObserver()
+    }
     
     private func removeAllObservers() {
         removeBoundaryObserver()