Fix race condition during sync (#861)

Resolves #859 

Swift SDK uses `isSubscribed` which checks if a track is actually
attached, but during reconnection, the `PeerConnection` hasn't fired the
`onTrack` event yet, so the track is `nil`, making `isSubscribed =
false`.

Using JS convention `isDesired` here.

Author: pblazej

.changes/sync-race-cond

@@ -0,0 +1 @@
+patch type="fixed" "Race condition during sync preventing track subscription"

Sources/LiveKit/Core/Room+Engine.swift

@@ -448,9 +448,12 @@ extension Room {
         // 2. autosubscribe off, we send subscribed tracks.
 
         let autoSubscribe = _state.connectOptions.autoSubscribe
+        // Use isDesired (subscription intent) instead of isSubscribed (actual state)
+        // to avoid race condition during quick reconnect where tracks aren't attached yet.
         let trackSids = _state.remoteParticipants.values.flatMap { participant in
             participant._state.trackPublications.values
-                .filter { $0.isSubscribed != autoSubscribe }
+                .compactMap { $0 as? RemoteTrackPublication }
+                .filter { $0.isDesired != autoSubscribe }
                 .map(\.sid)
         }
 

Sources/LiveKit/Track/Capturers/CameraCapturer.swift

@@ -50,9 +50,9 @@ public class CameraCapturer: VideoCapturer, @unchecked Sendable {
     public var isMultitaskingAccessSupported: Bool {
         #if (os(iOS) || os(tvOS)) && !targetEnvironment(macCatalyst)
         if #available(iOS 16, *, tvOS 17, *) {
-            self.capturer.captureSession.beginConfiguration()
-            defer { self.capturer.captureSession.commitConfiguration() }
-            return self.capturer.captureSession.isMultitaskingCameraAccessSupported
+            capturer.captureSession.beginConfiguration()
+            defer { capturer.captureSession.commitConfiguration() }
+            return capturer.captureSession.isMultitaskingCameraAccessSupported
         }
         #endif
         return false
@@ -62,15 +62,15 @@ public class CameraCapturer: VideoCapturer, @unchecked Sendable {
         get {
             #if (os(iOS) || os(tvOS)) && !targetEnvironment(macCatalyst)
             if #available(iOS 16, *, tvOS 17, *) {
-                return self.capturer.captureSession.isMultitaskingCameraAccessEnabled
+                return capturer.captureSession.isMultitaskingCameraAccessEnabled
             }
             #endif
             return false
         }
         set {
             #if (os(iOS) || os(tvOS)) && !targetEnvironment(macCatalyst)
             if #available(iOS 16, *, tvOS 17, *) {
-                self.capturer.captureSession.isMultitaskingCameraAccessEnabled = newValue
+                capturer.captureSession.isMultitaskingCameraAccessEnabled = newValue
             }
             #endif
         }

Sources/LiveKit/TrackPublications/RemoteTrackPublication.swift

@@ -52,6 +52,10 @@ public class RemoteTrackPublication: TrackPublication, @unchecked Sendable {
         return _state.isSubscribePreferred != false && super.isSubscribed
     }
 
+    var isDesired: Bool {
+        _state.isSubscribePreferred != false
+    }
+
     @objc
     public var subscriptionState: SubscriptionState {
         if !isSubscriptionAllowed { return .notAllowed }