Fix data races on Room's lazy member initialization

.changes/fix-room-lazy-init-race

@@ -0,0 +1 @@
+patch type="fixed" "Fix data races on Room's lazily initialized members (localParticipant, data channels, outgoingStreamManager, preConnectBuffer, metricsManager): concurrent first access could run a lazy initializer twice; they are now initialized eagerly in Room's initializer"

Sources/LiveKit/Core/Room.swift

@@ -32,7 +32,7 @@ public class Room: NSObject, @unchecked Sendable, ObservableObject, Loggable {
 
     // MARK: - Metrics
 
-    lazy var metricsManager = MetricsManager()
+    let metricsManager = MetricsManager()
 
     // MARK: - Public
 
@@ -270,6 +270,19 @@ public class Room: NSObject, @unchecked Sendable, ObservableObject, Loggable {
         // log sdk & os versions
         log("sdk: \(LiveKitSDK.version), ffi: \(LiveKitSDK.ffiVersion), os: \(String(describing: Utils.os()))(\(Utils.osVersionString())), modelId: \(String(describing: Utils.modelIdentifier() ?? "unknown"))")
 
+        // Force initialization of lazy members while `self` is still exclusively
+        // owned by this initializer. Lazy initialization is not atomic, and these
+        // members are reachable from isolation domains that do not serialize with
+        // each other, so a first touch after init could otherwise run an
+        // initializer twice. After this block every access is a plain read of
+        // already-initialized storage. The members stay `lazy` only because their
+        // initializers capture `self`, which a stored property cannot do.
+        _ = localParticipant
+        _ = subscriberDataChannel
+        _ = publisherDataChannel
+        _ = outgoingStreamManager
+        _ = preConnectBuffer
+
         signalClient._delegate.set(delegate: self)
 
         log()