fix: guard detachFromEngine to only clear channel owned by detaching engine (FSSDK-12503) (#105)

onDetachedFromEngine/detachFromEngine was unconditionally clearing the
static MethodChannel, even when a secondary engine (e.g. Firebase
background messaging) detached. This destroyed the primary engine's
channel and broke all SDK calls and notification callbacks.

Store the BinaryMessenger that created the channel during attach, and
only clear the channel in detach if the detaching engine's messenger
matches the stored one.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: muzahidul-opti

android/src/main/java/com/optimizely/optimizely_flutter_sdk/OptimizelyFlutterSdkPlugin.java

@@ -19,6 +19,7 @@
 
 import io.flutter.embedding.engine.plugins.FlutterPlugin;
 import io.flutter.embedding.engine.plugins.activity.ActivityPluginBinding;
+import io.flutter.plugin.common.BinaryMessenger;
 import io.flutter.plugin.common.MethodCall;
 import io.flutter.plugin.common.MethodChannel;
 import io.flutter.plugin.common.MethodChannel.MethodCallHandler;
@@ -47,6 +48,7 @@
 public class OptimizelyFlutterSdkPlugin extends OptimizelyFlutterClient implements FlutterPlugin, ActivityAware, MethodCallHandler {
 
   public static MethodChannel channel;
+  private static BinaryMessenger attachedMessenger;
   private Appender<ILoggingEvent> flutterLogbackAppender;
 
   /**
@@ -215,7 +217,8 @@ public void onAttachedToEngine(@NonNull FlutterPluginBinding binding) {
     if (channel != null) {
       return;
     }
-    channel = new MethodChannel(binding.getBinaryMessenger(), "optimizely_flutter_sdk");
+    attachedMessenger = binding.getBinaryMessenger();
+    channel = new MethodChannel(attachedMessenger, "optimizely_flutter_sdk");
     channel.setMethodCallHandler(this);
     context = binding.getApplicationContext();
 
@@ -234,8 +237,12 @@ public void onAttachedToEngine(@NonNull FlutterPluginBinding binding) {
 
   @Override
   public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {
+    if (binding.getBinaryMessenger() != attachedMessenger) {
+      return;
+    }
     channel.setMethodCallHandler(null);
     channel = null;
+    attachedMessenger = null;
     // Stop and detach the appender
     if (flutterLogbackAppender != null) {
         Logger rootLogger = (Logger) LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME);

ios/Classes/SwiftOptimizelyFlutterSdkPlugin.swift

@@ -30,7 +30,8 @@ public class SwiftOptimizelyFlutterSdkPlugin: NSObject, FlutterPlugin {
 
     // to communicate with optimizely flutter sdk
     static var channel: FlutterMethodChannel!
-    
+    private static weak var attachedMessenger: FlutterBinaryMessenger?
+
     // to track each unique userContext
     var uuid: String {
         return UUID().uuidString
@@ -41,7 +42,9 @@ public class SwiftOptimizelyFlutterSdkPlugin: NSObject, FlutterPlugin {
         if channel != nil {
             return
         }
-        channel = FlutterMethodChannel(name: "optimizely_flutter_sdk", binaryMessenger: registrar.messenger())
+        let messenger = registrar.messenger()
+        attachedMessenger = messenger
+        channel = FlutterMethodChannel(name: "optimizely_flutter_sdk", binaryMessenger: messenger)
         let instance = SwiftOptimizelyFlutterSdkPlugin()
         registrar.addMethodCallDelegate(instance, channel: channel)
 
@@ -55,8 +58,12 @@ public class SwiftOptimizelyFlutterSdkPlugin: NSObject, FlutterPlugin {
     }
 
     public func detachFromEngine(for registrar: FlutterPluginRegistrar) {
+        guard registrar.messenger() === Self.attachedMessenger else {
+            return
+        }
         Self.channel?.setMethodCallHandler(nil)
         Self.channel = nil
+        Self.attachedMessenger = nil
         OptimizelyFlutterLogger.clearChannel()
     }