fix: use deferred mutex unlocks for panic safety

Convert HandleStore.Put and Get to use defer mu.Unlock().
Wrap sendMu-protected stream.Send calls in closures with deferred
unlock to prevent mutex leaks if Send panics.

HandleStore.Release intentionally unlocks before DeleteGlobalRef
to avoid holding the mutex during JNI work — left as-is with comment.

Author: xaionaro@dx.center

grpc/server/jni_raw/proxy_stream.go

@@ -114,9 +114,12 @@ func (s *Server) Proxy(stream pb.JNIService_ProxyServer) error {
 			pendingMu.Unlock()
 		}
 
-		sendMu.Lock()
-		sendErr := stream.Send(event)
-		sendMu.Unlock()
+		var sendErr error
+		func() {
+			sendMu.Lock()
+			defer sendMu.Unlock()
+			sendErr = stream.Send(event)
+		}()
 		if sendErr != nil {
 			if ch != nil {
 				pendingMu.Lock()
@@ -311,15 +314,17 @@ func (s *Server) Proxy(stream pb.JNIService_ProxyServer) error {
 	// 7. proxyHandle was set inside the VM.Do callbacks above (local JNI
 	// refs are thread-local — must be stored before VM.Do returns).
 
-	sendMu.Lock()
-	err = stream.Send(&pb.ProxyServerMessage{
-		Msg: &pb.ProxyServerMessage_Created{
-			Created: &pb.CreateProxyResponse{
-				ProxyHandle: proxyHandle,
+	err = func() error {
+		sendMu.Lock()
+		defer sendMu.Unlock()
+		return stream.Send(&pb.ProxyServerMessage{
+			Msg: &pb.ProxyServerMessage_Created{
+				Created: &pb.CreateProxyResponse{
+					ProxyHandle: proxyHandle,
+				},
 			},
-		},
-	})
-	sendMu.Unlock()
+		})
+	}()
 	if err != nil {
 		return err
 	}

handlestore/handlestore.go

@@ -39,8 +39,8 @@ func (s *HandleStore) Put(env *jni.Env, obj *jni.Object) int64 {
 	globalRef := env.NewGlobalRef(obj)
 	id := s.nextID.Add(1)
 	s.mu.Lock()
+	defer s.mu.Unlock()
 	s.objects[id] = globalRef
-	s.mu.Unlock()
 	return id
 }
 
@@ -51,9 +51,8 @@ func (s *HandleStore) Get(handle int64) *jni.Object {
 		return nil
 	}
 	s.mu.RLock()
-	obj := s.objects[handle]
-	s.mu.RUnlock()
-	return obj
+	defer s.mu.RUnlock()
+	return s.objects[handle]
 }
 
 // Release deletes the JNI global reference for the given handle and removes
@@ -68,7 +67,7 @@ func (s *HandleStore) Release(env *jni.Env, handle int64) {
 	if ok {
 		delete(s.objects, handle)
 	}
-	s.mu.Unlock()
+	s.mu.Unlock() // Unlock before JNI call to avoid holding the mutex during DeleteGlobalRef.
 	if ok {
 		env.DeleteGlobalRef(obj)
 	}