fix: write操作在batchBuffer为nil时也触发重连

- 解决"假连接"边界情况：状态为connected但batchBuffer为nil
- 确保发送消息失败后能自动恢复连接

Sources/Nats/NatsConnection.swift

@@ -937,7 +937,6 @@ class ConnectionHandler: ChannelInboundHandler {
             if currentState == .disconnected || currentState == .closed {
                 return false  // Already in disconnected/closed state
             }
-            $0 = .disconnected
             return true
         }
         
@@ -945,6 +944,9 @@ class ConnectionHandler: ChannelInboundHandler {
             return
         }
         
+        // Set state to disconnected after check
+        state.withLockedValue { $0 = .disconnected }
+        
         // Clean up pending continuations to prevent leaks
         if let continuation = serverInfoContinuation.withLockedValue({ cont in
             let toResume = cont
@@ -1054,6 +1056,13 @@ class ConnectionHandler: ChannelInboundHandler {
 
     func write(operation: ClientOp) async throws {
         guard let buffer = self.batchBuffer else {
+            // If state is connected but batchBuffer is nil, this is a "fake connection" state
+            // Trigger reconnect to recover
+            let currentState = state.withLockedValue { $0 }
+            if currentState == .connected {
+                logger.error("Write failed: batchBuffer is nil but state is connected, triggering reconnect")
+                handleDisconnect()
+            }
             throw NatsError.ClientError.invalidConnection("not connected")
         }
         do {