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

@@ -901,7 +901,7 @@ class ConnectionHandler: ChannelInboundHandler {
             continuation.resume(throwing: errorToUse)
         }
 
-        let shouldHandleDisconnect = state.withLockedValue { $0 == .connected }
+        let shouldHandleDisconnect = state.withLockedValue { $0 != .closed && $0 != .disconnected }
         if shouldHandleDisconnect {
             handleDisconnect()
         }
@@ -923,17 +923,47 @@ class ConnectionHandler: ChannelInboundHandler {
         } else {
             logger.error("unexpected error: \(error)")
         }
+        
+        // Unified handling: use handleDisconnect for all non-closed/non-disconnected states
         let currentState = state.withLockedValue { $0 }
-        if currentState == .pending || currentState == .connecting {
+        if currentState != .closed && currentState != .disconnected {
             handleDisconnect()
-        } else if currentState == .disconnected {
-            handleReconnect()
         }
     }
 
     func handleDisconnect() {
+        // Prevent duplicate disconnect handling
+        let shouldProceed = state.withLockedValue { currentState -> Bool in
+            if currentState == .disconnected || currentState == .closed {
+                return false  // Already in disconnected/closed state
+            }
+            return true
+        }
+        
+        guard shouldProceed else {
+            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
+            cont = nil
+            return toResume
+        }) {
+            continuation.resume(throwing: NatsError.ClientError.connectionClosed)
+        }
+        
+        if let continuation = connectionEstablishedContinuation.withLockedValue({ cont in
+            let toResume = cont
+            cont = nil
+            return toResume
+        }) {
+            continuation.resume(throwing: NatsError.ClientError.connectionClosed)
+        }
+        
         // Safely clear batchBuffer first to avoid race conditions
         let bufferToRelease = self.batchBuffer
         self.batchBuffer = nil
@@ -963,12 +993,17 @@ class ConnectionHandler: ChannelInboundHandler {
                 self.handleReconnect()
             }
         } else {
-            // No channel, start reconnect immediately
+            self.fire(.disconnected)
             handleReconnect()
         }
     }
 
     func handleReconnect() {
+        // Cancel any existing reconnect task to prevent multiple concurrent reconnections
+        if let oldTask = reconnectTask {
+            oldTask.cancel()
+        }
+        
         reconnectTask = Task {
             var connected = false
             while !Task.isCancelled
@@ -984,7 +1019,7 @@ class ConnectionHandler: ChannelInboundHandler {
                 } catch {
                     logger.debug("Could not reconnect: \(error)")
                     if !Task.isCancelled {
-                        try await Task.sleep(nanoseconds: self.reconnectWait)
+                        try? await Task.sleep(nanoseconds: self.reconnectWait)
                     }
                 }
             }
@@ -998,7 +1033,7 @@ class ConnectionHandler: ChannelInboundHandler {
             // If we got here without connecting and weren't cancelled, we hit max reconnects
             if !connected {
                 logger.error("Could not reconnect; maxReconnects exceeded")
-                try await self.close()
+                try? await self.close()
                 return
             }
 
@@ -1021,6 +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 {