fix: 优化连接稳定性 - ping阈值从>2降为>1缩短断连检测窗口 - 单节点连接增加8秒超时保护防止TCP超时堆积

Sources/Nats/NatsConnection.swift

@@ -305,12 +305,31 @@ class ConnectionHandler: ChannelInboundHandler {
             }
 
             do {
-                try await connectToServer(s: s)
+                // ⭐️ 单节点连接超时保护：8秒内连不上就跳过该节点
+                // 防止 iOS 网络不可达时 TCP 超时堆积（默认30-75秒/节点）
+                try await withThrowingTaskGroup(of: Void.self) { group in
+                    group.addTask {
+                        try await self.connectToServer(s: s)
+                    }
+                    group.addTask {
+                        try await Task.sleep(nanoseconds: 8_000_000_000)
+                        throw NatsError.ConnectError.timeout
+                    }
+                    do {
+                        try await group.next()!
+                    } catch {
+                        group.cancelAll()
+                        throw error
+                    }
+                    group.cancelAll()
+                }
+            } catch is CancellationError {
+                throw CancellationError()
             } catch let error as NatsError.ConnectError {
                 if case .invalidConfig(_) = error {
                     throw error
                 }
-                logger.debug("error connecting to server: \(error)")
+                logger.debug("error connecting to server (8s timeout): \(error)")
                 lastErr = error
                 continue
             } catch {
@@ -847,7 +866,9 @@ class ConnectionHandler: ChannelInboundHandler {
     internal func sendPing(_ rttCommand: RttCommand? = nil) async {
         let pingsOut = self.outstandingPings.wrappingIncrementThenLoad(
             ordering: AtomicUpdateOrdering.relaxed)
-        if pingsOut > 2 {
+        if pingsOut > 1 {
+            // ⭐️ 从 > 2 改为 > 1：缩短断连检测窗口
+            // 原杣2次ping无响应(~20秒)即判定断连，加快用户感知
             handleDisconnect()
             return
         }