diff --git a/app-stream-network/app-stream-network-ws/pom.xml b/app-stream-network/app-stream-network-ws/pom.xml
index b045dae..48dd5e5 100644
--- a/app-stream-network/app-stream-network-ws/pom.xml
+++ b/app-stream-network/app-stream-network-ws/pom.xml
@@ -30,5 +30,10 @@
             <groupId>io.netty</groupId>
             <artifactId>netty-handler-proxy</artifactId>
         </dependency>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 </project>
diff --git a/app-stream-network/app-stream-network-ws/src/main/java/com/dingtalk/open/app/stream/network/ws/KeepAliveHandler.java b/app-stream-network/app-stream-network-ws/src/main/java/com/dingtalk/open/app/stream/network/ws/KeepAliveHandler.java
index b2fa344..5f8b81a 100644
--- a/app-stream-network/app-stream-network-ws/src/main/java/com/dingtalk/open/app/stream/network/ws/KeepAliveHandler.java
+++ b/app-stream-network/app-stream-network-ws/src/main/java/com/dingtalk/open/app/stream/network/ws/KeepAliveHandler.java
@@ -31,8 +31,8 @@
 public class KeepAliveHandler extends SimpleChannelInboundHandler<PongWebSocketFrame> {
     private static final InternalLogger LOGGER = InternalLoggerFactory.getLogger(KeepAliveHandler.class);
     private final Duration timeout;
-    private final  static HashedWheelTimer TIMER = new HashedWheelTimer();
-    private Channel channel;
+    private final static HashedWheelTimer TIMER = new HashedWheelTimer();
+    private volatile Channel channel;
     private final Map<String, Timeout> timeouts;
     private final AtomicBoolean active;
 
@@ -52,7 +52,15 @@ public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exc
         }
 
         if (evt instanceof IdleStateEvent) {
-            channel.eventLoop().execute(new PingTask());
+            // IdleStateHandler starts counting after TCP connect, before WS handshake.
+            // Never touch the channel field until handshake completes, otherwise NPE:
+            // connection operation failed (KeepAliveHandler.java:56)
+            if (active.get()) {
+                final Channel ch = channel != null ? channel : ctx.channel();
+                if (ch != null && ch.isActive()) {
+                    ch.eventLoop().execute(new PingTask(ch));
+                }
+            }
         }
         super.userEventTriggered(ctx, evt);
     }
@@ -69,6 +77,8 @@ protected void channelRead0(ChannelHandlerContext ctx, PongWebSocketFrame msg) t
 
     @Override
     public void channelInactive(ChannelHandlerContext ctx) throws Exception {
+        active.set(false);
+        channel = null;
         shutdown();
         super.channelInactive(ctx);
     }
@@ -84,24 +94,33 @@ private void shutdown() {
     }
 
     private class PingTask implements Runnable {
+        private final Channel target;
+
+        private PingTask(Channel target) {
+            this.target = target;
+        }
+
         @Override
         public void run() {
+            if (target == null || !target.isActive()) {
+                return;
+            }
             if (!timeouts.isEmpty()) {
                 return;
             }
             final String seq = UUID.randomUUID().toString();
             ByteBuf byteBuf = Unpooled.copiedBuffer(seq.getBytes());
             PingWebSocketFrame frame = new PingWebSocketFrame(byteBuf);
-            channel.writeAndFlush(frame).addListener(future -> {
+            target.writeAndFlush(frame).addListener(future -> {
                 if (future.isSuccess()) {
                     Timeout pingTimeout = TIMER.newTimeout(timeout -> {
                         LOGGER.warn("[DingTalk] connection ping timeout, channel is closing");
                         timeouts.remove(seq);
-                        channel.close();
+                        target.close();
                     }, timeout.toMillis(), TimeUnit.MILLISECONDS);
                     timeouts.put(seq, pingTimeout);
                 } else {
-                    channel.close();
+                    target.close();
                 }
             });
         }
diff --git a/app-stream-network/app-stream-network-ws/src/main/java/com/dingtalk/open/app/stream/network/ws/NettyClientHandler.java b/app-stream-network/app-stream-network-ws/src/main/java/com/dingtalk/open/app/stream/network/ws/NettyClientHandler.java
index c3a2dbb..71c7812 100644
--- a/app-stream-network/app-stream-network-ws/src/main/java/com/dingtalk/open/app/stream/network/ws/NettyClientHandler.java
+++ b/app-stream-network/app-stream-network-ws/src/main/java/com/dingtalk/open/app/stream/network/ws/NettyClientHandler.java
@@ -53,5 +53,9 @@ public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws E
         } else {
             LOGGER.error("[DingTalk] connection operation failed, connectionId={}", connectionId, cause);
         }
+        // Close the channel so session pool can reconnect instead of leaving a half-dead connection.
+        if (ctx != null && ctx.channel() != null && ctx.channel().isActive()) {
+            ctx.close();
+        }
     }
 }
diff --git a/app-stream-network/app-stream-network-ws/src/test/java/com/dingtalk/open/app/stream/network/ws/KeepAliveHandlerTest.java b/app-stream-network/app-stream-network-ws/src/test/java/com/dingtalk/open/app/stream/network/ws/KeepAliveHandlerTest.java
new file mode 100644
index 0000000..f444c67
--- /dev/null
+++ b/app-stream-network/app-stream-network-ws/src/test/java/com/dingtalk/open/app/stream/network/ws/KeepAliveHandlerTest.java
@@ -0,0 +1,45 @@
+package com.dingtalk.open.app.stream.network.ws;
+
+import io.netty.channel.embedded.EmbeddedChannel;
+import io.netty.handler.codec.http.websocketx.WebSocketClientProtocolHandler;
+import io.netty.handler.timeout.IdleStateEvent;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.time.Duration;
+
+/**
+ * Regression for Aone 84622857 / customer logs:
+ * IdleStateEvent before WS handshake must not NPE in KeepAliveHandler.
+ */
+public class KeepAliveHandlerTest {
+
+    @Test
+    public void idleBeforeHandshakeDoesNotThrow() {
+        KeepAliveHandler handler = new KeepAliveHandler(Duration.ofSeconds(5));
+        EmbeddedChannel channel = new EmbeddedChannel(handler);
+        try {
+            // Multiple idle events before handshake — reproduces Aone 84622857 NPE path.
+            channel.pipeline().fireUserEventTriggered(IdleStateEvent.FIRST_READER_IDLE_STATE_EVENT);
+            channel.pipeline().fireUserEventTriggered(IdleStateEvent.READER_IDLE_STATE_EVENT);
+            channel.pipeline().fireUserEventTriggered(IdleStateEvent.WRITER_IDLE_STATE_EVENT);
+            Assert.assertTrue(channel.isActive());
+        } finally {
+            channel.finishAndReleaseAll();
+        }
+    }
+
+    @Test
+    public void idleAfterHandshakeDoesNotThrow() {
+        KeepAliveHandler handler = new KeepAliveHandler(Duration.ofSeconds(5));
+        EmbeddedChannel channel = new EmbeddedChannel(handler);
+        try {
+            channel.pipeline().fireUserEventTriggered(
+                    WebSocketClientProtocolHandler.ClientHandshakeStateEvent.HANDSHAKE_COMPLETE);
+            channel.pipeline().fireUserEventTriggered(IdleStateEvent.FIRST_READER_IDLE_STATE_EVENT);
+            Assert.assertTrue(channel.isActive());
+        } finally {
+            channel.finishAndReleaseAll();
+        }
+    }
+}
diff --git a/app-stream-network/app-stream-network-ws/src/test/java/com/dingtalk/open/app/stream/network/ws/NettyClientHandlerTest.java b/app-stream-network/app-stream-network-ws/src/test/java/com/dingtalk/open/app/stream/network/ws/NettyClientHandlerTest.java
new file mode 100644
index 0000000..b93777b
--- /dev/null
+++ b/app-stream-network/app-stream-network-ws/src/test/java/com/dingtalk/open/app/stream/network/ws/NettyClientHandlerTest.java
@@ -0,0 +1,40 @@
+package com.dingtalk.open.app.stream.network.ws;
+
+import com.dingtalk.open.app.stream.network.api.ClientConnectionListener;
+import com.dingtalk.open.app.stream.network.api.Context;
+import io.netty.channel.embedded.EmbeddedChannel;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+
+/**
+ * Ensure exceptionCaught closes the channel so session pool can reconnect.
+ */
+public class NettyClientHandlerTest {
+
+    @Test
+    public void exceptionCaughtClosesActiveChannel() {
+        final AtomicBoolean disconnected = new AtomicBoolean(false);
+        NettyClientHandler handler = new NettyClientHandler("conn-test", new ClientConnectionListener() {
+            @Override
+            public void receive(Context context) {
+            }
+
+            @Override
+            public void onDisConnection(String connectionId) {
+                disconnected.set(true);
+            }
+        });
+
+        EmbeddedChannel channel = new EmbeddedChannel(handler);
+        Assert.assertTrue(channel.isActive());
+        channel.pipeline().fireExceptionCaught(new RuntimeException("simulated io failure"));
+
+        // EmbeddedChannel closes synchronously on close()
+        Assert.assertFalse("channel should be closed after exceptionCaught", channel.isActive());
+        // channelInactive should notify listener
+        Assert.assertTrue("onDisConnection should be triggered", disconnected.get());
+        channel.finishAndReleaseAll();
+    }
+}