fix: 连接状态判定修复 — 收到首个数据包后才标记已连接，CONNECTING 5秒超时回退

- ProtocolClient: 仅收到首个有效数据包后设置 CONNECTED，不再 socket 创建后立即标记
- ProtocolClient: timeoutCheckLoop 在 connect() 中立即启动，覆盖 CONNECTING(5s) 和 CONNECTED(3s)
- RobotConnection: 允许 CONNECTING → TIMEOUT 合法转换
- MainScreen: CONNECTING 时点击连接按钮仅断开回到 DISCONNECTED，不再自动重连

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

app/src/main/java/com/example/m20_gamepad/network/ProtocolClient.kt

@@ -89,9 +89,10 @@ class ProtocolClient(
     /**
      * 建立连接：
      * 1. 创建 UDP socket
-     * 2. 启动接收协程
+     * 2. 启动接收/发送协程
      * 3. 发送订阅请求
-     * 4. 启动心跳和断线检测
+     * 4. 启动断线检测（CONNECTING 5s / CONNECTED 3s 无数据 → TIMEOUT）
+     * 5. 首次收到有效数据包后标记已连接，并启动心跳 1Hz（在接收循环中处理）
      */
     fun connect() {
         if (_state.value != State.DISCONNECTED && _state.value != State.ERROR) return
@@ -131,14 +132,7 @@ class ProtocolClient(
             // 发送订阅请求（触发服务端 UDP 推送）
             sendSubscriptionRequests()
 
-            _state.value = State.CONNECTED
-
-            // 启动心跳
-            heartbeatJob = scope.launch(Dispatchers.IO) {
-                heartbeatLoop(sock, address)
-            }
-
-            // 启动断线检测
+            // 启动断线检测（立即开始，覆盖 CONNECTING 和 CONNECTED 状态）
             timeoutJob = scope.launch {
                 timeoutCheckLoop()
             }
@@ -232,6 +226,14 @@ class ProtocolClient(
                 if (report != null) {
                     _statusReport.tryEmit(report)
                 }
+
+                // 首次收到有效数据包：标记已连接，启动心跳
+                if (_state.value == State.CONNECTING) {
+                    _state.value = State.CONNECTED
+                    heartbeatJob = scope.launch(Dispatchers.IO) {
+                        heartbeatLoop(sock, remoteAddress!!)
+                    }
+                }
             } catch (_: SocketTimeoutException) {
                 // 超时正常，继续循环
                 continue
@@ -258,12 +260,22 @@ class ProtocolClient(
         }
     }
 
-    /** 断线检测：3 秒无数据 → 标记 TIMEOUT */
+    /** 断线检测：CONNECTED 状态 3 秒无数据 → TIMEOUT；CONNECTING 状态 5 秒无数据 → TIMEOUT */
     private suspend fun CoroutineScope.timeoutCheckLoop() {
         while (isActive && _state.value != State.DISCONNECTED) {
             val elapsed = System.currentTimeMillis() - lastPacketTimeMs
-            if (elapsed > 3000 && _state.value == State.CONNECTED) {
-                _state.value = State.TIMEOUT
+            when (_state.value) {
+                State.CONNECTED -> {
+                    if (elapsed > 3000) {
+                        _state.value = State.TIMEOUT
+                    }
+                }
+                State.CONNECTING -> {
+                    if (elapsed > 5000) {
+                        _state.value = State.TIMEOUT
+                    }
+                }
+                else -> { /* DISCONNECTED/TIMEOUT/ERROR: 无需超时处理 */ }
             }
             delay(500)
         }

app/src/main/java/com/example/m20_gamepad/service/RobotConnection.kt

@@ -50,6 +50,7 @@ class RobotConnection {
             ProtocolClient.State.CONNECTING ->
                 to == ProtocolClient.State.CONNECTED ||
                 to == ProtocolClient.State.ERROR ||
+                to == ProtocolClient.State.TIMEOUT ||
                 to == ProtocolClient.State.DISCONNECTED
             ProtocolClient.State.CONNECTED ->
                 to == ProtocolClient.State.TIMEOUT ||

app/src/main/java/com/example/m20_gamepad/ui/MainScreen.kt

@@ -172,7 +172,9 @@ fun MainScreen(
             onStatusClick = { statusPanelVisible = true },
             onSettingsClick = onSettingsClick,
             onConnectToggle = {
-                if (connectionState == ProtocolClient.State.CONNECTED) {
+                if (connectionState == ProtocolClient.State.CONNECTED ||
+                    connectionState == ProtocolClient.State.CONNECTING
+                ) {
                     viewModel.disconnect()
                 } else {
                     viewModel.connect()