fix: ensureDaemon 自动检测并重启过期守护进程

问题: 重新构建后 IPv6 等新功能不生效,客户端仍运行旧代码。
根因: ensureDaemon() 通过 IPC socket 拨号时,若旧 daemon 进程仍在
运行(重建后未退出),GUI 会直接复用旧进程,永不启动新二进制。
日志证实旧 daemon 处理连接(init 日志无 ip6 字段),新代码从未执行。

解决方案: 新增版本握手协议,GUI 启动时查询 daemon 构建版本,
版本不匹配则自动关闭旧进程并启动新的。

- 新建 internal/version 包,GUI 与 daemon 共享同一 Version 变量,
  均通过 Makefile ldflags 注入
- IPC 新增 CmdVersion 命令,daemon 返回 version.Version;
  Response 增加 Version 字段,Client 新增 QueryVersion() 方法
- ensureDaemon() 拨号后查询版本,不匹配则发 CmdShutdown、等待
  socket 释放、重新启动 daemon;旧 daemon 不识别 CmdVersion 时
  返回错误,同样触发重启
- Makefile LDFLAGS 改为注入 lmvpn/internal/version.Version

internal/daemon/daemon.go

@@ -26,6 +26,7 @@ import (
 	"lmvpn/internal/model"
 	"lmvpn/internal/paths"
 	"lmvpn/internal/stats"
+	"lmvpn/internal/version"
 	"lmvpn/internal/vpn"
 )
 
@@ -113,6 +114,8 @@ func (d *daemon) handle(conn net.Conn, req ipc.Request) {
 			d.server.Broadcast(ipc.Event{Event: ipc.EvStats, Stats: &snap})
 		}
 		_ = ipc.WriteOK(conn)
+	case ipc.CmdVersion:
+		_ = ipc.WriteVersion(conn, version.Version)
 	default:
 		_ = ipc.WriteErr(conn, "unknown command: "+req.Cmd)
 	}

internal/ipc/ipc.go

@@ -29,6 +29,7 @@ const (
 	CmdStop     = "stop"
 	CmdShutdown = "shutdown"
 	CmdStats    = "stats"
+	CmdVersion  = "version" // query daemon build version
 )
 
 // Event types sent from daemon to GUI.
@@ -49,8 +50,8 @@ type Request struct {
 // package (which needs root-only TUN) into the GUI.
 type ClientConfig struct {
 	ServerURL   string   `json:"server_url"`
-	SNIHost     string   `json:"sni_host"`    // TLS SNI hostname for CDN
-	ServerIPs   []string `json:"server_ips"`  // CDN edge IP list for failover
+	SNIHost     string   `json:"sni_host"`   // TLS SNI hostname for CDN
+	ServerIPs   []string `json:"server_ips"` // CDN edge IP list for failover
 	Username    string   `json:"username"`
 	Password    string   `json:"password"`
 	Token       string   `json:"token"`
@@ -203,8 +204,9 @@ func (c *Client) Close() error { return c.conn.Close() }
 
 // Response is a simple ack/error reply to a command.
 type Response struct {
-	OK    bool   `json:"ok"`
-	Error string `json:"error,omitempty"`
+	OK      bool   `json:"ok"`
+	Error   string `json:"error,omitempty"`
+	Version string `json:"version,omitempty"` // set for CmdVersion replies
 }
 
 // WriteOK sends a success response to a connection.
@@ -232,6 +234,28 @@ func SendShutdown(c *Client) error {
 	return c.Send(Request{Cmd: CmdShutdown})
 }
 
+// WriteVersion sends a version response to a connection.
+func WriteVersion(conn net.Conn, ver string) error {
+	return writeMsg(conn, Response{OK: true, Version: ver})
+}
+
+// QueryVersion sends a CmdVersion request and reads the daemon's
+// build version. It must be called before any VPN session starts (so
+// no Event messages are in flight on the connection).
+func (c *Client) QueryVersion() (string, error) {
+	if err := c.Send(Request{Cmd: CmdVersion}); err != nil {
+		return "", err
+	}
+	var resp Response
+	if err := readMsg(c.r, &resp); err != nil {
+		return "", err
+	}
+	if !resp.OK {
+		return "", fmt.Errorf("version query failed: %s", resp.Error)
+	}
+	return resp.Version, nil
+}
+
 // RoutingModeFromIPC converts an IPC routing mode string to route.Mode.
 func RoutingModeFromIPC(s string) route.Mode {
 	switch s {

internal/ui/daemon.go

@@ -10,6 +10,7 @@ import (
 	"lmvpn/internal/ipc"
 	"lmvpn/internal/log"
 	"lmvpn/internal/paths"
+	"lmvpn/internal/version"
 )
 
 // ensureDaemon checks if the daemon is running and launches it (as
@@ -25,9 +26,27 @@ import (
 // The --daemon-bin flag tells daemon-launch where to find lmvpnd. If
 // not given, daemon-launch auto-detects it relative to its own path.
 func ensureDaemon() (*ipc.Client, error) {
-	// Fast path: daemon already running.
+	// Fast path: a daemon is already running. Verify its build version
+	// matches ours; if not, it's a stale process from a previous build
+	// and must be restarted so the new code takes effect.
 	if c, err := ipc.Dial(); err == nil {
-		return c, nil
+		if ver, qerr := c.QueryVersion(); qerr == nil && ver == version.Version {
+			return c, nil
+		} else {
+			log.L().Info("stale daemon detected, restarting",
+				"got", ver, "expected", version.Version, "query_err", qerr)
+			_ = ipc.SendShutdown(c)
+			c.Close()
+			// Wait for the old daemon to exit and release the socket.
+			for i := 0; i < 30; i++ {
+				time.Sleep(100 * time.Millisecond)
+				if cc, err := ipc.Dial(); err == nil {
+					cc.Close()
+				} else {
+					break // socket gone
+				}
+			}
+		}
 	}
 
 	exe, err := os.Executable()
@@ -78,7 +97,7 @@ func ensureDaemon() (*ipc.Client, error) {
 }
 
 // shellQuote wraps a string in single quotes for shell safety.
-// Embedded single quotes are escaped using the '\'' pattern.
+// Embedded single quotes are escaped using the '\” pattern.
 func shellQuote(s string) string {
 	result := "'"
 	for _, r := range s {

internal/ui/version.go

@@ -1,3 +1,7 @@
 package ui
 
-var Version = "dev"
+import "lmvpn/internal/version"
+
+// Version is the application version, sourced from the shared version
+// package so the GUI and daemon report the same string.
+var Version = version.Version

internal/version/version.go

@@ -0,0 +1,15 @@
+// Package version holds the build version string shared by the GUI
+// (lmvpn) and daemon (lmvpnd) binaries. The value is injected at link
+// time via ldflags:
+//
+//	-X lmvpn/internal/version.Version=$(VERSION)
+//
+// Both binaries are built with the same LDFLAGS, so a version mismatch
+// between the running daemon and the GUI indicates a stale daemon
+// process that predates the current build.
+package version
+
+// Version is the application version. Overridden at link time; "dev"
+// when running an untagged build (e.g. go run / go build without
+// ldflags).
+var Version = "dev"