fix: Fixed agent msi update command

agent/internal/sync/sync.go

@@ -412,13 +412,55 @@ func handleUpdateAgentWindows(cmd *pb.ServerCommand) {
 	}
 
 	logPath := filepath.Join(os.TempDir(), "vantage-agent-msi.log")
-	log.Printf("launching msiexec for upgrade to v%s (cmd=%s)", u.Version, cmd.CommandId)
 
-	up := exec.Command("cmd", "/c", "start", "", "/wait", "msiexec", "/i", msiPath, "/qn", "/norestart", "/l*v", logPath)
-	if err := up.Start(); err != nil {
+	// The MSI stops the vantage-agent service as part of the upgrade. Anything
+	// descended from this process is killed with it, so msiexec must not be a
+	// child: run it from a scheduled task, which is parented to the Task
+	// Scheduler service instead.
+	if err := launchDetachedUpdate(msiPath, logPath, cmd.CommandId); err != nil {
 		log.Printf("failed to launch msiexec (cmd=%s): %v", cmd.CommandId, err)
 		return
 	}
+	log.Printf("scheduled msiexec for upgrade to v%s (cmd=%s)", u.Version, cmd.CommandId)
+}
+
+const updateTaskName = "VantageAgentUpdate"
+
+func launchDetachedUpdate(msiPath, logPath, commandID string) error {
+	scriptPath := filepath.Join(os.TempDir(), "vantage-agent-update.cmd")
+	script := fmt.Sprintf("@echo off\r\n"+
+		"timeout /t 5 /nobreak >nul\r\n"+
+		"msiexec /i \"%s\" /qn /norestart /l*v \"%s\"\r\n"+
+		"schtasks /delete /tn %s /f >nul 2>&1\r\n"+
+		"del /f /q \"%s\" >nul 2>&1\r\n"+
+		"(goto) 2>nul & del /f /q \"%%~f0\"\r\n",
+		msiPath, logPath, updateTaskName, msiPath)
+	if err := os.WriteFile(scriptPath, []byte(script), 0o600); err != nil {
+		return fmt.Errorf("write update script: %w", err)
+	}
+
+	// Stale task from a previous attempt would make /create fail even with /f
+	// if it is still running, so tear it down first and ignore the result.
+	exec.Command("schtasks", "/end", "/tn", updateTaskName).Run()
+	exec.Command("schtasks", "/delete", "/tn", updateTaskName, "/f").Run()
+
+	create := exec.Command("schtasks", "/create",
+		"/tn", updateTaskName,
+		"/tr", `"`+scriptPath+`"`,
+		"/sc", "once",
+		// Already in the past: the task never fires on its own, only via /run.
+		"/st", "00:00",
+		"/ru", "SYSTEM",
+		"/rl", "HIGHEST",
+		"/f")
+	if out, err := create.CombinedOutput(); err != nil {
+		return fmt.Errorf("schtasks create: %v: %s", err, strings.TrimSpace(string(out)))
+	}
+
+	if out, err := exec.Command("schtasks", "/run", "/tn", updateTaskName).CombinedOutput(); err != nil {
+		return fmt.Errorf("schtasks run: %v: %s", err, strings.TrimSpace(string(out)))
+	}
+	return nil
 }
 
 func downloadFile(url, dest string) error {