Fix command delivery: close dead sockets on write error, use cmd.exe for power commands

agent/client/commands_unix.go

@@ -3,10 +3,29 @@
 package client
 
 import (
+	"fmt"
 	"os/exec"
 	"strings"
 )
 
+// execPowerCommand runs shutdown or reboot on Unix/Linux/macOS.
+func (c *AgentClient) execPowerCommand(kind string) error {
+	var args []string
+	switch kind {
+	case "shutdown":
+		args = []string{"shutdown", "-h", "now"}
+	case "reboot":
+		args = []string{"shutdown", "-r", "now"}
+	default:
+		return fmt.Errorf("unknown power command: %s", kind)
+	}
+	out, err := exec.Command(args[0], args[1:]...).CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("%w: %s", err, strings.TrimSpace(string(out)))
+	}
+	return nil
+}
+
 func (c *AgentClient) platformRecon(action, command string) (handled bool, success bool, message string) {
 	var out []byte
 	var err error