Fix control pipe accept loop: create instances only after a client connects; CLI force-update never touches the service log file

cmd/gpu-turnstile/main.go

@@ -362,6 +362,10 @@ func forceUpdateCommand(configPath string, elevatedChild bool) int {
 		fmt.Fprintf(os.Stderr, "gpu-turnstile: cannot locate executable: %v\n", err)
 		return 1
 	}
+	// One-shot CLI: the updater logs to stderr, never to the service's
+	// LOG_FILE — that file is ACL'd to the service account, and a CLI run
+	// has nothing worth persisting there.
+	cfg.LogFile = ""
 	log, _, logCloser := newLogger(cfg)
 	defer logCloser.Close()
 	if cfg.AppVersion == "dev" {