Close UART gracefully on SIGINT/SIGTERM in goTool.

Go exits on Ctrl+C without running defers, leaving the serial port locked; register shutdown hooks for serve and CLI commands.

Co-authored-by: Cursor <cursoragent@cursor.com>

goTool/shutdown.go

@@ -0,0 +1,75 @@
+package main
+
+import (
+	"context"
+	"log"
+	"net/http"
+	"os"
+	"os/signal"
+	"sync"
+	"syscall"
+	"time"
+)
+
+var (
+	shutdownMu   sync.Mutex
+	shutdownFns  []func()
+	hooksOnce    sync.Once
+	bgHandlerOnce sync.Once
+)
+
+// registerShutdown runs fn on SIGINT/SIGTERM (LIFO order).
+func registerShutdown(fn func()) {
+	shutdownMu.Lock()
+	shutdownFns = append(shutdownFns, fn)
+	shutdownMu.Unlock()
+}
+
+func runShutdownHooks() {
+	hooksOnce.Do(func() {
+		shutdownMu.Lock()
+		fns := shutdownFns
+		shutdownMu.Unlock()
+		for i := len(fns) - 1; i >= 0; i-- {
+			fns[i]()
+		}
+	})
+}
+
+// enableShutdownOnInterrupt listens for SIGINT/SIGTERM in the background and exits
+// after running shutdown hooks. Use for one-shot CLI commands (OTA, etc.).
+func enableShutdownOnInterrupt() {
+	bgHandlerOnce.Do(func() {
+		ch := make(chan os.Signal, 1)
+		signal.Notify(ch, os.Interrupt, syscall.SIGTERM)
+		go func() {
+			sig := <-ch
+			signal.Stop(ch)
+			log.Printf("received %v, shutting down…", sig)
+			runShutdownHooks()
+			os.Exit(0)
+		}()
+	})
+}
+
+// waitForShutdown blocks until SIGINT/SIGTERM, runs hooks, and returns.
+// Use for long-running servers (serve/dashboard).
+func waitForShutdown() {
+	ch := make(chan os.Signal, 1)
+	signal.Notify(ch, os.Interrupt, syscall.SIGTERM)
+	sig := <-ch
+	signal.Stop(ch)
+	log.Printf("received %v, shutting down…", sig)
+	runShutdownHooks()
+}
+
+func shutdownHTTPServer(srv *http.Server) {
+	if srv == nil {
+		return
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+	if err := srv.Shutdown(ctx); err != nil {
+		log.Printf("HTTP shutdown: %v", err)
+	}
+}