convert systemd unit to Type=notify and report readiness

internal/daemon/daemon.go

@@ -3,6 +3,7 @@ package daemon
 import (
 	"context"
 	"fmt"
+	systemd "github.com/coreos/go-systemd/daemon"
 	"log/slog"
 	"uncloud/internal/machine"
 )
@@ -27,5 +28,18 @@ func New(dataDir string) (*Daemon, error) {
 
 func (d *Daemon) Run(ctx context.Context) error {
 	slog.Info("Starting machine.")
+
+	// Notify systemd that the daemon is ready when the machine is started.
+	go func() {
+		select {
+		case <-d.machine.Started():
+			_, err := systemd.SdNotify(false, systemd.SdNotifyReady)
+			if err != nil {
+				slog.Error("Failed to notify systemd that the daemon is ready.", "error", err)
+			}
+		case <-ctx.Done():
+		}
+	}()
+
 	return d.machine.Run(ctx)
 }