feat(multiplayer): acknowledge supervisor shutdown

server/supervisor/supervisor.go

@@ -499,6 +499,12 @@ func (s *Supervisor) Run(ctx context.Context, drainGrace time.Duration) error {
 		drainErr = s.Drain(drainCtx)
 		drainCancel()
 	}
+	var shutdownErr error
+	if s.config.ControlPlaneURL != "" && drainErr == nil {
+		shutdownCtx, shutdownCancel := context.WithTimeout(context.Background(), 5*time.Second)
+		shutdownErr = s.acknowledgeShutdown(shutdownCtx, "server_draining")
+		shutdownCancel()
+	}
 	timer := time.NewTimer(drainGrace)
 	defer timer.Stop()
 	select {
@@ -506,6 +512,9 @@ func (s *Supervisor) Run(ctx context.Context, drainGrace time.Duration) error {
 		if drainErr != nil {
 			return fmt.Errorf("child exited after drain failure: %w", drainErr)
 		}
+		if shutdownErr != nil {
+			return fmt.Errorf("child exited after shutdown acknowledgement failure: %w", shutdownErr)
+		}
 		return err
 	case <-timer.C:
 		if s.cmd != nil && s.cmd.Process != nil {
@@ -515,6 +524,9 @@ func (s *Supervisor) Run(ctx context.Context, drainGrace time.Duration) error {
 		if drainErr != nil {
 			return fmt.Errorf("drain failed and child was force-killed: %w", drainErr)
 		}
+		if shutdownErr != nil {
+			return fmt.Errorf("shutdown acknowledgement failed and child was force-killed: %w", shutdownErr)
+		}
 		return fmt.Errorf("child force-killed after drain deadline")
 	}
 }
@@ -542,6 +554,50 @@ func (s *Supervisor) Drain(ctx context.Context) error {
 	return nil
 }
 
+// acknowledgeShutdown records the supervisor's planned termination after the
+// local game process has been told to drain. It uses the same bound workload
+// credential as registration. The idempotency key makes a repeated call safe.
+func (s *Supervisor) acknowledgeShutdown(ctx context.Context, reason string) error {
+	if s.config.ControlPlaneURL == "" {
+		return nil
+	}
+	matchID := s.matchID()
+	if matchID == "" {
+		return fmt.Errorf("shutdown acknowledgement has no match ID")
+	}
+	token, err := s.workloadToken()
+	if err != nil {
+		return err
+	}
+	body, err := json.Marshal(struct {
+		Reason string `json:"reason"`
+	}{reason})
+	if err != nil {
+		return err
+	}
+	endpoint := strings.TrimRight(s.config.ControlPlaneURL, "/") + "/v1/servers/" + url.PathEscape(s.config.ServerID) + "/shutdown"
+	request, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, bytes.NewReader(body))
+	if err != nil {
+		return err
+	}
+	request.Header.Set("Content-Type", "application/json")
+	request.Header.Set("Authorization", "Bearer "+token)
+	key := "supervisor-shutdown-" + s.config.ServerID + "-" + matchID + "-" + reason
+	if len(key) > 128 {
+		key = key[:128]
+	}
+	request.Header.Set("Idempotency-Key", key)
+	response, err := s.client.Do(request)
+	if err != nil {
+		return err
+	}
+	defer response.Body.Close()
+	if response.StatusCode/100 != 2 {
+		return fmt.Errorf("control-plane shutdown returned %s", response.Status)
+	}
+	return nil
+}
+
 func (s *Supervisor) assignedEndpoint(ctx context.Context) (int, string, error) {
 	var server GameServer
 	if err := s.sdkGet(ctx, "/gameserver", &server); err != nil {