Automatically assign Activity.id if it has no id

    activity: Activity,

    { preferSharedInbox }: { preferSharedInbox?: boolean } = {},

  ): Promise<void> {

    // TODO: Give an id to the activity if it doesn't have one.

    if (activity.id == null) {

      activity = activity.clone({

        id: new URL(`urn:uuid:${crypto.randomUUID()}`),

      });

    }

    const { keyId, privateKey } = sender;

    validateCryptoKey(privateKey, "private");

    const inboxes = extractInboxes({