weblocks update widget from a new thread issue

thr-update.lisp

#|
UPDATE: use a websocket https://github.com/40ants/weblocks-websocket
because the response to the request was already sent so the thread has no way to communicate an update to the browser:
https://github.com/40ants/weblocks/issues/54
How to make the button "Add random task (with (update) called from a different thread)" work? Pressing on it results in this error:

Session was not created for this request!
   [Condition of type SIMPLE-ERROR]
|#
(ql:quickload '(:weblocks :weblocks-ui :find-port))
(defpackage todo
           (:use #:cl
                 #:weblocks-ui/form
                 #:weblocks/html)
           (:import-from #:weblocks/widget
                    #:render
                    #:update
                    #:defwidget)
           (:import-from #:weblocks/actions
                    #:make-js-action)
           (:import-from #:weblocks/app
                    #:defapp))
(in-package todo)

(defapp tasks)

(defapp tasks
         :prefix "/")

(weblocks/debug:on)

(defparameter *port* 4001)

(defmethod weblocks/session:init ((app tasks))
            "Hello world!")
(defwidget task ()
        ((title
          :initarg :title
          :accessor title)
         (done
          :initarg :done
          :initform nil
          :accessor done)))

(defun make-task (title &key done)
        (make-instance 'task :title title :done done))

(defwidget task-list ()
        ((tasks
          :initarg :tasks
          :accessor tasks)))

(defmethod render ((task task))
        "Render a task."
        (with-html
              (:span (if (done task)
                         (with-html
                               (:s (title task)))
                       (title task)))))

(defmethod render ((widget task-list))
        "Render a list of tasks."
        (with-html
              (:h1 "Tasks")
              (:ul
                (loop for task in (tasks widget) do
                      (:li (render task))))))

(defun make-task-list (&rest rest)
        (let ((tasks (loop for title in rest
                        collect (make-task title))))
          (make-instance 'task-list :tasks tasks)))

(defmethod add-task ((task-list task-list) title)
        (push (make-task title)
              (tasks task-list)))

(defmethod render ((task-list task-list))
        (with-html
          (:h1 "Tasks")
	  (:input :type "button" :value "Add random task (normal)" :onclick
		  (weblocks/actions:make-js-action
		   (lambda (&rest args)
		     (add-task task-list (format nil "~A" (random 1001)))
		     (update task-list))))
          (:input :type "button" :value "Add random task (with (update) called from a different thread)" :onclick
		  (weblocks/actions:make-js-action
		   (lambda (&rest args )
		     (add-task task-list (format nil "~A" (random 1001)))
		     (bt:make-thread
		      (lambda ()
			(weblocks/dependencies:with-collected-dependencies 
			  (sleep 0.5)
			  (update task-list) ; ERROR: Session was not created for this request!
			  ))))))
	  (loop for task in (tasks task-list) do
            (render task))
	  (with-html-form (:POST (lambda (&key title &allow-other-keys)
                                         (add-task task-list title)))
            (:input :type "text"
                    :name "title"
                    :placeholder "Task's title")
            (:input :type "submit"
                    :value "Add"))))

(defparameter *task-list* (make-task-list "Make my first Weblocks app"
                         "Deploy it somewhere"
                         "Have a profit"))

(defmethod weblocks/session:init ((app tasks))
         (declare (ignorable app))
         *task-list*)

(weblocks/debug:reset-latest-session)

;(weblocks/server:start :port *port*)