Module development and code questions

This is really about Layout Builder and layouts that are defined by a module. In this case I'm using Layout Discovery to make this example simple.

So I am building a page using Layout Builder and I have selected a layout (provided by the Layout Discovery module) for a section. Now I'd like to add a field to the layouts configuration form (the form where I can select column widths and set administrative title). Maybe I'd like to add something like a background color picker or a text field for an extra class or whatever. 

Hi there,

I am new to drupal module development.
Please forgive me if the question is too simple.

This question is two fold:
First about strategy: am I going in the right direction?
Second about how to do it... 

I am new to drupal 8 php unit test. I have written a custom service that will take user id and gives an array of user details. I have tried to unit test this function but getting error on $user->get() function.

Here is my module/custom/common/src/CommonService.php

I created a custom module based on the Drupal 8 Message mold.

This module creates a message when a comment is created. It's perfect.

Now I want the module to create a message when a node is flagged. I started a code but it doesn't work.

https://www.drupal.org/project/flag

How can I do this ?

https://www.drupal.org/project/message

message_activity_stream.info.yml :

I wrote a new back-end to process my queues (to delay items upon retrying). It works when I manually trigger the queue processing, but when the cron runs the corresponding QueueWorker it does not use my back-end but the default one.