How to make mandatory to have a main file to change the lifecycle state?

It is possible to define decision conditions within a transition in the lifecycle.

Enter the form lifecycle settings and on the transition you want to set the condition, click on the Advanced Admin access icon.

Then, in the advanced configuration area, in the "Condition" field you must enter:

fil.has_content()

You must also indicate a help text for the user in case the condition is not met. You can do this in the Condition Help text field.

Don't forget to save :)