Add trigger condition "action - closed"

We’re sending “your ticket has been closed” mails to our customers. Naturally we use the condition State - closed but this applies for every update inside a closed ticket since you can’t set a condition like Action - closed (there’s only created or changed available atm).

That’s a problem because some agents tend to close their tickets before putting every needed information in it. That creates a lot of those mails thus spamming the customer.

Current workaround including more problems
What where doing currently as a workaround is adding another condition:
Closed time - 1 minute ago

That way when 1 minute has passed after closing the ticket no more mails will be sent.
It works but it’s kinda quick & dirty + it creates another problem:

Opening a already closed ticket doesn’t seem to null the closed time so no more mail will be sent when the ticket is closed again.

Adding a Action - closed condition would handle all those problems and it should be relatively easy to implement because you just need to check for one thing:
Did the state change from ANY state except closed to closed?