Bugzilla handled mid-air-collisions by presenting the user with an in-between step showing the changes that happened while you were editing, and what the proposed edit result is. The user can accept this, or go back and re-apply their change manually to the latest state of the bug.

On https://phabricator.wikimedia.org/T78607 I supposedly removed user "Ciencia_Al_Poder" from the subscribers list. When really all I did was modify the description and save the task.