Detect "Agent" or "Ticket" collision

Detect and alert when two or more people are responding to the same ticket at the same time. At a minimum, when someone uses the "Click here to reply" button, alert them if someone else has already initiated a response but not yet submitted it. Ideally, show a real-time status of who's looking at the ticket, entering a reply, entering a note, or updating the ticket in any way.

Examples from other help desk systems: http://freshdesk.com/scaling-support/agent-collision-detection
https://blog.uservoice.com/helpdesk-collision-detection/