Problem
When a mentor uses Special:ClaimMentee to claim a mentee, the mentee will receive a notification about the change. The user's past mentor, however, isn't informed about that change. If someone misuses the claim mentee feature, it might go easily unnoticed. Especially since the claim mentee feature will become more advertised through GrowthExperiments-MentorDashboard, something should be done to make abuse noticeable.
Solution
If the claim mentee feature changes a mentor, inform the previous mentor about the change via a notification. The notification should be opt-out for the mentor.
The code should make to easy to suppres the notification for a given mentor change. This is important to support T280307: Mentor dashboard: M2 mentor tools/settings, which will basically do a batch of mentor changes if a mentor decides to quit mentoring.





