what still doesn't work is highlighted with // TODO in the code:
[x] actual mail sending, see EmailHelper.php. (i think that's related to my local email server though)
[ ] mail notification if agent filter matches new cat: page url generation for the created cat, unsubscribe token generation and actual email sending is missing. see GridFieldStatusChangeButton
you can reproduce the scenario the following way:
go to "Katzensuche" and filter for e.g. black cats
click on "Benachrichtigungen aktivieren" and provide a mail address
click on "Katze melden" and create a new entry (make sure it matches the filter you configured, e.g. black cats)
go to the admin menu, to pages, "Vermisst und gefunden"->"Katze melden" and view form submissions
click on the one with "status: neu", and scroll down until you see the accept/decline/review buttons
click the accept button and GridFieldStatusChangeButton.createCat should be called
A search agent for a specific search with email notifications would be nice