Guidelines for proactive vs reactive event definitions in openedx-events

The Open edX platform includes many types of events, and this post is specifically addressing event signals in this repo. These are mainly used for plugins within a service, or to put on the event bus for cross-service communication.

Most of my experience from the event bus work has been with what I'll call "reactive event definitions", which are signal events that were added once a known consumer needed the event. It is possible that some of the earlier events were implemented more proactively, where we weren't sure when and if there would be a consumer, but were making the events available just in case.

A question has arisen as to whether we should proactively be publishing create/update/delete events for all key models as part of their public API, and I'm wondering what others think.

No files, tests, or entry points are identified in the issue. Read the discussion and existing openedx-events event definitions first, then establish whether proactive and reactive events need documented guidelines; done means the project has an agreed, written policy.