Online Presence

It could be useful automatically determining who is online at a given point in time.

One use would be only showing online player characters in the character list by default and showing offline characters only when requested. This would make people not present for a session a little out of the way to avoid confusion.

Firestore does not automatically support this, but there is a guide for setting it up by using a combination of Realtime Database and Cloud Functions. We should explore its costs and how much effort is required to link it up.

Review the Firestore, Realtime Database, and Cloud Functions approach described in the issue, then investigate its expected costs and integration effort. Done means documenting whether the approach is viable and how it would support filtering online and offline player characters.

Written by the indexing model from the issue text.