Modern applications use "edges" to store most relationships between objects (like members of a project, or reviewers for a revision). Calendar does not have the edge tables on its application database yet, so it can't write any edges.
Edges are the best way to store relationships like "user X invited to event E", and adding storage is a prerequisite for implementing other core interfaces like Subscriptions and Tokens.
- Add the edge tables.
- Add related infrastructure.