Interface Merge Behaviour

[PascalSenn]

Currently, the composite schema specification does not support interface objects in the same way other federation implementations do. While we allow interfaces to merge, the post-validation process will fail if not all implementing types provide all required fields.

This behavior allows interfaces to span multiple services, but it introduces a significant constraint: if a field is added to the interface, all services implementing the interface must participate in the change. This limits flexibility and could lead to tight coupling across services.

How should the merging and validation of interfaces be handled in the composite schema specification?