In attempting to get the json viewer to run with the SQL object store, discovered that it makes the wrong call to the AdapterManager and so fails to load objects via its OID.
Exploring further, realized that the SqlOid impl does include the relevant information to call the right API of AdapterManager / PersistenceSession, namely that the className (=> objectSpec) is also included.
This change is therefore to introduce a new subtype of Oid, namely OidWithSpecification, that is a self-contained Oid, and have the json viewer depend only on object stores that support OidWithSpecification. (Note: it isn't practicable to do what the html and scimpi viewers do, which is to cache the spec per Oid in session state, since the idea is that the json viewer is entirely stateless).
Also retrofit SqlOid to implement this new interface.