API starts with Card CRUD w/ Hooks
Referenced but not created cards are given an entry in the DB, and flagged as 'trash' or 'missing'. Two reasons
1) it lets up keep 1-1 correspondence with Cache;
(assuming cache operation is such that not finding a card in the cache is cause to query the database, we need to keep these records in the cache. keeping them in DB preserves consistency )
2) it lets us keep records and do searches for cards that are references but not created yet.