SyncSource
Brings a source up to date with the warehouse: its table's uuid and columns, and for a table the Wow Sink describes, the wow_catalog row the trust rules adopt. The catalog sends it when it sees the table or its wow_catalog rows change; it creates the Wow source of a table it does not know yet, and changes nothing for a table that is neither known nor trusted. Only the catalog's watcher sends it: internal.