The store now journals the documents_v2 fields, previews without
journaling, files the issued copy and locks invoicing.first_number once a
number exists. This records the departures: the store's create commands
keep their signatures and delegate to _with variants, the issued-copy call
takes the create's arguments expanded (the store has no params struct),
schema 16 adds the document columns only (the projection has no parties
table), the over-the-wire document cut-over entry waits for S4.4, and a
refusal leaves the journal unchanged while a storage failure between the
invoice's lines and its attachment's is not rolled back.