Reject revision-state network/5xx and missing ledger on controlled
hydrate; never PATCH 0:0 unless the document is freeform.
Co-authored-by: Cursor <cursoragent@cursor.com>
Retain ledger author/reviewer/approver, fail-closed unknown users to
viewer, and send the opened revision ETag instead of a fresh GET.
Co-authored-by: Cursor <cursoragent@cursor.com>