Companion to website#TBD. §6.0b assigns this phase two documents; both land here.
ENGAGEMENT.md gains an "As built — 5a" section: the three decisions the survey
forced, the argument for two registries rather than one, why the ternaries stayed
at the call site, and the two behaviour changes an operator will notice.
BACKEND_DESIGN.md gains the `engagement_templates` table, the two-block-registry
split, the token grammar, and the §7 note that mail is now multipart.
Co-Authored-By: Claude <noreply@anthropic.com>
