# Domain 9 — Messaging (Ticket System)

[← Database Model](index.md)

### `tickets` / `ticket_participants` / `ticket_messages` [CORE]
**Role:** All post-booking communication, admin-readable, with no direct nurse↔customer channel. **Why intentionally constrained:** it protects vulnerable patients, creates dispute evidence, and prevents disintermediation (families and nurses pairing off-platform). `ticket_messages.is_internal` keeps admin-only notes out of user view. `reference_code` is the human-facing support id. **On-site emergencies** stay an operational playbook ("call the emergency contact from the app, then open a ticket") — surfaced prominently in the booking UI; no schema change, but documented so nurses don't seek the family's number off-platform. Fields unchanged; `UNIQUE(ticket_id, user_id)` on participants. **Relations:** `tickets` 1:N `ticket_participants`/`ticket_messages`; `tickets` optionally ↔ `bookings`, `refunds`.