doc clean up phase 2

dev/contracts/domains/messaging.md

@@ -1,3 +1,20 @@
+# messaging — MERGED into `docs/integration/domains/`
+
+> ⛔ **This headerless 851-byte fragment silently amended
+> [`messaging-notifications-admin.md`](messaging-notifications-admin.md) next to it** — two live files
+> describing one domain, which is contradiction **C-8**.
+>
+> Both are superseded. Phase 2 split the merged content three ways, along the client's actual domain
+> boundaries:
+>
+> | Content | Now |
+> | --- | --- |
+> | Tickets, threads, messages, `is_internal`, the staff queue | [`docs/integration/domains/tickets.md`](../../../docs/integration/domains/tickets.md) |
+> | The notification feed and unread badge | [`docs/integration/domains/notifications.md`](../../../docs/integration/domains/notifications.md) |
+> | Platform config, holidays, audit, support alerts | [`docs/integration/domains/admin.md`](../../../docs/integration/domains/admin.md) |
+>
+> Every REQ-028 amendment below is folded into `tickets.md` as current fact, not as a change log. Phase 6
+> archives this folder; until then, read it as a record.
 
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