docs(#771): bind tier importer to verified target

docs/design/storage-abstraction-middleware.md

@@ -70,6 +70,10 @@ export function createQueue(config?: QueueConfig): QueueHandle {
 
 ### `@mosaicstack/db` (packages/db/src/client.ts)
 
+> **Historical design specimen — status-only, not an operator instruction.** KBN-101 supersedes
+> this pre-split `DATABASE_URL` fallback shape; it cannot authorize runtime migration, DDL, or a
+> connection-string fallback. See the KBN-101 runner/role contract for the produced interface.
+
 ```typescript
 import { drizzle, type PostgresJsDatabase } from 'drizzle-orm/postgres-js';
 import postgres from 'postgres';