Heal the layer break around the Id<> type

src/model.ts

@@ -1,5 +1,22 @@
 import { randomBytes } from "crypto";
 
+/**
+ * An internal database id.
+ *
+ * We don't have any say over the protocols that we are implementing, and we
+ * would also like our internal data store to adhere to a consistent set of
+ * design principles. This type defines a fully opaque primary key data type
+ * for database records which should not be exposed to external clients under
+ * normal circumstances. Clients outside the SQL DB (or other persistent data
+ * storage) driver should make no assumptions about its structure or actual
+ * underlying data type.
+ *
+ * Database entities presented to external clients must be identified using
+ * alternative external identifiers in formats that are acceptable to those
+ * external systems.
+ */
+export type Id<T> = string & { __type: T };
+
 export type AimeId = number & { __aimeId: null };
 
 /** Generate a random 32-bit ID for use in external protocol messages */