feat: add models package

packages/models/src/Domain/Runtime/Collection/CollectionInterface.ts

@@ -0,0 +1,13 @@
+import { UuidMap } from '@standardnotes/utils'
+
+export interface CollectionInterface {
+  /** Maintains an index where the direct map for each item id is an array
+   * of item ids that the item references. This is essentially equivalent to
+   * item.content.references, but keeps state even when the item is deleted.
+   * So if tag A references Note B, referenceMap.directMap[A.uuid] == [B.uuid].
+   * The inverse map for each item is an array of item ids where the items reference the
+   * key item. So if tag A references Note B, referenceMap.inverseMap[B.uuid] == [A.uuid].
+   * This allows callers to determine for a given item, who references it?
+   * It would be prohibitive to look this up on demand */
+  readonly referenceMap: UuidMap
+}