Fix CoreData to-many relationships

Author: colemancda

Sources/CoreDataModel/NSRelationshipDescription.swift

@@ -24,7 +24,16 @@ internal extension NSRelationshipDescription {
         case .toMany:
             self.minCount = 0
             self.maxCount = 0
-            self.isOrdered = true
+            // - Note: To-many relationships are deliberately *unordered*.
+            //   CoreData forbids an ordered relationship whose inverse is also
+            //   ordered — `momc` rejects it at build time, but a model built
+            //   programmatically is never validated, so a many-to-many (e.g.
+            //   `Person.events` / `Event.people`) silently produced an invalid
+            //   model. Deleting an object then corrupted memory while CoreData
+            //   propagated the delete through the faulted ordered set, crashing
+            //   with EXC_BAD_ACCESS inside `-[NSManagedObject _propagateDelete:]`.
+            //   ``RelationshipValue/toMany(_:)`` carries no ordering guarantee
+            //   anyway, and unordered is CoreData's own default.
             assert(isToMany)
         }
     }