fix(related-list): compile the badge's parent scope by relationship arity

.changeset/related-badge-arity-8882.md

@@ -0,0 +1,26 @@
+---
+'@object-ui/core': minor
+'@object-ui/components': minor
+'@object-ui/plugin-detail': minor
+---
+
+fix(related-list): the tab badge compiles its parent scope by relationship ARITY, like the rows
+
+A related list on a `multiple: true` relationship rendered its rows above a tab
+with no count at all. The row query has compiled the parent-relationship
+condition to match the field's arity since objectui#7299 (`$contains` for a
+multi-value relationship, `=` for a single-value one), but the badge's count
+probe carried a second compiler that always sent bare equality — which the
+driver refuses on an array-valued column, and the count store swallows the
+refusal without caching anything.
+
+Rather than teaching the second compiler the same rule, there is now one:
+`@object-ui/core` exports `composeParentScopeFilter` (and the
+`isMultiValueRelationship` verdict behind it), and both the row query and the
+badge probe call it. The arity verdict remains `@objectstack/spec/data`'s own
+`isMultiValueField`, so the renderer and the driver that executes the query
+still decide on the same rule.
+
+`RelatedCountStore.fetch` takes the child object's field defs as a new optional
+last argument; callers that cannot see metadata keep the previous equality
+wire, byte for byte. Single-value related lists are unchanged on both sides.