fix(java,python): pre-merge review — own-only vs effective + missing parens

Two surgical correctness fixes caught by the pre-merge code-review gate. Both
were latent against the current corpus but real:

1. ValidationPhase.validateDataGridLayout used getChildren(MetaField.class,
   false) — own-only iteration. TS/C# use effective. A child entity with
   `layout.dataGrid @defaultSortField: "createdAt"` (inherited from the
   BaseEntity pattern CLAUDE.md actively recommends) would false-positive
   ERR_BAD_DEFAULT_SORT_FIELD in Java only. Two-char flip false→true.

2. expected_schema._matching_relationship_actions accessed
   child.object_ref and child.on_update as ATTRIBUTES, but they're METHODS
   on MetaRelationship. The bound-method objects are truthy, so the
   subsequent _strip_pkg(ref) would call .rfind on a method object and
   AttributeError. The corpus never reaches this branch today
   (relationships sit on parent entities, references on children), so the
   bug is dormant — but blows up on the first same-entity
   relationship+reference fixture. Add missing parens.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: dmealing

server/java/metadata/src/main/java/com/metaobjects/loader/ValidationPhase.java

@@ -798,7 +798,7 @@ static void validateDataGridLayouts(MetaRoot root) {
     private static void validateDataGridLayout(MetaObject obj, DataGridLayout grid) {
         java.util.Map<String, MetaField> fieldsByName = new java.util.HashMap<>();
         java.util.Set<String> filterable = new java.util.HashSet<>();
-        for (MetaField f : obj.getChildren(MetaField.class, false)) {
+        for (MetaField f : obj.getChildren(MetaField.class, true)) {
             fieldsByName.put(f.getShortName(), f);
             if (f.hasMetaAttr("filterable", false)) {
                 Object v = f.getMetaAttr("filterable", false).getValue();

server/python/src/metaobjects/migrate/expected_schema.py

@@ -177,7 +177,7 @@ def _build_indexes(entity: MetaObject):
         if not fields:
             continue
         cols = tuple(_column_for(entity, n) for n in fields)
-        unique_attr = child.attr("unique")
+        unique_attr = child.attr(ic.IDENTITY_ATTR_UNIQUE)
         unique = unique_attr is not False  # secondary is unique by default
         yield IndexDescriptor(name=child.name, columns=cols, unique=unique)
 
@@ -247,11 +247,11 @@ def _matching_relationship_actions(entity: MetaObject, target_entity: str) -> tu
     for child in entity.children():
         if not isinstance(child, MetaRelationship):
             continue
-        ref = child.object_ref
+        ref = child.object_ref()
         if ref is None:
             continue
         if _strip_pkg(ref) == _strip_pkg(target_entity):
-            return child.on_delete(), child.on_update
+            return child.on_delete(), child.on_update()
     return None, None
 
 
@@ -274,7 +274,7 @@ def _identity_fields(identity: MetaIdentity) -> tuple[str, ...]:
 
 def _column_of(field: MetaField) -> str:
     """@column override else field name (matches C# Literal default; cross-port)."""
-    col = field.attr("column")
+    col = field.attr(fc.FIELD_ATTR_COLUMN)
     return col if isinstance(col, str) and col else field.name