refactor: pre-merge review — lift inlined metamodel strings to named constants

CLAUDE.md rule: "Named constants for metamodel strings — always." The
review surfaced six call sites with inline literals that already had (or
warranted) constants:

Python:
- Add IDENTITY_ATTR_UNIQUE to identity_constants.py
- Add FIELD_ATTR_COLUMN to field_constants.py (cross-port; @column is the
  renamed-from-@dbColumn physical-name attr per CLAUDE.md)
- expected_schema.py: child.attr(ic.IDENTITY_ATTR_UNIQUE),
  field.attr(fc.FIELD_ATTR_COLUMN)
- expected_views.py: import field_constants; use FIELD_ATTR_COLUMN
- object_manager.py: import field+identity constants;
  pi.attr(ic.IDENTITY_ATTR_FIELDS), field.attr(fc.FIELD_ATTR_COLUMN)

Java:
- MetaRoot.java + MetaObject.java: use MetaLayout.TYPE_LAYOUT instead of
  the literal "layout"

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

Author: dmealing

server/java/metadata/src/main/java/com/metaobjects/MetaRoot.java

@@ -76,7 +76,7 @@ public class MetaRoot extends MetaData {
                 .optionalChild(MetaView.TYPE_VIEW, "*", "*")                // Any view type
                 .optionalChild(com.metaobjects.identity.MetaIdentity.TYPE_IDENTITY, "*", "*")        // Any identity type
                 .optionalChild(com.metaobjects.relationship.MetaRelationship.TYPE_RELATIONSHIP, "*", "*") // Any relationship type
-                .optionalChild("layout", "*", "*")                          // Any layout type (root-level shared layouts)
+                .optionalChild(com.metaobjects.layout.MetaLayout.TYPE_LAYOUT, "*", "*")  // Any layout type (root-level shared layouts)
                 .optionalChild(com.metaobjects.template.TemplateConstants.TYPE_TEMPLATE, "*", "*") // Any template type (FR-004)
             );
             // ADR-0006 Rule 1 — bare `metadata:` YAML key fuses to `metadata.root`.
@@ -106,7 +106,7 @@ public static void registerTypes(MetaDataRegistry registry) {
                 .optionalChild(MetaView.TYPE_VIEW, "*", "*")
                 .optionalChild(com.metaobjects.identity.MetaIdentity.TYPE_IDENTITY, "*", "*")
                 .optionalChild(com.metaobjects.relationship.MetaRelationship.TYPE_RELATIONSHIP, "*", "*")
-                .optionalChild("layout", "*", "*")
+                .optionalChild(com.metaobjects.layout.MetaLayout.TYPE_LAYOUT, "*", "*")
                 .optionalChild(com.metaobjects.template.TemplateConstants.TYPE_TEMPLATE, "*", "*")
             );
         } catch (Exception e) {

server/java/metadata/src/main/java/com/metaobjects/object/MetaObject.java

@@ -11,6 +11,7 @@
 import com.metaobjects.identity.MetaIdentity;
 import com.metaobjects.identity.PrimaryIdentity;
 import com.metaobjects.identity.SecondaryIdentity;
+import com.metaobjects.layout.MetaLayout;
 import com.metaobjects.relationship.MetaRelationship;
 import com.metaobjects.registry.MetaDataRegistry;
 import com.metaobjects.source.MetaSource;
@@ -119,7 +120,7 @@ public static void registerTypes(MetaDataRegistry registry) {
             def.optionalChild(MetaView.TYPE_VIEW, "*", "*");
 
             // OBJECTS CAN CONTAIN LAYOUTS (layout.dataGrid and future subtypes)
-            def.optionalChild("layout", "*", "*");
+            def.optionalChild(MetaLayout.TYPE_LAYOUT, "*", "*");
 
             // OBJECTS CAN CONTAIN RELATIONSHIPS
             def.optionalChild(MetaRelationship.TYPE_RELATIONSHIP, "*", "*");

server/python/src/metaobjects/meta/core/field/field_constants.py

@@ -42,6 +42,8 @@
 # Persistence-side storage shape for owned field.object data. Cross-port values.
 FIELD_ATTR_STORAGE = "storage"
 STORAGE_VALUES = ("flattened", "jsonb", "subdocument")
+# Physical column name override (cross-port; renamed from @dbColumn).
+FIELD_ATTR_COLUMN = "column"
 
 # Regex pattern for enum member symbols — must be identifier-safe.
 # Cross-language contract: every port enforces this pattern.

server/python/src/metaobjects/meta/core/identity/identity_constants.py

@@ -6,6 +6,7 @@
 
 IDENTITY_ATTR_FIELDS = "fields"
 IDENTITY_ATTR_GENERATION = "generation"
+IDENTITY_ATTR_UNIQUE = "unique"
 
 # Allowed values for @generation on identity.primary
 GENERATION_INCREMENT = "increment"

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

@@ -15,6 +15,7 @@
 from ..meta.core.identity.meta_identity import MetaIdentity
 from ..meta.core.identity import identity_constants as ic
 from ..meta.core.field.meta_field import MetaField
+from ..meta.core.field import field_constants as fc
 from ..meta.core.relationship.meta_relationship import MetaRelationship
 from ..meta.persistence.source.meta_source import MetaSource
 from ..meta.persistence.source import source_constants as sc
@@ -185,7 +186,7 @@ def _identity_fields(identity: MetaIdentity) -> tuple[str, ...]:
 
 
 def _column_of(field: MetaField) -> str:
-    col = field.attr("column")
+    col = field.attr(fc.FIELD_ATTR_COLUMN)
     return col if isinstance(col, str) and col else field.name
 
 

server/python/src/metaobjects/runtime/object_manager.py

@@ -21,6 +21,8 @@
 from ..meta.meta_root import MetaRoot
 from ..meta.core.object.meta_object import MetaObject
 from ..meta.core.field.meta_field import MetaField
+from ..meta.core.field import field_constants as fc
+from ..meta.core.identity import identity_constants as ic
 from ..meta.persistence.source.meta_source import MetaSource
 from ..meta.persistence.source import source_constants as sc
 
@@ -160,7 +162,7 @@ def _primary_pk_field(self, entity: MetaObject) -> str:
         pi = entity.primary_identity()
         if pi is None:
             raise ValueError(f"Entity '{entity.name}' has no primary identity")
-        raw = pi.attr("fields")
+        raw = pi.attr(ic.IDENTITY_ATTR_FIELDS)
         if isinstance(raw, str):
             return raw
         if isinstance(raw, (list, tuple)) and raw:
@@ -234,7 +236,7 @@ def _op_clause(col: str, op: str, value: Any) -> tuple[str, list[Any]]:
 def _column_of(field: MetaField | None) -> str:
     if field is None:
         return ""
-    col = field.attr("column")
+    col = field.attr(fc.FIELD_ATTR_COLUMN)
     return col if isinstance(col, str) and col else field.name