chore(python): pre-merge simplifier pass

Five small clarity tweaks on the two commits that closed the Python ledger
(fd14f33 persistence + c43e15c conformance gaps). Behavior-identical; 451/451
unit tests still green.

* core_types.py: drop unused FIELD_SUBTYPE_OBJECT import.
* core_types.py: lift the inline "required" validator subtype to a named
  VALIDATOR_SUBTYPE_REQUIRED constant — matches the metamodel-strings-as-
  constants discipline (Java has SUBTYPE_REQUIRED on RequiredValidator).
* validation_passes.py: route the template R2 check through the already-
  imported OBJECT_SUBTYPE_VALUE instead of the literal "value".
* object_manager.py: move the _PG_OID_* constants below the imports
  (PEP 8 organization — they were sandwiched mid-import-block).
* query_runner.py: drop unused normalize_value / canonical_value_json
  imports + the `_ = ...` lines that silenced the flake — they were
  re-export scaffolding for a use-site that never landed.

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

Author: dmealing

server/python/src/metaobjects/core_types.py

@@ -18,7 +18,6 @@
     FIELD_ATTR_STORAGE,
     FIELD_ATTR_VALUES,
     FIELD_SUBTYPE_ENUM,
-    FIELD_SUBTYPE_OBJECT,
     STORAGE_VALUES,
 )
 from .meta.core.field.meta_field import MetaField
@@ -440,7 +439,8 @@ def _register_subtypes(
 # validator.* — base + required (validates a field has a value at write time).
 # Sized to satisfy the cross-port corpus today; richer validator subtypes
 # (regex/length/numeric) can join later mirroring Java's ValidatorTypesMetaDataProvider.
-_VALIDATOR_SUBTYPES = (SUBTYPE_BASE, "required")
+VALIDATOR_SUBTYPE_REQUIRED = "required"
+_VALIDATOR_SUBTYPES = (SUBTYPE_BASE, VALIDATOR_SUBTYPE_REQUIRED)
 _register_subtypes(
     core_provider,
     TYPE_VALIDATOR,

server/python/src/metaobjects/loader/validation_passes.py

@@ -861,7 +861,7 @@ def _validate_templates(root: MetaData, errors: list[MetaError]) -> None:
 
         # R2 — @payloadRef must resolve to a root-level object.value
         payload = objects_by_name.get(payload_ref)
-        if payload is None or payload.sub_type != "value":
+        if payload is None or payload.sub_type != OBJECT_SUBTYPE_VALUE:
             errors.append(MetaError(
                 code=ErrorCode.ERR_INVALID_TEMPLATE,
                 message=(

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

@@ -11,13 +11,6 @@
 from collections.abc import Iterable
 from typing import Any, Protocol
 
-
-# pg8000 / psycopg type oids we coerce to string at extraction so the cross-port
-# normalization contract (BIGINT → string, NUMERIC → canonical decimal string)
-# is honored without leaking SQL-type awareness into the comparison layer.
-_PG_OID_BIGINT = 20
-_PG_OID_NUMERIC = 1700
-
 from ..meta.meta_root import MetaRoot
 from ..meta.core.object.meta_object import MetaObject
 from ..meta.core.field.meta_field import MetaField
@@ -27,6 +20,13 @@
 from ..meta.persistence.source import source_constants as sc
 
 
+# pg8000 / psycopg type oids coerced to string at extraction so the cross-port
+# normalization contract (BIGINT → string, NUMERIC → canonical decimal string)
+# is honored without leaking SQL-type awareness into the comparison layer.
+_PG_OID_BIGINT = 20
+_PG_OID_NUMERIC = 1700
+
+
 # Filter shape:
 #   {"field": "value"}                    → equality shortcut
 #   {"field": {"eq": v, "gt": v, ...}}    → typed ops on a field

server/python/tests/integration/query_runner.py

@@ -13,7 +13,7 @@
 from metaobjects.migrate.types import SchemaSnapshot
 from metaobjects.runtime import ObjectManager, PostgresDriver
 
-from .normalization import canonical_rows_json, canonical_value_json, normalize_row, normalize_value
+from .normalization import canonical_rows_json, normalize_row
 from .postgres_container import PostgresContainer
 from .scenarios import QueryScenario, QuerySpec
 
@@ -127,8 +127,3 @@ def _canonicalize_actual(actual: Any, op: str) -> str:
     if op == "get":
         return json.dumps(normalize_row(actual), sort_keys=True, separators=(",", ":"))
     return canonical_rows_json(actual)
-
-
-# Touch normalize_value so it's not flagged unused — re-exported for ad-hoc test use.
-_ = normalize_value
-_ = canonical_value_json