feat(core): add structured documentation localization contract

tests/test_documentation_topic_contract.py

@@ -10,6 +10,7 @@ from govoplan_core.core.modules import (
     DocumentationSourceDefinition,
     DocumentationTopic,
     ModuleManifest,
+    localized_documentation_metadata,
     user_workflow_scope_condition_issues,
 )
 from govoplan_core.core.registry import PlatformRegistry, RegistryError
@@ -83,6 +84,58 @@ class DocumentationTopicContractTests(unittest.TestCase):
         self.assertEqual(user_workflow_scope_condition_issues(user_reference), ())
         registry_for(scoped, admin_workflow, user_reference).validate()
 
+    def test_versioned_structured_translation_preserves_metadata_shape(self) -> None:
+        topic = DocumentationTopic(
+            id="example.workflow.localized",
+            title="Run task",
+            summary="Run the task.",
+            metadata={
+                "kind": "workflow",
+                "steps": ["Review", "Execute"],
+                "verification": "Confirm the result.",
+            },
+            structured_translation_version="1",
+            structured_translations={
+                "de": {
+                    "steps": ["Prüfen", "Ausführen"],
+                    "verification": "Das Ergebnis bestätigen.",
+                }
+            },
+        )
+
+        registry_for(topic).validate()
+        self.assertEqual(
+            ["Prüfen", "Ausführen"],
+            localized_documentation_metadata(topic, "de")["steps"],
+        )
+        self.assertEqual(
+            "workflow", localized_documentation_metadata(topic, "de")["kind"]
+        )
+
+    def test_structured_translation_requires_version_and_complete_shape(self) -> None:
+        missing_version = DocumentationTopic(
+            id="example.localized.missing-version",
+            title="Localized",
+            summary="Invalid contract.",
+            metadata={"limitations": ["One", "Two"]},
+            structured_translations={"de": {"limitations": ["Eins", "Zwei"]}},
+        )
+        with self.assertRaisesRegex(
+            RegistryError, "require structured_translation_version"
+        ):
+            registry_for(missing_version).validate()
+
+        incomplete_shape = DocumentationTopic(
+            id="example.localized.incomplete",
+            title="Localized",
+            summary="Invalid shape.",
+            metadata={"limitations": ["One", "Two"]},
+            structured_translation_version="1",
+            structured_translations={"de": {"limitations": ["Eins"]}},
+        )
+        with self.assertRaisesRegex(RegistryError, "preserve list length"):
+            registry_for(incomplete_shape).validate()
+
     def test_documentation_configuration_and_source_extensions_are_validated(self) -> None:
         resolver = lambda _context, keys: {  # noqa: E731
             key: DocumentationConfigurationDecision(key=key, state="enabled")