fix(migrations): enforce schema ownership safety

server/tests/test_schema_ownership.py

@@ -0,0 +1,26 @@
+from __future__ import annotations
+
+from sqlalchemy import create_engine, inspect
+
+from app.db.schema_ownership import MIGRATION_OWNED_TABLES, create_legacy_schema
+
+
+def test_create_legacy_schema_never_creates_migration_owned_tables() -> None:
+    engine = create_engine("sqlite+pysqlite:///:memory:")
+    try:
+        create_legacy_schema(engine)
+
+        table_names = set(inspect(engine).get_table_names())
+    finally:
+        engine.dispose()
+
+    assert MIGRATION_OWNED_TABLES == frozenset(
+        {
+            "auth_sessions",
+            "business_events",
+            "expense_case_links",
+            "expense_cases",
+        }
+    )
+    assert table_names
+    assert table_names.isdisjoint(MIGRATION_OWNED_TABLES)