Replace core database utcnow defaults (#1457)

Co-authored-by: ghreprimand <203024559+ghreprimand@users.noreply.github.com>

tests/test_database_utcnow.py

@@ -0,0 +1,33 @@
+import types
+
+import pytest
+
+sqlalchemy = pytest.importorskip("sqlalchemy")
+if not isinstance(sqlalchemy, types.ModuleType):
+    pytest.skip("sqlalchemy is stubbed in this environment", allow_module_level=True)
+
+from core.database import ChatMessage, DocumentVersion, Session, TaskRun, UserToolData, utcnow_naive
+
+
+def test_utcnow_naive_returns_naive_utc_datetime():
+    now = utcnow_naive()
+
+    assert now.tzinfo is None
+    assert abs((now - utcnow_naive()).total_seconds()) < 2
+
+
+def test_database_timestamp_defaults_use_utcnow_naive():
+    defaults = (
+        Session.created_at.default.arg,
+        Session.updated_at.default.arg,
+        Session.updated_at.onupdate.arg,
+        ChatMessage.timestamp.default.arg,
+        DocumentVersion.created_at.default.arg,
+        UserToolData.created_at.default.arg,
+        UserToolData.updated_at.default.arg,
+        UserToolData.updated_at.onupdate.arg,
+        TaskRun.started_at.default.arg,
+    )
+
+    for fn in defaults:
+        assert fn.__name__ == "utcnow_naive"