test: lock in that levels union replaces default_filter's level, not AND

Manual code-review pass (code-review-python checklist) flagged that no test
exercised default_filter already restricting level (e.g. Alerts' ERROR-only
default) combined with every active group specifying its own levels. The
replace-not-AND behavior is deliberate per SIENTIAPDE-2011's design doc and
ticket text, but was previously only covered by a docstring comment. Adds
test_compute_query_time_filter_union_replaces_default_level_restriction so a
future change reintroducing AND semantics fails a test instead of passing
silently.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/orchestrator/workflows/subworkflows/test_load_notification_package.py

@@ -199,6 +199,27 @@ def test_compute_query_time_filter_mixed_groups_no_levels_restriction(load_notif
     assert result == {'level': 'ERROR'}
 
 
+def test_compute_query_time_filter_union_replaces_default_level_restriction(
+    load_notification_package,
+):
+    # default_filter already restricts level (e.g. Alerts' ERROR-only default),
+    # but every active group specifies levels of its own -> the union REPLACES
+    # default_filter's level restriction, it does not AND with it. This is
+    # deliberate per SIENTIAPDE-2011's design doc and ticket text ("Alerts'
+    # hard-coded level: ERROR should become whatever levels the active groups
+    # actually care about"), not a bug -- this test locks the behavior in so a
+    # future "fix" reintroducing AND semantics fails loudly instead of passing
+    # silently.
+    sending_configs = [
+        {'group_name': 'group_a', 'levels': ['WARNING'], 'ignore_models_id': []},
+    ]
+    default_filter = {'level': 'ERROR'}
+
+    result = load_notification_package._compute_query_time_filter(sending_configs, default_filter)
+
+    assert result == {'level': {'$in': ['WARNING']}}
+
+
 def test_compute_query_time_filter_model_ignored_by_only_one_group_not_excluded(
     load_notification_package,
 ):