filter_notification_alerts tripped Sonar's cognitive-complexity gate
(16 > 15 allowed) from its nested loop/if structure. Split into
_filter_group_notifications (per-group notification selection) and
_determine_alert_type (Redis TTL classification), leaving the public
method as a simple loop over receiver groups. Behavior and call order
are unchanged -- verified against the existing filter_notification_alerts
unit tests by inspection (sientia_do isn't installable in this local
environment, so the real suite can't run here; CI will confirm).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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