Single source: app/utils/voucher_guard.py (NOT EXISTS on voucher_void_marks,
key = entity_id+voucher_no+voucher_date and revoked_at IS NULL; same caliber as
the DB view cma.v_voucher_details_active). No hardcoded voucher numbers.
Consumers now guarded: cash.py import linkage (2 fns), reports.py subject/BS
amount (2 sites, also entity_id isolation added), dashboard.py _bep_sum_field,
alert_attribution.py build_subject_attribution. kpi_value_collector.py now
delegates to the shared guard (removes the previous duplicate implementation).
Tests: new tests/test_void_marker_consumers_20260914.py (6 cases).
