Batch 7 hardening tests:
- T7.1 Concurrency: SemaphoreSlim barrier + Task.WhenAll; exactly 1 winner,
2 losers receive SqlException; post-race vigente count = 1.
- T7.2 SYSTEM_VERSIONING: exact 0-before / 1-after history row count on close;
history captures pre-close state (ValidTo was NULL at snapshot).
- T7.3 FOR SYSTEM_TIME AS OF: temporal snapshot at T0 returns row as it existed
before the close UPDATE (ValidTo=NULL, original price).
- T7.4 Per-medio + global fallback: ELDIA override for % wins over global;
ELPLATA falls back to V022 global seed at 1.00; service-layer priority verified.
- T7.6 WordCounterService x ChargeableCharConfig integration contract (pure unit):
documents PRC-002+ billing pattern; asserts charge computation for 6 scenarios.
Total .NET tests: 1603 (was 1591; +12 new).
