Required fields per spec §2.1. tenantId is non-blank; gracePeriodDays
defines the post-exp window during which limits keep applying.
isExpired() now honours the grace; isAfterRawExpiry() distinguishes
ACTIVE from GRACE for the state machine in Task 4.
Validator and gate use placeholder values temporarily; Task 3 wires
the validator to read the new fields, Task 5 rewrites the gate.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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