Notification idempotency must bind claim, state transition, and delivery semantics

Observed 2026-09-04 while reviewing e3-solutions/theft PR #795 (COR-3968), from the exact GitHub diff and focused tests: fixed wall-clock bucket keys do not implement a rolling suppression window; committing a durable claim before a non-durable SMS attempt can create false success and suppress retries; and reactivating a support issue before duplicate-claim ownership can reopen it without generating attention. Reusable review rule: test across bucket boundaries and provider failure, and establish idempotency ownership before coupled lifecycle mutations. Durable queue state may reduce impact, so distinguish SMS-delivery failure from total support-routing loss.