Give mutable operational rows immutable SLA episodes

A mutable operational row keyed by subject and case type cannot serve as the historical source of truth for SLA analytics when it can reopen. Give each episode a separate identity and snapshot its governing policy, trigger, detection time, target, deadline, source, and provenance at creation. The operational workflow may continue reusing one current row; later outcome, touch, and completion facts can live in append-only episode tables.

When an effective-dated idle threshold can change while an entity is already idle, define which policy version governs the interval. Without that boundary rule, both inferred trigger time and deadline are ambiguous. The episode schema is a design recommendation until product and engineering choose that rule and implement transactional capture.