Function route 

pub fn route(records: Vec<AuditRecord>, mode: RetentionMode) -> Routing

Route records according to the retention policy.

• RetentionMode::AutoArchive — every record goes to archived; inbox is empty.
• RetentionMode::ManualTriage — every record goes to inbox; nothing is archived until an explicit later keep decision.

This is a pure partition of the input (every record lands in exactly one bucket), so re-running it on archived ∪ inbox with the same mode is idempotent.