SCD2 (validity-windowed) apply strategy, dispatched from Apply.apply_change/3 when Info.history_scd2?(resource). Each change CLOSES the current open version (an Ash bulk_update through the host close action, tenant-scoped, so it never retires another tenant's identically-keyed version) and OPENS a new version (host :create upsert by the (business_key, valid_from_lsn) identity), inside the sink's outer transaction (transaction: false). Op-dependent close predicate: the re-opened record's close uses valid_from_lsn < lsn (don't clobber the version being re-opened at lsn); a TERMINAL close — a delete, or the retired OLD key of a pk-changing update — uses valid_from_lsn <= lsn (retire a version opened in the same commit too). Value-free: every raising op is scrubbed to a structural reason.