Process-dictionary store for the current tenant/org id, mirroring AuditTrail.ActorStore. Not meant to be called directly — use AuditTrail.set_tenant/1, AuditTrail.get_tenant/0, and AuditTrail.clear_tenant/0 instead, which delegate here. Set once per request/job; every subsequent emit/monitor/schema-tracked Repo call in the same process is tagged with it automatically.