D11 — Session variable name locked to stables.current_tenant
Architecture decision record, relocated verbatim from the retired single-file
docs/tenancy/decision log. Status, thematic clusters, and how to record a new ADR: the decision log index.
Set in config/tenancy.php before any policy is generated. Baked into every policy body
(current_setting('stables.current_tenant')), so it must never change afterwards.