docs: declare institutional architecture boundary

docs/ORGANIZATION_MODEL.md

@@ -16,6 +16,13 @@ The organization model answers where responsibility lives.
 - Function: a named responsibility in an organization unit, such as clerk,
   reviewer, approver, committee secretary, intake desk, or resource manager.
 
+A function says what responsibility exists and where. It does not by itself
+prove that the institution or function is legally or organizationally
+competent for a subject, territory, population, decision type, signature, or
+period. That effective mandate/jurisdiction belongs to a separate shared
+Mandates contract. Organizations retains only stable references needed to
+explain how a mandate attaches to a unit or function.
+
 ## Governance And Templates
 
 Concrete organization models are tenant-owned. Units, structures, relation