Add purpose and demand model extension

README.md

@@ -74,3 +74,11 @@ Agent-facing retrieval assets live under `infospace/agent/`:
 - per-artifact briefs in `agent/briefs/`
 - consumer brief templates in `agent/consumer-briefs/`
 - Canon Interface Card template in `agent/templates/`
+
+## Purpose And Demand
+
+The PURPOSES candidate model is registered as a governance extension at
+`infospace/models/governance/InfoTechCanonPurposeDemandExtension.md`. It defines
+consumer purposes, demand signals, purpose fit, scope pressure, and evolution
+requests so consumer demand can inform repo governance without silently changing
+producer scope.