Add purpose and demand model extension

infospace/agent/templates/consumer-brief.template.md

@@ -13,6 +13,8 @@ generated: true
 - Intent:
 - Scope:
 - Purposes:
+- Use cases:
+- Demand signals:
 
 ## Canon Surfaces
 
@@ -26,3 +28,10 @@ generated: true
 - Commands:
 - Evidence:
 - Known gaps:
+
+## Purpose Fit
+
+- State:
+- Matched producer capabilities:
+- Scope pressure:
+- Requested evolution: