feat: add typed tier assurance guardrails

docs/GovernanceWorkflows.md

@@ -1,6 +1,6 @@
 # Governance Workflows
 
-Status: MVP for `ADAPTIVE-WP-0008`.
+Status: MVP for `ADAPTIVE-WP-0008` and `ADAPTIVE-WP-0009`.
 
 ## Purpose
 
@@ -14,6 +14,7 @@ The repository now exposes:
 - a customer-facing safe-tuning contract surface
 - pricing health checks
 - provider-publication audit and revision surfaces
+- one-time approval for new or changed tier assurance definitions
 
 ## Core And Adapter Layers
 
@@ -42,6 +43,19 @@ The policy model covers:
 For Coulomb, the current policy keeps customer-visible tuning disabled and
 requires approval for candidate rollouts and approximate Stripe mappings.
 
+## Tier Assurance Definition Gate
+
+`assess_tier_definition_assurance()` compares a proposed pricing model with
+its previously approved definition. Adding, changing, or removing an
+`assurance_claims` entry returns `approval_required`, with the claim's evidence
+reference attached to the blocking requirement. An unchanged definition
+returns `proceed`.
+
+This gate runs when a tier definition changes. It is deliberately not a
+campaign, publication, or per-customer approval: the approved tier records the
+commercial wording and typed tenancy-posture minimum once, while service and
+provider owners remain authoritative for current operational posture.
+
 ## Recommendation Workflow
 
 Recommendations now include: