diff --git a/src/protocol.js b/src/protocol.js
index fbbf3a8..fa916ed 100644
--- a/src/protocol.js
+++ b/src/protocol.js
@@ -1,12 +1,35 @@
 // Lightweight protocol scaffold for Open-EnergyMesh 0.2 core ontology
 // This file provides tiny, versioned data contracts used by adapters.
 
+// Privacy budget and audit trail primitives to support privacy-preserving
+// aggregation and governance provenance in the MVP.
+class PrivacyBudget {
+  constructor(limit = 0, allocated = 0) {
+    this.limit = limit; // maximum allowed budget (abstract unit)
+    this.allocated = allocated; // amount currently allocated/used
+  }
+}
+
+class AuditLog {
+  constructor(entries = []) {
+    this.entries = entries; // array of audit entries
+  }
+  addEntry(entry) {
+    this.entries.push(entry);
+  }
+}
+
+// Lightweight protocol scaffold for Open-EnergyMesh 0.2 core ontology
+// This file provides tiny, versioned data contracts used by adapters.
+
 class LocalProblem {
   constructor(version = '0.2') {
     this.version = version;
     this.variables = {}; // local optimization variables
     this.constraints = []; // local constraints
     this.objective = null; // objective description or function reference
+    this.privacyBudget = new PrivacyBudget();
+    this.auditLog = new AuditLog();
   }
 }
 
@@ -27,5 +50,7 @@ class PlanDelta {
 module.exports = {
   LocalProblem,
   SharedVariables,
-  PlanDelta
+  PlanDelta,
+  PrivacyBudget,
+  AuditLog
 };