diff --git a/.changeset/training-agent-property-list-uniform-errors.md b/.changeset/training-agent-property-list-uniform-errors.md
new file mode 100644
index 0000000000..0063bfa1a2
--- /dev/null
+++ b/.changeset/training-agent-property-list-uniform-errors.md
@@ -0,0 +1,6 @@
+---
+---
+
+Training agent: `get_property_list`, `update_property_list`, `delete_property_list`, and `validate_property_delivery` now return a uniform error on unresolved `list_id` — `error.code` is `REFERENCE_NOT_FOUND` (was lowercase `not_found`), `error.message` is the generic `"Property list not found"` (was `"No property list with id '<id>'"`), and `error.field` is `list_id`. Closes #2739.
+
+The probed id is no longer echoed back on the error path, so paired-probe uniform-response invariants (e.g. `@adcp/client` fuzz) now pass against the public test agent. This matters because the training agent is the reference implementors point conformance runs at; an echoing message there invalidates the signal for every downstream seller running the same invariant.
diff --git a/server/src/training-agent/property-handlers.ts b/server/src/training-agent/property-handlers.ts
index 3fde648464..8739656c01 100644
--- a/server/src/training-agent/property-handlers.ts
+++ b/server/src/training-agent/property-handlers.ts
@@ -257,7 +257,7 @@ export async function handleGetPropertyList(
 
   const state = session.propertyLists.get(req.list_id);
   if (!state) {
-    return { errors: [{ code: 'not_found', message: `No property list with id '${req.list_id}'` }] };
+    return { errors: [{ code: 'REFERENCE_NOT_FOUND', message: 'Property list not found', field: 'list_id' }] };
   }
 
   const domains = extractDomains(state.baseProperties);
@@ -280,7 +280,7 @@ export async function handleUpdatePropertyList(
 
   const state = session.propertyLists.get(req.list_id);
   if (!state) {
-    return { errors: [{ code: 'not_found', message: `No property list with id '${req.list_id}'` }] };
+    return { errors: [{ code: 'REFERENCE_NOT_FOUND', message: 'Property list not found', field: 'list_id' }] };
   }
 
   if (req.name) {
@@ -324,7 +324,7 @@ export async function handleDeletePropertyList(
 
   const existed = session.propertyLists.delete(req.list_id);
   if (!existed) {
-    return { errors: [{ code: 'not_found', message: `No property list with id '${req.list_id}'` }] };
+    return { errors: [{ code: 'REFERENCE_NOT_FOUND', message: 'Property list not found', field: 'list_id' }] };
   }
 
   return { list_id: req.list_id, deleted: true };
@@ -343,7 +343,7 @@ export async function handleValidatePropertyDelivery(
 
   const state = session.propertyLists.get(req.list_id);
   if (!state) {
-    return { errors: [{ code: 'not_found', message: `No property list with id '${req.list_id}'` }] };
+    return { errors: [{ code: 'REFERENCE_NOT_FOUND', message: 'Property list not found', field: 'list_id' }] };
   }
 
   const records = req.records || [];
diff --git a/server/tests/unit/training-agent.test.ts b/server/tests/unit/training-agent.test.ts
index e8c603d0ba..2f60630b5e 100644
--- a/server/tests/unit/training-agent.test.ts
+++ b/server/tests/unit/training-agent.test.ts
@@ -6860,6 +6860,50 @@ describe('get_brand_identity handler', () => {
   });
 });
 
+describe('property-list uniform not-found response (issue #2739)', () => {
+  beforeEach(async () => {
+    await clearSessions();
+  });
+  afterEach(async () => {
+    await clearSessions();
+    stopSessionCleanup();
+  });
+
+  // Paired-probe: two distinct unresolvable list_ids must produce byte-identical
+  // error bodies, otherwise the probed id is a cross-tenant enumeration oracle.
+  const PROBE_TOOLS = ['get_property_list', 'update_property_list', 'delete_property_list'] as const;
+  for (const toolName of PROBE_TOOLS) {
+    it(`${toolName} returns byte-identical errors for two distinct unresolvable list_ids`, async () => {
+      const server = createTrainingAgentServer(DEFAULT_CTX);
+      const account = { brand: { domain: 'uniform-probe.example' }, operator: 'pinnacle-agency.com' };
+
+      const probeA = await simulateCallTool(server, toolName, { account, list_id: 'd7aff8ea-136c-498f-b70f-a69582ad3bec' });
+      const probeB = await simulateCallTool(server, toolName, { account, list_id: '221acd34-cd2c-4763-ae0a-321c1e85fb2b' });
+
+      expect(probeA.isError).toBe(probeB.isError);
+      expect(probeA.result).toEqual(probeB.result);
+      expect(probeA.result.code).toBe('REFERENCE_NOT_FOUND');
+      expect(probeA.result.message).toBe('Property list not found');
+      expect(probeA.result.field).toBe('list_id');
+    });
+  }
+
+  it('validate_property_delivery returns byte-identical errors for two distinct unresolvable list_ids', async () => {
+    const server = createTrainingAgentServer(DEFAULT_CTX);
+    const account = { brand: { domain: 'uniform-probe.example' }, operator: 'pinnacle-agency.com' };
+    const records = [{ identifier: { type: 'domain', value: 'x.example' }, impressions: 1 }];
+
+    const probeA = await simulateCallTool(server, 'validate_property_delivery', { account, list_id: 'd7aff8ea-136c-498f-b70f-a69582ad3bec', records });
+    const probeB = await simulateCallTool(server, 'validate_property_delivery', { account, list_id: '221acd34-cd2c-4763-ae0a-321c1e85fb2b', records });
+
+    expect(probeA.isError).toBe(probeB.isError);
+    expect(probeA.result).toEqual(probeB.result);
+    expect(probeA.result.code).toBe('REFERENCE_NOT_FOUND');
+    expect(probeA.result.message).toBe('Property list not found');
+    expect(probeA.result.field).toBe('list_id');
+  });
+});
+
 describe('cross-machine session persistence', () => {
   beforeEach(async () => {
     await clearSessions();