diff --git a/src/shared/support/hooks.ts b/src/shared/support/hooks.ts
index 65ac27a..6725a22 100644
--- a/src/shared/support/hooks.ts
+++ b/src/shared/support/hooks.ts
@@ -325,13 +325,24 @@ async function ensureAuth(): Promise<void> {
 BeforeAll({ timeout: 10 * 60 * 1000 }, async function () {
   console.log('Starting Festipod BDD tests...');
 
+  // `--format=iife` IS LOad-BEARING, not tidiness. Both bundles are loaded as
+  // CLASSIC scripts (`<script src="/harness.js">` for the NG harness,
+  // `addScriptTag({path})` for the mock one), so every top-level declaration in
+  // an unwrapped bundle becomes a GLOBAL binding. `@tanstack/query-core` — pulled
+  // in by Refine — exports a class named `MutationObserver`, which then shadows
+  // the DOM's for anything that runs afterwards in that page. Playwright's own
+  // injected script does `new MutationObserver(...)`, so it got TanStack's and
+  // every `waitForFunction` died with "defaultMutationOptions is not a function".
+  // The IIFE wrapper keeps the bundle's declarations to itself; `window.__testData`
+  // is still published explicitly, so the bridge is unaffected.
+
   // Build the mock harness (always needed for non-@data or fallback)
-  execSync(`bun build ${HARNESS_ENTRY} --outfile ${HARNESS_OUT} --bundle`, { stdio: 'pipe' });
+  execSync(`bun build ${HARNESS_ENTRY} --outfile ${HARNESS_OUT} --bundle --format=iife`, { stdio: 'pipe' });
   console.log(`[Harness] Built mock (${(fs.statSync(HARNESS_OUT).size / 1024).toFixed(0)} KB)`);
 
   // Try to build the real broker harness
   try {
-    execSync(`bun build ${HARNESS_NG_ENTRY} --outfile ${HARNESS_NG_OUT} --bundle`, { stdio: 'pipe' });
+    execSync(`bun build ${HARNESS_NG_ENTRY} --outfile ${HARNESS_NG_OUT} --bundle --format=iife`, { stdio: 'pipe' });
     console.log(`[Harness] Built NG (${(fs.statSync(HARNESS_NG_OUT).size / 1024).toFixed(0)} KB)`);
 
     // Ensure wallet exists in persistent profile (opens browser if needed)
diff --git a/src/shared/test-harness/harness-ng.tsx b/src/shared/test-harness/harness-ng.tsx
index 5b714b0..cef00f2 100644
--- a/src/shared/test-harness/harness-ng.tsx
+++ b/src/shared/test-harness/harness-ng.tsx
@@ -10,6 +10,7 @@
 import React, { useEffect, useState } from 'react';
 import { createRoot } from 'react-dom/client';
 import { NextGraphProvider, useNextGraph } from '../context/NextGraphContext';
+import { RefineProvider } from '../refine/RefineProvider';
 import { FestipodDataProvider, useFestipodData } from '../context/FestipodDataContext';
 import { useShape } from '@ng-org/orm/react';
 import { ng } from '@ng-org/web';
@@ -21,7 +22,6 @@ import {
 } from '../shapes/orm/festipodShapes.shapeTypes';
 import type { FpEvent, FpUserProfile, FpParticipation } from '../shapes/orm/festipodShapes.typings';
 import { seedEvents, seedUsers, seedParticipations } from '../data/seedData';
-import { bootstrapWallet } from '../utils/ngBootstrap';
 import { ensureGraphNuri } from '../utils/ngGraph';
 
 // ============================================================================
@@ -31,9 +31,13 @@ import { ensureGraphNuri } from '../utils/ngGraph';
 function DataHarnessNG() {
   return (
     <NextGraphProvider>
-      <FestipodDataProvider>
-        <HarnessRouter />
-      </FestipodDataProvider>
+      {/* Same order as the real app (app/App.tsx): the data context reads events
+          through Refine's hooks, so it cannot mount outside <Refine>. */}
+      <RefineProvider>
+        <FestipodDataProvider>
+          <HarnessRouter />
+        </FestipodDataProvider>
+      </RefineProvider>
     </NextGraphProvider>
   );
 }
@@ -148,9 +152,18 @@ function ConnectedHarness() {
           }
         },
 
-        /** Load the app's default seed data into the wallet */
+        /**
+         * Load the app's default seed data into the wallet.
+         *
+         * Delegates to the data context instead of calling `bootstrapWallet`
+         * directly: seeding events now goes through Refine's `create` (one
+         * document per event), and the callback that does it lives in the
+         * context. Calling the bootstrap from here with raw ORM sets would seed
+         * by a DIFFERENT path than the app's — which is the divergence this
+         * harness exists to avoid.
+         */
         loadTestData() {
-          return bootstrapWallet(events as any, users as any, participations as any);
+          return appData.loadTestData();
         },
 
         // --- Stopgap multi-store validation (see brief_2026-06-15_shared-wallet-shim) ---