diff --git a/apps/rich-text-versioning/AGENTS.md b/apps/rich-text-versioning/AGENTS.md
index 5db4157c88..2099f2790b 100644
--- a/apps/rich-text-versioning/AGENTS.md
+++ b/apps/rich-text-versioning/AGENTS.md
@@ -28,6 +28,7 @@ Standard Vite app.
 
 ## Sharp Edges & Invariants
 
+- **`@tanstack/react-query` major uniqueness:** `field-editor-reference` hard-deps RQ `^4` while `field-editor-rich-text@6` / `field-editor-shared@4` peer-accept `^4 || ^5`. A dual-major install tree lets Vite bundle the wrong single major and crashes embedded entry/asset cards (`reading 'sys'`). `test/reactQueryMajors.spec.ts` fails CI if more than one major is present under `node_modules`. Do not remove the direct `@tanstack/react-query` pin without re-checking the install tree.
 - **`@contentful/field-editor-rich-text`** is embedded to provide the actual editing experience — this is the standard Contentful rich-text editor. Do not replace it with a custom editor.
 - **Versions stored as JSON** in a separate Contentful JSON field (not in the rich-text field itself). The versioning field must exist on the content type alongside the rich-text field — document this requirement clearly to users.
 - **Snapshot schema**: each snapshot has `{ id, timestamp, label, value: Document }`. Changing this schema requires migrating all existing version data.
diff --git a/apps/rich-text-versioning/test/reactQueryMajors.spec.ts b/apps/rich-text-versioning/test/reactQueryMajors.spec.ts
new file mode 100644
index 0000000000..f6e8835f70
--- /dev/null
+++ b/apps/rich-text-versioning/test/reactQueryMajors.spec.ts
@@ -0,0 +1,47 @@
+import { describe, expect, it } from 'vitest';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { analyzeReactQueryMajors, findReactQueryPackages } from './reactQueryMajors';
+
+const appRoot = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..');
+
+describe('analyzeReactQueryMajors', () => {
+  it('passes when there are no copies (package not in tree)', () => {
+    const result = analyzeReactQueryMajors([]);
+    expect(result.ok).toBe(true);
+    expect(result.majors).toEqual([]);
+  });
+
+  it('passes when every copy shares one major', () => {
+    const result = analyzeReactQueryMajors([
+      { version: '4.44.0', path: '/a/node_modules/@tanstack/react-query' },
+      { version: '4.36.1', path: '/a/node_modules/nested/@tanstack/react-query' },
+    ]);
+    expect(result.ok).toBe(true);
+    expect(result.majors).toEqual(['4']);
+  });
+
+  it('fails when majors 4 and 5 both appear (RTV crash-class tree)', () => {
+    const result = analyzeReactQueryMajors([
+      { version: '5.101.2', path: '/a/node_modules/@tanstack/react-query' },
+      {
+        version: '4.44.0',
+        path: '/a/node_modules/@contentful/field-editor-reference/node_modules/@tanstack/react-query',
+      },
+    ]);
+    expect(result.ok).toBe(false);
+    expect(result.majors).toEqual(['4', '5']);
+    expect(result.message).toMatch(/multiple majors/i);
+  });
+});
+
+describe('findReactQueryPackages (install tree)', () => {
+  it('finds only one major under this app node_modules', () => {
+    const copies = findReactQueryPackages(path.join(appRoot, 'node_modules'));
+    const result = analyzeReactQueryMajors(copies);
+
+    expect(copies.length).toBeGreaterThan(0);
+    expect(result.ok, result.message).toBe(true);
+    expect(result.majors).toHaveLength(1);
+  });
+});
diff --git a/apps/rich-text-versioning/test/reactQueryMajors.ts b/apps/rich-text-versioning/test/reactQueryMajors.ts
new file mode 100644
index 0000000000..08d05f2c1f
--- /dev/null
+++ b/apps/rich-text-versioning/test/reactQueryMajors.ts
@@ -0,0 +1,108 @@
+import fs from 'node:fs';
+import path from 'node:path';
+
+export type ReactQueryCopy = {
+  version: string;
+  path: string;
+};
+
+export type ReactQueryMajorsResult = {
+  ok: boolean;
+  majors: string[];
+  copies: ReactQueryCopy[];
+  message: string;
+};
+
+export function analyzeReactQueryMajors(copies: ReactQueryCopy[]): ReactQueryMajorsResult {
+  const majors = [
+    ...new Set(copies.map((copy) => copy.version.split('.')[0]).filter(Boolean)),
+  ].sort();
+
+  if (majors.length <= 1) {
+    return {
+      ok: true,
+      majors,
+      copies,
+      message:
+        majors.length === 0
+          ? 'No @tanstack/react-query copies found.'
+          : `Single @tanstack/react-query major found: ${majors[0]}.`,
+    };
+  }
+
+  const listed = copies.map((copy) => `  ${copy.version} @ ${copy.path}`).join('\n');
+  return {
+    ok: false,
+    majors,
+    copies,
+    message: [
+      `Found multiple majors of @tanstack/react-query (${majors.join(', ')}).`,
+      'Vite collapses these to a single major at bundle time; the wrong one',
+      'breaks embedded entry/asset cards in field-editor-rich-text (sys crash).',
+      'Ensure the install tree resolves to one major.',
+      listed,
+    ].join('\n'),
+  };
+}
+
+/**
+ * Walk node_modules for every physical @tanstack/react-query package.json.
+ * Nested installs under field-editor-reference are the interesting case.
+ */
+export function findReactQueryPackages(nodeModulesRoot: string): ReactQueryCopy[] {
+  const hits: ReactQueryCopy[] = [];
+
+  function walk(dir: string, depth: number): void {
+    if (depth > 12) return;
+
+    let entries: fs.Dirent[];
+    try {
+      entries = fs.readdirSync(dir, { withFileTypes: true });
+    } catch {
+      return;
+    }
+
+    for (const entry of entries) {
+      if (!entry.isDirectory()) continue;
+      // Skip Vite/Vitest caches and bin stubs
+      if (entry.name === '.bin' || entry.name === '.vite' || entry.name === '.cache') continue;
+
+      const full = path.join(dir, entry.name);
+
+      if (entry.name === '@tanstack') {
+        const pkgPath = path.join(full, 'react-query', 'package.json');
+        if (fs.existsSync(pkgPath)) {
+          try {
+            const pkg = JSON.parse(fs.readFileSync(pkgPath, 'utf8')) as { version?: string };
+            if (pkg.version) {
+              hits.push({ version: pkg.version, path: path.dirname(pkgPath) });
+            }
+          } catch {
+            // ignore unreadable package.json
+          }
+        }
+        continue;
+      }
+
+      if (
+        entry.name === 'node_modules' ||
+        dir.endsWith(`${path.sep}node_modules`) ||
+        entry.name.startsWith('@')
+      ) {
+        walk(full, depth + 1);
+        continue;
+      }
+
+      const nested = path.join(full, 'node_modules');
+      if (fs.existsSync(nested)) {
+        walk(nested, depth + 1);
+      }
+    }
+  }
+
+  if (fs.existsSync(nodeModulesRoot)) {
+    walk(nodeModulesRoot, 0);
+  }
+
+  return hits;
+}