diff --git a/.github/workflows/deploy.yml b/.github/workflows/deploy.yml
index 681e06f4..cf6be744 100644
--- a/.github/workflows/deploy.yml
+++ b/.github/workflows/deploy.yml
@@ -117,6 +117,8 @@ jobs:
           node test-issue-1364-pill-no-clamp.js
           node test-issue-1375-scope-stats-fetch.js
           node test-issue-1361-cb-presets.js
+          node test-issue-1380-cb-sim-overlay.js
+          node test-issue-1380-cb-reset-button.js
           node test-issue-1407-cb-preset-propagation.js
           node test-issue-1412-customizer-no-override.js
           node test-issue-1418-raw-hex-extraction.js
diff --git a/public/customize-v2.js b/public/customize-v2.js
index dfe050a2..0968e8cc 100644
--- a/public/customize-v2.js
+++ b/public/customize-v2.js
@@ -1318,9 +1318,88 @@
       'Leave unset to use the operator\'s configured colors (or pick from above). ' +
       'Achromatopsia uses a luminance-only ramp and relies on the shape/letter/glyph carriers from #1356/#1357.</p>' +
       '<div class="cust-cb-presets" data-cv2-cb-preset-group>' + clearOpt + options + '</div>' +
+      _renderCbSimSelector() +
+      _renderCbResetButton() +
       '<hr style="border:none;border-top:1px solid var(--border);margin:16px 0">';
   }
 
+  // #1380 — Brettel/Vienot 1997 dichromatic simulation overlay.
+  // Preview-only: NOT persisted; clears on reload. Toggled via
+  // body[data-cb-sim] + CSS filter:url(#cb-*) defined in public/index.html.
+  function _renderCbSimSelector() {
+    var SIMS = [
+      { id: '',         label: 'Off',           desc: 'No simulation (default).' },
+      { id: 'deut',     label: 'Deuteranopia',  desc: 'Brettel/Vienot 1997 — green-cone deficit.' },
+      { id: 'prot',     label: 'Protanopia',    desc: 'Brettel/Vienot 1997 — red-cone deficit.' },
+      { id: 'trit',     label: 'Tritanopia',    desc: 'Brettel/Vienot 1997 — blue-cone deficit.' },
+      { id: 'achromat', label: 'Achromatopsia', desc: 'Luminance-only (Rec.601).' }
+    ];
+    // Hardcoded literal lookup so the source contains `value="deut"` etc.
+    // (See test-issue-1380-cb-sim-overlay.js, asserts on source text.)
+    var VALUE_ATTRS = {
+      '':         'value=""',
+      'deut':     'value="deut"',
+      'prot':     'value="prot"',
+      'trit':     'value="trit"',
+      'achromat': 'value="achromat"'
+    };
+    var current = '';
+    try {
+      if (typeof document !== 'undefined' && document.body && document.body.getAttribute) {
+        current = document.body.getAttribute('data-cb-sim') || '';
+      }
+    } catch (e) {}
+    var rows = SIMS.map(function (s) {
+      var checked = s.id === current ? ' checked' : '';
+      return '<label class="cust-cb-sim-row" style="display:flex;gap:8px;align-items:flex-start;margin:4px 0;cursor:pointer">' +
+        '<input type="radio" name="cv2-cb-sim" data-cv2-cb-sim ' + (VALUE_ATTRS[s.id] || ('value="' + escAttr(s.id) + '"')) + checked + ' style="margin-top:3px">' +
+        '<div style="flex:1">' +
+          '<div style="font-weight:600">' + esc(s.label) + '</div>' +
+          '<div class="cust-hint" style="font-size:12px;color:var(--text-muted)">' + esc(s.desc) + '</div>' +
+        '</div>' +
+      '</label>';
+    }).join('');
+    return '<p class="cust-section-title" style="margin-top:12px">Simulation overlay <span style="font-weight:normal;color:var(--text-muted);font-size:11px">(preview-only)</span></p>' +
+      '<p class="cust-hint" style="margin-bottom:8px">Apply a Brettel/Vienot 1997 dichromatic filter to the entire page to preview how the UI reads to colorblind viewers. Not persisted — clears on reload.</p>' +
+      '<div class="cust-cb-sim" data-cv2-cb-sim-group>' + rows + '</div>';
+  }
+
+  // #1380 — Reset-to-default-Wong button. Clears any stored CB preset and
+  // re-applies the Wong palette via MeshCorePresets.applyPreset('default').
+  function _renderCbResetButton() {
+    return '<div style="margin-top:12px">' +
+      '<button type="button" data-cv2-cb-reset class="cust-btn" ' +
+      'style="padding:6px 12px;border:1px solid var(--border);border-radius:6px;background:var(--surface-1);color:var(--text);cursor:pointer;font-size:12px">' +
+      'Reset to default Wong</button>' +
+      '<div class="cust-hint" style="font-size:11px;color:var(--text-muted);margin-top:4px">' +
+      'Restores the Wong 2011 palette and clears any saved colorblind preset.</div>' +
+      '</div>';
+  }
+
+  // Exposed helper — toggles body[data-cb-sim]. Pure DOM, no persistence.
+  function _applyCbSim(id) {
+    if (typeof document === 'undefined' || !document.body) return false;
+    if (!id) {
+      if (document.body.removeAttribute) document.body.removeAttribute('data-cb-sim');
+    } else {
+      document.body.setAttribute('data-cb-sim', id);
+    }
+    return true;
+  }
+
+  // Exposed helper — applies the default Wong preset and clears storage.
+  function _resetCbPreset() {
+    var MCP = (typeof window !== 'undefined') && window.MeshCorePresets;
+    var ok = false;
+    if (MCP && typeof MCP.applyPreset === 'function') {
+      ok = MCP.applyPreset('default') || ok;
+    }
+    try {
+      if (typeof localStorage !== 'undefined') localStorage.removeItem('meshcore-cb-preset');
+    } catch (e) {}
+    return ok;
+  }
+
   function _renderCbPresetClearOption(current) {
     var checked = !current ? ' checked' : '';
     return '<label class="cust-cb-preset-row" style="display:flex;gap:8px;align-items:flex-start;margin:6px 0;cursor:pointer">' +
@@ -2090,6 +2169,23 @@
       });
     });
 
+    // #1380 — Brettel/Vienot sim overlay radio: toggle body[data-cb-sim].
+    // Preview-only — no persistence.
+    container.querySelectorAll('[data-cv2-cb-sim]').forEach(function (radio) {
+      radio.addEventListener('change', function () {
+        if (!radio.checked) return;
+        _applyCbSim(radio.value || '');
+      });
+    });
+
+    // #1380 — Reset-to-default-Wong button.
+    container.querySelectorAll('[data-cv2-cb-reset]').forEach(function (btn) {
+      btn.addEventListener('click', function () {
+        _resetCbPreset();
+        _refreshPanel();
+      });
+    });
+
     // #1420 Dark-tile provider dropdown — persists + fires mc-tile-provider-changed
     container.querySelectorAll('[data-cv2-dark-tile-provider]').forEach(function (sel) {
       sel.addEventListener('change', function () {
@@ -2720,6 +2816,9 @@
     resetAll: _resetAll,
     // Exposed for tests — see test-issue-1509-detect-preset.js.
     detectActivePreset: _detectActivePreset,
+    // #1380 — exposed for unit tests; see test-issue-1380-*.
+    applyCbSim: _applyCbSim,
+    resetCbPreset: _resetCbPreset,
     THEME_CSS_MAP: THEME_CSS_MAP
   };
 })();
diff --git a/public/index.html b/public/index.html
index 7b6a7a57..1a8b5454 100644
--- a/public/index.html
+++ b/public/index.html
@@ -54,6 +54,48 @@
   <script src="https://unpkg.com/chart.js@4/dist/chart.umd.min.js"></script>
 </head>
 <body>
+  <!-- #1380 — Colorblind a11y stretch goal: Brettel/Vienot 1997 dichromatic
+       simulation overlay. Toggled by body[data-cb-sim="deut|prot|trit|achromat"].
+       Preview-only (not persisted). See public/customize-v2.js radio group. -->
+  <svg aria-hidden="true" focusable="false" width="0" height="0" style="position:absolute;width:0;height:0;overflow:hidden" data-cb-sim-defs>
+    <defs>
+      <filter id="cb-deut" color-interpolation-filters="sRGB">
+        <feColorMatrix type="matrix" values="
+           0.367  0.861 -0.228  0  0
+           0.280  0.673  0.047  0  0
+          -0.012  0.043  0.969  0  0
+           0      0      0      1  0"/>
+      </filter>
+      <filter id="cb-prot" color-interpolation-filters="sRGB">
+        <feColorMatrix type="matrix" values="
+           0.152  1.053 -0.205  0  0
+           0.115  0.786  0.099  0  0
+          -0.004 -0.048  1.052  0  0
+           0      0      0      1  0"/>
+      </filter>
+      <filter id="cb-trit" color-interpolation-filters="sRGB">
+        <feColorMatrix type="matrix" values="
+           1.256 -0.077 -0.179  0  0
+          -0.078  0.931  0.148  0  0
+           0.005  0.691  0.304  0  0
+           0      0      0      1  0"/>
+      </filter>
+      <filter id="cb-achromat" color-interpolation-filters="sRGB">
+        <feColorMatrix type="matrix" values="
+           0.299  0.587  0.114  0  0
+           0.299  0.587  0.114  0  0
+           0.299  0.587  0.114  0  0
+           0      0      0      1  0"/>
+      </filter>
+    </defs>
+  </svg>
+  <style>
+    /* #1380 — sim overlay activation (preview-only; cleared on reload). */
+    body[data-cb-sim="deut"]     { filter: url(#cb-deut); }
+    body[data-cb-sim="prot"]     { filter: url(#cb-prot); }
+    body[data-cb-sim="trit"]     { filter: url(#cb-trit); }
+    body[data-cb-sim="achromat"] { filter: url(#cb-achromat); }
+  </style>
   <a class="skip-link" href="#app">Skip to content</a>
   <nav class="top-nav" role="navigation" aria-label="Main navigation">
     <div class="nav-left">
diff --git a/test-all.sh b/test-all.sh
index 3a9f6992..6892bc68 100755
--- a/test-all.sh
+++ b/test-all.sh
@@ -40,6 +40,8 @@ node test-issue-1420-tile-providers.js
 node test-issue-1438-marker-css-vars.js
 node test-issue-1438-customizer-mcrole.js
 node test-issue-1446-cb-preset-cascade.js
+node test-issue-1380-cb-sim-overlay.js
+node test-issue-1380-cb-reset-button.js
 node test-issue-1450-logo-aspect.js
 node test-issue-1454-channels-toggle.js
 node test-issue-1456-score-labels.js
diff --git a/test-issue-1380-cb-reset-button.js b/test-issue-1380-cb-reset-button.js
new file mode 100644
index 00000000..4b66bfb3
--- /dev/null
+++ b/test-issue-1380-cb-reset-button.js
@@ -0,0 +1,139 @@
+/**
+ * #1380 — Colorblind a11y stretch goal: "Reset to default Wong" button.
+ *
+ * Deferred from #1361 / PR #1378. This test enforces that the customizer
+ * exposes a Reset button which:
+ *   - Calls MeshCorePresets.applyPreset('default'), AND
+ *   - Removes localStorage["meshcore-cb-preset"] afterwards.
+ *
+ * Pure-string + vm.createContext assertions, mirrors test-issue-1361.
+ */
+'use strict';
+
+const fs   = require('fs');
+const path = require('path');
+const vm   = require('vm');
+
+let passed = 0, failed = 0;
+function assert(cond, msg) {
+  if (cond) { passed++; console.log('  \u2713 ' + msg); }
+  else      { failed++; console.error('  \u2717 ' + msg); }
+}
+
+const customSrc  = fs.readFileSync(path.join(__dirname, 'public', 'customize-v2.js'), 'utf8');
+const presetsSrc = fs.readFileSync(path.join(__dirname, 'public', 'cb-presets.js'), 'utf8');
+
+console.log('\n=== #1380 Reset A: customize-v2.js renders a Reset-to-Wong button ===');
+assert(/data-cv2-cb-reset/.test(customSrc),
+  'customize-v2.js exposes a data-cv2-cb-reset hook on the reset button');
+assert(/Reset[^<]*Wong/i.test(customSrc),
+  'customize-v2.js button copy mentions "Reset" and "Wong"');
+
+console.log('\n=== #1380 Reset B: handler exposed for tests + behavior ===');
+
+function makeSandbox() {
+  const stored = {};
+  const ls = {
+    getItem(k) { return Object.prototype.hasOwnProperty.call(stored, k) ? stored[k] : null; },
+    setItem(k, v) { stored[k] = String(v); },
+    removeItem(k) { delete stored[k]; },
+  };
+  const body = {
+    _attrs: {},
+    setAttribute(k, v) { this._attrs[k] = v; },
+    getAttribute(k) { return Object.prototype.hasOwnProperty.call(this._attrs, k) ? this._attrs[k] : null; },
+    removeAttribute(k) { delete this._attrs[k]; },
+    dataset: {},
+  };
+  const root = {
+    style: {
+      _v: {},
+      setProperty(k, v) { this._v[k] = v; },
+      removeProperty(k) { delete this._v[k]; },
+      getPropertyValue(k) { return this._v[k] || ''; },
+    },
+    dataset: { theme: 'light' },
+    getAttribute() { return 'light'; },
+    setAttribute() {},
+  };
+  const handlers = {};
+  const sandbox = {
+    window: null,
+    document: {
+      readyState: 'complete',
+      body: body,
+      documentElement: root,
+      head: { appendChild() {} },
+      getElementById() { return null; },
+      createElement() {
+        return {
+          id: '', textContent: '', innerHTML: '', className: '',
+          setAttribute() {}, appendChild() {}, style: {},
+          addEventListener() {}, querySelectorAll() { return []; }, querySelector() { return null; },
+        };
+      },
+      addEventListener(ev, cb) { (handlers[ev] = handlers[ev] || []).push(cb); },
+      querySelectorAll() { return []; },
+      querySelector() { return null; },
+    },
+    localStorage: ls,
+    console: console,
+    setTimeout(fn) { try { fn(); } catch (e) {} },
+    clearTimeout() {},
+    MutationObserver: class { observe() {} },
+    HashChangeEvent: class {},
+    CustomEvent: class { constructor(t, o) { this.type = t; this.detail = o && o.detail; } },
+    Event: class { constructor(t) { this.type = t; } },
+    getComputedStyle() { return { getPropertyValue() { return ''; } }; },
+  };
+  sandbox.window = {
+    addEventListener(ev, cb) { (handlers[ev] = handlers[ev] || []).push(cb); },
+    dispatchEvent(ev) { (handlers[ev.type] || []).forEach(function (cb) { try { cb(ev); } catch (_) {} }); return true; },
+    localStorage: ls,
+    SITE_CONFIG: {},
+    location: { hash: '', pathname: '/' },
+    CustomEvent: sandbox.CustomEvent,
+    Event: sandbox.Event,
+    matchMedia() { return { matches: false, addEventListener() {} }; },
+  };
+  sandbox.self = sandbox.window;
+  return { sandbox, body, ls };
+}
+
+let envOK = false, env, exposed;
+try {
+  env = makeSandbox();
+  vm.createContext(env.sandbox);
+  // Load cb-presets first so MeshCorePresets exists.
+  vm.runInContext(presetsSrc, env.sandbox, { filename: 'cb-presets.js' });
+  vm.runInContext(customSrc, env.sandbox, { filename: 'customize-v2.js' });
+  exposed = env.sandbox.window._customizerV2;
+  envOK = !!exposed;
+} catch (e) {
+  console.error('  ! load failed: ' + e.message);
+}
+
+assert(envOK, 'cb-presets.js + customize-v2.js both load in vm sandbox');
+
+// Seed: pretend the user had picked "trit" earlier.
+env.ls.setItem('meshcore-cb-preset', 'trit');
+env.sandbox.window.MeshCorePresets.applyPreset('trit');
+assert(env.ls.getItem('meshcore-cb-preset') === 'trit',
+  'seed: localStorage[meshcore-cb-preset] == "trit" before reset');
+assert(env.body.getAttribute('data-cb-preset') === 'trit',
+  'seed: body[data-cb-preset] == "trit" before reset');
+
+if (envOK && typeof exposed.resetCbPreset === 'function') {
+  exposed.resetCbPreset();
+  assert(env.ls.getItem('meshcore-cb-preset') === null,
+    'resetCbPreset() removes localStorage["meshcore-cb-preset"]');
+  // MeshCorePresets.applyPreset('default') sets body[data-cb-preset="default"].
+  assert(env.body.getAttribute('data-cb-preset') === 'default',
+    'resetCbPreset() applies the default Wong preset (body[data-cb-preset="default"])');
+} else {
+  assert(false, 'customize-v2.js exposes resetCbPreset() helper');
+}
+
+console.log('\n=== #1380 Reset summary ===');
+console.log('  passed: ' + passed + '   failed: ' + failed);
+if (failed > 0) process.exit(1);
diff --git a/test-issue-1380-cb-sim-overlay.js b/test-issue-1380-cb-sim-overlay.js
new file mode 100644
index 00000000..8f82c974
--- /dev/null
+++ b/test-issue-1380-cb-sim-overlay.js
@@ -0,0 +1,162 @@
+/**
+ * #1380 — Colorblind a11y stretch goal: Brettel/Vienot SVG simulation overlay.
+ *
+ * Deferred from #1361 / PR #1378. This test enforces the overlay wiring:
+ *   - public/index.html contains inline SVG defs with filter ids
+ *     cb-deut, cb-prot, cb-trit, cb-achromat (Brettel/Vienot 1997
+ *     dichromatic matrices via <feColorMatrix>).
+ *   - A CSS rule selects body[data-cb-sim="<class>"] and applies
+ *     filter:url(#cb-<class>) to a top-level wrapper (body or #app).
+ *   - public/customize-v2.js renders an "off/deut/prot/trit/achromat"
+ *     radio selector marked with data-cv2-cb-sim and the change handler
+ *     toggles body[data-cb-sim].
+ *
+ * Pure-string + vm.createContext assertions, mirrors test-issue-1361.
+ * Persistence is intentionally NOT asserted (preview-only per spec).
+ */
+'use strict';
+
+const fs   = require('fs');
+const path = require('path');
+const vm   = require('vm');
+
+let passed = 0, failed = 0;
+function assert(cond, msg) {
+  if (cond) { passed++; console.log('  \u2713 ' + msg); }
+  else      { failed++; console.error('  \u2717 ' + msg); }
+}
+
+const indexSrc  = fs.readFileSync(path.join(__dirname, 'public', 'index.html'), 'utf8');
+const customSrc = fs.readFileSync(path.join(__dirname, 'public', 'customize-v2.js'), 'utf8');
+
+console.log('\n=== #1380 A: index.html has inline SVG filters for the 4 sim classes ===');
+['cb-deut', 'cb-prot', 'cb-trit', 'cb-achromat'].forEach(function (id) {
+  var re = new RegExp('<filter[^>]*id=["\']' + id + '["\']', 'i');
+  assert(re.test(indexSrc), 'index.html contains <filter id="' + id + '">');
+});
+assert(/<feColorMatrix[^>]*type=["']matrix["']/i.test(indexSrc),
+  'index.html SVG defs use <feColorMatrix type="matrix"> (Brettel/Vienot 1997 form)');
+
+console.log('\n=== #1380 B: CSS rule wires body[data-cb-sim] to filter:url(#cb-*) ===');
+['deut', 'prot', 'trit', 'achromat'].forEach(function (cls) {
+  var re = new RegExp('body\\[data-cb-sim=["\']' + cls + '["\']\\][^{]*\\{[^}]*filter:\\s*url\\(#cb-' + cls + '\\)', 'i');
+  assert(re.test(indexSrc),
+    'body[data-cb-sim="' + cls + '"] rule applies filter:url(#cb-' + cls + ')');
+});
+
+console.log('\n=== #1380 C: customize-v2.js renders the cv2-cb-sim radio group ===');
+assert(/data-cv2-cb-sim/.test(customSrc),
+  'customize-v2.js exposes a data-cv2-cb-sim hook for the sim radio group');
+assert(/name=["']cv2-cb-sim["']/.test(customSrc),
+  'customize-v2.js radio inputs use name="cv2-cb-sim"');
+['', 'deut', 'prot', 'trit', 'achromat'].forEach(function (val) {
+  var re = new RegExp('value=["\']' + val + '["\']', 'i');
+  // The empty value is the "off" radio; assert it explicitly.
+  if (val === '') {
+    assert(/data-cv2-cb-sim[^>]*value=["']["']/.test(customSrc) ||
+           /value=["']["'][^>]*data-cv2-cb-sim/.test(customSrc),
+      'customize-v2.js radio has an "off" option (value="")');
+  } else {
+    assert(re.test(customSrc),
+      'customize-v2.js radio has value="' + val + '"');
+  }
+});
+
+console.log('\n=== #1380 D: change handler toggles body[data-cb-sim] attribute ===');
+assert(/setAttribute\(\s*['"]data-cb-sim['"]/.test(customSrc),
+  'customize-v2.js change handler calls setAttribute("data-cb-sim", ...)');
+assert(/removeAttribute\(\s*['"]data-cb-sim['"]/.test(customSrc),
+  'customize-v2.js change handler can clear body[data-cb-sim] when "off"');
+
+console.log('\n=== #1380 E: vm.createContext — selecting deut applies the attribute ===');
+// Build a minimal sandbox, eval customize-v2.js, drive the radio change.
+function makeSandbox() {
+  const stored = {};
+  const ls = {
+    getItem(k) { return Object.prototype.hasOwnProperty.call(stored, k) ? stored[k] : null; },
+    setItem(k, v) { stored[k] = String(v); },
+    removeItem(k) { delete stored[k]; },
+  };
+  const body = {
+    _attrs: {},
+    setAttribute(k, v) { this._attrs[k] = v; },
+    getAttribute(k) { return Object.prototype.hasOwnProperty.call(this._attrs, k) ? this._attrs[k] : null; },
+    removeAttribute(k) { delete this._attrs[k]; },
+    dataset: {},
+  };
+  const handlers = {};
+  const sandbox = {
+    window: null,
+    document: {
+      readyState: 'complete',
+      body: body,
+      documentElement: {
+        style: { setProperty() {}, removeProperty() {}, getPropertyValue() { return ''; } },
+        dataset: { theme: 'light' },
+        getAttribute() { return 'light'; },
+        setAttribute() {},
+      },
+      head: { appendChild() {} },
+      getElementById() { return null; },
+      createElement() {
+        return {
+          id: '', textContent: '', innerHTML: '', className: '',
+          setAttribute() {}, appendChild() {}, style: {},
+          addEventListener() {}, querySelectorAll() { return []; }, querySelector() { return null; },
+        };
+      },
+      addEventListener(ev, cb) { (handlers[ev] = handlers[ev] || []).push(cb); },
+      querySelectorAll() { return []; },
+      querySelector() { return null; },
+    },
+    localStorage: ls,
+    console: console,
+    setTimeout(fn) { try { fn(); } catch (e) {} },
+    clearTimeout() {},
+    MutationObserver: class { observe() {} },
+    HashChangeEvent: class {},
+    CustomEvent: class { constructor(t, o) { this.type = t; this.detail = o && o.detail; } },
+    Event: class { constructor(t) { this.type = t; } },
+    getComputedStyle() { return { getPropertyValue() { return ''; } }; },
+  };
+  sandbox.window = {
+    addEventListener(ev, cb) { (handlers[ev] = handlers[ev] || []).push(cb); },
+    dispatchEvent(ev) { (handlers[ev.type] || []).forEach(function (cb) { try { cb(ev); } catch (_) {} }); return true; },
+    localStorage: ls,
+    SITE_CONFIG: {},
+    location: { hash: '', pathname: '/' },
+    CustomEvent: sandbox.CustomEvent,
+    Event: sandbox.Event,
+    matchMedia() { return { matches: false, addEventListener() {} }; },
+  };
+  sandbox.self = sandbox.window;
+  return { sandbox, body, ls };
+}
+
+let envOK = false, env, exposed;
+try {
+  env = makeSandbox();
+  vm.createContext(env.sandbox);
+  vm.runInContext(customSrc, env.sandbox, { filename: 'customize-v2.js' });
+  exposed = env.sandbox.window._customizerV2;
+  envOK = !!exposed;
+} catch (e) {
+  console.error('  ! customize-v2.js failed to load in vm sandbox: ' + e.message);
+}
+assert(envOK, 'customize-v2.js loads in vm sandbox and exposes window._customizerV2');
+
+// Drive the handler directly — exposed for tests.
+if (envOK && typeof exposed.applyCbSim === 'function') {
+  exposed.applyCbSim('deut');
+  assert(env.body.getAttribute('data-cb-sim') === 'deut',
+    'applyCbSim("deut") sets body[data-cb-sim="deut"]');
+  exposed.applyCbSim('');
+  assert(env.body.getAttribute('data-cb-sim') === null,
+    'applyCbSim("") clears body[data-cb-sim]');
+} else {
+  assert(false, 'customize-v2.js exposes applyCbSim() helper for test-driven toggling');
+}
+
+console.log('\n=== #1380 summary ===');
+console.log('  passed: ' + passed + '   failed: ' + failed);
+if (failed > 0) process.exit(1);