diff --git a/packages/dom/src/serialize-pseudo-classes.js b/packages/dom/src/serialize-pseudo-classes.js
index 7fca97f74..a7ca35069 100644
--- a/packages/dom/src/serialize-pseudo-classes.js
+++ b/packages/dom/src/serialize-pseudo-classes.js
@@ -146,6 +146,49 @@ function markInteractiveStates(ctx) {
   });
 }
 
+// Walk the LIVE document and every shadow root (open, or closed via the CDP
+// WeakMap) WITHOUT relying on data-percy-shadow-host markers. walkShadowDOM
+// descends through those markers, but they are only stamped later during
+// cloning — so during this pre-clone marking pass it cannot reach shadow
+// content. We descend via the live shadowRoot directly instead.
+function eachScopeIncludingShadow(root, visit) {
+  if (!root || typeof root.querySelectorAll !== 'function') return;
+  visit(root);
+  for (const el of root.querySelectorAll('*')) {
+    const shadow = getShadowRoot(el);
+    if (shadow) eachScopeIncludingShadow(shadow, visit);
+  }
+}
+
+// Auto-detect open native popovers page-wide, INCLUDING inside shadow roots.
+// `:popover-open` is an unambiguous serialize-time state (like :checked /
+// :disabled), so it is stamped automatically rather than only on
+// pseudoClassEnabledElements. The renderer's popover-element-helper already
+// re-opens any [popover][data-percy-popover-open] across shadow boundaries;
+// without this stamp a popover open at snapshot time renders hidden via the
+// UA `[popover]:not(:popover-open){display:none}` rule. If `:popover-open`
+// is unsupported the selector throws — we stop querying and warn once.
+function markOpenPopovers(ctx) {
+  let supported = true;
+  eachScopeIncludingShadow(ctx.dom, scope => {
+    if (!supported) return;
+    // Only the `:popover-open` SELECTOR can legitimately throw a SyntaxError
+    // (engines without popover support). Scope the try to the query and
+    // materialize the matches; stamp OUTSIDE the try. Otherwise a throw from
+    // stampOnce mid-iteration would be misreported as "unsupported" AND would
+    // silently skip every remaining scope.
+    let matches;
+    try {
+      matches = scope.querySelectorAll('[popover]:popover-open');
+    } catch (e) {
+      supported = false;
+      ctx.warnings.add('Browser does not support :popover-open pseudo-class.');
+      return;
+    }
+    for (const el of matches) stampOnce(ctx, el, POPOVER_OPEN_ATTR, 'true');
+  });
+}
+
 function isPopoverOpen(ctx, element) {
   try {
     return element.matches(':popover-open');
@@ -258,6 +301,7 @@ export function getElementsToProcess(ctx, config, markWithId = false) {
 export function markPseudoClassElements(ctx, config) {
   ctx._liveMutations = [];
   markInteractiveStates(ctx);
+  markOpenPopovers(ctx);
   if (config) getElementsToProcess(ctx, config, true);
 }
 
diff --git a/packages/dom/test/serialize-pseudo-classes.test.js b/packages/dom/test/serialize-pseudo-classes.test.js
index 7bd0c28f9..febc30d23 100644
--- a/packages/dom/test/serialize-pseudo-classes.test.js
+++ b/packages/dom/test/serialize-pseudo-classes.test.js
@@ -366,6 +366,106 @@ describe('serialize-pseudo-classes', () => {
     });
   });
 
+  // Regression guard for the customer scenario: a native popover opened via
+  // showPopover() and living inside an open shadow root (e.g. Tecton q2-popover).
+  // The open/top-layer state is lost on serialization unless the pre-clone pass
+  // pierces shadow DOM and stamps data-percy-popover-open — and it must do so
+  // automatically, with no pseudoClassEnabledElements config.
+  describe('popover auto-detection inside shadow DOM', () => {
+    let host;
+    // For the closed-root case: keep a handle to the (otherwise unreachable)
+    // closed root, and remember the previous WeakMap so we can restore it.
+    let closedRoot;
+    let origClosedMap;
+
+    function popoverSupported() {
+      return typeof document.createElement('div').showPopover === 'function';
+    }
+
+    function openShadowPopover({ mode = 'open', type = 'manual', open = true } = {}) {
+      host = document.createElement('div');
+      host.id = 'shadow-popover-host';
+      const root = host.attachShadow({ mode });
+      // nosemgrep: javascript.browser.security.insecure-document-method.insecure-document-method
+      root.innerHTML = `<div id="sp" popover="${type}">menu</div>`;
+      document.body.appendChild(host);
+      if (mode === 'closed') {
+        // host.shadowRoot is null for closed roots. Mimic the CDP closed-shadow
+        // exposure path: register host -> root in the WeakMap that
+        // getShadowRoot()/getClosedShadowRoot() reads, so the marking walk can
+        // reach inside.
+        closedRoot = root;
+        origClosedMap = window.__percyClosedShadowRoots;
+        const map = new WeakMap();
+        map.set(host, root);
+        window.__percyClosedShadowRoots = map;
+      }
+      const popover = root.getElementById('sp');
+      if (open) popover.showPopover();
+      return popover;
+    }
+
+    afterEach(() => {
+      if (!host) return;
+      try {
+        const root = host.shadowRoot || closedRoot;
+        const p = root && root.querySelector('[popover]');
+        if (p && typeof p.hidePopover === 'function' && p.matches(':popover-open')) p.hidePopover();
+      } catch (e) { /* ignore */ }
+      host.remove();
+      host = null;
+      if (closedRoot) {
+        window.__percyClosedShadowRoots = origClosedMap;
+        closedRoot = null;
+        origClosedMap = undefined;
+      }
+    });
+
+    it('auto-stamps an open popover inside an open shadow root with NO config', () => {
+      if (!popoverSupported()) { pending('Popover API not supported in this environment'); return; }
+      const popover = openShadowPopover();
+
+      // No pseudoClassEnabledElements passed — auto-detection must still reach it.
+      markPseudoClassElements(ctx);
+
+      expect(popover.getAttribute('data-percy-popover-open')).toBe('true');
+    });
+
+    it('removes the shadow-DOM popover marker from the live DOM on cleanup', () => {
+      if (!popoverSupported()) { pending('Popover API not supported in this environment'); return; }
+      const popover = openShadowPopover();
+
+      markPseudoClassElements(ctx);
+      expect(popover.hasAttribute('data-percy-popover-open')).toBe(true);
+
+      cleanupInteractiveStateMarkers(ctx);
+      expect(popover.hasAttribute('data-percy-popover-open')).toBe(false);
+    });
+
+    it('does NOT stamp a closed popover inside a shadow root', () => {
+      if (!popoverSupported()) { pending('Popover API not supported in this environment'); return; }
+      const popover = openShadowPopover({ open: false });
+
+      markPseudoClassElements(ctx);
+
+      expect(popover.hasAttribute('data-percy-popover-open')).toBe(false);
+    });
+
+    it('auto-stamps an open popover inside a CLOSED shadow root (via the CDP WeakMap)', () => {
+      if (!popoverSupported()) { pending('Popover API not supported in this environment'); return; }
+      const popover = openShadowPopover({ mode: 'closed' });
+
+      // host.shadowRoot is null for closed roots — reaching the popover relies
+      // ENTIRELY on getShadowRoot() falling back to __percyClosedShadowRoots.
+      // This guards the closed-root path from diverging from the open-root one.
+      expect(host.shadowRoot).toBe(null);
+
+      markPseudoClassElements(ctx);
+
+      expect(popover.getAttribute('data-percy-popover-open')).toBe('true');
+    });
+  });
+
   describe('rewriteCustomStateCSS', () => {
     it('rewrites :state() selectors in style elements', () => {
       withExample('<style>my-el:state(open) { color: green; }</style><my-el id="myel"></my-el>');