diff --git a/apps/web/e2e/a11y.spec.ts b/apps/web/e2e/a11y.spec.ts
index 2d323ab..3a34089 100644
--- a/apps/web/e2e/a11y.spec.ts
+++ b/apps/web/e2e/a11y.spec.ts
@@ -120,37 +120,66 @@ async function expectNoHorizontalScroll(page: Page, label: string): Promise<void
   const report = await page.evaluate(() => {
     const doc = document.documentElement;
     const limit = doc.clientWidth;
-    /** Content inside its own scroll container is allowed to be wider than
-     *  the viewport — that is the prescribed remedy, not the defect. Only
-     *  what pushes the PAGE is a finding. */
-    const insideScroller = (el: HTMLElement): boolean => {
+    const describe = (el: HTMLElement): string => {
+      const cls =
+        el.className && typeof el.className === 'string'
+          ? `.${el.className.trim().split(/\s+/).join('.')}`
+          : '';
+      return `${el.tagName.toLowerCase()}${cls}`;
+    };
+
+    /**
+     * Content inside a scroll container may exceed the viewport — that is the
+     * remedy, not the defect. But only if the CONTAINER itself fits: a
+     * scroller that is wider than the viewport still pushes the page, and its
+     * children are then symptoms, not causes.
+     */
+    const containedByFittingScroller = (el: HTMLElement): boolean => {
       for (let node = el.parentElement; node && node !== doc; node = node.parentElement) {
         const overflowX = getComputedStyle(node).overflowX;
-        if (overflowX === 'auto' || overflowX === 'scroll' || overflowX === 'hidden') return true;
+        if (overflowX === 'auto' || overflowX === 'scroll' || overflowX === 'hidden') {
+          return node.getBoundingClientRect().right <= limit + 1;
+        }
       }
       return false;
     };
 
     const offenders: string[] = [];
+    let widest: HTMLElement | null = null;
     for (const el of Array.from(document.querySelectorAll<HTMLElement>('body *'))) {
       const rect = el.getBoundingClientRect();
       // 1 px Toleranz gegen Subpixel-Rundung.
-      if (rect.width > 0 && rect.right > limit + 1 && !insideScroller(el)) {
-        const cls =
-          el.className && typeof el.className === 'string'
-            ? `.${el.className.trim().split(/\s+/).join('.')}`
-            : '';
+      if (rect.width > 0 && rect.right > limit + 1 && !containedByFittingScroller(el)) {
         offenders.push(
-          `${el.tagName.toLowerCase()}${cls} (right=${Math.round(rect.right)}, width=${Math.round(rect.width)})`,
+          `${describe(el)} (right=${Math.round(rect.right)}, width=${Math.round(rect.width)})`,
         );
+        if (!widest || rect.width > widest.getBoundingClientRect().width) widest = el;
       }
     }
-    return { scrollWidth: doc.scrollWidth, clientWidth: limit, offenders: offenders.slice(0, 20) };
+
+    // Where does the inflation start? The chain from body down to the widest
+    // offender, with each box's width — the first entry wider than the
+    // viewport is the element that actually needs constraining.
+    const chain: string[] = [];
+    for (let node: HTMLElement | null = widest; node && node !== doc; node = node.parentElement) {
+      chain.unshift(`${describe(node)} w=${Math.round(node.getBoundingClientRect().width)}`);
+    }
+
+    return {
+      scrollWidth: doc.scrollWidth,
+      clientWidth: limit,
+      offenders: offenders.slice(0, 20),
+      chain,
+    };
   });
   expect(
-    { overflowBy: report.scrollWidth - report.clientWidth, offenders: report.offenders },
+    {
+      overflowBy: report.scrollWidth - report.clientWidth,
+      offenders: report.offenders,
+      chain: report.chain,
+    },
     `${label}: horizontaler Überlauf bei 320 px`,
-  ).toEqual({ overflowBy: 0, offenders: [] });
+  ).toEqual({ overflowBy: 0, offenders: [], chain: [] });
 }
 
 test.describe('reflow at 320px', () => {