Preserve unresolved linked CSS selectors

AI assistance disclosure: Codex implemented and verified this fix under maintainer direction.

cli/engine/browser/injected/index.mjs

@@ -1332,7 +1332,12 @@ if (IS_BROWSER) {
         }
         const cssText = rule.cssText || '';
         if (rule.selectorText) {
-          if (selectorNodesForLiveDom(document, rule.selectorText)?.length > 0) parts.push(cssText);
+          const matches = selectorNodesForLiveDom(document, rule.selectorText);
+          // A null result means the DOM selector API cannot resolve the CSSOM
+          // selector (commonly a hostless pseudo-element), not that it is
+          // unused. Keep those valid stylesheet rules; only a definitive empty
+          // result proves that no live element can receive the declaration.
+          if (matches === null || matches.length > 0) parts.push(cssText);
           continue;
         }
         let nested = [];

cli/engine/detect-antipatterns-browser.js

@@ -8233,7 +8233,12 @@ if (IS_BROWSER) {
         }
         const cssText = rule.cssText || '';
         if (rule.selectorText) {
-          if (selectorNodesForLiveDom(document, rule.selectorText)?.length > 0) parts.push(cssText);
+          const matches = selectorNodesForLiveDom(document, rule.selectorText);
+          // A null result means the DOM selector API cannot resolve the CSSOM
+          // selector (commonly a hostless pseudo-element), not that it is
+          // unused. Keep those valid stylesheet rules; only a definitive empty
+          // result proves that no live element can receive the declaration.
+          if (matches === null || matches.length > 0) parts.push(cssText);
           continue;
         }
         let nested = [];

tests/detect-antipatterns-browser.test.mjs

@@ -1409,6 +1409,11 @@ describe('detectUrl — browser-only fixtures', () => {
       assert.equal(stripes.length, 1, JSON.stringify({ linkedFindings, linkedCssom }));
       assert.equal(stripes[0].severity, 'advisory');
       assert.equal(stripes[0].advisory, true);
+      assert.equal(
+        linkedFindings.some(finding => finding.type === 'bounce-easing'),
+        true,
+        JSON.stringify({ linkedFindings, linkedCssom }),
+      );
       assert.equal(linkedFindings.some(finding => finding.type === 'codex-grid-background'), false);
       assert.equal(linkedFindings.some(finding => finding.type === 'layout-transition'), false);
       await linkedPage.close();

tests/fixtures/antipatterns/linked-url-patterns.css

@@ -6,6 +6,19 @@
   }
 }
 
+/* A valid hostless pseudo-element selector cannot be queried through the DOM
+   selector API. It must remain in the corpus rather than count as unused. */
+main > ::before {
+  content: "Rendered pseudo-element text";
+  display: block;
+  width: 160px;
+  animation: bounce-linked-pseudo 1s ease-in-out infinite;
+}
+
+@keyframes bounce-linked-pseudo {
+  50% { transform: translateY(2px); }
+}
+
 /* Shipped but unused selectors must remain outside live URL findings, even
    inside grouping rules or when their check does not serialize a selector. */
 @supports (display: grid) {