fix(ui): block active HTML in assistant markdown

packages/ui/src/components/chat/composer/language/__tests__/mentions.test.ts

@@ -138,6 +138,11 @@ describe('classifyMention', () => {
         expect(classifyMention('', classifier)).toBeNull();
     });
 
+    test('HTML fragments do not classify as file references', () => {
+        expect(classifyMention('import</style>', classifier)).toBeNull();
+        expect(classifyMention('src/<style.css', classifier)).toBeNull();
+    });
+
     test('an agent name wins over a file-looking name', () => {
         const shadowed = {
             knownAgentNames: new Set(['a.ts']),
@@ -152,4 +157,3 @@ describe('classifyMention', () => {
         expect(looksLikeFilePath('plain', new Set(['plain']))).toBe(true);
     });
 });
-

packages/ui/src/components/chat/composer/language/mentions.ts

@@ -116,6 +116,9 @@ export function classifyMention(
     classifier: MentionClassifier,
 ): MentionKind | null {
     if (!name) return null;
+    // HTML fragments are prompt text, never references. In particular, do not
+    // interpret CSS syntax such as `@import</style>` as a local file path.
+    if (name.includes('<') || name.includes('>')) return null;
     if (classifier.knownAgentNames.has(name.toLowerCase())) return 'agent';
     if (looksLikeFilePath(name, classifier.confirmedMentions)) return 'file';
     return null;