fix(markdown): open local file links

packages/ui/src/components/chat/MarkdownRendererImpl.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, test } from 'bun:test';
 
-import { parseFileReference, type ParsedFileReference } from './fileReferenceParser';
+import { localPathFromFileUrl, parseFileReference, type ParsedFileReference } from './fileReferenceParser';
 
 const parse = (value: string): ParsedFileReference | null => parseFileReference(value);
 
@@ -96,3 +96,17 @@ describe('parseFileReference', () => {
         expect(result).toEqual({ path: 'src/foo.ts', line: 42, endLine: 58 });
     });
 });
+
+describe('localPathFromFileUrl', () => {
+    test('converts local file URLs to absolute paths', () => {
+        expect(localPathFromFileUrl('file:///private/tmp/report%20viewer.html')).toBe('/private/tmp/report viewer.html');
+        expect(localPathFromFileUrl('file://localhost/private/tmp/REPORT.md')).toBe('/private/tmp/REPORT.md');
+        expect(localPathFromFileUrl('file:///C:/Users/test/report.html')).toBe('C:/Users/test/report.html');
+    });
+
+    test('rejects non-file URLs and remote file hosts', () => {
+        expect(localPathFromFileUrl('https://example.com/report.html')).toBeNull();
+        expect(localPathFromFileUrl('file://remote-host/share/report.html')).toBeNull();
+        expect(localPathFromFileUrl('file:///tmp/bad%ZZpath')).toBeNull();
+    });
+});

packages/ui/src/components/chat/MarkdownRendererImpl.tsx

@@ -38,6 +38,7 @@ import { createMermaidViewerRegistry, MERMAID_BLOCK_SELECTOR, shouldRefreshMerma
 import {
   BLOCK_PATH_TOKEN_RE,
   isAbsoluteReferencePath,
+  localPathFromFileUrl,
   normalizeReferencePath,
   parseFileReference,
   type ParsedFileReference,
@@ -300,6 +301,10 @@ const unwrapBlockCodePathTokens = (container: HTMLElement): void => {
 const extractPathCandidateFromElement = (element: HTMLElement): string => {
   if (element.tagName.toLowerCase() === 'a') {
     const href = element.getAttribute('href')?.trim();
+    const fileUrlPath = href ? localPathFromFileUrl(href) : null;
+    if (fileUrlPath) {
+      return fileUrlPath;
+    }
     if (href && isLikelyFilePath(href)) {
       return href;
     }

packages/ui/src/components/chat/fileReferenceParser.ts

@@ -24,6 +24,29 @@ export const normalizeReferencePath = (value: string): string => normalizeFilePa
 
 export const isAbsoluteReferencePath = (value: string): boolean => isAbsoluteFilePath(value);
 
+export const localPathFromFileUrl = (value: string): string | null => {
+    let parsed: URL;
+    try {
+        parsed = new URL(value.trim());
+    } catch {
+        return null;
+    }
+
+    if (parsed.protocol !== 'file:' || (parsed.hostname && parsed.hostname !== 'localhost')) {
+        return null;
+    }
+
+    try {
+        const decodedPath = decodeURIComponent(parsed.pathname);
+        if (/^\/[A-Za-z]:\//.test(decodedPath)) {
+            return decodedPath.slice(1);
+        }
+        return decodedPath.startsWith('/') ? decodedPath : null;
+    } catch {
+        return null;
+    }
+};
+
 const trimPathCandidate = (value: string): string => {
     let next = (value || '').trim();
     if (!next) {

packages/ui/src/components/chat/markdown/markdownCore.test.ts

@@ -11,7 +11,7 @@ mock.module('./markdown-worker', () => ({
   highlightCodeInWorker: async () => null,
 }));
 
-import { escapeRawMarkdownHtml, MARKDOWN_FORBIDDEN_TAGS } from './markdownSecurity';
+import { escapeRawMarkdownHtml, isLocalFileUrl, MARKDOWN_FORBIDDEN_TAGS } from './markdownSecurity';
 
 const { extractMarkdownImageCandidates, renderMarkdownSync } = await import('./markdownCore');
 const { resolveMarkdownImageSource } = await import('./markdownImageAssets');
@@ -29,6 +29,13 @@ describe('markdown sanitization', () => {
     expect(MARKDOWN_FORBIDDEN_TAGS).toContain('script');
     expect(MARKDOWN_FORBIDDEN_TAGS).toContain('style');
   });
+
+  test('allows only local file URLs through the sanitizer policy', () => {
+    expect(isLocalFileUrl('file:///private/tmp/report%20viewer.html')).toBe(true);
+    expect(isLocalFileUrl('file://localhost/private/tmp/REPORT.md')).toBe(true);
+    expect(isLocalFileUrl('file://remote-host/share/report.html')).toBe(false);
+    expect(isLocalFileUrl('javascript:alert(1)')).toBe(false);
+  });
 });
 
 describe('Markdown images', () => {

packages/ui/src/components/chat/markdown/markdownCore.ts

@@ -5,7 +5,7 @@ import DOMPurify from 'dompurify';
 import { buildAgentMentionUrl, parseAgentHref, parseSkillHref } from '@/lib/messages/inlineMessageLinks';
 import { isVSCodeRuntime } from '@/lib/desktop';
 import { highlightCodeInWorker } from './markdown-worker';
-import { escapeRawMarkdownHtml, MARKDOWN_FORBIDDEN_TAGS } from './markdownSecurity';
+import { escapeRawMarkdownHtml, isLocalFileUrl, MARKDOWN_FORBIDDEN_TAGS } from './markdownSecurity';
 
 const escapeAttr = (value: string): string =>
   value.replace(/&/g, '&amp;').replace(/"/g, '&quot;').replace(/</g, '&lt;').replace(/>/g, '&gt;');
@@ -400,6 +400,10 @@ const ensureSanitizeHook = (): void => {
   if (sanitizeHookInstalled) return;
   if (typeof window === 'undefined' || !DOMPurify.isSupported) return;
   sanitizeHookInstalled = true;
+  DOMPurify.addHook('uponSanitizeAttribute', (node, data) => {
+    if (!(node instanceof HTMLAnchorElement) || data.attrName !== 'href') return;
+    if (isLocalFileUrl(data.attrValue)) data.forceKeepAttr = true;
+  });
   DOMPurify.addHook('afterSanitizeAttributes', (node) => {
     if (!(node instanceof HTMLAnchorElement)) return;
     if (node.target !== '_blank') return;

packages/ui/src/components/chat/markdown/markdownSecurity.ts

@@ -4,3 +4,12 @@ export const escapeRawMarkdownHtml = (value: string): string =>
 
 /** Active elements forbidden again at the final DOMPurify boundary. */
 export const MARKDOWN_FORBIDDEN_TAGS = ['script', 'style'] as const;
+
+export const isLocalFileUrl = (value: string): boolean => {
+  try {
+    const parsed = new URL(value);
+    return parsed.protocol === 'file:' && (!parsed.hostname || parsed.hostname === 'localhost');
+  } catch {
+    return false;
+  }
+};