Fix Windows local browse paths

src/server/localBrowseUi.test.ts

@@ -0,0 +1,19 @@
+import { describe, expect, it } from 'vitest'
+import { decodeBrowsePath } from './localBrowseUi'
+
+describe('decodeBrowsePath', () => {
+  it('removes the browse-route slash before Windows drive paths', () => {
+    expect(decodeBrowsePath('/C:/Users/Nulled/video.mp4', 'win32')).toBe('C:/Users/Nulled/video.mp4')
+    expect(decodeBrowsePath('/%43%3A/Users/Nulled/file.ps1', 'win32')).toBe('C:/Users/Nulled/file.ps1')
+  })
+
+  it('preserves Unix, UNC, and already normalized paths', () => {
+    expect(decodeBrowsePath('/home/codex/file.txt', 'linux')).toBe('/home/codex/file.txt')
+    expect(decodeBrowsePath('//server/share/file.txt', 'win32')).toBe('//server/share/file.txt')
+    expect(decodeBrowsePath('C:/Users/Nulled/file.txt', 'win32')).toBe('C:/Users/Nulled/file.txt')
+  })
+
+  it('leaves malformed URL encoding usable for the normal validation path', () => {
+    expect(decodeBrowsePath('/tmp/100%/file.txt', 'linux')).toBe('/tmp/100%/file.txt')
+  })
+})

src/server/localBrowseUi.ts

@@ -69,13 +69,23 @@ export function normalizeLocalPath(rawPath: string): string {
   return trimmed
 }
 
-export function decodeBrowsePath(rawPath: string): string {
+export function decodeBrowsePath(rawPath: string, platform: NodeJS.Platform = process.platform): string {
   if (!rawPath) return ''
+  let decoded: string
   try {
-    return decodeURIComponent(rawPath)
+    decoded = decodeURIComponent(rawPath)
   } catch {
-    return rawPath
+    decoded = rawPath
   }
+
+  // Browse URLs keep an absolute-path slash after the route prefix. On Windows,
+  // that turns `C:/path` into `/C:/path`, which Node resolves as `C:\C:\path`.
+  // Remove only that synthetic slash; Unix and UNC absolute paths stay intact.
+  if (platform === 'win32' && /^\/[A-Za-z]:[\\/]/u.test(decoded)) {
+    return decoded.slice(1)
+  }
+
+  return decoded
 }
 
 export function isTextEditablePath(pathValue: string): boolean {

tests/chat-composer-rendering/index.md

@@ -27,6 +27,7 @@ Return to the [manual test index](../../tests.md).
 | [Feature: Inline thread image payloads are rewritten to renderable local file URLs](inline-thread-image-payloads-are-rewritten-to-renderable-local-file-urls.md) |
 | [Feature: Markdown file links with spaces and parentheses in path](markdown-file-links-with-spaces-and-parentheses-in-path.md) |
 | [Feature: Markdown link with backticked label renders as file link](markdown-link-with-backticked-label-renders-as-file-link.md) |
+| [Feature: Windows absolute file links open through local browse](windows-absolute-file-links-open-local-browse.md) |
 | [Feature: Backticked bare filenames render as file links](backticked-bare-filenames-render-as-file-links.md) |
 | [Feature: Lazy message rendering (windowed conversation)](lazy-message-rendering-windowed-conversation.md) |
 | [Assistant generated image rendering](assistant-generated-image-rendering.md) |

tests/chat-composer-rendering/windows-absolute-file-links-open-local-browse.md

@@ -0,0 +1,25 @@
+### Feature: Windows absolute file links open through local browse
+
+## Prerequisites
+
+- Run CodexApp on Windows.
+- Open TestChat with a project that contains an existing text file and MP4 file on a drive-letter path.
+
+## Steps
+
+1. Send a message containing Markdown links to `C:/path/to/file.ps1` and `C:/path/to/video.mp4`.
+2. Inspect both rendered links and confirm their `href`, title, and visible text preserve the complete drive-letter paths.
+3. Open the text-file link and confirm the request returns the existing file instead of a 404 response.
+4. Open the MP4 link and seek within the video.
+5. Inspect the MP4 request and confirm byte-range requests return `206 Partial Content` with `Accept-Ranges: bytes`.
+
+## Expected Results
+
+- Windows drive paths are decoded as `C:/...`, not `/C:/...` or `C:\\C:\\...`.
+- Existing files return successfully through `/codex-local-browse/C:/...`.
+- MP4 files use the correct media content type and support browser range requests.
+- Unix absolute paths and UNC paths retain their existing behavior.
+
+## Rollback / Cleanup
+
+- Close the opened file and video tabs. No files are modified by this test.