fix(web): make Windows file links clickable

[peculiarnewbie]

Problem

On Windows, Markdown links with direct drive paths such as [artifact](C:/Users/.../artifact.mp4) rendered as blue text with no usable target. rehype-sanitize interpreted the drive letter as a URL scheme and removed the href before React Markdown's URL transform could normalize it.

Fix

Rewrite only Windows drive-path link destinations to the already-allowed file:/// form while the document is still Markdown AST. The existing URL transform then restores the drive path and sends it through T3 Code's existing file-link renderer. Forward- and backslash drive paths, including encoded and unencoded Unicode segments, are canonicalized to the same lookup key, while unsafe schemes remain subject to the normal sanitizer.

Absolute Windows paths outside the workspace also remain absolute in tooltips and copied paths. The composer's existing mention-chip behavior is unchanged and out of scope.

Before

The label looked like a link, but it had no target and could not be clicked.

After

The same destination reaches the existing file-link component; hovering reveals the full path and the link is actionable.

Verification

• vp test run apps/web/src/markdown-links.test.ts apps/web/src/markdown-links-rendering.test.tsx apps/web/src/filePathDisplay.test.ts — 46 tests passed
• vp run --filter @t3tools/web typecheck
• Targeted vp lint and vp fmt --check for all six changed files
• Manually verified in the Windows web client; desktop inherits the same web renderer

Implemented with GPT-5.6-Sol in the Codex harness via T3 Code.

---

Note

Medium Risk
Touches markdown href sanitization and file-link resolution, which are security-adjacent URL handling paths. Scope is narrow and unsafe schemes still go through the existing sanitizer.

Overview
Fixes Windows drive-path markdown links (e.g. C:/... or C:\\...) that rendered as non-clickable text because rehype-sanitize treated the drive letter as a URL scheme and stripped the href.

Adds remarkRewriteWindowsFileLinks, which rewrites only Windows drive destinations to allowed file:/// form in mdast before sanitization. The existing URL transform then restores the drive path for the normal file-link renderer. Also canonicalizes backslash/unicode variants into a shared lookup key via normalizeMarkdownFileLinkHrefKey.

Separately, formatWorkspaceRelativePath now treats Windows drive paths as absolute, so paths outside the workspace stay absolute in tooltips/copied paths instead of getting a workspace label prefix.

^{Reviewed by Cursor Bugbot for commit 2e03244. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Fix Windows file path links to be clickable in chat markdown

• Adds remarkRewriteWindowsFileLinks remark plugin to convert Windows drive-path links (e.g. C:\foo) into file:///C:/... URIs before HTML sanitization, preventing the sanitizer from stripping them.
• Adds normalizeMarkdownFileLinkHrefKey to produce stable canonical keys for Windows file links regardless of backslashes or percent-encoding, replacing the local helper in ChatMarkdown.tsx.
• Fixes formatWorkspaceRelativePath in filePathDisplay.ts to avoid prefixing absolute Windows drive paths with the workspace label.

^{Macroscope summarized 2e03244.}

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[macroscopeapp]

Approvability

Verdict: Approved 2e03244

Straightforward bug fix making Windows file paths clickable in markdown by converting them to file:// URIs before HTML sanitization. Changes are self-contained with good test coverage, including verification that unsafe schemes remain blocked.

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Dismissing prior approval to re-evaluate 6717343

[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

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Dismissing prior approval to re-evaluate 2e03244

[Defmon3]

Confirmed on Windows. We reproduced drive-letter Windows Markdown links failing to open, then tested the current PR head (2e03244) in our downstream build. The links now resolve and open correctly, including the chat rendering path with line breaks. Thanks for the fix.

[carlosesl1]

I reproduced one remaining gap with the current PR head: valid angle-bracketed destinations containing spaces or balanced parentheses survive the Markdown pipeline, but MARKDOWN_LINK_HREF_PATTERN misses them. That leaves markdownFileLinkMetaByHref empty, so the anchor falls through to the external-link path instead of the existing file-link behavior.

I opened a small, tested follow-up against this branch: peculiarnewbie#1

It keeps the precomputed map as the fast path and falls back to resolving the parsed/normalized href. Regression coverage uses the issue reproduction: <C:/Users/Carlos/My Project/docs/Plan (final).md>. All 43 focused tests, web typecheck, targeted lint, and formatting checks pass.

[CDVolvik]

46/46 across markdown-links.test.ts, markdown-links-rendering.test.tsx and filePathDisplay.test.ts on Linux (Node 24).

I went looking for a mismatch between the rendering test's pipeline and the real one, since markdown-links-rendering.test.tsx builds its own ReactMarkdown rather than rendering ChatMarkdown. There isn't one today. The test uses

protocols: { ...defaultSchema.protocols, href: [...(defaultSchema.protocols?.href ?? []), "file"] }
urlTransform={(href) => rewriteMarkdownFileUriHref(href) ?? defaultUrlTransform(href)}

and ChatMarkdown uses exactly the same protocol list in CHAT_MARKDOWN_SANITIZE_SCHEMA, plus

const markdownUrlTransform = useCallback((href: string) => {
  return rewriteMarkdownFileUriHref(href) ?? defaultUrlTransform(href);
}, []);

So the behaviour is faithfully mirrored. Worth flagging anyway, because the mirroring is by hand and there are now three things that have to stay in step: the file protocol entry, remarkRewriteWindowsFileLinks sitting in the remark list, and that urlTransform. Drop any one of them from ChatMarkdown and every test in the new file still passes, because the test supplies its own. CHAT_MARKDOWN_SANITIZE_SCHEMA and markdownUrlTransform are both module-local, so exporting them and importing them into the test would turn this from a parallel implementation into an actual guard, without changing what is asserted.

The still removes unsafe schemes case is the right instinct given this widens what survives sanitization. One more worth adding next to it: a single-letter scheme that is not a drive path. WINDOWS_DRIVE_PATH_PATTERN keys off [A-Za-z]:, and the reason javascript: is safe is that it is many letters, not one. Something like [x](c:/Users/x) versus a genuine one-letter scheme would pin that the widening is limited to drive paths rather than to any short scheme.

isAbsolutePath in filePathDisplay.ts only matches a forward slash after the drive letter:

return path.startsWith("/") || /^[A-Za-z]:\//.test(path);

That is fine where it is called, since the value has already been through normalizeMarkdownLinkDestination, but the function name reads general and the next caller will not necessarily normalize first. C:\Users\... returns false from a function called isAbsolutePath. Either accepting both separators or naming it for the normalized input would stop that being a trap later.

[fbal98]

we need this merged

[t3dotgg]

Note

🤖 GPT-5.6 Sol responding on behalf of Theo

Closing in favor of merged #8081, which fixes Windows drive-path file links in chat without weakening Markdown URL sanitization. Your work is credited in #8081.