Copilot Chat: Markdown links with Windows drive letters fail — "ENOPRO: No file system provider" on click

[YIM-boss]

Does this issue occur when all extensions are disabled?: No — Copilot Chat extension is required to reproduce, but the link resolution failure is in VS Code's core markdown link handler, not the extension.

• VS Code Version: 1.98.0 (Insiders)
• OS Version: Windows 10

Summary

When Copilot Chat produces markdown links to local files using Windows absolute paths (e.g., [file.md](c:/Project/docs/file.md)), clicking them fails with:

ENOPRO: No file system provider found for resource 'c:/Project/docs/file.md'

VS Code interprets the drive letter c: as a URI scheme rather than a Windows drive path. Since no provider is registered for the scheme c, the link breaks.

Steps to Reproduce

1. Open VS Code on Windows with a multi-root workspace
2. Open Copilot Chat (Agent mode or Ask mode)
3. Ask the agent to reference a file that exists in the workspace
4. Agent produces a markdown link like: [file.md](c:/MyProject/docs/file.md)
5. Click the rendered link in the chat response
6. Error dialog appears: "ENOPRO: No file system provider found for resource 'c:/...'"

Expected Behavior

The file opens in the editor.

Why This Is Hard to Work Around

• Copilot's built-in system instructions tell agents to use workspace-relative paths, but agents consistently produce absolute Windows paths regardless. This happens across all models (Claude, GPT-4o, etc.).
• Users cannot instruct their way out via copilot-instructions.md — I've tried explicit rules, constant reminders, alternate slash directives, and external research. Agents sporadically comply but frequently revert.
• The file:/// URI scheme is prohibited by Copilot's system instructions, so agents can't produce working absolute links even if they wanted to.
• Workspace-relative paths DO work when agents comply, but compliance is inconsistent.

Suggested Fix

Have VS Code's chat panel markdown link handler detect Windows drive letter patterns and normalize them:

// Before resolving the URI
if (/^[a-zA-Z]:[\\/]/.test(linkTarget)) {
    linkTarget = "file:///" + linkTarget.replace(/\\/g, '/');
}

[YIM-boss]

This is a small, non-breaking change that would fix every agent-produced link on Windows, regardless of agent compliance with formatting instructions.

[YIM-boss]

Workaround

Workspace-relative paths work. If the agent strips the drive letter and workspace root (e.g., C:\MyProject\docs\file.md becomes docs/file.md), VS Code resolves correctly. Getting agents to consistently do this is the challenge.

Impact

This affects every Copilot Chat interaction on Windows where the agent references a file. A typical session produces 5-50+ broken links. It is not model-specific.

See also companion issue on Copilot extension repo: