[Desktop, Windows] File links outside the session folder get no file menu, and no pane can show them

What's wrong
In the Code tab on Windows, a markdown link only gets the file context menu (Attach as context, Copy path, Open in) when its target is a path relative to the session folder with no :line suffix. These all fall back to the plain message menu, so there is no "Open in VS Code":

• absolute target: [x](C:/Users/me/.claude/CLAUDE.md)
• absolute target inside the session folder: [x](D:/proj/CLAUDE.md)
• relative target with a line: [x](CLAUDE.md:5)
• relative target using ..
• file:/// and vscode:// targets

Only [x](CLAUDE.md) works. Files the agent edits outside the session folder (for example ~/.claude) therefore cannot be opened from chat at all, and the file pane and diff pane refuse them too ("could not be resolved inside this session's working directory or granted folders"; diff pane shows "No changes to show").

Expected

• Any link that resolves to an existing file gets the file menu, including absolute paths and :line, and Open in passes the line to the editor.
• The diff pane can show changes in granted or additional directories that are git repos (desktop counterpart of #92108).
• Optional: a default-editor setting so one click opens the external editor (#54027, #89598 were closed as not planned).

Steps

1. Windows 11, Claude desktop, Code tab, session in D:\proj.
2. Have the assistant output the link forms above.
3. Right-click each.

Environment

• Claude desktop 2.110.0.0 (MSIX)
• Claude Code 2.1.263
• Windows 11 Pro 10.0.26200

Related: #61443, #72423, #68559, #92108