[BUG] VS Code extension chat panel fails to render on UNC workspace — regression in 2.1.220, works in 2.1.219 (Windows)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

On the Claude Code VS Code extension 2.1.220, opening a workspace located on a Windows UNC path (\\<server>\<share>) leaves the extension's chat panel in a permanently half-initialised state:

The panel chrome renders and the header shows an Untitled session.
The prompt / chat input box never appears.
Session history sits on "Loading sessions" indefinitely — on both the Local and Web tabs.
No error is thrown and no dialog appears. It simply hangs.

Rolling the extension back to 2.1.219, changing nothing else, restores full functionality immediately.

_Note on the version checklist item: I am deliberately not on the latest version. 2.1.220 reproduces this bug and 2.1.219 does not, so I have pinned the extension to 2.1.219 in order to keep working. The version boundary is the substance of this report._

What Should Happen?

The chat panel should render with a usable prompt input, and the session list should resolve (or fail with a visible error) when the workspace is on a UNC path, as it did in 2.1.219 and earlier.

Error Messages/Logs

Steps to Reproduce

1. On Windows, ensure the UNC host is allow-listed in VS Code user settings: "security.allowedUNCHosts": ["<server>"]
2. Open a folder on a UNC path as the VS Code workspace, e.g. \\<server>\htdocs. (Not a mapped drive — a raw UNC path.)
3. Install / update the Claude Code extension to 2.1.220.
4. Open the Claude Code panel.
5. Observe: header shows Untitled, no prompt input, session list stuck loading.
6. Right-click the extension → Install Another Version → 2.1.219, reload window.
7. Observe: panel renders correctly and sessions load.

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.219

Claude Code Version

2.1.220 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

%USERPROFILE%\.claude\projects\ contains a single directory for this workspace, with a trailing hyphen:

--<server>-htdocs-

There is no separate mapped-drive-encoded directory, so the extension and CLI do appear to be resolving to the same session store here. That distinguishes this from the slug-mismatch issues below.

The UNC host is correctly configured in security.allowedUNCHosts, and an unrelated UNC host access is not allowed error from the built-in JSON language server was resolved by that setting. That error was incidental — it was fixed before the panel problem was, and the panel remained broken until the downgrade.

Possibly related, but not duplicates
#76205 — /resume / session history always empty on mapped network drives; extension and CLI compute different project slugs.
#63527 — Session history empty in VS Code extension when working directory is on a mapped Windows drive.

Both concern session history being empty due to slug mismatch on mapped drives. This report is a different failure mode — the panel itself never renders, on a raw UNC path — and has a clean single-release version boundary. Linking in case a common change underlies them.