VS Code: Codex Diff crashes with "Thread context is unavailable for non-thread routes"

Summary

Opening a Codex Diff in the VS Code ChatGPT extension crashes the diff webview instead of rendering the changes.

Reproduction

1. Use the ChatGPT/Codex extension in VS Code.
2. Create any Codex file change.
3. Open the Codex Diff view for that turn.

Actual result

The diff webview fails to open. The Webview Developer Tools console reports:

Error: Thread context is unavailable for non-thread routes
    at R (editor-diff-page-*.js)
Caused by: React ErrorBoundary Error: Thread context is unavailable for non-thread routes

The stack shows VS Code opening the view as a webview editor (openWebview -> openEditor), while editor-diff-page reads thread context that is unavailable on that route.

Expected result

The Codex Diff view should receive the thread context or gracefully render without it.

Environment

• VS Code ChatGPT/Codex extension: 26.721.41059
• Codex CLI: 0.145.0
• macOS on Apple Silicon

Notes

• Reinstalling the extension, clearing regenerable Codex caches, and updating the CLI did not resolve the issue.
• Git diffs themselves are valid; the failure occurs in the extension webview.
• Unrelated console warnings about iframe sandboxing, local-network-access, and a blocked embedded font are also present, but the React error above is the direct failure.