[BUG] Confusing UI for fast mode in VS Code extension

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?

When you select the Fast mode option in the VS Code extension, it opens a side terminal that launches a separate instance of Claude Code that allows enabling fast mode for that terminal session.
Then, fast mode is shown as activated in the VS Code session with a small lightning icon on top of the microphone icon, only when the input field is selected. (Why not always displayed?)
I'm not sure the output was faster, but since it spent hundreds of extra credits in less than an hour, I suppose it was enabled. The lightning icon appears in all instances/projects of VS Code, regardless of whether the fast mode was enabled for them, and after disabling fast mode where it was enabled, the lightning icon still appears when the input field is selected.
In addition to the "/fast isn't available in this environment" message (that I got when typing /fast but couldn't reproduce a second time), we can say that, at the very least, the UI is confusing if not misleading.

What Should Happen?

Fast mode should work in the VS Code session.

Error Messages/Logs

Steps to Reproduce

Open the VS Code Claude Code extension, type "/" in the input field, click on Toggle fast mode.

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.143

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Cursor

Additional Information