[BUG] VSCode extension: tab autocomplete for slash commands no longer working on new interface (v2.0.0+)

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?

Since updating the interface for the Claude Code VSCode extension, tab-completion of slash commands has stopped working.

What Should Happen?

Ideally, pressing tab would just fill in the rest of the highlighted prediction and allow you to either submit (Enter) or continue typing arguments. This is the behavior of the in-terminal interactive interface as it currently and has always been.

Steps to Reproduce

Starting to type a slash command correctly shows the suggested command, but pressing tab just changes the focused element (like it does in other programs for accessibility/mouseless navigation). Pressing enter instead of tab at this point just sends the full suggested command, which is great for some commands which don't require arguments, but those that do are no longer auto-completable and must be typed out entirely.

_Mid-typed slash command_
<img width="417" height="184" alt="Image" src="https://github.com/user-attachments/assets/a55c0485-3892-4676-b3b2-62373398f4fd" />

_After pressing tab on the mid-typed slash command_
<img width="417" height="186" alt="Image" src="https://github.com/user-attachments/assets/fae5bdaa-3a55-4000-a6d2-c2673d7b06bb" />