Slash command autocomplete can select the wrong command after fast typing

## Description

When typing a slash command quickly and pressing Enter before the autocomplete list finishes filtering, the wrong command can be inserted or executed.

## Steps to reproduce

1. Open the prompt in the terminal UI.
2. Type `/co` and immediately press Enter while the suggestion list is still updating.
3. Observe that a command other than the intended one is selected.

## Expected behavior

Enter should run the command matching the current input, or wait until the suggestion list has settled before accepting a selection.

## Actual behavior

The stale suggestion is accepted and the wrong command runs.

## Environment

- Claude Code: latest
- OS: Linux
- Terminal: any

## Notes

Likely a race between the debounced filter and the key handler. A small guard that ignores Enter until the list matches the current input would fix it.

Start in the terminal UI code for slash-command autocomplete, tracing the debounced filtering and the Enter key handler described in the issue. Reproduce by typing /co and pressing Enter immediately; done means Enter no longer accepts a stale suggestion and runs the command matching the current input.

Written by the indexing model from the issue text.